Piezoelectric superstructure duct sound insulation design and regulation and control method for rotorcraft

Abstract

The invention discloses a rotor craft piezoelectric superstructure duct sound insulation design and regulation method, and belongs to the technical field of rotor craft duct sound insulation. The sound insulation duct is suitable for sound insulation and noise reduction of various rotorcraft ducts and comprises a rotorcraft body, a sound insulation duct, piezoelectric patches and a piezoelectric patch external shunt circuit. For a rotor craft, high-speed rotation of blades can generate large noise, a sound insulation duct is often thin and poor in sound insulation effect due to the requirement for light weight, piezoelectric patches are periodically added outside the duct and connected with an external circuit, a local resonance piezoelectric superstructure is formed, and the sound insulation performance of the structure can be effectively enhanced. The piezoelectric patches are additionally arranged on the inner surface and the outer surface of the duct, under the condition that the original working efficiency of the aircraft is not affected, the sound insulation capacity of the structure is enhanced, the manned comfort of the rotor aircraft is improved, and noise pollution to the environment is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of rotorcraft ducted sound insulation, and in particular relates to a rotorcraft piezoelectric superstructure ducted sound insulation design and control method based on a local resonance piezoelectric superstructure shell. Background Art

[0002] Among the many types of low-altitude aircraft, multi-rotor aircraft, due to their numerous advantages, have become the preferred aircraft in the development of the low-altitude economy. However, as manned multi-rotor aircraft continue to advance to higher levels, ride comfort has begun to attract attention. For these aircraft, effectively reducing cabin noise while maintaining their original flight efficiency has become a key bottleneck restricting the further development of multi-rotor aircraft. Furthermore, the noise pollution generated by multi-rotor aircraft on the ground during flight is also not to be underestimated. This not only affects the living environment quality of surrounding residents but also indirectly affects the overall sustainable development of the low-altitude economy. Therefore, in order to promote the high-quality and sustainable development of the low-altitude economy, it is particularly important to carry out scientific, reasonable, and effective sound insulation and noise reduction design work for low-altitude aircraft.

[0003] Locally resonant piezoelectric metastructures offer the advantage of intelligent, controllable sound insulation, and have been proven to exhibit significant sound insulation at certain critical frequencies. Furthermore, by varying circuit parameters, the resonant frequency of the circuit can be precisely controlled, further optimizing the sound insulation effect. Furthermore, attaching the piezoelectric sheet to the duct does not damage the original structure of the aircraft, and the added mass is minimal, meeting the stringent engineering requirements for lightweight structures. This lays a solid foundation for its practical application in the sound insulation and noise reduction of rotorcraft. Summary of the Invention

[0004] The first purpose of the present invention is to provide a piezoelectric superstructure duct sound insulation design method for rotorcraft to solve related problems such as rotorcraft noise pollution, and to design a piezoelectric superstructure sound insulation duct that is both lightweight and has strong sound insulation performance, so that it can meet the needs of low-altitude economic sustainable development of rotorcraft.

[0005] A second object of the present invention is to provide a method for controlling the sound insulation of a piezoelectric superstructure duct in a rotorcraft, so as to solve the problem that conventional sound insulation ducts cannot control the sound insulation performance, so that the sound insulation design proposed in the present invention can meet the needs of rotorcraft in different working environments.

[0006] In order to achieve the above-mentioned object of the invention, the specific technical solutions of the present invention are as follows:

[0007] The present invention provides a method for designing sound insulation for a piezoelectric superstructure duct on a rotorcraft. The sound insulation duct is installed on the rotorcraft; piezoelectric sheets are periodically arranged on the sound insulation duct to form a piezoelectric superstructure, and each piezoelectric sheet is connected to an external shunt circuit; the circuit is used to regulate the vibration of the piezoelectric sheets; attaching the piezoelectric sheets has a minimal impact on mass and does not affect the lightweight design of the aircraft; the piezoelectric sheets have strong mechanical-electrical coupling, which can better regulate the sound insulation performance; lightweight and efficient sound insulation are achieved by combining the piezoelectric superstructure duct with the external circuit. The method specifically includes the following components: a rotorcraft, a sound insulation duct, periodically arranged piezoelectric sheets, and an external shunt circuit;

