MONITORING SYSTEM FOR EXTRACTING CRITICAL INHERENT FREQUENCIES OF A FREQUENCY VESSEL

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to US provisional application serial no. 63 / 271,430 filed on October 25, 2021.BACKGROUND

[0002] This disclosure relates generally to methods and systems for monitoring the dynamics of shipping containers stacked on a cargo ship subjected to waves.

[0003] Examples of stacks of containers that are monitored are illustrated in FIG. 1. The original lashing solution was introduced for stacks 3 containers high. Then lashing bridges were added and later increased in height. Current designs are stretching the capabilities of the existing lashing components. DK 2018 70089 A1 discloses a method to predict a bearing life cycle.

[0004] The lashings may now be failing because accelerations (e.g., lateral accelerations) at the top of the stacks are getting higher. For example, as the metacentric height (GM) increases and the height of the stack increases, the lateral acceleration of the containers also increases, as shown in FIG. 2. Increased waterplane on larger vessels increases GM, formerly about 3 meters, now about 10 meters or more. At GM of 8 meters, the roll period of the cargo ship approaches the wave period (as indicated by a step in the graph of FIG. 2). The applicant has investigated some failures and has determined that the failures appear when the lateral acceleration is about 1 g. Parametric roll resonances can lead to similar or greater levels of acceleration. When the lateral acceleration is sufficiently high, containers may pivot around one corner while the contact at the opposite corner is broken and gaps open.

[0005] In general, the dynamics of shipping containers stacked on a cargo ship involves multiple natural periods or frequencies: (i) ship global natural periods or frequencies - roll primarily; (ii) periods or frequencies of wave motions in a seaway; and (iii) natural frequencies of container stacks.

[0006] Existing software for calculating lashing capacity usually captures the effects of the ship roll. Wave motions may also be captured in the standard formulas provided by Classification Societies. However, the natural frequencies of container stacks, if taken into account, assume that the contact between the containers in the stack is static and that any container will not pivot around one corner while the contact at the opposite corner is broken and gaps open. The shortcomings of existing software are summarized in the Table below. • Standard industry loading software assume Quasi-Static response- Loads are calculated using vessel global dynamics- Responses are Static - stack dynamics are assumed to be zero- If connections are rigid, this assumption is valid BUT even small gaps can fundamentally change behavior• Twistlocks have mechanical play (Gaps) - 2 implications:- Increased Dynamic Modal Response - Greater freedom introduces new dynamic modal responses, which increase total loads by 30-40%- Natural frequency dynamic response excited by either 1) Gap stroking out OR 2) Collisions between different stacks- Load sharing between twistlocks and lashings changes unpredictably∘ Exact gap sizes are important for dynamic performance but per-unit measurement and tracking is impractical∘ Load can be concentrated either on the twistlock OR the lashing- This effect becomes more important with higher container stacks• Lashings also have mechanical play - can back off due to ship motions- May reduce lashing capacity and increase snap loads if loose

[0007] The applicant has determined that dynamics may no longer be ignored. The applicant has conducted a root cause assessment of an actual failure. Calculations were performed using CLash versions 4.0 and 5.0 with feedback from the original software developer at ABS. A Finite Element Model was created for the purpose of being able to assess various potential solutions. The modeling involved multi-body problems with non-linear connections and contacts. The assessment took into account dynamics to capture effects more fully. FIG. 3 illustrates a snapshot of the deformation of a stack of containers. FIG. 4 illustrates graphs of the tension force in the lashing and the force in a container twist lock as a function of time. FIGs. 3 and 4 show that both lashing and twist lock loads are in the failure range (note that the lashing capacity is calculated as fully engaged, but the lashing can have lower capacity if backed off).

[0008] FIGs. 3 and 4 also indicate that both types of failures (lashing and twist lock) may occur at different bays. The applicant believes that in cases of lashing-initiated failure, the following scenario likely occurs: a first lashing fails (calculated at breaking load), second lashing fails (now 200% of breaking load), a bottom twist lock fails (now 500% of breaking load), then the next stack now fails. The applicant believes that in cases of twist lock-initiated failure, the following scenario likely occurs: a first twist lock failure is just above the lashing bridge (tension-side twist lock is calculated at breaking load in a fully intact condition), after initiating failure, stack now leans on next stack, a tension-side twist lock of next stack now fails (now 200% of breaking load).

[0009] Therefore, there is a need in the art for methods and systems for monitoring the dynamics of shipping containers stacked on a cargo ship subjected to waves.

