Dynamic real-time forecasting method for towing cable length of underwater towing system

Abstract

The invention relates to a dynamic real-time forecasting method for the length of a towing cable of an underwater towing system, which comprises the following steps of: constructing a discretization model of the towing system containing kinematics and dynamics equations of the towing cable, and carrying out numerical simulation on the dynamic forecasting of the length of the towing cable according to the discretization model. According to the invention, the cable length required by the towed body under the given operation depth can be continuously and accurately forecasted, so that the towed body is ensured to stably operate at the specified operation position.

Description

Technical Field

[0001] The invention relates to a technology in the field of ship control, in particular to a method for dynamic real-time prediction of the length of a towing cable of a towing system. Background Art

[0002] In view of the dynamic change in the relative height between the support platform and the towed body of the underwater towing system, the cable length needs to be continuously changed so that the towed body can operate at a specified depth or at a variable depth. The prior art previously used the method of releasing all the tow cables at once, without considering the influence of the cable releasing process on the calculation of the tow cable model of the towing system. In the previous algorithms for studying tow cables, the length of the tow cables released by the mother ship mostly remained unchanged, and few people paid attention to the cable length required for the towed body to be stably towed at different operating depths. At this time, it is necessary to continuously predict the cable length required for the towed body to operate at a specified operating depth or at a variable depth. Summary of the invention

[0003] In view of the obvious limitations of the prior art in dynamic and real-time prediction of tow cable length, and the inability to dynamically, continuously and accurately predict the cable length required for a towed body at different operating depths, the present invention proposes a dynamic real-time prediction method for the tow cable length of a reverse towing system, which can continuously and accurately predict the cable length required for a towed body at a given operating depth, thereby ensuring that the towed body can operate stably at a designated operating position.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to a method for dynamic real-time prediction of the length of a tow cable of an underwater towing system, comprising:

[0006] Step 1. Construct a discretized model of the towing system including the kinematic and dynamic equations of the towed cable. Specifically, in the reference coordinate system, a single towed cable is discretized into N segments of infinitesimal elements ds, then there are N+1 mass points, and the mass points are numbered from top to bottom. The node number at the surface mother ship is 0, and the node number at the end of the towed cable is N. Each infinitesimal element is approximately a spring-damper system, and the tension, bending moment, gravity, damping force, etc. it is subjected to are approximately acted on one mass point. Then, Newton's second law is used to list all differential equations for solution. For any infinitesimal element between the i-th node and the i-1 node at the j-th towed cable segment, the tension remains unchanged, and the tension direction is along the tangential direction.

[0007] The origin of the reference coordinate system is selected at the mass point where the surface mother ship is connected to the tow cable, the positive direction of the X-axis is parallel to the waterline, horizontally to the right, and the positive direction of the Z-axis is vertically downward.

[0008] The kinematic equation of the tow cable is: the position vector of each particle in: and Represent the position vectors of the j+1th and jth particles respectively. The unit vector of the cable segment

[0009] The dynamic equation of the tow cable refers to: the force analysis of each node i of the tow cable is performed, and the dynamic equation group of the discretized tow cable microelement is: and Where: M represents the mass matrix composed of each node of the streamer, T represents the tension matrix of each node of the streamer, N e It represents the shear force matrix of each node of the towed cable, F represents the various external force matrices of the towed cable nodes, including gravity, buoyancy, and fluid damping force, M and H represent the bending moment and torque matrices of the towed cable nodes due to bending and torsion, q is the distributed load generated by the ds bending moment of the towed cable micro-segment, and R represents the position vector matrix of each node of the towed cable.