[0008] The design method specifically includes the following steps:

[0009] 1) Reasonably arrange sound insulation ducts around the rotor of the rotorcraft, and the shape of the sound insulation ducts must meet the aerodynamic performance requirements of the rotorcraft;

[0010] 2) Periodically attach the piezoelectric sheets to the inner and outer surfaces of the sound insulation duct;

[0011] 3) Lead out the two electrodes of the piezoelectric piece separately, connect one end of the electrode to the duct body, and the duct body is connected to the ground; the other end of the electrode is connected to the external shunt circuit.

[0012] In step 2), the piezoelectric sheets are periodically attached to the surface of the sound insulation duct. The polarization direction of the periodically arranged piezoelectric sheets should be along the radial direction of the duct, and bending strain is generated under the action of the external shunt circuit. The piezoelectric sheets are tightly bonded to the duct using a two-component conductive adhesive of copper powder and epoxy resin to ensure the stability of the connection. The circumferential spacing between adjacent piezoelectric sheets can be 50 to 100 mm, the axial spacing can be 80 to 150 mm, and the coverage rate is 20% to 50%. They are arranged in 3 to 5 columns along the length of the duct, and the axial spacing can be 80 to 150 mm. The piezoelectric sheet material can be made of PZT-5H piezoelectric ceramic, with its high electromechanical coupling coefficient and excellent stability, ensures strong sound insulation control capabilities, thereby effectively controlling noise and improving overall sound insulation. The piezoelectric plates are bonded to the duct surface using a two-component conductive adhesive made of copper powder and epoxy resin (30% copper powder). The duct surface is sanded (roughness Ra 1.6) before bonding, cleaned with anhydrous ethanol, and then coated with adhesive. The bonding thickness can be 0.1-0.3mm, and the curing pressure can be 0.2-0.5MPa, with curing in a 60°C oven for 12 hours. The piezoelectric plates are periodically arranged on the duct substrate to form a piezoelectric superstructure. The core of the structure is the periodic array of unit cells, forming a designable overall structure. This periodicity not only matches the wave control requirements of the acoustic superstructure (such as precisely suppressing noise in a specific frequency band through the bandgap effect), but also allows the periodic distribution of the piezoelectric plates to impart unified electromechanical conversion properties to the structure, resulting in a unified structure that combines the wave confinement capabilities of the acoustic superstructure with the energy conversion function of the piezoelectric effect, achieving efficient noise control.

[0013] In step 3), the shunt circuit may adopt an RLC resonant circuit, wherein the capacitance is provided by the capacitance of the piezoelectric piece itself, the resistance may be 10 to 1000Ω, and the inductance is realized by a synthetic circuit.

[0014] The piezoelectric superstructure duct for rotorcraft incorporates a resonant piezoelectric shunt circuit into the duct's overall design, leveraging the local resonance effect to create a piezoelectric superstructure sound insulation design with low-frequency noise attenuation. This design offers the advantages of conveniently adjusting the local resonance frequency through circuitry, minimizing added mass, and enabling relatively easy fabrication. Crucially, it does not damage the duct's base structure, ensuring the integrity and stability of the entire structure.

[0015] When the piezoelectric superstructure duct of the rotorcraft is in an operating state, the sound waves will cause the structure to vibrate during the transmission process. The locally resonant piezoelectric superstructure regulates the vibration of the structure by adjusting the structural stiffness, thereby achieving effective control of the sound wave transmission and achieving the purpose of reducing noise propagation.

