Mooring cable simulation method for ship physical model test

Abstract

The invention relates to the technical field of ship physical model tests, in particular to a mooring rope simulation method for a ship physical model test. A simulation device is configured, wherein the simulation device comprises a spring assembly, a variable-diameter spiral shaft assembly, a rigid mooring rope and an I-shaped shaft sleeve; the top of the spring assembly is connected into the spiral shaft assembly, and the bottom is rigidly fixed; one end of the rigid cable is arranged on the I-shaped shaft sleeve, and the other end of the rigid cable vertically extends upwards and is pulled; presetting a target nonlinear curve, and recording theoretical displacement values corresponding to different counterweights; installing a displacement sensor and a force sensor which are respectively used for monitoring the elongation and tension of the rigid cable in real time; the tension of the spring assembly and the tension of the cable end are inversely proportional to the corresponding diameters of the spring assembly and the cable end; the ratio of the tension at the cable end to the tension of the spring assembly is adjusted, and the stress-displacement of the mooring cable is simulated as the required nonlinear relation. According to the invention, accurate simulation of the nonlinear stress and deformation relation of the mooring cable can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of ship physical model testing, in particular to a mooring cable simulation method for ship physical model testing. Background Art

[0002] In complex marine environments, ships are subject to multiple external forces such as wind, currents, and waves while at berth. These forces can easily lead to uneven stress on mooring lines or breakage, potentially causing serious safety accidents. Therefore, ensuring the safety and reliability of ship mooring systems has become a key research topic.

[0003] The core of a ship's mooring system lies in the analysis and control of the forces acting on the mooring lines. In physical model tests, the stress-strain relationship of the mooring lines is typically simulated to determine their tension and deformation. However, existing testing methods have the following problems: First, the nonlinear stress-strain relationship of mooring cables is segmented, exhibiting different stiffness characteristics in different load ranges. While existing technologies can achieve basic force-displacement measurements, simulating this segmented nonlinearity often requires complex mechanical structures or electronic control systems, resulting in high test equipment costs and complex operation. Secondly, in scaled model tests, existing methods often use a single elastic element (such as a single spring or rubber cable) to simulate cable characteristics. Although this simplified approach can achieve a certain degree of simulation accuracy (the error is usually within the range of 10% to 15%), it is difficult to flexibly adjust to the nonlinear characteristic curves of different types of cables. Thirdly, when conducting dynamic load tests, existing technologies have prominent problems with mechanical inertia and response delay. In particular, when simulating high-frequency wave loads (>1Hz), the dynamic following performance of the system degrades significantly. Finally, existing test equipment has a limited range of parameter adjustments. Simulating mooring lines of varying materials and specifications often requires replacing the entire system or undergoing significant modifications, resulting in a lack of versatility and flexibility. While these technical limitations do not affect the basic functionality of conventional testing, they still leave much room for improvement in the adaptability and cost-effectiveness of existing technical solutions when faced with the challenges of simulating complex sea conditions, testing multiple cable types, and requiring high-precision dynamic response.

[0004] Furthermore, with the advancement of deep-sea resource development and large-scale marine engineering projects, the environmental conditions faced by ships and offshore structures are becoming increasingly harsh, placing increasing demands on the performance of mooring systems. Accurately simulating the forces and deformations of cables in complex marine environments has become a key technical challenge in improving ship safety and operational efficiency.

[0005] Therefore, developing a test device with a simple structure, flexible adjustments, low cost, and the ability to accurately simulate the nonlinear characteristics of mooring lines is of great practical significance for improving test efficiency, reducing test costs, and expanding its scope of application. This invention addresses this need. Through innovative mechanical design, while maintaining simulation accuracy, it significantly simplifies the device's complexity, providing a more practical technical solution for experimental research on mooring systems. Summary of the Invention

[0006] In view of the shortcomings of the existing technology such as complex devices, inconvenient adjustment, and poor versatility, the present invention proposes a mooring cable simulation method for ship physical model testing. The present invention realizes the flexible adjustment of nonlinear characteristics through simple mechanical structure design; improves the stability of the system through multi-spring parallel design; and through the clever application of variable diameter spiral shafts, the same set of devices can adapt to the simulation requirements of various cable characteristics, while ensuring the simulation accuracy, significantly reducing the cost of the device and the complexity of operation. The tension of the spring assembly and the tension of the cable end are inversely proportional to their corresponding diameters. By adjusting the spiral shaft diameter d1 of the spiral shaft assembly, the ratio of the cable end tension to the spring assembly tension is adjusted to simulate the force-displacement relationship of the mooring cable to the desired nonlinear relationship. The present invention can achieve accurate simulation of the nonlinear force and deformation relationship of the mooring cable.