[0010] In the discrete model, during the continuous cable laying process of the surface mother ship, the number of each particle point of the towline changes continuously with the cable laying process, and the position vector update process is as follows: This dynamic prediction numerical calculation model of the towline length takes the initial cable laying process into consideration, discretizes the towline into several segments, and lays the unit cable in segments for multiple times, thereby simulating the actual dynamic cable laying process, and then predicting the cable length required for the towed body at different specified operating depths. The basic idea is to lay the towline in n times. Since the towline is discretized into N micro-elements, the number of micro-segments laid each time is counter = N / n, and the cable length laid each time is counter*ds, where ds is the length of the unit cable. After each laying is completed and the numerical calculation converges, that is, after the towline reaches a stable state, the next stage of cable length laying is carried out. When the next laying is carried out, that is, after the k-th cable laying (k = 1, 2...n), the position vectors of all particles after the k-th laying are updated, specifically: Where: δ is the position vector of the end point of the i-th streamer micro-segment released each time, θ = k*counter+1, It is the position vector of the last mass point of the towline after the last towline deployment is completed and the numerical calculation converges. Based on this node, the position vectors of all nodes after the next deployment is completed are obtained.

[0011] Since the towed body is connected to the end of the tow cable during the numerical calculation, the size of the towed body is negligible compared to the total length of the tow cable, so the ordinate value of the particle at the end of the tow cable in the coordinate system is the depth of the towed body. In this way, the depth of the towed body that changes with the cable length can be continuously obtained during the continuous cable release process, that is, the position of the towed body under different cable lengths.

[0012] Step 2: Based on the streamer discretization model established in step 1, an iterative numerical simulation of the dynamic prediction of the streamer length is performed, which specifically includes:

[0013] 2.1. Assign values ​​to the parameters of the tow cable and tow body of the underwater towing system, and set the initial state of the tow cable and tow body. The parameters of this numerical model include: tow cable diameter, fluid tangential and normal damping coefficients, elastic modulus, linear density, fluid density; tow body mass, towing speed, and fluid relative speed. Start the tow cable numerical calculation model and perform numerical calculations.

[0014] 2.2. Perform the kth cable release, and update the position vector, velocity vector and mass of each particle point of the towline after this cable release, where: k = 1, 2...n, n represents the number of cable releases.

[0015] 2.3. After the deployment of the towline is completed, the gravity and buoyancy of each particle of the currently deployed towline are calculated; according to the relative velocity of the fluid at each particle of the towline at this moment, the fluid damping force of the towline particle and the water flow damping force of the towed body of the towing system are calculated, so as to calculate the total damping force of the current towing system; and the additional mass force of each particle of the towline is calculated.

[0016] 2.4. Calculate the strain of each micro-segment of the towed cable according to the position vector of each particle point of the towed cable, thereby calculating the tension of each micro-segment of the towed cable, and finally obtain the resultant force of each particle point of the towed cable.

[0017] 2.5. According to Newton's second law, calculate the acceleration of each particle of the tow cable; then use the Runge-Kutta method to calculate the velocity and displacement of each particle.

[0018] 2.6. Repeat steps 2.3 to 2.5 until the position vectors of the mass points of the towline reach the convergence condition, that is, the one-norm of the position vectors of the same mass points is less than the convergence condition, then return to step 2.2 to lower the towline once.

[0019] 2.7. When the towed body reaches the required operating depth or the preset total cable length has been fully released, the numerical calculation is stopped.

[0020] The present invention relates to a system for realizing the above method, comprising: a towing cable modeling unit for a towing system, a numerical calculation model parameter assignment unit, a numerical calculation unit and a cable length prediction unit, wherein: the towing cable modeling unit for the towing system generates kinematic and dynamic equations of the towing cable based on a lumped mass method and considers the boundary conditions of the cable body; the numerical calculation model parameter assignment unit inputs various parameters of the towing cable and the towing body and gives the initial states of the towing cable and the towing body according to actual working conditions; the numerical calculation unit continuously calculates the towing cable posture data based on the lumped mass method and the influence of the cable releasing process on the cable length prediction; the cable length prediction unit generates the relationship between the cable length and the towing body operating depth corresponding to the towing cable when the towing cable is continuously released, realizes the continuous prediction of the cable length required for the towing body at a variable depth or a specified operating position, and improves the calculation efficiency and the prediction accuracy. Technical Effects