[0016] The present invention also provides a piezoelectric superstructure duct sound insulation control method based on a resonant circuit, which is applicable to the design of the above-mentioned piezoelectric superstructure sound insulation duct. Specifically, the control method is based on the above-mentioned design method and uses the principle of local resonance for control. The control method includes the following steps:

[0017] 1) Constructing an RLC resonant circuit as a resonant circuit, wherein the capacitor C is provided by a piezoelectric plate, the inductor L is implemented by a synthetic circuit, and the resistor R is provided by a resistive element to suppress the amplitude of the circuit signal; the synthetic circuit includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first operational amplifier, a second operational amplifier, and a capacitor C1, wherein R4 is a variable resistor;

[0018] 2) Achieving efficient sound insulation performance at different frequencies for the duct: By adjusting the resistance of the variable resistor R4 in the synthesis circuit, the equivalent inductance L is changed, thereby adjusting the resonant frequency of the RLC resonant circuit;

[0019] 3) Improve the sound insulation performance of ducts with different radii: for the duct ring frequency , adjust the resonant frequency To bypass ring frequency , using the local resonance effect to improve the sound transmission loss at the ring frequency;

[0020] 4) For the piezoelectric superstructure duct at the natural frequency The sound insulation performance at the duct natural frequency , adjust the resonant frequency To ducted natural frequency Nearby, the piezoelectric shunt circuit suppresses the duct resonance and improves the sound insulation performance at the natural frequency.

[0021] In step 1), the resonant frequency of the resonant circuit ,in represents the inherent capacitance of the piezoelectric piece, and L represents the inductance of the resonant circuit. By changing the inductance value, the resonant frequency of the shunt circuit can be adjusted, and the sound insulation performance of the corresponding frequency can be adjusted accordingly, so as to achieve the purpose of adjusting the sound insulation performance of the duct at different frequencies.

[0022] In step 2), in order to adjust the duct to achieve efficient sound insulation performance at different frequencies, a composite circuit is used to realize variable inductance, and it can achieve a large inductance value, thereby improving the sound insulation performance in the low frequency band. The fourth resistor R4 in the composite circuit is a variable resistor, which is used to adjust the equivalent inductance L. The relationship between the equivalent inductance and the composite circuit components is: .

[0023] The resistance of the fourth resistor R4 can be adjusted in a range of 100-100 kΩ to ensure the stability and adjustability of the circuit.

[0024] In step 3), due to the effect of sound waves on the duct, the duct is Circumferential vibration will be generated at the ring frequency, resulting in a valley in the sound transmission loss of the duct at the ring frequency, where K is the equivalent tensile stiffness of the duct, m is the equivalent mass of the duct, and R is the radius of the duct; for ducts of different radii, the sound insulation performance can be improved by adjusting the inductance , the circuit resonant frequency can be Adjust to the bypass frequency Due to the local resonance effect, the sound insulation performance of the duct at this frequency is enhanced, and the sound transmission loss of the duct is improved.

[0025] In step 4), the piezoelectric superstructure duct is regulated at the natural frequency When the frequency of the incident sound wave is equal to the natural frequency of the duct, the duct will cause the sound insulation performance to decrease due to resonance. By adjusting the inductance , the circuit resonant frequency Adjust to the duct natural frequency Nearby, the piezoelectric shunt circuit can suppress the resonance of the duct, thereby improving the sound insulation performance of the duct at the natural frequency.

[0026] Preferably, the piezoelectric superstructure and duct are periodically attached to the rotorcraft duct via PZT piezoelectric sheets. This attachment method creates minimal additional mass on the duct. This feature minimizes the impact on the rotorcraft's inherent performance, enabling the rotorcraft to maintain excellent flight and controllability while achieving sound insulation, making it more compatible with the stringent weight and stability requirements of actual flight applications.

[0027] The piezoelectric superstructure duct for rotorcraft exhibits multiple benefits in practical applications. On the one hand, it significantly reduces cabin noise generated by the rotors, effectively improving cabin comfort and protecting passengers from noisy noise. On the other hand, it effectively reduces the noise impact of the aircraft on the surrounding environment, aligning with current development concepts of green, environmentally friendly, and low-noise flight. It helps reduce noise pollution during aircraft operation and enhances social acceptance of aircraft in low-altitude flight scenarios.