[0007] In order to achieve the above technical effects, the present invention proposes a mooring cable simulation method for ship physical model testing, comprising the following steps: S1. Configure the simulation device: including a high-strength spring assembly, a variable-diameter spiral shaft assembly, a rigid cable, and an I-shaped shaft sleeve; the spring assembly includes n parallel spring units with the same parameters; S2. The top of the spring assembly is suspended in the spiral groove of the spiral shaft assembly, and the bottom is rigidly fixed; one end of the rigid cable is wrapped in the I-shaped shaft sleeve, and the other end extends vertically upward, serving as the simulated cable end; S3. Preset the target nonlinear curve and record the theoretical deformation value L corresponding to different weights; S4. Install a displacement sensor and a force sensor to monitor the elongation L and tension T of the rigid cable in real time; S5, the tension of the spring assembly and the tension of the cable end satisfy the following formula. By adjusting the spiral shaft diameter d1 of the spiral shaft assembly, the nonlinear force characteristics of the mooring cable can be simulated; ; Where k is the sum of the stiffness coefficients of n spring units, which matches the desired cable stiffness; x is the elongation of the spring assembly; d1 is the diameter of the spiral shaft; d2 is the outer diameter of the I-shaped sleeve; T is the tension on the rigid cable; S6. Compare the simulation results with the target nonlinear curve to verify the simulation accuracy.

[0008] Furthermore, the screw shaft assembly includes a horizontal screw shaft and a pair of support bearings at both ends thereof; The two ends of the spiral shaft are smooth parts, each of which is fastened to the axis of a support bearing, thereby driving the spiral shaft to rotate through the support bearing; there is a threaded part between the two smooth parts, and the diameter of the threaded part is d1 and is variable.

[0009] Furthermore, the top of the spring assembly is connected to the spiral groove of the spiral shaft through a rigid rope, and the bottom is rigidly fixed; the I-shaped sleeve is fixed to the smooth part of the spiral shaft.

[0010] Furthermore, the tops of all the spring units are fixed to a rigid connecting rod as a whole, and the center of the rigid connecting rod is suspended in the spiral groove of the spiral shaft through a rigid rope.

[0011] Furthermore, the spiral shaft includes a spiral shaft body of equal diameter and a plurality of spiral sleeves of different outer diameters, and a spiral inner hole matching the spiral shaft is provided inside the sleeve; during the test, d1 is changed by replacing different sleeves, and the spring assembly is suspended outside the selected sleeve.

[0012] Furthermore, before conducting the test, it is necessary to calibrate the nonlinear curve. In step S3, different hanging weights are applied, and the corresponding displacement data are observed and recorded to ensure that the displacement data points conform to the target nonlinear curve.

[0013] Furthermore, the data recording interval of the target nonlinear curve is one theoretical displacement value L for every 50g of counterweight, and the counterweight range is 50g to 750g.

[0014] Furthermore, in S5, the displacement sensor and the force sensor are connected to a data acquisition system for real-time storage and processing of the collected elongation L and tension T data.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention boasts a simple structure, ease of operation, and low cost, making it suitable for studying the nonlinear stress characteristics of mooring cables during physical model testing of ships. By combining a spring assembly with a variable-diameter helical shaft assembly, the force ratio between the spring and the cable can be flexibly controlled, enabling accurate simulation of the nonlinear characteristics of the mooring cable. Furthermore, the device is constructed entirely of metal, making it suitable for underwater environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the overall structure of the mooring cable simulation device of the present invention; Figure 2 is the target nonlinear curve of the present invention; Figure 3It is a comparison diagram of the simulation data of the present invention and the target nonlinear curve.

[0017] In the picture: 1. Screw shaft; 2. Support bearing; 3. Rigid cable; 4. I-shaped bushing; 5. Spring assembly. DETAILED DESCRIPTION

[0018] To facilitate understanding of the present invention, the present invention will be described in more detail below, with preferred embodiments of the present invention provided. However, it should be understood that these embodiments are merely for the purpose of further explanation and are not to be construed as limiting the present invention in any form, i.e., they are not intended to limit the scope of protection of the present invention.

