Filling level monitoring device for monitoring filling level of fluid container, hydrogen tank and aircraft comprising such hydrogen tank

Abstract

A fill level monitoring device (100) for monitoring a fill level (210) of a fluid container (200), a hydrogen tank and an aircraft comprising such a hydrogen tank are provided. The fill level monitoring device comprises an excitation element (10), a sensing element (21), a signal source (30), a suspension element (70) having a defined stiffness, and a processing unit (40). The excitation element (10) is configured to be mounted on a fluid container (200) or a suspension element (70) to activate a specific suspension mode (25) of vibration. The suspension element (70) is rigidly attached to the fluid container (200) such that both vibrate together. A sensing element (21) detects these vibrations and sends data to a processing unit (40). The signal source (30) generates a multi-frequency input signal (31) for exciting the element (10). The processing unit (40) uses the vibration data to identify the suspension mode (25), determines its modal frequency (80) and calculates a current filling level (210) of the fluid container (200) based on the frequency.

Description

Technical Field

[0001] This disclosure relates to a filling level monitoring device for fluid tanks, and more particularly to hydrogen tanks for aircraft applications having such a monitoring device. Background Technology

[0002] In light of growing environmental protection efforts, alternative propulsion sources for aircraft have been developed. These alternative propulsion sources can use fuels other than kerosene, such as liquid hydrogen, which cannot be stored in conventional fuel tanks. Therefore, hydrogen fuel or other liquid gaseous fuels need to be stored in suitable tanks that must, for example, withstand the internal pressures and cryogenic temperatures (20 K) required for storing gases in a liquid state. However, for safety reasons, it is also necessary to monitor the fuel tank's fill level accurately at all times. Currently, the fill level of a fluid tank can be determined, for example, by measuring the weight of the tank or indirectly by monitoring the flow rate leaving the tank. However, these methods are not very accurate or may not be suitable for use in aircraft applications. For example, soft suspension (such as that found in weighing scales) cannot be readily introduced into mobile vehicles. For example, an aircraft may experience altitude changes, and during such ascent or descent segments of flight, the gravity vector relative to the fuel tank may not be constant, making it difficult to determine an accurate weight value and therefore, a fill level. The same applies to curved flight segments where the aircraft changes its flight vector.

[0003] Furthermore, for safety reasons (electronic instruments and hydrogen should be kept separate) and insulation (leakage) reasons, sensing solutions such as those used for kerosene sensing implemented in aircraft wings today cannot be used in hydrogen tanks.

[0004] Overall, there is a need to develop a non-invasive sensing system for cryogenic tanks, particularly in aircraft applications. Currently, a very limited set of technological options is available for this purpose. Interpretation of vibration-based measurements is one such solution.

[0005] Methods for determining the filling level of a fluid tank by monitoring its resonant frequency are known in principle in the art. A general method for such monitoring is described in the applicant's patent application WO 2023 / 217 807 A1 (briefly described below), which illustrates the concept and measurement principles. However, in some cases, this method may present problems in identifying and tracking / monitoring stable vibration modes.

[0006] WO 2023 / 217 807 A1 describes a fill level monitoring device for liquid tanks (such as hydrogen tanks), a hydrogen tank including such a fill level monitoring device, and an aircraft including such a hydrogen tank. The fill level monitoring device uses a signal source and an excitation element to couple a vibration load having multiple frequency components into the container. The resonant frequency of the container depends on the fill level of the container. After the excitation element couples the vibration load into the container, a sensing element measures the vibration in the container. A processing unit performs spectral analysis on the input signal from the signal source and the vibration signal from the sensing element, and compares the spectral functions of the input signal and the vibration signal to extract the resonant frequency. The resonant frequency of the container also depends on the spatial orientation of the container. A fill level indicator unit calculates the current fill level of the container based on the extracted resonant frequency and the spatial orientation signal from a spatial orientation sensor by correlating the collected data with reference data. Summary of the Invention

[0007] The aim is to provide accurate and stable monitoring of fuel levels in fluid tanks used in aircraft applications.

[0008] This objective is achieved through the subject matter of the main aspects of the invention. Other embodiments are described in other aspects of the invention and in the following description.

[0009] According to a first aspect, a filling level monitoring device is provided for monitoring the filling level of a fluid container. The filling level monitoring device includes at least one excitation element, at least one sensing element, a signal source, at least one suspension element having suspension stiffness, and a processing unit. The at least one excitation element is configured to be mounted to the fluid container and / or the at least one suspension element, such that the at least one excitation element is operable to excite at least one suspension mode of vibration. The suspension mode is a different vibration mode of the at least one suspension element. The at least one suspension element is configured to be fixedly connected to the fluid container such that when excited by the at least one excitation element, the fluid container and the at least one suspension element vibrate together in unison. The at least one sensing element is configured to be mounted to the fluid container and / or the at least one suspension element and sense vibrations corresponding to the at least one suspension mode. The signal source is connected to the at least one excitation element and configured to generate an input signal including multiple frequency components. Each of the at least one sensing element is connected to the processing unit and configured to sense vibrations within the fluid container and generate a corresponding vibration signal and send it to the processing unit. The processing unit is configured to identify at least one suspension mode based on the vibration signal of at least one sensing element and the input signal, determine the modal frequency of at least one suspension mode, and determine the current filling level of the fluid container based on the modal frequency of at least one suspension mode.

[0010] This fill level monitoring device can be used in any fluid container for liquids, such as gas cylinders or containers for hydrogen. However, the fill level monitoring device is not limited to hydrogen containers. For example, it can also be used with containers for liquefied petroleum gas (LPG), methane gas, or any other fluid stored in liquefied form under pressure. Furthermore, the fill level monitoring device can also be used in conventional liquid tanks. Generally, as used herein, the term fluid encompasses liquids (such as pressurized gases in liquid form), mixtures of liquids and gases (i.e., the filling of a container in which the container's filling exists in two phases simultaneously, both liquid and gas), and pure gases. A fluid container can be, for example, a Dewar tank. However, this is merely a non-limiting example.

[0011] Typically, like any other tangible structure, fluid containers used to store fluids exhibit characteristic vibrational or oscillatory modes under force-based excitation, where the amplitude of oscillations or vibrations within a specific frequency range exhibits a relative maximum. While some of these so-called resonant frequencies depend solely on the container's structure and are independent of its filling material, others can be clearly attributed to the stored contents. In particular, liquefied gas fillings such as liquid hydrogen alter specific resonant frequencies of the container, where changes in frequency are proportional to or at least clearly correlated with the fluid container's filling level, i.e., changes in the mass and / or volume of the filling material. These resonances shift in frequency with changes in filling level and can therefore be used to infer the fluid container's filling level.

[0012] Furthermore, in any spring-mass system, the resonant frequency is a function of the stiffness of the spring (or typically an elastic or spring-like element) and the mass attached to it. This invention utilizes this fact by providing a suspension element (at least one suspension element; when discussed herein, "suspension element" means "at least one suspension element") with defined stiffness, which is fixedly attached to a fluid container and serves as a mounting element for the fluid container to connect it to surrounding structures such as an aircraft fuselage. The fluid container and the suspension element together constitute a spring-mass system that exhibits certain resonant modes, referred to herein as suspension modes. Typically, depending on the configuration, such a suspension element may include multiple degrees of freedom (up to six, three translational degrees of freedom and three rotational degrees of freedom), each including its own resonant frequency. However, to determine the filling level, optionally, the movement / oscillation of the system comprising the fluid container and the suspension element (also referred to herein as a "container / suspension system") can be restricted, for example, by means of corresponding limiting elements, to one or a subset of these possible degrees of freedom. The resonant frequency of the suspension mode is a function of the mass of the fluid container, and therefore can be used to infer the filling level of the fluid container by means of its mass. Since the suspension element is fixedly connected to the fluid container, when excited, the suspension element and the fluid container vibrate in unison, where the vibration frequency is determined by the suspension element and its stiffness.