[0028] Preferably, the piezoelectric superstructure duct of the rotorcraft has excellent adjustability and can be tuned by flexibly changing the parameters of the external shunt circuit. With this powerful function, not only can the sound insulation performance of the piezoelectric superstructure at the ring frequency and natural frequency be enhanced, and the sound insulation effect within a specific frequency range be further optimized, but it can also precisely control the noise of different frequency bands generated by the rotor at different speeds. In other words, no matter what flight state the aircraft is in or what speed the rotor is running at to generate noise of different frequencies, the noise of the corresponding frequency band can be effectively suppressed by adjusting the external circuit parameters, comprehensively and dynamically improving the sound insulation and noise reduction effect of the aircraft under different operating conditions, so that it can always maintain good acoustic performance in the complex and changing actual flight environment.

[0029] In summary, the technical solution proposed in the present invention presents many advantages compared to the existing technology. The present invention uses the duct structure as the basis for sound insulation design and sound insulation regulation, and has universal applicability. The present invention cleverly adds a piezoelectric superstructure duct to the rotor part of the rotorcraft. While achieving efficient sound insulation, its additional mass is small and the adjustability is strong. It can effectively isolate noise, providing strong technical support for the high-quality and sustainable development of rotorcraft in the low-altitude economic field. It has broad application prospects and significant practical value, and is expected to become an effective technical means to solve the noise problem of rotorcraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the overall structure of a rotorcraft containing a piezoelectric superstructure sound insulation duct according to the present invention;

[0031] Figure 2 Schematic diagram of a piezoelectric superstructure unit cell connected to an external RLC resonant circuit of the present invention;

[0032] Figure 3 A synthetic circuit for realizing equivalent inductance of the present invention;

[0033] Figure 4 The acoustic transmission loss at the control loop frequency of the present invention;

[0034] Figure 5 The present invention controls the sound transmission loss when the duct natural frequency is used. DETAILED DESCRIPTION

[0035] In order to make the technical solutions, objectives and advantages of the present invention more clearly presented, the following content will combine the corresponding schematic diagrams and specific embodiments to provide a detailed and comprehensive description of the present invention. It should be clear that the present invention has a wide range of applicability. It can be applied to various forms of ducts and various types of rotorcraft, and is not limited to the specific embodiments described later in the present invention. The main purpose of providing these embodiments is to help readers more thoroughly understand the relevant content disclosed in the present invention, so as to better grasp its core points and application value.

[0036] like Figure 1 As shown, it shows a schematic diagram of the overall structure of a rotorcraft equipped with a piezoelectric superstructure sound insulation duct. The aircraft mainly includes the following parts: a rotorcraft body 1, a rotor 2, a sound insulation duct 3, periodically attached piezoelectric sheets 4 and an external shunt circuit 5.

[0037] The rotors 2 are rigidly connected to the hub of the rotorcraft 1 via a hub assembly. The noise generated by these rotors due to aerodynamic loads during rotorcraft operation becomes a major noise source, with the frequency band primarily concentrated between 50 and 5000 Hz, significantly impacting the overall acoustic environment. Because rotorcraft aerodynamic noise is widely distributed and varies with rotational speed, an adjustable acoustic superstructure is required. The sound insulation duct 3 is fixed to the rotorcraft body 1 and tightly connected to the rotorcraft's main structure via welding or other mounting methods (such as flange connections or high-strength bolts). This ensures the rotorcraft's aerodynamic characteristics and does not affect its flight performance. Rotorcrafts can be large commercial manned rotorcraft or small unmanned rotorcraft. Since their rotor radii generally vary, the size of the sound insulation duct needs to be tailored to the rotorcraft model. The structure of the sound insulation duct 3 must meet aerodynamic requirements. The present invention imposes no specific restrictions on the shape or size of the sound insulation duct. The sound insulation duct is made of high-strength, low-density aluminum or alloy materials. This can not only ensure the sound insulation performance of the duct, but also reduce the weight of the rotorcraft and improve the overall performance of the aircraft.