[0019] like Figures 1-3 As shown, this embodiment discloses a mooring cable simulation method for ship physical model testing, comprising the following steps: S1. Device configuration: Since the force-displacement relationship of the mooring cable to be simulated is a nonlinear curve relationship, and this nonlinearity is one of its basic characteristics, a variable diameter spiral shaft assembly is used to adjust the ratio of the tension at the cable end to the tension of the spring assembly, so as to simulate the force-displacement relationship of the mooring cable to be the required nonlinear relationship, ensuring that the actual force state of the mooring cable can be accurately reflected during the test; The adjustable diameter screw shaft assembly is used to precisely control the tension and elongation of the mooring line, thereby meeting the requirements of the cable under different test conditions. The screw shaft assembly includes a horizontally arranged solid screw shaft 1 and a pair of support bearings 2. The screw shaft 1 includes smooth portions at both ends and a threaded portion between them, and the shaft diameter d1 of the screw shaft can be adjusted according to the test. In addition, a rigid cable 3 and an I-shaped sleeve 4 with a diameter of d2 are provided; S2. Assemble the device: The two smooth parts of the screw shaft 1 are each fastened to the axis of a support bearing 2, thereby driving the screw shaft to rotate through the support bearing; The spring assembly 5 comprises n parallel spring units with identical parameters. The tops of all the spring units are fixed together with a rigid connecting rod. The center of the rigid connecting rod is suspended in the spiral groove of the spiral shaft via a rigid rope. The bottom of the spring assembly 5 is rigidly fixed. A smooth portion of the spiral shaft 1 is fixed integrally with the I-shaped sleeve; One end and the main body of the rigid cable 3 are wound in the sleeve, and the other end extends vertically upward to simulate the cable tension; S3, such as Figure 2As shown, the target nonlinear curve is preset. Before conducting the test, the nonlinear curve needs to be calibrated. This step involves applying different hanging weights, observing and recording the corresponding displacement data to ensure that these data points can conform to the expected nonlinear curve model. Once this process is completed, the calibrated simulation device can be used for subsequent testing. Specifically, in this embodiment, the theoretical deformation value L of the rigid cable end corresponding to the counterweight from 0g to 750g is found by recording data every 50g; S4. Installing displacement sensors and force sensors for real-time monitoring of the elongation L and tension T of the rigid cable, respectively; these sensors are used to transmit the collected data to a data acquisition system for storage and preliminary processing; S5, the spring assembly tension and the cable end tension satisfy the following formula. On the nonlinear curve, different points L correspond to a cable tension T. Simply adjust the inner diameter d1 of the spiral shaft so that the elongation L and tension T of the rigid cable satisfy the nonlinear curve in S3 to complete the simulation of the required cable. ; Where k is the sum of the stiffness coefficients of the n spring units, which matches the desired cable stiffness; x is the elongation of the spring assembly (theoretically, the elongations of the n spring units are equal and equal to the elongation of the spring assembly); d1 is the inner diameter of the helical shaft; d2 is the outer diameter of the I-shaped sleeve; and T is the tension on the rigid cable. Specifically, the spiral shaft is rotated by supporting the bearing 2, so that the rigid rope connected to the spring assembly rotates into the spiral groove at different positions, thereby obtaining different values ​​of d1. In order to adapt to different test parameter requirements, the diameter of the spiral shaft can be flexibly adjusted according to the test requirements. The diameter adjustment method of the spiral shaft can be any of the following: 1) Prefabricate spiral sleeves of different outer diameters for several target diameters commonly used in the test. The spiral shaft includes a spiral shaft body of constant diameter, and the interior of the sleeve is provided with a spiral inner hole that matches the spiral shaft body. The spring assembly is suspended on the outside of the selected sleeve. In this case, the outer diameter of the sleeve is d1. During the test, the parameter d1 is changed by replacing different sleeves. 2) Directly prefabricate the variable diameter spiral shaft through 3D printing or other methods; 3) Paste tapes of different thicknesses in the spiral groove of the equal-diameter spiral shaft body to adjust the spiral shaft diameter d1.