[0013] The inventors discovered that the suspension mode is also highly sensitive to the filling level within the fluid container, causing its modal frequencies to drift in a predictable manner with changes in the filling level. Furthermore, measurements can be easily taken from outside the fluid container by attaching a corresponding vibration sensor (i.e., at least one sensing element). If multiple sensing elements are used, some redundancy in the measurement can be achieved through individual measurements by the sensing elements, or the sensing elements can be used together to determine the suspension mode, for example, by averaging the individual measurements. This, along with the predictability of the modal frequency drift, significantly increases the signal-to-noise ratio of the filling level measurement and makes it highly predictable.

[0014] Therefore, the filling level of the container can be determined by monitoring the resonant frequency of the suspension modes. Due to their natural dependence on the mass of the fluid container, suspension modes are particularly suitable for accurately measuring the filling level of a fluid container, regardless of the orientation of the fluid container. A suspension mode refers to a vibration / oscillation mode in which the fluid container and the mounting elements (i.e., the suspension elements) oscillate synchronously together. In other words, because the fluid container is fixedly connected to the suspension elements in the mounted state, the fluid container and the suspension elements oscillate together in the same manner.

[0015] Typically, vibration-based determination of fill level offers a very attractive alternative to conventional methods. Higher frequency displacements can be small and still visible to vibration sensors (i.e., sensing elements). Therefore, the stiffness of suspension elements is chosen to be sufficiently high (and their strength is significantly increased) to shift the relevant suspension patterns (at least one of which is observed by the fill level monitoring device) towards higher frequency ranges. Consequently, the response amplitude caused by any load (e.g., landing or maneuvering) is significantly reduced (by orders of magnitude). The same applies to overall pressure levels.

[0016] For example, a fluid container can be a component of a tank that actually holds the (fluid) contents of the tank, such as a pressure-sealed gas cylinder or other suitable structure, or it can be the entire tank itself. In a non-limiting example, the fluid container can be a Dewar canister. However, because the suspension configuration is independent of the fluid tank itself, the fill level monitoring device can also be used with any other fluid container.

[0017] Suspension elements can be, for example, springs, correspondingly formed beams, or any other suitable suspension element that allows oscillation / vibration in at least one degree of freedom. The suspension element is at least partially elastic and, together with the current mass of the fluid container, comprises different resonant frequencies. Repeatability is improved by avoiding any friction, for example, by using metallic materials within the suspension element, and by minimizing any sources of nonlinearity within the suspension element. While other alternatives may be considered, welded components or tightly assembled parts are recommended. For example, elastomeric materials should be avoided because they are both highly nonlinear (due to their hyperelastic behavior) and very sensitive to operating conditions (temperature, humidity, etc.). Furthermore, adding damping to the suspension element should be avoided to prevent large resonances, as most dissipative mechanisms tend to alter the linear behavior of the suspension. More importantly, it is essential to ensure that the suspension element exhibits reasonably high modal frequencies to reduce large displacement resonances.

[0018] A signal source, or more precisely, the output terminal of the signal source, is connected to at least one excitation element and generates an electrical signal having a predetermined signal pattern, i.e., the input signal to the excitation element. Specifically, the signal source generates multiple electrical signals covering a range of corresponding resonant (i.e., modal) frequencies, which respond to frequency variations at any possible filling level of the container. Thus, the electrical signals specifically cover all modal frequencies that at least one suspension mode can exhibit at any conceivable filling level of the fluid container. As mentioned above, the suspension modes are highly visible from the outside, and their modal frequencies are highly correlated with the filling level of the fluid container. Therefore, for each filling level of the fluid container, each suspension mode has a specific modal frequency. The signal source can, for example, output a signal with a uniformly distributed spectral distribution, such as a white noise signal. However, other signal shapes covering the corresponding frequencies are also possible. For example, such a white noise signal can be limited, for example, to the modal frequency range of suspension modes that may occur for all possible filling levels by applying a corresponding window function to the signal.

[0019] At least one excitation element can be any element or device suitable for mechanically exciting the container, i.e., suitable for causing the container to vibrate or oscillate. Specifically, the excitation element can be directly attached to the container or to a suspension element, and can be configured to vibrate in response to an electrical signal applied to the excitation element. The excitation element is specifically configured (specifically arranged and oriented) such that a desired suspension mode is excited. The excitation element can be, for example, an oscillator, an impact hammer, a piezoelectric element, or any other device that introduces vibratory / oscillatory motion into the container / suspension system. However, the excitation element does not necessarily need to be directly attached to the container or suspension element, and alternatively, it can be, for example, a loudspeaker or a similar device that emits sound waves. In such a configuration, the loudspeaker's emission direction can be directed towards the container at a desired location, such that the emitted sound waves coupled into the container mechanically excite the container / suspension system, particularly at least one of the suspension modes. Furthermore, instead of an additional excitation element, in aircraft or vehicles, aircraft (or vehicle) noise originating from turbines, pumps, etc., can also be directly coupled to the container / suspension element and thus act as an excitation element. Preferably, though not limited thereto, at least one excitation element is located in the same position as one of the sensing elements, such that at least one suspension mode in the suspension modes is specifically excited. Because at least one excitation element is connected to the output terminal of a signal source, the electrical signal output from the signal source (the input signal of the excitation element) is converted by at least one excitation element into a corresponding mechanical vibration or oscillation coupled to the container / suspension system. It will be apparent to those skilled in the art that the frequency component of the input signal corresponding to the resonant frequency of the container (i.e., in particular the current modal frequency of at least one suspension mode in the suspension modes), or more precisely, the frequency component of the input signal corresponding to the resonant frequency of the system of the container (with its filling) and the suspension elements, exhibits the relative amplitude maximum of the oscillation or vibration of the container at a given time, while other frequency components do not.

[0020] At least one sensing element (also referred to herein as a "sensing element") can be any sensing or sensor element adapted to detect vibrations or oscillations of the container / suspension system and to generate a corresponding electrical signal, particularly a signal comprising the frequency component of the oscillation or vibration mode of the container / suspension system. For example, the sensing element can be an accelerometer or a laser vibrometer. These signals are input to a processing unit.

[0021] The processing unit can be any computerized device capable of analyzing electrical signals, particularly by performing spectral or modal analysis. The processing unit can be, for example, a general-purpose computer with a CPU and memory components, as is well known in the art. The processing unit can also be any other microcomputer device, such as an ASIC, FPGA, or TPU device. The processing unit receives output signals, i.e., vibration signals, from the sensing element and performs joint data analysis algorithms on these vibration signals along with the input signals from the signal source to calculate / determine at least one suspension mode based on the vibration signals received from the sensing element, and to determine the current fill level of the fluid container based on the current modal frequency of the determined suspension mode (e.g., by correlating the determined modal frequency with a reference suspension mode frequency, as further described below).

