Method for dynamic real-time prediction of tow cable length for underwater towing systems

Abstract

The application discloses a dynamic real-time prediction method for the length of a tow cable of an underwater towing system, which comprises the following steps: constructing a discrete model of the towing system containing the kinematics and dynamics equations of the tow cable; and performing numerical simulation for dynamic prediction of the length of the tow cable according to the discrete model. The application can continuously and accurately predict the required cable length of a tow body at a given working depth, thereby ensuring stable work of the tow body at a specified working position.

Description

Technical Field

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

[0002] The relative height between the support platform and the towed body in an underwater towing system can change dynamically, requiring continuous adjustment of the cable length to enable the towed body to operate at specified or varying depths. Existing technologies typically release the entire tow cable at once, without considering the impact of the cable release process on the towing system's cable model calculations. In previous studies of tow cable algorithms, the length of the tow cable released by the mother ship has mostly remained constant, with little attention paid to the cable length required for stable towing of the towed body at different operating depths. Therefore, it is necessary to continuously predict the cable length required for the towed body to operate at specified or varying depths. Summary of the Invention

[0003] This invention addresses the significant limitations of existing technologies in dynamically and accurately predicting tow cable length at different working depths. It proposes a method for dynamically and accurately predicting the tow cable length of a reverse towing system, which can continuously and accurately predict the cable length required by the tow body at a given working depth, thereby ensuring stable operation of the tow body at a designated working position.

[0004] This invention is achieved through the following technical solution:

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

[0006] Step 1: Construct a discretized model of the towing system containing the kinematic and dynamic equations of the towing cable. Specifically, in the reference coordinate system, the single towing cable is discretized into N infinitesimal elements ds, resulting in N+1 mass points. The mass points are numbered from top to bottom, with the node number at the mother ship on the water surface being 0 and the node number at the end of the towing cable being N. Each infinitesimal element is approximated as a spring-damped system, and the tension, bending moment, gravity, and damping force acting on it are approximately applied to a single mass point. Then, Newton's second law is used to list and solve all the differential equations. For any infinitesimal element between the i-th node and the i-1-th node at any j-th infinitesimal segment of the towing cable, the tension magnitude remains constant, 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 mother ship is connected to the towing cable on the water surface. The positive X-axis is parallel to the waterline and points horizontally to the right, while the positive Z-axis points vertically downward.

[0008] The aforementioned kinematic equations of the towing cable refer to: the position vectors of each mass point in: and These represent the position vectors of the (j+1)th and jth particles, respectively. The unit vector of the cable segment.

[0009] The aforementioned dynamic equations of the tow cable refer to the set of dynamic equations for the discretized infinitesimal element of the tow cable, obtained by analyzing the forces acting on each node i of the tow cable: and Where: M represents the mass matrix formed by the nodes of the tow cable, T represents the tension matrix of the nodes of the tow cable, and N... e The shear force matrix of each node of the towing cable is represented by F, which represents the matrix of various external forces acting on the node of the towing cable, including gravity, buoyancy, and fluid damping force. M and H represent the bending moment and torque matrices of the node of the towing cable due to bending and torsion, respectively. q is the distributed load generated by the bending moment ds of the micro-segment of the towing cable. R represents the position vector matrix of each node of the towing cable.

[0010] The discretized model described above, during the continuous deployment of the towline by the surface mother ship, shows that the number of mass points on the towline changes continuously with the deployment process. The position vector update process is as follows: This towline length dynamic prediction numerical calculation model considers the initial deployment process, discretizes the towline into several segments, and deploys unit cables multiple times in segments to simulate the actual dynamic deployment process, thereby predicting the cable length required by the towed body at different specified operating depths. The basic idea is to divide the towline deployment into n stages. Since the towline is discretized into N infinitesimal elements, the number of segments deployed each time (counter) is N / n, and the cable length deployed each time is counter*ds, where ds is the length of the unit cable. After each deployment is completed and the numerical calculation converges, i.e., after the towline reaches a stable state, the next stage of cable length deployment is carried out. When the next deployment is carried out, i.e., after the k-th deployment (k = 1, 2...n), the position vectors of all mass points after the k-th deployment are updated, specifically as follows: Where: δ is the position vector of the end mass of the i-th newly released tow cable micro-segment each time, θ = k*counter+1, The position vector of the last mass point of the tow cable after the previous tow cable deployment was completed and the numerical calculation converged is used as the basis for obtaining the position vectors of all nodes after the next deployment is completed.

[0011] Since the towed body is connected to the end of the tow cable during the numerical calculation, and its dimensions are negligible compared to the total length of the tow cable, the ordinate of the mass point at the end of the tow cable in the coordinate system represents the descent depth of the towed body. Thus, during the continuous cable laying process, the depth of the towed body as the cable length changes can be continuously obtained, i.e., the position of the towed body at different cable lengths.