[0021] The present invention considers the influence of continuous change of cable length during the cable release process, takes the initial cable release process into account, discretizes the towing cable into several sections, and lays the unit cable in sections for multiple times, so as to simulate the actual dynamic cable release process, and then predict the cable length required for the towing body at different specified operating depths. Compared with the prior art, the present invention can accurately predict the depth of the towing body of the underwater towing system during the cable length change process, and can also dynamically correct the cable length according to the actual operation requirements to ensure that the towing body can operate at the specified operating position; in addition, due to the limitation of the space size of the underwater submersible, engineers pay great attention to the continuous prediction of the cable length during the operation, which has important guiding significance for the size selection and spatial layout design of the winch in the overall plan, and plays a vital role in ensuring the stability, safety and reliability of the underwater towing system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a flow chart of the present invention;

[0023] Figure 2 It is a schematic diagram of an application scenario of an embodiment;

[0024] Figure 3 This is a simulation result diagram of the cable length of the towing body continuously predicted at a speed of 4kn during the cable-releasing process of the present invention;

[0025] Figure 4 This is a simulation result diagram of the cable length of the towing body continuously predicted at a speed of 5 kn during the cable-releasing process of the present invention;

[0026] Figure 5 This is a simulation result diagram of the cable length of the towing body continuously predicted at a speed of 6kn during the cable-releasing process of the present invention;

[0027] Figure 6 It is a time history diagram of the lifting height of the towing body at a speed of 4kn changing with the cable length during the cable-releasing process of the present invention;

[0028] Figure 7 It is a time history diagram of the lifting height of the towing body at a speed of 5kn changing with the cable length during the cable-releasing process of the present invention;

[0029] Figure 8 It is a time history diagram of the lifting height of the towing body at a speed of 6kn changing with the cable length during the cable releasing process of the present invention. DETAILED DESCRIPTION

[0030] like Figure 1 As shown, a method for dynamic real-time prediction of the length of the tow cable of an underwater towing system involved in this embodiment is provided, by constructing a discretized model of the towing system including the kinematic and dynamic equations of the tow cable, and performing numerical simulation of the dynamic prediction of the tow cable length according to the discretized model.

[0031] After specific experiments, the towline simulation under various working conditions shown in Table 2 was carried out with the parameters described in Table 1.

[0032] Table 1 Initial parameter settings.

[0033] Table 2 Test conditions

[0034] like Figure 3-Figure 5 As shown in Table 3, the simulation results of the cable length when the towed body reaches a depth of 300 m under different working conditions and the prediction results of the depth of the towed cable and the towed body when the cable is released to 100, 200, 300, 400 and 500 m are shown.

[0035] Table 3 Calculation results of cable length of towed body at specified lifting height

[0036] like Figure 6-Figure 8 Table 4 shows the time history curve and results of the descent depth of the towed body during the cable release process.

[0037] Table 44kn-Calculation results of the descent depth of the towed body during the cable release process

[0038] Table 5 5kn-Calculation results of the towing body descent depth during the cable release process

[0039] Table 66 kn - Calculation results of the towed body descent depth during the cable release process

[0040] Through numerical calculation, the cable length calculation results of the towed body at the working depth of 300 meters as shown in Table 3 can be obtained. This embodiment can predict the cable length required for different towed bodies to reach the depth of 300 meters at different towing speeds. As the flow velocity increases, the cable length required for the towed body to descend to the working position of 300 meters needs to be longer. Under the same flow velocity, the longer the tow cable is released, the depth of the towed body descending for each 1 meter of cable length released is continuously reduced during the cable release process, and the lower the flow velocity, the shorter the cable length required for the towed body to reach the working depth of 300 meters, which is also consistent with the experimental phenomenon.

[0041] like Figure 3-Figure 5 As shown in FIG. 1 , the towing system of this embodiment with a towing cable having a total length of 500 m is subjected to numerical simulation calculation, and the result graphs when the cable is released to 100, 200, 300, 400 and 500 m are selected. Figure 3As shown in Figure 1, the continuous change process of the towed body's descending depth as the tow cable is released at a towing speed of 4 kn. As the length of the tow cable gradually increases, the number of its nodes continues to increase, and the towed body's descending depth gradually increases.