[0022] For example, as described in more detail below with respect to certain embodiments, the processing unit can determine the transfer function (e.g., frequency response function (FRF)) between the vibration signal of the sensing element and the input signal in order to identify and determine the modal frequencies of the suspension pattern. The current fill level can then be determined based on the determined current modal frequencies of the suspension pattern. However, these are merely examples of corresponding data analysis algorithms for identifying suspension patterns and determining their modal frequencies. Other suitable algorithms are also conceivable. As long as the suspension pattern and its current modal frequencies can be determined, the fill level of the fluid container can be easily determined by correlating the current modal frequencies with reference data (because the modal frequencies of the suspension pattern are highly visible (even under dynamic conditions) and highly correlated with the fill level of the fluid container).

[0023] While pressure and / or temperature do not have a very significant effect on suspension patterns, they may, in principle, have at least a limited effect. Therefore, to further improve accuracy, optionally, the temperature of the fluid container can be considered when determining the fill level. The container temperature can be taken into account by incorporating it into the corresponding reference suspension pattern frequency data or a machine learning algorithm, as described below. Therefore, the fill level monitoring system may also include a corresponding temperature sensor.

[0024] According to an embodiment, the processing unit is further configured to identify at least one suspension mode and determine the modal frequency of at least one suspension mode by determining a transfer function in the frequency domain for the vibration signal of each of the at least one sensing element in the following manner: normalizing and transforming each vibration signal and the input signal in the vibration signal of the at least one sensing element into a frequency domain representation using a Fast Fourier Transform (FFT); and comparing the FFT of each vibration signal in the vibration signal of the at least one sensing element with the FFT of the input signal to determine the corresponding transfer function.

[0025] The processing unit receives and analyzes the input signal from the signal source at any given time to calculate the frequency components included in the input signal. However, instead of directly using the input signal, sensor signals from corresponding feedback sensors at at least one excitation element can also be used. The processing unit also receives and analyzes the vibration signal from each of the sensing elements. Typically, both the input signal and the vibration signal are time-series data.

[0026] Therefore, the frequency components (i.e., frequency domain representations) of the input signal and the vibration signal can be determined, for example, by performing any spectrum analysis algorithm (such as, in this embodiment, Fast Fourier Transform (FFT)) on the corresponding data, thereby creating a corresponding spectrum function indicating the signal components at the frequency (i.e., the corresponding signals (input signal and vibration signal) in the frequency domain).

[0027] These spectral functions of the vibration signal and the input signal can then be used to determine the corresponding transfer function (also known as the frequency response function (FRF)) of each vibration signal relative to the input signal. This frequency response function is defined as:

[0028]

[0029] in These are the corresponding transfer functions. These transfer functions indicate the amplification or attenuation of the amplitude of certain frequency components at frequency f. It is the corresponding measurement signal in the frequency domain (i.e., the vibration signal of the corresponding sensing element in the frequency domain, such as the corresponding FFT of the signal), and This is the input signal (or excitation signal) in the frequency domain (e.g., the FFT of the input signal). Index i refers to the corresponding sensing element, i.e. It is the first transfer function, and It is the vibration signal of the first sensing element in the frequency domain; It is the second transfer function, and It is the vibration signal of the second sensing element in the frequency domain. Therefore, the function and The transfer function corresponds to the spectral function of the vibration signal and the input signal, such as the spectral function obtained by FFT or other spectral analysis of the corresponding signal, and indicates how certain frequencies of the vibration signal deviate from the input signal and thus show their attenuation or amplification. The calculation of FFT itself is well known in the art and will not be described in detail here. The corresponding transfer function can then be determined using the corresponding FFT (spectral function), as described above. Although described as using Fast Fourier Transform (FFT) as a spectral analysis process to transform the corresponding time series data into the frequency domain, it should be understood that any other spectral analysis algorithm can also be used.

[0030] As mentioned above, suspension modes are the resonant modes of suspension elements. Therefore, when the container / suspension system is excited at these frequencies, the oscillations of the system at these frequencies are amplified, and thus exhibit significant local maxima in the transfer function. These local maxima can be identified, and their frequencies can be determined by the processing unit using any suitable spectral analysis algorithm, which will be readily apparent. Identifying the locations of local maxima can be accomplished, for example, through standard data analysis procedures, and can be further refined, for example, through additional signal processing techniques such as spline interpolation. This makes it possible to determine the current modal frequency corresponding to the suspension mode.

[0031] If more than one sensing element is used, a corresponding transfer function can be determined individually for each sensing element, and the modal frequency of the suspension mode can be determined based on each such transfer function. Then, in a non-limiting example, the individual results can be averaged or used for redundancy. Furthermore, in another non-limiting example, a weighted averaging function can be used to assign higher weights to measurements detected, for example, by sensing elements directly arranged at one of the suspension elements. Moreover, if more than one suspension mode is obtained / detected, the modal frequency of each of these suspension modes can be determined individually.

[0032] The current fill level of the fluid container can be determined by the processing unit by obtaining the current modal frequency of at least one suspension mode from the transfer function and correlating it with reference data. Furthermore, if more than one suspension mode is detected, this correlation (and thus the fill level) can be determined for each suspension mode, and the results can be reused redundantly (e.g., for consistency checks) or averaged.

[0033] Although the processing unit is described as an independent unit, it should be understood that it can also be part of a higher-level system, such as a flight computer in the cockpit of an aircraft or other vehicle, or at a remote location, such as a ground station. Furthermore, the processing unit may include multiple independent units that perform different steps of the overall process. Additionally, the processing unit, or the higher-level system including the processing unit, may include a display component that outputs a current fill level in the sense of a fuel gauge after determining the current fill level of a fluid container, or the processing unit may output a corresponding fill level signal, which may, for example, be transmitted to an onboard computer (such as a flight computer) or other control and monitoring systems. The term "processing unit" encompasses any conceivable combination of these elements.

[0034] According to another embodiment, the processing unit is configured to independently determine at least one suspension mode for each of at least one sensing element by determining the frequency of the corresponding maximum peak value of the corresponding transfer function.

[0035] This can increase deterministic redundancy and also makes it possible to account for small biases (e.g., due to flight dynamics) by averaging individual results.

[0036] According to another embodiment, the processing unit is configured to determine the current filling level of the fluid container by correlating the modal frequency of each of the determined suspension modes with the frequency of a reference suspension mode corresponding to a specific filling level.

[0037] As further described above, suspension modes are highly sensitive and stable to the filling level of the fluid container and drift in a predictable manner. Therefore, reference suspension mode frequencies can be predetermined, for example, in a laboratory environment or during a calibration process (optionally, for each suspension mode if more than one mode is examined). In this process, the fluid container can, for example, first be fully filled and then emptied in a controlled manner while tracking the measured modal frequencies of the suspension modes for different filling levels and retaining these modal frequencies as reference data. However, the reference data can also be determined in another suitable manner, such as through computer modeling or machine learning and artificial intelligence methods. Furthermore, it is conceivable to store multidimensional reference data (e.g., each sensing element corresponds to one dimension if more than one sensing element is used), i.e., a “mapping” of the reference frequency for each sensing element relative to the corresponding filling level.

[0038] The current filling level of the fluid container can then be determined by correlating the frequencies of the determined suspension modes (or multiple frequencies) with reference data. However, this correlation can also be accomplished via machine learning and artificial intelligence algorithms.

