CN113720576A - Multi-wet-end co-dragging safety analysis method based on formation calculation - Google Patents

Abstract

The invention relates to a multi-wet-end co-towing safety analysis method based on formation calculation, which comprises the following steps of S1: taking the dynamic parameters of each towing wet end as input, considering the navigational speed, the turning radius and the heave of the movement of the surface ship and the influence of the environmental parameters of sea waves and ocean currents, and establishing a cable system dynamic model; s2, calculating the towing wet end underwater formation numerical value: determining a preliminary overall layout scheme, inputting relevant parameters by using the dynamic model, and carrying out the calculation of underwater space formations of the towing wet ends by adopting a numerical calculation method; s3, multi-wet-end common-dragging safety analysis and judgment: screening the space intersection conditions of the dragging wet ends under different working conditions, comparing the depth change trend of the wet ends at the intersection points, evaluating the collision and winding risks of the dragging of the multiple dragging wet ends together, and determining the feasibility of the overall layout scheme. The invention can be used for solving the problem of the multi-towing wet-end towing safety of the surface ship and supporting the underwater towing wet-end integrated design of different surface platforms.

Description

Multi-wet-end co-dragging safety analysis method based on formation calculation

Technical Field

The invention belongs to the technical field of overall integrated design, and particularly relates to an analysis method for the towing safety of a plurality of towing wet ends, which can be used for guiding the overall layout design of the towing wet ends of a surface ship.

Background

Due to the overall or equipment integration requirement of the surface ship, a plurality of towing linear arrays need to be towed at the stern simultaneously for use. The towing line array is towed at the tail of the water surface ship at a certain distance, and the working depth of the towing line array is adjusted by adjusting the cable laying length and the towing speed. Due to the adoption of flexible towing cables for towing, under the combined action of hydrodynamic force, towing force and the like, the shape and the attitude of the towed linear array and the towing cables thereof under water can be changed along with the change of parameters such as the speed, the rudder angle and the like of the surface ship.

Due to different hydrodynamic parameters, the laws of each tow linear array and each tow cable of each tow linear array, which change along with the characteristics of the platform of the surface vessel, are different, so that the safety problems of collision or winding and the like of each tow wet end (including the tow linear array and the tow cable) under different working conditions of the surface vessel are ensured under a specific overall layout scheme, and the method has great significance for evaluating the feasibility and the rationality of the overall layout of the tow wet ends. The patent proposes a multi-towing wet-end common-towing safety analysis method based on formation calculation aiming at the problems.

Disclosure of Invention

The invention aims to solve the technical problem that in the prior art, multiple towing wet ends are in a common towing state and an effective safety analysis method is lacked, and provides a multi-towing wet end common towing safety analysis method based on formation calculation.

The technical scheme adopted by the invention for solving the technical problems is as follows:

s1 hydrodynamic analysis of towed wet end

The towing wet end is towed by the surface ship to move, and the underwater space formation of the towing wet end is related to the hydrodynamic characteristics (including length, diameter, density, tangential force coefficient, normal force coefficient, elastic modulus and the like) of the towing wet end, and is also influenced by the navigational speed, the turning radius and the heave of the surface ship, the environmental parameters of sea waves, ocean currents and the like. In the step, the dynamic parameters of each towing wet end are taken as input, the navigation speed, the turning radius and the heave of the movement of the surface ship and the influence of the environmental parameters of sea waves and ocean currents are considered, and a cable system dynamic model is established. The method specifically comprises the following steps:

s1.1, establishing a towing wet end system, wherein a front end point of a towing cable is connected with a point A on a surface ship; there are 3 coordinate systems in the towed wet end system: space fixed coordinate system O-xyz, surface ship coordinate system O₁-x₁y₁z₁Dragging a local coordinate system (t, n, b) of the wet end, wherein an xy plane of a fixed coordinate system O-xyz is taken as a still water surface, and each coordinate system is a right-handed screw; for an orthonormal unit vector (i, j, k) of a fixed coordinate system (x, y, z), the two can be related by the euler angle (α, β, γ), i.e. (t, n, b) ═ i, j, k) a, if b is kept parallel to the plane formed by i, j but perpendicular to k, then there is a coordinate transformation matrix