[0042] like Figure 4 and Figure 5 The following figure shows the cable release process of the towing body at 5kn and 6kn towing speeds. Under the same working condition, as the length of the released cable gradually increases, the descent depth of the towing body gradually increases. The descent depth of the towing body during the cable release process changes continuously, which can dynamically predict the cable length required for the towing body under different operating conditions.

[0043] As shown in Tables 4 to 6, the calculation results of the descent depth of the towed body and the length of the tow cable under different working conditions are obtained through numerical calculation, which verifies that the present invention does not need to continuously change the cable length like the previous methods to obtain the operating depth of the towed body under different cable lengths. The present invention can perform real-time, efficient and continuous prediction of the cable length during actual towing operations.

[0044] like Figure 6-Figure 8 As shown in the figure, it is a time history curve of the descent depth of the towed body as the cable release process occurs within the 125s simulation calculation time. Under different operating conditions, the descent depth of the towed body gradually increases as the towline is continuously released. When the ship speed remains unchanged, the resistance of the towline and the towed body is small at the beginning of cable release, and the increase in the descent depth of the towed body is greater when the same cable length is released. However, as the released towline becomes longer, it becomes more difficult for the towed body to descend, which is consistent with the expected actual physical experimental phenomenon.

[0045] Compared with the prior art, the present invention can predict the cable length of the towed body at a fixed operating depth when the tow cable is not fully released. It does not need to continuously change the cable length as in the prior art. The depth of the towed body under multiple cable lengths can be obtained, and the operating depth of the towed body under continuous cable length changes can be obtained, thus realizing dynamic real-time prediction of the tow cable length. It not only improves the prediction accuracy, but also greatly improves the calculation efficiency, and can meet the operational requirements of continuously correcting the tow cable length due to changes in the towed body operating depth.

[0046] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for dynamic real-time prediction of tow cable length of a reverse towing system, characterized in that: include: Step 1, construct a discretized model of the towing system including the kinematic and dynamic equations of the towing cable, specifically: discretize a single tow cable into N segments of micro-elements ds in the reference coordinate system, then there are N+1 mass points, and the mass points are numbered from top to bottom. The node number at the surface mother ship is 0, and the node number at the end of the tow cable is N. Each micro-element is approximately a spring-damper system, and the tension, bending moment, gravity, and damping force it is subjected to are approximately applied to one mass point. Then, Newton's second law is used to list all differential equations for solution. The tension of the micro-element between the i-th node and the i-1 node at any j-th tow cable micro-segment remains unchanged, and the tension direction is along the tangential direction; Step 2: Based on the streamer discretization model established in step 1, an iterative numerical simulation of the dynamic prediction of the streamer length is performed, which specifically includes: 2.

1. Assign values ​​to the parameters of the tow cable and towed body of the underwater towing system, and set the initial state of the tow cable and towed body; the parameters of this numerical model include: tow cable diameter, fluid tangential and normal damping coefficients, elastic modulus, linear density, fluid density; mass of the towed body, towing speed, and fluid relative speed; start the tow cable numerical calculation model and perform numerical calculation; 2.

2. Perform the kth cable release, and update the position vector, velocity vector and mass of each particle point of the towline after this cable release, where: k = 1, 2…n, n represents the number of cable releases; 2.

3. After the towline is deployed, the gravity and buoyancy of each particle of the currently deployed towline are calculated; according to the relative velocity of the fluid at each particle of the towline at this moment, the fluid damping force of the towline particle and the water flow damping force of the towed body of the towing system are calculated, so as to calculate the total damping force of the current towing system; and the additional mass force of each particle of the towline is calculated; 2.

4. Calculate the strain of each micro-segment of the towline according to the position vector of each particle point of the towline, thereby calculating the tension of each micro-segment of the towline, and finally obtain the resultant force of each particle point of the towline; 2.