[0039] According to another embodiment, the processing unit is configured to determine the current filling level by averaging the current filling level determined independently for each sensing element in the sensing element.

[0040] According to another embodiment, at least one excitation element is configured to be located at the same position as at least one sensing element among the sensing elements.

[0041] Specifically, the corresponding excitation element and the corresponding sensing element can be located at the same position in the container / suspension system, preferably (but not limited to) at one of the at least one suspension element. If the excitation element has a defined direction of action and the sensing element has a defined direction of detection, the excitation element and the sensing element can be oriented such that the direction of action of the excitation element corresponds to the desired suspension pattern direction and the direction of action corresponds to the detection direction. This configuration enables the target excitation of the desired suspension pattern and further increases the signal-to-noise ratio because the sensing element directly and accurately acquires the target suspension pattern.

[0042] According to another embodiment, at least one suspension element is made of a metallic material, and / or the suspension stiffness of at least one suspension element, expressed in terms of Young's modulus, is in the range of 2 GPa to 420 GPa.

[0043] Preferably, the suspension stiffness is in the range of 20 GPa to 350 GPa, more preferably in the range of 40 GPa to 280 GPa, and most preferably in the range of 60 GPa to 220 GPa.

[0044] As further described above, nonlinear materials such as elastomeric materials and damping of suspension elements should be avoided for various reasons (hyperelastic behavior, alterations in linear behavior). Metals have proven to be particularly suitable. For example, the stiffness of a material can be related to Young's modulus. However, it is a complex quantity that depends on both the material stiffness (Young's modulus of isotropic materials such as most metals) and the geometry. For example, aluminum with a stiffness of, for example, 70 GPa (in terms of Young's modulus), titanium with a stiffness of, for example, 120 GPa, or steel with a stiffness of, for example, 210 GPa are suitable. However, these are merely non-limiting examples. Stiffness can also be described, for example, by the displacement u caused by the force F acting on the material, i.e. , where k is the stiffness. For example, in a non-limiting example, this stiffness k, expressed in terms of displacement caused by force, can range from 10 N / m to 10 N / m. 7 Within the range of N / m. Specifically, in a non-limiting example, the frequency of the suspension mode can be in the range of approximately 50 Hz to 100 Hz, and the frequency depends on the mass of the fluid container. However, all these ranges are merely exemplary, and all system considerations and constraints must be taken into account to determine the actual stiffness of the suspension elements.

[0045] Furthermore, suspension elements must still be carefully designed to find a good trade-off between softness and stiffness. Specifically, if the suspension (i.e., the suspension elements) is too soft, displacement and stress become too high. On the other hand, if the suspension is too stiff, the vibrations of the mounted components (i.e., suspension modes) are pushed into the high-frequency range and become less pronounced across a wide range of tank modes. Therefore, the suspension modes must lie in the mid-frequency range. Unlike a standard non-motion suspension, the suspension itself can be considered a mounted component because it is mechanically and well connected to the object to be weighed. This results in a strong dynamic coupling between the object and the mounted component, where they cannot be separated: they vibrate as a whole.

[0046] The aforementioned stiffness range has proven to be a good compromise between softness and stiffness.

[0047] According to another embodiment, at least one suspension mode includes at least one of the following modes associated with the corresponding degree of freedom: translational vibration mode and rotational vibration mode.

[0048] Translational vibration modes correspond to modes in which the fluid container oscillates, causing it to displace linearly relative to a certain direction of extension of the fluid container. Such modes can include, for example: lateral modes, where the container oscillates in the lateral direction (e.g., if the fluid container is a Dewar flask, this would correspond to a linear displacement perpendicular to the longitudinal extension of the fluid container); longitudinal modes, where the fluid container displaces (i.e., oscillates) along its longitudinal extension; and vertical modes, where the fluid container oscillates linearly in the vertical direction. For example, if the fluid container is mounted to the floor inside the aircraft via a suspension element (which also serves as a mounting element), the vertical direction would be perpendicular to the floor.

[0049] Rotational vibration modes correspond to any rotational movement / displacement of the fluid container relative to the suspension element along at least one of its main axes (i.e., rotational oscillations) (rotation along axes other than the main axes can be described by a linear combination of rotations along the main axes).

[0050] For each mass of a fluid container (i.e., the filling level), each of these degrees of freedom can have a different mode frequency mode.

[0051] According to another embodiment, at least one suspension element is configured to connect a fluid container to a surrounding structure.

[0052] In other words, suspension elements also act as mounts to connect fluid containers to surrounding structures, such as the aircraft fuselage or internal components within the aircraft fuselage (e.g., floor panels).

[0053] According to another embodiment, at least one suspension element is a spring, and / or the fill level monitoring device further includes a limiting element that restricts the vibrational movement of the fluid container and at least one suspension element to a specified degree of freedom.

[0054] In some cases, to completely constrain movement in one direction, a standard prismatic joint or slider can be used as a limiting element. For example, if the spring is set vertically, it may be desirable to avoid any horizontal movement in order to obtain a crisp frequency response for the corresponding suspension mode. However, other limiting elements can also be used. Furthermore, such limiting elements can be used in conjunction with other types of suspension elements (i.e., with suspension elements other than springs).

[0055] According to another embodiment, at least one suspension element is a metal frame that can vibrate in at least one of the vertical, longitudinal, and lateral directions.

[0056] Such a metal frame can be, for example, an arched metal beam that can be attached (e.g., welded) to a fluid container. The stiffness of the metal frame can be defined, for example, by the thickness of the beams of the metal frame (which can be formed from a beam structure). The metal frame can be shaped such that it allows vibration / oscillation in the desired degrees of freedom (particularly through corresponding temporary deformation of the metal frame). For example, if the metal frame is shaped to support the fluid container by providing symmetrical holding forces from the lateral sides, and wherein the metal beams of the metal frame primarily undergo bending, then the metal frame can restrict movement in the lateral direction but allow oscillation in the longitudinal and vertical directions. On the other hand, if the metal beams of the metal frame extend substantially vertically between the fluid container and the surrounding structure, then the metal frame can allow longitudinal, lateral, and vertical movement. By carefully designing the metal frame, the desired degrees of freedom and available suspension modes can be achieved. For example, suitable shapes can be designed using simulation, physical models, generative AI algorithms, or any other suitable method. Examples of possible shapes will become clearer below in conjunction with the accompanying drawings.

[0057] This metal frame can also be used to mount fluid containers in a suspended configuration, rather than an upright configuration.

[0058] According to another embodiment, at least one excitation element is arranged at and in contact with at least one suspension element, and is configured to couple a vibration load corresponding to an input signal from a signal source to at least one suspension element and a fluid container.

[0059] In this configuration, the excitation element directly couples the vibrational movement to the suspension element itself, resulting in direct excitation of the suspension mode.

[0060] According to another embodiment, the filling level monitoring device further includes at least one end stop to restrict the movement of the fluid container.

[0061] In very rare cases, such as emergencies like collisions, having a fail-safe system can be beneficial. End stops are common and can be made of elastomers or foam (to achieve gradual behavior). Such end stops restrict the movement of fluid containers under extreme load conditions and increase safety.

[0062] According to a second aspect, a hydrogen tank is provided, comprising a fluid container for containing liquefied hydrogen and a fill level monitoring device according to any embodiment described herein.

[0063] The filling level monitoring device can be implemented according to any of the above embodiments and is configured to monitor the filling level of the fluid container of the hydrogen tank according to the above principle.