[0012] Step 2: Based on the discretized model of the tow cable established in Step 1, perform iterative numerical simulations for dynamic prediction of the tow cable length, specifically including:

[0013] 2.1 Assign values ​​to the various 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; mass of the tow body, towing speed, and fluid relative velocity. Start the numerical calculation model of the tow cable and perform numerical calculations.

[0014] 2.2. Perform the k-th cable release and update the position vector, velocity vector, and mass of all mass points of the towed cable after this cable release, where: k = 1, 2...n, and n represents the number of cable releases.

[0015] 2.3 After the tow cable is deployed, calculate the gravity and buoyancy of each mass point of the tow cable that has been deployed; based on the relative fluid velocity of each mass point of the tow cable at this moment, calculate the fluid damping force of the tow cable mass points and the water flow damping force of the tow body of the towing system, thereby calculating the total damping force of the towing system; and calculate the additional mass force of each mass point of the tow cable.

[0016] 2.4 Calculate the strain of each micro-segment of the towing cable based on the position vector of each mass point of the towing cable, thereby calculating the tension of each micro-segment of the towing cable, and finally obtaining the resultant force of each mass point of the towing cable.

[0017] 2.5. Calculate the acceleration of each mass point in the towing cable according to Newton's second law; then use the Runge-Kutta method to calculate the velocity and displacement of each mass point.

[0018] 2.6 Repeat steps 2.3 to 2.5 until the position vectors of each mass point of the tow cable reach the convergence condition, that is, the first norm of the position vector of the same mass point is less than the convergence condition, then return to step 2.2 and drop the tow cable for the next stage.

[0019] 2.7 The numerical calculation stops when the towed body reaches the required working depth or the preset total cable length has been fully released.

[0020] This invention relates to a system for implementing the above-mentioned method, comprising: a towing system cable modeling unit, a numerical calculation model parameter assignment unit, a numerical calculation unit, and a cable length prediction unit, wherein: the towing system cable modeling unit generates the kinematic and dynamic equations of the towing cable based on the lumped mass method and considers the cable body boundary conditions; the numerical calculation model parameter assignment unit inputs various parameters of the towing cable and the towing body according to the actual working conditions and provides the initial state of the towing cable and the towing body; the numerical calculation unit continuously calculates the towing cable pose 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 towing body operating depth when the towing cable is continuously released, realizing continuous prediction of the cable length required by the towing body at varying depths or specified operating positions, thereby improving calculation efficiency and prediction accuracy.

[0021] Technical effect

[0022] This invention considers the impact of continuous cable length changes during cable deployment. By taking the initial deployment process into account, the towing cable is discretized into several segments, and unit cables are deployed multiple times in segments to simulate the actual dynamic cable deployment process. This allows for the prediction of the cable length required for the towed body at different specified operating depths. Compared to existing technologies, this invention can accurately predict the depth of the towed body in the underwater towing system during variable cable length deployment. It can also dynamically adjust the cable length according to actual operational needs to ensure the towed body can operate at the designated working position. Furthermore, due to the spatial limitations of underwater submersibles, engineers pay close attention to the continuous prediction of cable length during operations. This has significant guiding significance for the selection of winch size and spatial layout design in the overall scheme, and plays a crucial role in ensuring the stability, safety, and reliability of the underwater towing system. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention;

[0024] Figure 2 This is a schematic diagram illustrating an application scenario for an example.

[0025] Figure 3 This is a simulation result diagram of the continuous prediction of cable length by the towed body at a speed of 4 knots during the cable laying process of the present invention.

[0026] Figure 4 This is a simulation result diagram of the continuous prediction of cable length by the towed body at a speed of 5 knots during the cable laying process of the present invention.

[0027] Figure 5 This is a simulation result diagram of the continuous prediction of cable length by the towed body at a speed of 6 knots during the cable laying process of the present invention.

[0028] Figure 6 This is a time-series diagram showing the change in the lifting height of the towed body at a speed of 4 knots during the cable laying process of this invention as a function of the cable length.

[0029] Figure 7 This is a time-series diagram showing the change in the lifting height of the towed body at a speed of 5 knots during the cable laying process of this invention, as a function of the cable length.

[0030] Figure 8 This is a time-series diagram showing the change in the lifting height of the towed body at a speed of 6 knots during the cable laying process of this invention, as a function of the cable length. Detailed Implementation

[0031] like Figure 1 As shown in this embodiment, a method for dynamic real-time prediction of the towing cable length of an underwater towing system is proposed. This method involves constructing a discretized model of the towing system that includes the kinematic and dynamic equations of the towing cable, and then performing numerical simulations to dynamically predict the towing cable length based on the discretized model.