5. According to Newton's second law, calculate the acceleration of each particle of the tow cable; then use the Runge-Kutta method to calculate the velocity and displacement of each particle; 2.

6. Repeat steps 2.3 to 2.5 until the position vectors of the mass points of the towline reach the convergence condition, that is, the one-norm of the position vectors of the same mass points is less than the convergence condition, then return to step 2.2 to lower the towline once; 2.

7. When the towed body reaches the required operating depth or the preset total cable length has been fully released, the numerical calculation is stopped.

2. The method for dynamic real-time prediction of tow cable length of reverse towing system according to claim 1 is characterized in that: The origin of the reference coordinate system is selected at the mass point where the surface mother ship is connected to the tow cable, the positive direction of the X-axis is parallel to the waterline, horizontally to the right, and the positive direction of the Z-axis is vertically downward.

3. The method for dynamic real-time prediction of tow cable length of reverse towing system according to claim 1 is characterized in that: The kinematic equation of the tow cable is: the position vector of each particle in: and Respectively represent the position vectors of the j+1th and jth particles, and the unit vector of the cable segment 4. The method for dynamic real-time prediction of tow cable length of reverse towing system according to claim 1 is characterized in that: The dynamic equation of the tow cable refers to: the force analysis of each node i of the tow cable is performed, and the dynamic equation group of the discretized tow cable microelement is: and Where: M represents the mass matrix of each node of the streamer, T represents the tension matrix of each node of the streamer, N e It represents the shear force matrix of each node of the towed cable, F represents the various external force matrices of the towed cable nodes, including gravity, buoyancy, and fluid damping force, M and H represent the bending moment and torque matrices of the towed cable nodes due to bending and torsion, q is the distributed load generated by the ds bending moment of the towed cable micro-segment, and R represents the position vector matrix of each node of the towed cable.

5. The method for dynamic real-time prediction of tow cable length of reverse towing system according to claim 1 is characterized in that: In the discrete model, during the continuous cable laying process of the surface mother ship, the number of each particle point of the towline changes continuously with the cable laying process, and the position vector update process is as follows: This dynamic prediction numerical calculation model of the towline length takes the initial cable laying process into consideration, discretizes the towline into several segments, and lays the unit cable in segments for multiple times, thereby simulating the actual dynamic cable laying process, and then predicting the cable length required for the towed body at different specified operating depths. The basic idea is to lay the towline in n times. Since the towline is discretized into N micro-elements, the number of micro-segments laid each time is counter=N / n, and the cable length laid each time is counter*ds, where ds is the length of the unit cable. After each laying is completed and the numerical calculation converges, that is, after the towline reaches a stable state, the cable length is laid in the next stage. When the next laying is carried out, that is, after the k-th cable laying (k=1,2…n), the position vectors of all particles after the k-th laying are updated, specifically: Where: δ is the position vector of the end point of the i-th streamer micro-segment released each time, θ = k*counter+1, It is the position vector of the last mass point of the towline after the last towline deployment is completed and the numerical calculation converges. Based on this node, the position vectors of all nodes after the next deployment is completed are obtained.

6. A dynamic real-time prediction system for the length of a tow cable of a reverse towing system implementing any of the methods described in claims 1-5, characterized in that: include: The towing system tow cable modeling unit, the numerical calculation model parameter assignment unit, the numerical calculation unit and the cable length prediction unit, wherein: the tow cable modeling unit of the tow system generates the kinematic and dynamic equations of the tow cable based on the lumped mass method and considers the boundary conditions of the cable body; the numerical calculation model parameter assignment unit inputs various parameters of the tow cable and the tow body according to the actual working conditions and gives the initial state of the tow cable and the tow body; The numerical calculation unit continuously calculates the tow cable posture data based on the lumped mass method and the influence of the cable release process on the cable length prediction; the cable length prediction unit generates the relationship between the cable length and the operating depth of the towed body when the tow cable is continuously released, thereby realizing continuous prediction of the cable length required for the towed body at variable depth or specified operating position, thereby improving calculation efficiency and prediction accuracy.

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