S1.2, according to the dynamics theory of the cable system, in a local coordinate system (t, n, b) of a towing wet end, the following matrix equation exists:

My′＝Ny&+q (1)

wherein y (s, T) [ T, V ]_t,V_n,V_b,α,γ]^T,

The meaning of the physical quantities in the formula is as follows:

s: the arc length measured from the trailing point a;

t: time;

t: tension on the cable;

V(s,t)＝(V_t,V_n,V_b): a velocity vector represented by a local coordinate system (t, n, b);

m: the mass of the streamer per unit length;

a: cross-sectional area of the streamer;

ρ: density of seawater;

m₁: m + ρ a (virtual mass of streamer per unit length);

g: acceleration of gravity;

w: (m- ρ A) g (weight in water per unit length of streamer) or mg (weight in air per unit length of streamer);

e: 1/EA (E is the modulus of elasticity of the streamer);

C_t,C_n: the tangential and normal resistance coefficients of the towing cable are determined by experiments;

d: the diameter of the streamer;

J＝(J_t,J_n,J_b): a water or air velocity vector represented by a local coordinate system (t, n, b);

a partial derivative of the water or air flow velocity vector J versus time;

U＝(U_t,U_n,U_b): V-J (relative to the velocity of the water or air stream).

S2, calculating towing wet end underwater formation numerical value

And determining a preliminary overall layout scheme, inputting relevant parameters by using the dynamic model, and carrying out calculation of underwater space formations of the towing wet ends by adopting a numerical calculation method. The method specifically comprises the following steps:

and S2.1, determining a preliminary layout scheme and a motion parameter at a dragging point.

The retraction system of the towing wet end is generally arranged on a tail deck of the surface ship, and when a plurality of the retraction systems of the towing wet end are arranged, the distance between two towing cables is generally not less than 3 m. And comprehensively considering the arrangement of the towing mooring device, the gangway ladder and the like of the tail deck, and preliminarily determining the overall layout scheme.

The tow point a is on the surface vessel and its speed and position obviously depend on the movement of the surface vessel. When the surface ship moves on the water surface, the mathematical model is a 4-degree-of-freedom manipulation motion equation of the water surface, and the origin O of the surface ship is set₁And (4) acquiring the speed and the position at the dragging point A through the overall layout scheme.

And S2.2, determining boundary conditions.

The boundary condition exists at tow point a, which has the same absolute velocity as the surface vessel velocity, i.e.:

V(0,t)＝v(t) (2)

or written as:

Cy(0,t)＝v(t) (3)

wherein:

v(t)＝(v_t,v_n,v_b) And represents the speed of the surface vessel represented by the local coordinate system (t, n, b) as a known quantity.

And S2.3, performing steady state solution according to the boundary conditions to obtain the attitude of the streamer in a space fixed coordinate system O-xyz.

The steady state refers to a state that the surface ship moves linearly at a constant speed and the whole dragging wet end is in a constant attitude relative to fluid, and at the moment, the partial derivative of any physical quantity to the time t is zero, and the following conditions are provided:

where ε represents streamer strain;

note (U)_t,U_n,U_b)＝(U_x,U_y,U_z) And A, the three formulas are a ternary ordinary differential equation set about T, alpha and gamma, the equation set is calculated by a Longdan-Kutta method (Runge-Kutta), and a specific solution method of a steady state is as follows: taking the intersection point B of the towing cable and the towing line array as an initial point, starting integration along the reverse direction of the cable length according to equations (4) to (6), and integrating until the towing point A, thus obtaining T, alpha and gamma at each position along the cable length;

respectively solving the partial derivatives of the cable length s and the time t by the vector r ═ xi + yj + zk of any point on the towing cable to obtain

r′＝(1+ε)t＝x′i+y′j+z′k (7)

The position coordinates (x, y, z) of the streamer in a spatially-fixed coordinate system are then given by:

after T, alpha and gamma are obtained, integration is carried out along the forward direction of the cable length according to the formula (8), and the attitude of the streamer in a space fixed coordinate system O-xyz can be obtained.