[0032] Through specific experiments, using the parameters described in Table 1, cable dragging simulations were performed under various working conditions as shown in Table 2.

[0033] Table 1 Initial parameter settings.

[0034]

[0035] Table 2 Test Conditions

[0036]

[0037] like Figures 3-5 Table 3 shows the simulation results of cable length when the towed body reaches a depth of 300 m under different working conditions, and the predicted depth results of the towed cable and towed body when the cable is laid to 100 m, 200 m, 300 m, 400 m and 500 m.

[0038] Table 3. Calculation results of cable length for towed vehicles at specified lifting heights.

[0039]

[0040] like Figures 6-8 Table 4 shows the time-history curves and results of the towed body's descent depth as a function of the cable laying process.

[0041] Table 44 shows the calculation results of the descent depth of the towed body during the cable laying process.

[0042]

[0043]

[0044] Table 55 shows the calculation results of the descent depth of the towed body during the cable laying process.

[0045]

[0046] Table 66 shows the calculation results of the descent depth of the towed body during the cable laying process.

[0047]

[0048] Numerical calculations yielded the cable length calculation results for the towed body at a working depth of 300 meters, as shown in Table 3. This embodiment can predict the cable length required for different towed bodies to reach a 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 300-meter working position becomes longer. At the same flow velocity, the longer the tow cable is released, the shallower the depth the towed body descends for every meter of cable released during the cable release process. Furthermore, the lower the flow velocity, the shorter the cable length required for the towed body to reach the 300-meter working depth, which is consistent with experimental observations.

[0049] like Figures 3-5As shown, numerical simulation calculations were performed on a towing system with a total towing cable length of 500m in this embodiment. The results were selected when the cable was laid to 100m, 200m, 300m, 400m, and 500m. Figure 3 As shown, this illustrates the continuous variation of the towed body's descent depth as the tow cable is released at a towing speed of 4kN. As the tow cable length gradually increases, the number of its nodes also increases, leading to a gradual increase in the towed body's descent depth.

[0050] like Figure 4 and Figure 5 The figures show the cable deployment process of the towed body at towing speeds of 5kN and 6kN, respectively. Under the same operating conditions, as the length of the released cable gradually increases, the descent depth of the towed body gradually increases. The descent depth of the towed body during the cable deployment process is a continuous change, which allows for dynamic prediction of the cable length required by the towed body under different operating conditions.

[0051] As shown in Tables 4-6, the calculation results of the towing body descent depth and towing cable length under different working conditions were obtained through numerical calculation. This verifies that the present invention does not require the cable length to be constantly changed as in the previous method in order to obtain the working depth of the towing body under different cable lengths. The present invention can provide real-time and efficient continuous prediction of cable length during actual towing operations.

[0052] like Figures 6-8 As shown, the descent depth of the towed body during the 125s simulation calculation time is a time-history curve of the cable release process. Under different operating conditions, the descent depth of the towed body gradually increases as the tow cable is continuously released. When the speed is constant, the increase in descent depth of the towed body is greater when the cable is released for the same length because the resistance of the tow cable and the towed body is small at the beginning of the cable release. However, the longer the tow cable is released, the more difficult it is for the towed body to descend, which is consistent with the expected actual physical experiment phenomenon.

[0053] Compared with existing technologies, this invention can predict the cable length of the tow body at a fixed operating depth even when the tow cable is not fully released. Unlike previous technologies that required continuously changing the cable length to determine the tow body's depth at multiple cable lengths, this invention provides dynamic, real-time prediction of the tow cable length. This not only improves prediction accuracy but also significantly increases computational efficiency, meeting the operational requirements of continuously adjusting the tow cable length as the tow body's operating depth changes.