[0010] The invention provides a system as defined in claim 1.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more detailed description of the embodiments of the disclosure, reference will now be made to the accompanying drawings, wherein: FIG. 1 illustrates the evolution of typical stacks of containers with a typical inboard lashing; FIG. 2 is a graph of the magnitude of lateral acceleration as a function of GM; FIG. 3 shows a heat map of simulated deformation in a stack of containers subjected to roll. FIG. 4 shows graphs of lashing and twist lock forces as a function of time; FIG. 5 is a perspective view of a monitoring system for predicting failures to secure shipping containers stacked on a cargo ship; FIG. 6 is a perspective view of a portion of the system shown in FIG. 5; FIG. 7 is a perspective view of a monitoring system for predicting failures to secure shipping containers stacked on a cargo ship; FIG. 8 is another perspective view of the system shown in FIG. 7; FIG. 9 is a perspective view of a monitoring system for predicting failures to secure shipping containers stacked on a cargo ship; and FIG. 10 is a flowchart of a method for predicting failures to secure shipping containers stacked on a cargo ship. DETAILED DESCRIPTION

[0012] It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the disclosure may repeat reference numerals and / or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and / or configurations discussed in the various Figures.

[0013] A preferred example of a monitoring system is able to both measure the loads in the lashings and rapidly detect the natural frequencies of the stack, identify the major ones and provide alerts for potential overloading. In particular, natural frequencies that occur when containers pivot can be detected.

[0014] The monitoring system involves a load pin, which includes a load cell coupled to a board having a processor, wherein the sampling rate is sufficiently high to be able to detect the stack modes of resonance. At least 10 Hz may be required depending on the weights of the containers and the height of the overall stack.

[0015] Such a system is illustrated in FIGs. 5 and 6. The monitoring system, as shown, includes a track 70 adapted to be secured to the lashing bridge 16 or, more generally, to any structure of a cargo ship and even to another container. A clamp 74 is configured to slide on track 70 such that the position of the clamp 74 along track 70 can be adjusted. The clamp 74 can be locked at one of a plurality of discrete positions. There are several ways this can be achieved, and only one example is shown. Optionally, a portable winch 12A is coupled to a foundation formed by track 70 through a pad eye 36a and is configured to adjust the position of the clamp 74 along track 70. The winch 12A is driven by an operator and assists the operator in positioning the clamp 74 in a position where the lashing 24 can be placed under tension. The tension in the lashing 24 can be further adjusted using the turnbuckle 34.

[0016] FIGs. 5 and 6 also illustrate a load pin 38 that can be used to monitor the tension in the lashing 24. Measurements performed by the load pin 38 may be transmitted (e.g., broadcasted) to other locations using the Wi-Fi terminal 40, which is fixedly coupled to the cargo ship (e.g., to the lashing bridge 16 of the cargo ship). The housing of the Wi-Fi terminal 40 may also protect an accelerometer and / or gyroscope that can be used to determine the ship's pitch and roll. The measurements performed by the accelerometer and / or gyroscope can also be transmitted (e.g., broadcasted) using the Wi-Fi terminal 40. Communication protocols other than Wi-Fi can alternatively be used.

[0017] FIGs. 7 and 8 illustrate another example of a monitoring system. In this example, the monitoring system can be interfaced with a standard lashing as well as with a lashing that uses a track as shown in FIGs. 5 and 6. The monitoring system is built by swapping out the passive pin in a turnbuckle to a load pin 38 with the appropriate board / battery / communication system in the terminal 40. An adapter 42 can be used to accommodate ships lashing connections that can vary in pin size.

[0018] As shown, the adaptor 42 is able to interface with the existing ship lashing clip 50 if the load pin 38 has a different diameter from the diameter of the pin coupling the turnbuckle 34 to the clip 50. However, if they are the same diameter, the load pin 38 can interface directly with the ship lashing clip 50 and the turnbuckle 34. The adapter 42 includes first and second 2-prong forks. The first 2-prong fork has an end having two holes sized to interface with a pin of the lashing clip 50 and another opposite end having one hole sized to interface with the load pin 38. The second 2-prong fork has an end having two holes sized to interface with the load pin 38 and another opposite end having one hole sized to interface with the turnbuckle 34 and the lashing.

[0019] FIG. 9 illustrates yet another configuration of the monitoring system. The load pin 38 goes through its analog / digital card (or similar) and then is cabled to an external device 40. The external device may or may not have a display. The external device transmits data (raw or processed data, as explained below) to receivers using a long-distance protocol (LORA, BTLE, or similar) and to a computer (e.g., central data processor). Optionally, it is possible that the packaging will be restructured to integrate all the components (e.g., load pin, analog / digital card, processor programmed to perform signal analysis, transmitter) of the monitoring system into a single housing that fits directly to the load pin 38. Also, the lashing, while shown secured to the lashing bridge 16, may alternatively be secured to the deck of the cargo ship.

[0020] An example method of use of any of the systems previously described is illustrated in FIG. 10.

[0021] In reference to FIG. 10, in the first step, the load cell reads in the loads at the sampling rate and then stores the readings into a buffer, which is constantly analyzed for natural frequency identification.