[0038] Periodically arranged piezoelectric plates 4 are attached to the inner and outer surfaces of the sound insulation duct 3, forming a piezoelectric superstructure. They are bonded using a two-component conductive adhesive composed of epoxy resin and copper powder, although other adhesives can also be used. The advantage of using a two-component conductive adhesive is that one end of the piezoelectric plate can be directly connected to the sound insulation duct, eliminating the need for excessive wires. Furthermore, the epoxy resin ensures a better bond between the piezoelectric plate and the duct itself. In practice, the outer surface of the duct can be lightly sanded with sandpaper and wiped with anhydrous ethanol. Then, the two-component conductive adhesive is evenly applied. The piezoelectric plate is positioned in the desired position, and pressure is applied. The plate is then cured at room temperature for 24 hours, or in an incubator at 60°C for 12 hours to ensure a tight connection. The piezoelectric plate is made of PZT-5H piezoelectric ceramic. This material, with its unique piezoelectric properties and excellent stability, effectively ensures strong sound insulation control capabilities, thereby effectively controlling noise within the entire sound insulation system and improving the overall sound insulation effect.

[0039] The piezoelectric sheets 3 are neatly arranged in a periodic manner on the inner and outer surfaces of the sound insulation duct 4. From the perspective of structural composition, the entire piezoelectric superstructure duct is composed of a plurality of piezoelectric superstructure cells. Such a structural design lays the foundation for achieving its specific sound insulation function.

[0040] In this embodiment, the piezoelectric piece 4 is made of PZT-5H piezoelectric ceramic (size 50 mm × 50 mm × 0.5 mm), and its polarization direction is along the radial direction of the duct to ensure the maximum piezoelectric effect during bending vibration. The piezoelectric constant d 33 ≥-274 pC / N.

[0041] like Figure 2 The figure shows a single unit cell of a piezoelectric superstructure sound-isolating duct. A sound-isolating duct can be formed from this single unit cell array. An external shunt circuit 5 is connected to the two piezoelectric plates on the inner and outer surfaces at one end and grounded at the other. The duct itself contains a resistor and an inductor. The duct itself 3 is grounded. Because the piezoelectric plate 4 is bonded to the duct body with conductive adhesive, the end where the piezoelectric plate is bonded to the duct body is also grounded, forming a circuit. The resistor uses an existing resistor element to provide damping for the sound-isolating system. The inductor is implemented using a composite circuit. This is because controlling sound insulation performance at low frequencies often requires a large inductance L, which existing inductor elements cannot meet.

[0042] The periodic arrangement in this embodiment uses the piezoelectric superstructure unit cell shown in Figure 2 as the basic unit. The unit cell has a circumferential length of 100 mm along the duct and an axial length of 100 mm. Each unit cell contains two piezoelectric sheets (attached to corresponding positions on the inner and outer surfaces of the duct, respectively), with an overall coverage ratio of 25% (balancing sound insulation and added mass). The unit cell is composed of a duct base with piezoelectric sheets attached to the top and bottom, and the unit cells are connected to each other.

[0043] The working principle of the present invention is given below:

[0044] The rotors of rotorcraft generate considerable noise due to vibration during operation. To prevent this noise from affecting passengers and the surrounding environment, sound insulation ducts are added. Traditional plate-shell structures, due to the law of mass, are severely limited in engineering structures with strict mass requirements, such as rotorcraft. To address this issue, the present invention introduces a piezoelectric superstructure.

[0045] A locally resonant piezoelectric superstructure duct is formed by periodically attaching PZT piezoelectric plates to the inner and outer surfaces of the duct and connecting the piezoelectric plates to an RLC circuit. When sound waves strike the sound-isolating duct, they cause it to vibrate, generating bending strain in the piezoelectric plates. Due to the inverse piezoelectric effect, the piezoelectric plates' electrodes develop induced charges, converting the vibrational energy into electrical energy. When the PZT piezoelectric plates are connected to an external circuit, an induced current is generated in the circuit. When the sound wave's excitation frequency equals the circuit's resonant frequency, the circuit resonates and exhibits extremely low impedance, ultimately generating a large current, significantly improving the sound insulation performance of the piezoelectric superstructure duct. Simultaneously, the resistor R in the RLC circuit dissipates some of the energy by converting electrical energy into heat. When the piezoelectric oscillator resonates, the unit's vibration phase is antiphase to the incident sound wave, causing the scattered wave to destructively interfere with the incident wave, preventing sound waves of that frequency from propagating through the superstructure (forming a "phonon band gap"), fundamentally preventing sound transmission.