[0020] At the same time, the counterweight is adjusted to simulate the tension change of the cable to be tested, and the values ​​of L and T are obtained respectively using the displacement sensor and force sensor, thereby realizing accurate simulation of the nonlinear characteristics of the mooring cable; The following data can be obtained through the test: Table 1 Experimental simulation results

[0021] S6. Expand the scope of test data Table 2 Extended load range test results

[0022] S7. Add material performance comparison test Table 3 Comparative test results of different spring materials

[0023] S8. Dynamic load simulation test: A servo motor drive was used to apply periodic tension to the rigid cable to simulate dynamic loads such as waves and wind. The test frequency range was 0.47 Hz to 2.36 Hz, with an amplitude variation of ±30%. The experimental results are shown in Table 4: Table 4 Dynamic load test results

[0024] S9. Compare the simulation results with the target nonlinear curve, e.g. Figure 3 As shown in the figure, it can be seen from the test results that the patented device of the present invention can better simulate the nonlinear force characteristics of the mooring cable and has high measurement accuracy.

[0025] The above content is a further detailed description of the present invention in conjunction with specific implementation methods, and the specific implementation of the present invention should not be considered to be limited to these descriptions. The dimensional data of this embodiment does not limit the technical solution of this invention, but only illustrates one specific working condition. For those skilled in the art of the present invention, simple improvements and modifications can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A mooring cable simulation method for ship physical model testing, characterized in that: The following steps are involved: S1. Configure the simulation device: including a high-strength spring assembly, a variable-diameter spiral shaft assembly, a rigid cable, and an I-shaped shaft sleeve; the spring assembly includes n parallel spring units with the same parameters; S2. The top of the spring assembly is suspended in the spiral groove of the spiral shaft assembly, and the bottom is rigidly fixed; one end of the rigid cable is wrapped in the I-shaped shaft sleeve, and the other end extends vertically upward, serving as the simulated cable end; S3. Preset the target nonlinear curve and record the theoretical deformation value L corresponding to different weights; S4. Install a displacement sensor and a force sensor to monitor the elongation L and tension T of the rigid cable in real time; S5, the tension of the spring assembly and the tension of the cable end satisfy the following formula. By adjusting the spiral shaft diameter d1 of the spiral shaft assembly, the nonlinear force characteristics of the mooring cable can be simulated; ； Where k is the sum of the stiffness coefficients of n spring units, which matches the desired cable stiffness; x is the elongation of the spring assembly; d1 is the diameter of the spiral shaft; d2 is the outer diameter of the I-shaped sleeve; T is the tension on the rigid cable; S6. Compare the simulation results with the target nonlinear curve to verify the simulation accuracy.

2. The mooring cable simulation method for ship physical model testing according to claim 1, characterized in that: The screw shaft assembly includes a horizontal screw shaft and a pair of support bearings at both ends thereof; The two ends of the spiral shaft are smooth parts, each of which is fastened to the axis of a support bearing, thereby driving the spiral shaft to rotate through the support bearing; there is a threaded part between the two smooth parts, and the shaft diameter of the threaded part is d1 and is variable.

3. The mooring line simulation method for ship physical model testing according to claim 2, characterized in that: The top of the spring assembly is connected to the spiral groove of the spiral shaft through a rigid rope, and the bottom is rigidly fixed; the I-shaped shaft sleeve is fixed to the smooth part of the spiral shaft.

4. The mooring cable simulation method for ship physical model testing according to claim 3, characterized in that: The tops of all spring monomers are fixed as a whole with a rigid connecting rod, and the center position of the rigid connecting rod is suspended in the spiral groove of the spiral shaft through a rigid rope.

5. The mooring line simulation device according to claim 2, characterized in that: The spiral shaft includes a spiral shaft body of equal diameter and multiple spiral sleeves of different outer diameters. The interior of the sleeve is provided with a spiral inner hole matching the spiral shaft. During the test, d1 is changed by replacing different sleeves, and the spring assembly is suspended outside the selected sleeve.

6. The mooring line simulation method according to claim 1, characterized in that: Before conducting the test, it is necessary to calibrate the nonlinear curve. In step S3, different hanging weights are applied, and the corresponding displacement data are observed and recorded to ensure that the displacement data points conform to the target nonlinear curve.

7. The mooring line simulation method for ship physical model testing according to claim 6, characterized in that: The data recording interval of the target nonlinear curve is one theoretical displacement value L for every 50g of counterweight, and the counterweight range is 50g to 750g.

8. The mooring line simulation method according to claim 1, characterized in that: In S5, the displacement sensor and the force sensor are connected to a data acquisition system for real-time storage and processing of the collected elongation L and tension T data.

Images