[0022] In the second step, the signal is processed using a suitable systems identification algorithm, such as Prony's Method or Systems Identification methods (Auto-Regressive Moving Average, or similar), which can detect the frequencies in the system based on very short time signals. The duration of the time series can be very short - generally just like the 1-2 seconds range. For example, this method will find the appropriate signals in 8-12 data points using a 10Hz sampling rate, so the duration will be .8-1.2 seconds.

[0023] This can be useful because the high natural frequency excitations happen quickly and then die out, meaning that any method that looks at a longer time series will be averaging too much and will understate the magnitude of the resonance.

[0024] Prony's method, for example, will be able to detect analytically at least N / 2 frequencies in a time series that is N samples long. Instead of using this at N / 2, a larger matrix using Singular Value Decomposition can be used to be able to reject the least likely frequency components, thereby increasing the reliability of the frequency detection.

[0025] At this step, there can still be extraneous frequency components that need to be eliminated further. Using the property that a signal should show the same frequency content forward as when it is in reversed order, the extracted modes from each processing can then be compared. The ones that match are very reliably the actual modes.

[0026] The data can then be placed into a matrix in a form that will allow the decomposition of the amplitudes. At this point, the natural frequencies and amplitudes will be known, and these can then be sent back to the control room for further processing.

[0027] Note that this method will be detecting the natural roll period and the container stack natural periods but may not accurately define the wave frequency response (which is a low frequency and requires a long sequence of samples to be analyzed). Nevertheless, this method may be sufficient to detect the natural roll period and the container stack natural periods and provide useful alerts for potential overloading.

[0028] In the third step, once these magnitudes are calculated, they are combined together to estimate a maximum expected value of the tension in the lashing, given the current dynamics, is left to a variety of methods that are known in the industry.

[0029] Alternatively or additionally, in the fourth step, cumulated damage caused by cyclic loads (fatigue) in the lashing can be estimated.

[0030] In the fifth step, an alarm is triggered.

[0031] If bandwidth (and / or reliability) is a concern, the calculations can be done on the device itself (e.g., by the processor in the board coupled to the load cell). Given the potentially large number of signals that may be received, it may be advantageous to perform all the calculations on the device. Otherwise, all of the data could be sent to a computer (e.g., central data processor) on the bridge, where it will be processed using the described methodology.

Claims

1. A system including load cells coupled to a lashing (24) adapted to secure shipping containers stacked on a cargo ship, the load cells having a processor programmed to: acquire a time series of tension in a lashing (24); characterized in that the processor is further programmed to decompose the time series into a sum of sinusoidal signals, each having a frequency and an amplitude; wherein the load cells are configured to transmit data related to the frequencies and amplitudes to a computer.

2. The system of claim 1, wherein at least one of the load cells includes a load pin (38) and an adapter (42) configured to connect a clip (50) of the cargo ship to a turnbuckle (34) of the lashing (24).

3. The system of claim 2, wherein the adapter (42) includes first and second 2-prong forks, wherein the first 2-prong fork has an end having two holes sized to interface with a pin of a lashing clip (50) and another opposite end having one hole sized to interface with a load pin (38), and wherein the second 2-prong fork has an end having two holes sized to interface with the load pin (38) and another opposite end having one hole sized to interface with the lashing (24).

4. The system of any one of claims 1 to 3, further comprising accelerometer cells coupled to shipping containers stacked on a cargo ship, the accelerometer cells having a processor programmed to: acquire a time series of acceleration of a shipping container; and decompose the time series into a sum of sinusoidal signals, each having a frequency and an amplitude; wherein the accelerometer cells are configured to transmit data related to the frequencies and amplitudes to the computer.

5. The system of any one of claims 1 to 4, wherein the transmitting is performed through a relay station that is located at a top of a stack of containers.

6. The system of any one of claims 1 to 5, further comprising an inclinometer cell coupled to the cargo ship, the inclinometer cell having a processor programmed to: acquire a time series of roll angle of the cargo ship; and decompose the time series of the roll into a sum of sinusoidal signals, each having a frequency and an amplitude.

7. The system of any one of claims 1 to 6, wherein the computer or the processor in the cells is programmed to identify the sinusoidal signals caused by resonances in shipping container stacks based on the frequencies of the sinusoidal signals.

8. The system of any one of claims 1 to 7, wherein the computer or the processor in the cells is programmed to identify the sinusoidal signals caused by roll of the cargo ship based on the frequencies of the sinusoidal signals.

9. The system of any one of claims 1 to 8, wherein the computer or the processor in the cells is programmed to run an algorithm that extrapolates an energy or amplitude of at least some of the sinusoidal signals; and optionally, wherein the computer or the processor in the cells is programmed to generate a maximum value of the tension in the lashing (24) based on an extrapolation of the energy or amplitude and to trigger an alarm if the maximum value of the tension in the lashing (24) exceeds a predetermined value.