[0064] According to a third aspect, an aircraft is provided. The aircraft includes an aircraft fuselage and a hydrogen tank according to any embodiment described herein. A fill level monitoring device is configured to monitor the hydrogen fill level of the fluid container.

[0065] This type of aircraft can use hydrogen as an alternative fuel, meaning it can use hydrogen as an energy source to power the aircraft's turbines. Hydrogen can be used as a primary energy source, for example, by burning hydrogen directly inside the turbine, or it can be used as a secondary energy source, for example, by using hydrogen fuel cells to produce electricity and then using the electricity generated in this way to power the turbines.

[0066] The fill level monitoring device according to this disclosure enables accurate monitoring of the hydrogen tank fill level under any flight conditions. Specifically, the fill level monitoring device can continuously monitor the fill level during flight and report the corresponding fill level to the pilot. The fluid container of the hydrogen tank can be positioned, for example, within the fuselage such that the longitudinal axis of the container coincides with the longitudinal axis of the fuselage. However, the hydrogen tank can also be positioned within the fuselage in any other suitable manner.

[0067] In summary, this disclosure provides an accurate monitoring system for maintaining the tracking of the fill level of fluid containers, such as liquid hydrogen tanks. Conventional fill level monitoring methods, such as measuring the flow rate of fluid leaving the tank or determining the weight of the tank, are inherently inaccurate due to varying flight conditions in aircraft (and the cryogenic nature of LiH2). These inaccuracies can be avoided by measuring the fill level of the fluid container via monitoring the resonant frequency of the tank associated with the fill level, particularly by monitoring the modal frequencies of suspension modes, which are highly sensitive to fill level, predictable, and insensitive to external influences. Therefore, this disclosure enables more accurate and non-invasive monitoring of the fill level of fluid containers, typically and particularly in aircraft applications, thereby increasing the safety of aircraft using alternative fuels such as hydrogen.

[0068] Although this disclosure is primarily described in relation to aircraft applications, it should be noted that this disclosure can be used for any suitable application, such as for automotive and similar applications. Attached Figure Description

[0069] In the following description, exemplary embodiments are illustrated in more detail with reference to the accompanying drawings. These illustrations are schematic and not drawn to scale. The same reference numerals refer to the same or similar elements. The drawings show:

[0070] Figure 1 This is a schematic overview of a hydrogen tank having a filling level monitoring device for a fluid container used in the hydrogen tank, which includes a spring as a suspension element.

[0071] Figure 2 It is possible Figure 1 An exemplary configuration of a suspension element in the form of a spring used in a filling level monitoring system.

[0072] Figure 3 It is possible Figure 1 Another exemplary configuration of a suspension element in the form of a metal frame used in a filling level monitoring system to prevent lateral movement.

[0073] Figure 4 It is possible Figure 1 Another exemplary configuration used in a filling level monitoring system is a suspension element in the form of a metal frame that also allows lateral movement.

[0074] Figure 5 These are exemplary transfer functions (frequency response functions) for sensing elements mounted on fluid containers with different stiffnesses, wherein each transfer function is determined for two specific fill levels of the fluid container (i.e., empty state and fully filled state).

[0075] Figure 6It uses a metal frame as a suspension element (such as...) Figure 3 and Figure 4 The transfer function is obtained using the first (low) stiffness of the metal frame in both the empty and fully filled states of the fluid container.

[0076] Figure 7 It uses a metal frame as a suspension element (such as...) Figure 3 and Figure 4 The transfer function is obtained by using the second (intermediate) stiffness of the metal frame in both the empty and fully filled states of the fluid container.

[0077] Figure 8 It uses a metal frame as a suspension element (such as...) Figure 3 and Figure 4 The transfer function is obtained using the third (high) stiffness of the metal frame in both the empty and fully filled states of the fluid container.

[0078] Figure 9 This is a schematic diagram of an aircraft that includes a hydrogen tank with a filling level monitoring device. Detailed Implementation

[0079] Figure 1 An exemplary liquid hydrogen tank 300 is schematically illustrated. The hydrogen tank 300 includes a fluid container 200 and a fill level monitoring device 100. In the depicted configuration, the fluid container 200 is implemented as a cylindrical Dewar flask, shown in a top view of one of its end faces or tips. Furthermore, in the depicted configuration, the fill level monitoring device 100 includes an excitation element 10 and a sensing element 21; however, it should be understood that more than one excitation element 10 and more than one sensing element 21 may be provided. Additionally, the fill level monitoring device 100 includes a signal source 30, a processing unit 40, and optional spatial orientation and acceleration sensors 60 and / or optional temperature and / or pressure sensors 60 (both indicated by the same reference numerals, which may also refer to a common sensor unit including all of these sensors). The excitation element 10 is electrically connected to the signal source 30. In addition, signal source 30 is electrically connected to processing unit 40, sensing elements 21 and 22 are electrically connected to processing unit 40, and optional spatial orientation and acceleration sensor 60 (and / or optional temperature and / or pressure sensor 60) are electrically connected to processing unit 40.

[0080] Fluid container 200 contains a liquid hydrogen filler (not explicitly shown). Fluid container 200 is a pressure-sealed gas container configured to contain pressurized liquefied hydrogen. In the depicted configuration, fluid container 200 is a cylindrical Dewar flask 200, including a first tip 221 and a second tip (not explicitly shown). The first tip 221 and the second tip are arranged opposite each other and spaced apart from each other along the length of fluid container 200. Sensing element 21 is co-located with excitation element 10 at the top of fluid container 200. However, it should be understood that excitation element 10 and sensing element 21 may be arranged in different locations, and neither element 10 nor 21 necessarily must be arranged at the top of fluid container 200. Excitation element 10 only needs to be able to excite at least one suspension mode as described herein, and sensing element 21 needs to be able to sense the motion / vibration / oscillation of fluid container 200 and at least one suspension element 70 (also collectively referred to herein as the “container / suspension system”) so that the suspension mode can be observed.

[0081] The suspension element 70 also serves as a mounting element 70 to interconnect the fluid container 200 to a surrounding structure 410, such as an aircraft fuselage 410 or components within the aircraft fuselage 410, such as a floor panel. In the depicted configuration, the suspension element 70 is a spring 71 and is fixedly connected (e.g., welded) to the fluid container 200 and attached to the surrounding structure 410. A restraining element 73 (which may be, for example, a slider or a prismatic joint) restricts the movement of the fluid container 200 and the suspension element 70 in one direction (or degree of freedom), particularly in the vertical direction. Typically, without such a restraining element 73, the suspension element 70 and the fluid container 200 can move in up to six degrees of freedom (three translational degrees of freedom and three rotational degrees of freedom).

[0082] As described above, signal source 30 can be any signal source that generates an electrical signal covering multiple frequency components. The frequency range of signal source 30 particularly spans the possible modal frequencies 80 of the fluid container 200 at different filling levels. Figure 1 Not described in the text, see Figures 5 to 8 This frequency span can be determined, for example, through computer simulations of the structural dynamics of the container / suspension system. It can also be predetermined in a laboratory setting, which would be obvious. Several possibilities have already been described above and will not be repeated here. In the depicted configuration, signal source 30 is a Gaussian white noise signal source 30 that generates a wide range of uniformly distributed frequency components.