[0054] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for dynamic real-time prediction of the length of a streamer cable of an underwater towed system, characterized in that, Comprise: Step 1, the discrete model of the towing system including the kinematics and dynamics equations of the towrope is built, specifically: the single towrope is discretized into N segments of microelements ds in the reference coordinate system, there are N+1 particles, the particle number is from top to bottom, the node number of the mother ship on the water surface is 0, and the node number of the end of the towrope is N, each microelement is approximated as a spring-damper system, which is subjected to tension, bending moment, gravity and damping force, which are approximated to act on a particle, then all the differential equations are listed to solve, the tension between the i-th node and the i-1-th node of the j-th towrope microelement remains unchanged, and the tension direction is along the tangential direction; Step 2, according to the discrete model of the towrope established in step 1, the iterative numerical simulation of the dynamic prediction of the towrope length is carried out, specifically including: 2.1, the parameters of the towrope and the towed body of the underwater towing system are assigned, and the initial state of the towrope and the towed body is set; the parameters of the numerical model include: towrope diameter, fluid tangential and normal damping coefficient, elastic modulus, linear density, fluid density; mass of the towed body, towing speed, fluid relative velocity; start the numerical calculation model of the towrope, and carry out numerical calculation; 2.2, the k-th cable is released, and the position vector, velocity vector and mass of each particle of the towrope after this cable release are updated, wherein: k=1, 2…n, n represents the number of cable release; 2.3, after the completion of this time cable deployment, the gravity and buoyancy of each particle of the currently deployed towrope are calculated; according to the fluid relative velocity of each particle of the towrope at this moment, the fluid damping force of the towrope particles 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 towrope is calculated; 2.4, the strain of each microelement of the towrope is calculated according to the position vector of each particle of the towrope, so as to calculate the tension of each microelement of the towrope, and finally the resultant force of each particle of the towrope is obtained; 2.5, according to Newton's second law, the acceleration of each particle of the towrope is calculated; then the Runge-Kutta method is used to calculate the velocity and displacement of each particle; 2.6, steps 2.3 to 2.5 are repeatedly executed until the position vector of each particle of the towrope reaches the convergence condition, that is, the norm of the position vector of the same particle is less than the convergence condition, and then the step 2.2 is returned to release the next stage of the towrope; 2.7, when the towed body reaches the required operating depth or the preset total cable length has been completely released, the numerical calculation is stopped.

2. The method of claim 1, wherein the method further comprises: The coordinate system origin of the reference coordinate system is selected at the particle where the mother ship on the water surface is connected with the towrope, 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 of claim 1, wherein the method further comprises: The aforementioned kinematic equations of the towing cable refer to: the position vectors of each mass point ,in: and They represent the first and the The position vector of a point mass, the unit vector of the cable segment. .

4. The method of claim 1, wherein the method further comprises, The dynamic equation of the said towrope is that: the force analysis is carried out on each node i of the towrope, and the dynamic equation group of the discretized towrope microelement is as follows: and Wherein: Z represents the mass matrix composed of each node of the towrope, T represents the tension matrix of each node of the towrope, F represents the various external force matrix suffered by the nodes of the towrope, including gravity, buoyancy, fluid damping force, M and H respectively represent the bending moment and torsion moment matrix suffered by the nodes of the towrope due to bending and torsion, q is the distributed load generated by the bending moment of the towrope microsection ds, and R represents the position vector matrix of each node of the towrope.

5. The method of claim 1, wherein the method further comprises: The discrete model, in the process of continuously releasing the cable by the surface mother ship, the number of particles of the tow cable changes continuously, and the position vector updating process is: the dynamic numerical prediction model of the length of the tow cable, considering the initial releasing process, discretizes the tow cable into several segments, and releases the unit cable in multiple stages, thereby simulating the actual dynamic releasing process, and further predicting the required cable length of the tow body at different specified operating depths. The basic idea is to divide the tow cable into n times of releasing. Since the tow cable is discretized into N micro-segments, the number of micro-segments counter released each time is The cable length released each time is counter*ds, and ds is the length of the unit cable. After each releasing is completed and the numerical calculation converges, the next stage of cable length releasing is performed. When the next releasing is performed, that is, after the kth releasing cable (k = 1, 2…n), the position vector of all particles after the kth releasing is updated, which is specifically: Wherein: is the position vector of the end particle of the ith micro-segment of the tow cable released each time, , is the position vector of the last particle of the tow cable after the last releasing is completed and the numerical calculation converges, and the position vectors of all nodes after the next releasing are obtained on the basis of the node.

6. An underwater towed system dynamic real-time prediction system of the length of the tow cable, which implements the method according to any one of claims 1-5, characterized in that, Comprise: The towing system towrope modeling unit, the numerical calculation model parameter assignment unit, the numerical calculation unit and the cable length prediction unit, wherein: the towing system towrope modeling unit generates the kinematics and dynamics equations of the towrope based on the lumped mass method and considers the boundary conditions of the cable body; the numerical calculation model parameter assignment unit inputs the parameters of the towrope and the towed body according to the actual working condition and gives the initial state of the towrope and the towed body; The numerical calculation unit continuously calculates the position data of the tow cable based on the lumped mass method and the influence of the cable releasing process on the cable length prediction; and the cable length prediction unit generates the relationship between the cable length and the working depth of the tow body when the cable is continuously released, thereby continuously predicting the cable length required by the tow body at the variable depth or the specified working position, and improving the calculation efficiency and the prediction accuracy.

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