[0046] In order to illustrate and verify the sound insulation performance of the piezoelectric superstructure sound insulation duct for rotorcraft proposed in the embodiment of the present invention, Figure 1 The piezoelectric superstructure sound-isolating duct for a rotorcraft shown in the figure is simplified and analyzed using a partial shell consisting of 9×9 unit cells. The aerodynamic noise generated by the rotor is simulated by applying white noise with an amplitude of 1 Pa to the air domain on the inner surface of the duct. The sound transmission loss during transmission is then calculated. The sound transmission loss formula is: ,in and represent the average sound pressure on the inner and outer surfaces of the piezoelectric superstructure duct, respectively.

[0047] When the sound pressure is incident vertically, the main frequency that affects the sound insulation performance of the duct is the ring frequency and natural frequency At these two frequencies, the sound insulation performance is significantly reduced, and the sound transmission loss will produce a large valley value. Figure 4 , by adjusting the circuit resonant frequency to the ring frequency , the sound transmission loss at this location increases from 20 dB to 60 dB; if Figure 5 , adjust the circuit resonant frequency to the natural frequency , the sound transmission loss there is increased from 25 dB to 85 dB; and the sound transmission loss is improved within a certain frequency band.

[0048] The present invention also provides a piezoelectric superstructure duct sound insulation control method based on a resonant circuit, which is applicable to the design of the above-mentioned piezoelectric superstructure sound insulation duct, and mainly includes the following steps:

[0049] The resonant circuit adopts an RLC resonant circuit, wherein the capacitor C is provided by a piezoelectric plate, the inductor L is realized by a synthetic circuit, and the inductance value can adjust the resonant frequency of the shunt circuit and accordingly adjust the sound insulation performance of the corresponding frequency. The resistance R can be provided by a resistive element to suppress the circuit signal amplitude;

[0050] The resonant frequency of the resonant circuit ,in represents the inherent capacitance of the piezoelectric piece, L represents the inductance of the resonant circuit, and the purpose of regulating the sound insulation performance of the duct at different frequencies is achieved by adjusting the resonant frequency;

[0051] like Figure 3 As shown, an equivalent synthetic circuit of inductance is given, which replaces the inductor L in the external shunt circuit 5 to provide inductance for the RLC circuit, and includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first operational amplifier, a second operational amplifier, and a capacitor C1; wherein the left and right nodes represent the input node and the output node respectively. Among them, the first operational amplifier is configured as an inverting amplifier, whose inverting input receives the input signal through R1, and the non-inverting input is grounded, providing initial signal amplification and phase inversion; the second operational amplifier is also configured as an inverting amplifier, whose inverting input is connected to the output of the first operational amplifier through R3, and the non-inverting input is grounded through R4, and the output node serves as the output end of the circuit. The second operational amplifier interacts with the capacitor C1 through a feedback path to convert the capacitive behavior into an inductive impedance; the first resistor R1 connects the input node to the inverting input of the first operational amplifier, sets the input current and controls the equivalent inductance ratio; the second resistor R2 connects the output of the second operational amplifier to the inverting input of the first operational amplifier, providing a negative feedback path and reducing the equivalent inductance when its value increases. The third resistor R3 connects the output of the first operational amplifier to the inverting input of the second operational amplifier, setting the gain ratio between the two operational amplifiers. The capacitor C1 connects the inverting input of the second operational amplifier to the ground terminal and acts as an energy storage element, which is converted into an equivalent inductance by the feedback network. The fourth resistor R4 connects the non-inverting input of the second operational amplifier to the ground terminal. In addition to providing a DC bias path, its value directly participates in the equivalent inductance calculation. Adjusting R4 can linearly change the inductance value. The final equivalent inductance expression is: .