[0083] The container 200, together with the suspension element 70, has various resonant frequencies, some of which are related only to the structural dynamics of the container 200 itself, while others depend on the filling liquid level. Specifically, some of the resonant frequencies are proportional to or otherwise related to the filling liquid level of the fluid container 200 in a defined manner, and shift when the filling liquid level changes. In particular, suspension pattern 25, as further defined above (see...) Figure 5 The system is highly sensitive to the filling level of the fuel container 200 and highly insensitive to external factors, making it ideal for monitoring the filling level of the fluid container 200. The fluid container 200 and suspension element 70 together form a spring / mass system with a resonant frequency that depends on the mass of the fluid container 200 (and therefore the filling level) and the stiffness of the suspension element 70. Therefore, when the filling level changes, the modal frequency 80 of suspension mode 25 shifts. Thus, by determining at least one suspension mode 25 (in... Figure 1 In the configuration, especially in the vertical suspension mode, the current modal frequency is 80 (see...). Figure 3 This allows for accurate determination of the current filling level of the fluid container 200.

[0084] The Gaussian white noise signal source 30 is configured to generate a corresponding electrical signal or input signal 31 for the excitation element 10 (it should be understood that although only one excitation element 10 is used in the depicted configuration, multiple excitation elements 10 and / or multiple sensing elements 22, as further described above, may also be used). The excitation element 10 can be any element or device capable of generating mechanical oscillations or vibrations. In the depicted configuration, for example, the excitation element 10 is a vibrator or impact hammer that introduces vertical motion (i.e., oscillation) into the container / suspension system. The excitation element 10 is directly attached to the fluid container 200 and generates vibrations / oscillations corresponding to the input signal 31 from the signal source 30, coupled to the fluid container 200 and the suspension element 70. However, the excitation element 10 can also be any other device capable of coupling mechanical vibrations to the container / suspension system, and in particular, it does not need to be directly attached to the container 200. For example, the excitation element can also be an acoustic source pointing towards the fluid container 200 at a desired location. However, these are merely examples, and in principle, any other excitation element 10 can be used.

[0085] The oscillation or vibration from the excitation element 10 that corresponds to the resonant frequency of the fluid container 200 at the current filling level 210 at the time of measurement (in particular, that corresponds to the current modal frequency 80 of the suspension mode 25 defined by the design of the suspension element 70) is amplified within the container / suspension system, and produces corresponding oscillations in the fluid container 200 and the suspension element 70, while other frequency components are not amplified.

[0086] Sensing element 21 is then configured to acquire or measure these oscillating movements of container 200 and generate a corresponding vibration signal 23 for processing unit 40. Sensing elements 21 and 22 can be any sensing element capable of measuring oscillations or vibrations within fluid container 200. In the exemplary embodiment shown, sensing element 21 is an accelerometer or laser vibrometer. When fluid container 200 vibrates or oscillates, sensing element 21 measures these oscillations and generates a corresponding time-series signal (vibration signal 23) for processing unit 40. Since the oscillations of fluid container 200 include certain frequency components, vibration signal 23 follows a frequency pattern of vibration. However, other suitable sensing elements may also be used.

[0087] It should be noted that although shown and described as having one excitation element 10 and one sensing element 21, any other number of excitation elements 10 and sensing elements 21 may be used depending on the specific requirements, as long as the excitation element 10 is arranged to excite the desired suspension pattern and the sensing element 21 also measures the suspension pattern 25.

[0088] The processing unit 40 can be any computing device for processing signals, such as a general-purpose computer, microcomputer, FPGA, ASIC, TPU, or any combination thereof, or any other suitable computing device, having a CPU and memory components. The processing unit 40 receives vibration signals 23 (or multiple vibration signals 23, if multiple sensing elements 21 are used) from sensing element 21 and an input signal 31 from signal source 30. By comparing the input signal 31 with each of at least one vibration signal 23, the processing unit 40 can determine a corresponding transfer function 27 for each sensing element in the sensing element 21 (see [link to relevant documentation]). Figures 5 to 8 The suspension mode 25 and its current modal frequency 80 can be determined based on the transfer function 27, which can in turn be used to determine the current filling level of the fluid container 200. The filling level monitoring device 100, or more precisely its processing unit 40, can then output a filling level signal 51, or, if implemented accordingly (i.e., if a display component is provided), can display the current filling level.

[0089] exist Figure 1 In this configuration, an additional end stop 74 is arranged above the fluid container 200, which may also be connected to surrounding structures. In emergency situations such as collisions, the end stop 74 limits the movement of the fluid container 200 to a maximum extent.

[0090] Figures 2 to 4 It shows Figure 1 An alternative implementation of the suspension element 70. For clarity, in Figures 2 to 4Other functional components, such as the processing unit 40, signal source 30, end stop 74, excitation element 10, sensing element 21, sensor 60, and limiting element 73, are not shown. However, Figures 2 to 4 Each embodiment of the suspension element 70 can be implemented in Figure 1 This is implemented in the filling liquid level monitoring system.

[0091] Figure 2 An embodiment is shown in which two springs 71 are configured as suspension elements 70, spaced apart from each other along the longitudinal direction of the fluid container 200. Each of the springs 71 is connected to the tank via a reinforcing metal arch 75, which provides increased mechanical stability to the fuel container 200. According to the limiting element 73 ( Figure 1 The settings of ) can control the excitation element 10 ( Figure 1 ) Incentive suspension mode.

[0092] Figure 3 Another embodiment is shown in which two metal frames 72 are provided as suspension elements 70. The metal frames 72 include an arcuate central portion 76 and foot-shaped side portions 77. The metal frames 72 are shaped such that they provide symmetrical retaining forces from the lateral sides. Therefore, the metal frames 72 laterally support the fuel container 200, making lateral movement virtually impossible. However, the arched shape allows oscillations / vibrations in the vertical direction 90 and the longitudinal direction 91, but prevents movement in the lateral direction. The metal frames 72 primarily undergo bending, resulting in two suspension modes (one along the vertical direction 90 and one along the longitudinal direction 91). By changing the cross-section of the beams of the metal frames 72, both the frequency and prominence of the suspension modes can be altered.

[0093] Figure 4 An alternative is shown in which two metal frames 72 are provided as suspension elements 70. Figure 4 Structure and Figure 3 The structural difference lies in the provision of a vertical beam 78 instead of... Figure 3 The foot-shaped sides 77. Clearly, these vertical beams 78 can be bent in every direction, and can also be stretched and compressed vertically. Therefore, Figure 4 The configuration enables oscillations in three translational degrees of freedom: vertical (90°), longitudinal (91°), and lateral (92°). Therefore, Figure 4 The suspension element 70 enables three suspension modes: vertical 90, longitudinal 91, and lateral 92. Similarly, by changing the cross-section of the beams in the metal frame 72, both the frequency and intensity of the suspension modes can be altered. For example, using a short, hollow beam can strengthen the vertical mode and weaken the other modes. Specifically… Figure 3 and Figure 4 The suspension can also be reversed (i.e., by suspending the fluid container 200 on the ceiling) to reduce any buckling issues.

[0094] Reference Figures 1 to 4 Typically, the excitation element 10 (e.g., a vibrator or impact hammer) and the sensing element 21 (e.g., an accelerometer) are unidirectional. Therefore, if monitoring a vertical mode, it may be advantageous to also place both the excitation element 10 and the sensing element vertically, and so on. The preferred location for the excitation element 10 and the sensing element 21 is where the modal amplitude of the corresponding suspension mode being monitored is largest. Furthermore, some filtering effects can be achieved by combining locations, for example, by simultaneously exciting (and sensing) below each suspension element 70. This can cause the modal peak of the suspension mode to become much larger and more pronounced than all other peaks, thus enabling very clear peak location estimation.

[0095] Figure 5 An exemplary diagram of transfer function 27 is shown. Reference is still made to this diagram below. Figure 1 . Figure 5 Each line in the graph is represented as a separate transfer function 27 on the frequency (x-axis) and y-axis (y-axis) in the form of a frequency response function, that is, for Figure 5 For each line in the given line, the following relationship holds:

[0096]

[0097] in These are the corresponding transfer functions 27. These transfer functions 27 indicate the amplification or attenuation of the amplitude of certain frequency components at frequency f. It is the corresponding measurement signal in the frequency domain (i.e., the vibration signal 23 of the corresponding sensing element 21 in the frequency domain, for example, the corresponding FFT of the vibration signal 23), and This refers to the input signal (or excitation signal) in the frequency domain (e.g., the FFT of the input signal). Index i refers to the corresponding sensing element 21, i.e. It is the first transfer function 27, and It is the vibration signal 23 of the first sensing element 21 in the frequency domain; It is the second transfer function 27, and It is the vibration signal 23 of the second sensing element 21 in the frequency domain. Therefore, the function and The corresponding spectral functions of the vibration signal 23 and the input signal 31, such as those obtained through FFT or other spectral analysis of the corresponding signals, and the transfer function 27, indicate how certain frequencies of the vibration signal 23 deviate from the input signal 31 and thus show their attenuation or amplification. The corresponding transfer function 27 can then be determined using the corresponding FFT (spectral function), as described above. Figure 5 As shown. Although described as using the Fast Fourier Transform (FFT) as a spectral analysis process to transform the corresponding time series data into the frequency domain, it should be understood that any other spectral analysis algorithm can also be used.

[0098] In order to determine Figure 5 The chart, Figure 1 The excitation element 10 is driven by a signal source 30, for example, by driving a white noise input signal 31. This input signal 31 introduces vibration / oscillation within the container / suspension system, which in particular also includes suspension modes. The sensing element 21 then senses a vibration signal 23 relating to the vibration / oscillation within the container / suspension system. Based on these signals 31 and 23, a [missing information - likely a measurement or measurement] is determined as described above. Figure 5 The transfer function 27 has been determined for three stiffnesses: E / 100, E / 10, and E, where E = 210 GPa is the Young's modulus of the steel. For each of these stiffnesses, a transfer function 27 has been determined for the fluid container 200 in a completely empty state and for the fluid container 200 in a completely filled state.

[0099] Figure 5 An example of a spring-type suspension element 70 is shown. Figure 1 and Figure 2 The transfer function 27 of the spring-type suspension element 70 shown. In Figure 5In the transfer function 27, each transfer function shows a clearly distinguishable maximum peak 29 corresponding to the suspension mode. The results show that the suspension modes are very distinct, their amplitude decreasing with increasing stiffness, and the frequency gap (7.1 Hz here) between the empty and fully filled fluid container 200 is larger at higher spring stiffness. Therefore, higher stiffness of the suspension element 70 is safer and more efficient. Stiffness can be related, for example, to Young's modulus E. Therefore, a stiffness of the suspension element 70 in the range of 2 GPa to 420 GPa, preferably in the range of 20 GPa to 350 GPa, even more preferably in the range of 40 GPa to 280 GPa, and most preferably in the range of 60 GPa to 220 GPa (expressed in Young's modulus; as mentioned above, stiffness can also be expressed in other ways, for example by displacement caused by forces acting on the fluid container; the letter k in this document generally refers to a measure of stiffness (which may include Young's modulus), independent of the representation used) seems particularly preferred, although other stiffnesses are also possible.

[0100] Figures 6 to 8 It shows the use of a metal frame 72, such as Figure 3 and Figure 4 The transfer function 27 is obtained by using the metal frame 72 as a suspension element 70. The transfer function is then determined again in the empty state and the fully filled state of the fluid container 200. Figure 6 The transfer function 27 is shown for the relatively thin beam of the metal frame 72. Figure 7 It shows the target relative to Figure 6 The transfer function of a thicker beam is 27, and Figure 8 It shows the target relative to Figure 6 and Figure 7 The transfer function of the relatively thick beam is 27.

[0101] Figures 6 to 8 As shown, Figure 1 and Figure 2 Similar to the spring-like suspension element 70, the stiffer (thicker) beam of the metal frame 72 performs better (wider clearance, less displacement). Furthermore, Figures 6 to 8 The different maximum peak values ​​29 observed in each case of the suspension pattern at different fill levels are clearly shown.

[0102] Generally speaking, regarding Figures 1 to 8The filling level of the fluid container 200 can therefore be determined by: using a suitable suspension element, coupling vibration / oscillation to the container / suspension system, measuring the frequency response of the vibration / oscillation by means of sensing element 21 (as described above), identifying the maximum peak 29 and determining its modal frequency 80. The filling level can then be determined, for example, by comparison with a reference database, by using a machine learning (AI) algorithm, or by any other suitable method. Optionally, it can be determined by means of... Figure 1 An optional sensor 60 can be used to account for the possible effects of temperature, orientation, pressure, etc. If more than one sensing element 21 (and / or more than one excitation element 10) is used (typically, one excitation element 10 and one sensing element 21 are sufficient; however, using multiple excitation elements 10 and / or sensing elements 21 can increase accuracy), for example, for each pair of excitation element 10 and sensing element 21, individual results (expressed as modal frequencies or fill levels) can be determined and averaged. This possibility has been described in further detail above and will not be repeated here.

[0103] In addition, other vibration modes besides the suspension mode can be (optionally) considered to increase accuracy or provide redundancy. For example, a sensing element 21 can be mounted to each tip of the fluid container 200. In this arrangement, a horizontal vibration mode can be further determined, which corresponds to vibrations propagating horizontally within the fluid container 200 itself, and is also well-suited for determining the fill level. The horizontal vibration mode is the vibration mode in which the tips of the fluid container 200 (or possible positions of the fluid container 200 located on opposite sides of the container 200) vibrate synchronously. This mode and its frequency also depend on the fill level and can be determined in a manner similar to the suspension mode. However, here, the indication function is further determined as follows: :

[0104]

[0105] in, It is an indicator function. It is the first transfer function of the sensing element 21 at a tip. The second transfer function of sensing element 21 at the relative tips, where conj indicates complex conjugate and Re indicates taking the real part, allows for easy extraction of the parallel vibration components measured by the first sensing element 21 and the second sensing element 22. Based on the obtained indication function, the current modal frequency of the horizontal vibration mode (and thus the current filling level of the fluid container 200) can also be determined. The horizontal vibration mode is the vibration mode in which the tips of the fluid container vibrate synchronously relative to each other at any given time. It also exhibits high resonance.

[0106] Just like the suspension mode, the horizontal vibration mode can be used to determine the filling level of the fluid container 200 independently. This result can be used redundantly, or it can be incorporated into the averaging process, as already described with respect to the different suspension modes and the different sensing elements 21.