[0052] Piezoelectric superstructure controls the sound insulation of ducts with different radius sizes: Due to the effect of sound waves on the ducts, the ducts are regulated by the surrounding frequency. Circumferential vibration will be generated at the ring frequency, which will cause the sound transmission loss of the duct to have a valley value at the ring frequency, where C is the equivalent tensile stiffness of the duct, m is the equivalent mass of the duct, and R is the radius of the duct; by adjusting the inductance , the circuit resonant frequency can be Adjust to the bypass frequency Due to the local resonance effect, the sound insulation performance of the duct at this frequency is enhanced, and the sound transmission loss of the duct is improved, such as Figure 4 shown.

[0053] Piezoelectric superstructure duct control Piezoelectric superstructure duct at different natural frequencies Sound insulation control method: When the frequency of the incident sound wave is equal to the natural frequency of the duct, the duct will cause the sound insulation performance to decrease due to resonance. By adjusting the inductance , the circuit resonant frequency Adjust to the duct natural frequency The piezoelectric shunt circuit can suppress the resonance of the duct, thereby improving the sound insulation performance of the duct at the natural frequency, such as Figure 5 shown.

[0054] Traditional inductors have low inductance and are difficult to adjust. This invention uses an equivalent circuit to synthesize the inductor, enabling wide-range inductance adjustment. Experiments have demonstrated significant technical effectiveness in the design and control method for piezoelectric superstructure duct sound insulation. Within the 50-5000 Hz frequency range, by adjusting the circuit's resonant frequency to match the duct ring frequency with its natural frequency, the sound transmission loss can be improved by up to 54 dB (depending on the duct structure), significantly reducing cabin noise to a comfortable level. The adjustable range of the equivalent inductance covers critical noise frequency bands, adapting to ducts of varying sizes. The added mass accounts for only 3.2% of the duct's total mass, resulting in excellent long-term operational stability and balancing sound insulation with aircraft aerodynamic and lightweight requirements.

[0055] Those skilled in the art will understand that, unless otherwise defined, the terms used herein have the same meanings as those commonly understood by those skilled in the art. Furthermore, terms defined in common dictionaries should be understood within the context of the prior art and, unless otherwise defined, should not be interpreted in an idealized or overly formal sense.

[0056] The above specific embodiments further illustrate the objectives, technical solutions, and beneficial effects of the present invention. However, it should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A design method for the sound insulation of a piezoelectric superstructure duct for a rotorcraft, characterized in that The invention comprises a rotorcraft, a sound insulation duct, periodically arranged piezoelectric sheets, and an external shunt circuit; the design method specifically comprises the following steps: 1) Reasonably arrange sound insulation ducts around the rotor of the rotorcraft, and the shape of the sound insulation ducts must meet the aerodynamic performance requirements of the rotorcraft; 2) Periodically attach the piezoelectric sheets to the inner and outer surfaces of the sound insulation duct; 3) Lead out the two electrodes of the piezoelectric piece separately, with one end of the electrode grounded and connected to the duct body through conductive glue; the other end of the electrode is connected to the external shunt circuit.

2. The method for designing sound insulation of a piezoelectric superstructure duct for a rotorcraft according to claim 1, characterized in that In step 2), the piezoelectric sheets are periodically attached to the inner and outer surfaces of the sound insulation duct. The polarization direction of the periodically arranged piezoelectric sheets should be along the radial direction of the duct, and bending strain should be generated under the action of the external shunt circuit; the piezoelectric sheets are tightly bonded to the duct using a two-component conductive adhesive of copper powder and epoxy resin to ensure the stability of the connection; the piezoelectric sheet material is PZT-5H piezoelectric ceramic, and the piezoelectric sheets are bonded to the inner and outer surfaces of the duct.

3. The method for designing a piezoelectric superstructure duct for sound insulation of a rotorcraft according to claim 2, characterized in that The circumferential spacing between adjacent piezoelectric sheets is 50-100 mm, the axial spacing is 80-150 mm, and the coverage rate is 20%-50%; they are arranged in 3-5 rows along the axial direction of the duct, with a spacing of 80-150 mm to match the spatial distribution of the main frequency bands of rotor noise.