[0107] Figure 9 The image shows an aircraft 400 with a fuselage 410 and two turbines 420. The aircraft also includes a liquid hydrogen tank 300, as described above. Figure 1 The liquid hydrogen tank 300 is described. The hydrogen tank 300 serves as a fuel source for the turbine 420. The turbine 420 can directly burn hydrogen from the hydrogen tank 300 as its primary energy source, or it can be an electric turbine, for example, using electrical energy generated by a fuel cell that consumes hydrogen from the hydrogen tank 300.

[0108] The vibration of the Turbo 420 can also be found in Figure 1 The excitation element 10 is directly coupled to the container 200 of the hydrogen tank 300 at its location. Therefore, the turbine 420 itself acts as the excitation element 10 of the container 200 and couples vibrations into the container 200. However, this is optional. Different excitation elements 10 as described herein can also be used.

[0109] Optionally, the yaw, pitch, and roll sensors of the aircraft 400 itself can be connected to the processing unit 40 and can act as... Figure 1 The spatial orientation and acceleration sensor 60, however, is optional, as the use of suspension mode 25 (and optional additional horizontal vibration mode) to monitor the fill level 210 is at least largely independent of external influences. The tank is fixed in the appropriate position within the body 410.

[0110] However, by incorporating the spatial orientation data of the fluid container 200 into the fill level monitoring device 100, the fill level of the hydrogen tank 300 can be monitored more accurately, even in aircraft applications, particularly under any flight conditions.

[0111] It should be noted that "comprising" or "including" does not exclude other elements or steps, and "a" or "an" does not exclude multiple. It should also be noted that features or steps described with reference to any of the above embodiments may also be used in combination with other features or steps of the other above embodiments. Reference numerals in the claims should not be considered limiting.

[0112] List of reference numerals

[0113] 10 Excitation Elements

[0114] 21 Sensing Element

[0115] 23 Vibration signal (from sensing element)

[0116] 25 Suspension Modes

[0117] 27 Transfer Function

[0118] 29 Maximum peak value

[0119] 30 signal sources

[0120] 31 Input Signal

[0121] 40 processing units

[0122] 51 Filling level signal

[0123] 60 Spatial orientation and acceleration sensors, temperature and / or pressure sensors

[0124] 70 Suspension components and mounting parts

[0125] 71 Spring

[0126] 72 Metal Frame

[0127] 73 Limiting Components

[0128] 74 End stop

[0129] 75 Reinforced metal arched components

[0130] 76. Arc-shaped central part

[0131] 77 Foot-like lateral portion

[0132] 78 Vertical beam

[0133] 80 (suspension mode) modal frequency

[0134] 90° Vertical direction

[0135] 91. Vertical direction

[0136] 92 Lateral direction

[0137] 100 Filling level monitoring device

[0138] 200 fluid container

[0139] 221 First Tip

[0140] 300 Liquid Hydrogen Tank

[0141] 400 aircraft

[0142] 410 Aircraft fuselage and surrounding structure

[0143] 420 aircraft turbine

Claims

1. A filling level monitoring device (100) for monitoring the filling level (210) of a fluid container (200), the filling level monitoring device (100) comprising: At least one excitation element (10); At least one sensing element (21); Signal source (30); At least one suspension element (70) having suspension stiffness; and Processing unit (40); The at least one excitation element (10) is configured to be mounted to the fluid container (200) and / or the at least one suspension element (70) such that the at least one excitation element (10) is operable to excite at least one suspension mode (25) of vibration, wherein the suspension mode (25) is a different vibration mode of the at least one suspension element (70); The at least one suspension element (70) is configured to be fixedly connected to the fluid container (200) such that when excited by the at least one excitation element (10), the fluid container (200) and the at least one suspension element (70) vibrate together in unison; The at least one sensing element (21) is configured to be mounted to the fluid container (200) and / or the at least one suspension element (70) and to sense vibrations corresponding to the at least one suspension mode (25); The signal source (30) is connected to the at least one excitation element (10) and is configured to generate an input signal (31) comprising multiple frequency components. Each of the at least one sensing element (21) is connected to the processing unit (40) and configured to sense vibrations within the fluid container (200), generate a corresponding vibration signal (23), and send the vibration signal (23) to the processing unit (40); and The processing unit (40) is configured to: The at least one suspension mode (25) is identified based on the vibration signal (23) of the at least one sensing element (21) and the input signal (31). Determine the modal frequency (80) of the at least one suspension mode (25); and The current filling level (210) of the fluid container (200) is determined based on the modal frequency of the at least one suspension mode (25).

2. The filling liquid level monitoring device (100) according to claim 1, wherein, The processing unit (40) is further configured to identify the at least one suspension mode (25) and determine the modal frequency (80) of the at least one suspension mode (25) by determining a transfer function (27) in the frequency domain for the vibration signal (23) of each of the at least one sensing element (21): Each vibration signal in the vibration signal (23) of the at least one sensing element (21) and the input signal (31) are normalized and transformed into a frequency domain representation using the Fast Fourier Transform (FFT); as well as The FFT of each vibration signal (23) of the at least one sensing element (21) is compared with the FFT of the input signal (31) to determine the corresponding transfer function (27).

3. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The processing unit (40) is configured to independently determine the at least one suspension mode (25) for each of the at least one sensing element (21) by determining the frequency of the corresponding maximum peak value (29) of the corresponding transfer function (27).

4. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The processing unit (40) is configured to determine the current filling level (210) of the fluid container (200) by correlating the modal frequency (80) of each of the determined suspension modes (25) with the frequency of a reference suspension mode corresponding to a specific filling level (210).

5. The filling liquid level monitoring device (100) according to claim 4, wherein, The processing unit (40) is configured to determine the current filling level (210) by averaging the current filling level (210) determined independently for each of the sensing elements (21).

6. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The at least one excitation element (10) is configured to be located at the same position as at least one of the sensing elements (21).

7. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The at least one suspension element (70) is made of a metallic material; and / or The suspension stiffness of the at least one suspension element (70), expressed in terms of Young's modulus, is in the range of 2 GPa to 420 GPa.

8. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The at least one suspension mode (25) includes at least one of the following modes associated with the corresponding degree of freedom: Translational vibration modes; and Rotational vibration mode.

9. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The at least one suspension element (70) is configured to connect the fluid container (200) to the surrounding structure (410).

10. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The at least one suspension element (70) is a spring (71); and / or The filling level monitoring device (100) further includes a limiting element (73) that restricts the vibrational movement of the fluid container (200) and the at least one suspension element (70) to a specified degree of freedom.

11. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The at least one suspension element (70) is a metal frame (72) capable of vibrating in at least one of the vertical, longitudinal, and lateral directions.

12. The filling liquid level monitoring device (100) according to any one of the preceding claims, wherein, The at least one excitation element (10) is arranged at and in contact with the at least one suspension element (70) and is configured to couple a vibration load corresponding to the input signal (31) from the signal source (30) to the at least one suspension element (70) and the fluid container (200).

13. The filling level monitoring device (100) according to any one of the preceding claims further includes at least one end stop (74) to restrict the movement of the fluid container (200).

14. A hydrogen tank (300), comprising: Fluid container (200) for containing liquefied hydrogen; and The filling liquid level monitoring device (100) according to any one of the preceding claims.

15. An aircraft (400), comprising: Aircraft fuselage (410); as well as The hydrogen tank (300) according to claim 14; The filling level monitoring device (100) is configured to monitor the hydrogen filling level (210) of the fluid container (200).

Images