4. The method for designing sound insulation of a piezoelectric superstructure duct for a rotorcraft according to claim 1, characterized in that In step 2), in step 3), the shunt circuit adopts an RLC resonant circuit, wherein the capacitance is provided by the capacitance of the piezoelectric piece itself, the resistance is 10 to 1000Ω, and the inductance is realized by a synthetic circuit.

5. A piezoelectric superstructure duct designed according to the method for designing sound insulation of a piezoelectric superstructure duct for a rotorcraft as claimed in any one of claims 1 to 4.

6. A piezoelectric superstructure duct sound insulation control method based on a resonant circuit, characterized in that Applicable to the piezoelectric superstructure duct according to claim 5, the control method comprises the following steps: 1) Constructing an RLC resonant circuit as a resonant circuit, wherein the capacitor C is provided by a piezoelectric plate, the inductor L is implemented by a synthetic circuit, and the resistor R is provided by a resistive element to suppress the amplitude of the circuit signal; the synthetic circuit includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first operational amplifier, a second operational amplifier, and a capacitor C1, wherein R4 is a variable resistor; 2) Achieving efficient sound insulation performance at different frequencies for the duct: By adjusting the resistance of the variable resistor R4 in the synthesis circuit, the equivalent inductance L is changed, thereby adjusting the resonant frequency of the RLC resonant circuit; 3) Improve the sound insulation performance of ducts with different radii: for the duct ring frequency , adjust the resonant frequency To bypass ring frequency , using the local resonance effect to improve the sound transmission loss at the ring frequency; 4) For the piezoelectric superstructure duct at the natural frequency The sound insulation performance at the duct natural frequency , adjust the resonant frequency To ducted natural frequency Nearby, the piezoelectric shunt circuit suppresses the duct resonance and improves the sound insulation performance at the natural frequency.

7. A piezoelectric superstructure duct sound insulation control method based on a resonant circuit as claimed in claim 6, characterized in that In step 1), the resonant frequency of the resonant circuit ,in represents the inherent capacitance of the piezoelectric piece, and L represents the inductance of the resonant circuit; By changing the inductance value to adjust the resonant frequency of the shunt circuit, the sound insulation performance of the corresponding frequency is adjusted accordingly, thereby achieving the purpose of adjusting the sound insulation performance of the duct at different frequencies.

8. A piezoelectric superstructure duct sound insulation control method based on a resonant circuit as claimed in claim 6, characterized in that In step 2), in order to adjust the duct to achieve efficient sound insulation performance at different frequencies, a composite circuit is used to realize variable inductance and achieve a large inductance value, thereby improving the sound insulation performance in the low frequency band. The fourth resistor R4 in the composite circuit is a variable resistor, which is used to adjust the equivalent inductance L. The relationship between the equivalent inductance and the composite circuit components is: .

9. A piezoelectric superstructure duct sound insulation control method based on a resonant circuit as claimed in claim 6, characterized in that In step 3), due to the effect of sound waves on the duct, the duct is Circumferential vibration will be generated at the ring frequency, resulting in a valley in the sound transmission loss of the duct at the ring frequency, where K is the equivalent tensile stiffness of the duct, m is the equivalent mass of the duct, and R is the radius of the duct; for ducts of different radii, the sound insulation performance can be improved by adjusting the inductance , the circuit resonant frequency Adjust to the bypass frequency Due to the local resonance effect, the sound insulation performance of the duct at this frequency is enhanced, and the sound transmission loss of the duct is improved.

10. A piezoelectric superstructure duct sound insulation control method based on a resonance circuit as claimed in claim 6, characterized in that In step 4), the piezoelectric superstructure duct is regulated at the natural frequency When the frequency of the incident sound wave is equal to the natural frequency of the duct, the duct will cause the sound insulation performance to decrease due to resonance. By adjusting the inductance , the circuit resonant frequency Adjust to the duct natural frequency Nearby, the piezoelectric shunt circuit suppresses the resonance of the duct, thereby improving the sound insulation performance of the duct at its natural frequency.

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