And S2.4, further carrying out unsteady state solution according to the steady state solution to obtain the attitude of the streamer at each moment.

And when the unsteady state solution is carried out, taking the result of the steady state calculation as an initial value. In the unsteady state solution, the influence of the fluctuation of the surface vessel along with the waves needs to be considered. Because the towing wet end is most concerned about the depth, the vertical heaving motion has influence on the depth, the transverse and longitudinal oscillating motions mainly influence the motion attenuation of the towing wet end in the horizontal plane, and almost have no influence on the vertical depth, so that the vertical heaving motion is only considered when calculating the influence of the waves on the towing wet end. The concrete steps of the unsteady state solving are as follows:

firstly, setting a steady-state calculation result as an initial value of unsteady-state calculation: the steady state calculation can obtain T, alpha and gamma at each point of the cable length, and the speed at each point on the cable is the same as that at the dragging point A, so that V at each point of the cable length can be obtained through a coordinate transformation matrix A_t、V_nAnd V_bThus, each point of the cable length has 6 unknowns; the cable is divided into N sections from A point to B point, and N +1 end points are provided, and T, alpha, gamma and V are provided for each end point_t、V_n、V_bThese 6 unknowns, there are 6(N +1) unknowns in total;

in the second step, the equation for the unsteady state calculation is listed: the midpoint of each segment is listed as 6 equations according to equation (1), for a total of 6N equations; adding 6 boundary conditions, and totally 6(N +1) equations; solving by adopting a Newton iteration method, and obtaining a value at the t (i +1) moment from a value at the t (i) moment;

thirdly, after T, alpha and gamma of each position of the cable length are obtained, giving the position of the towing point A in the fixed coordinate system, integrating along the forward direction of the cable length according to the formula (8) until the position reaches the towing point B, and thus obtaining the attitude of the towing cable in the fixed coordinate system;

and fourthly, giving the value of the time t (i +1) as an initial value to t (i), and repeating the second step and the third step to obtain the attitude of the streamer at any time.

S3, multi-wet-end common-towing safety analysis and judgment

Screening the space intersection conditions of the dragging wet ends under different working conditions, comparing the depth change trend of the wet ends at the intersection points, evaluating the collision and winding risks of the dragging of the multiple dragging wet ends together, and determining the feasibility of the overall layout scheme. The specific method comprises the following steps:

on the basis of numerical simulation, analyzing the safety of the multiple dragging wet ends by utilizing the relative relation of the spatial array of the dragging wet ends; the premise that the two dragging wet ends are twisted is judged to be collision, and the method for judging whether the two dragging ends are collided is as follows:

a. firstly, judging whether the postures of the two objects have an intersection point (called space intersection) on a horizontal plane, if the postures of the two objects do not have the intersection point, the two objects do not collide with each other;

b. if there is an intersection, the vertical distance dz (algebraic value) between the two at this intersection is calculated, and the sign of this distance is determined, for example, by assuming that dz is equal to z (left-dragging) -z (right-dragging), and if left-dragging-up and right-dragging-down are present at this intersection, then dz is <0, whereas if left-dragging-up and left-dragging-down are present, then dz > 0. If the left drag and the right drag have spatial intersection in two adjacent steps of calculation and the sign of dz is opposite, it indicates that the two drags collide at the moment;

c. when a collision occurs between the two towed wet ends and the tension of the cable at the collision point is sufficiently small, the possibility of entanglement between the two tows exists, so that the most dangerous situation is that the two tows collide at the tail, and therefore the judgment is generally started from the tail when the spatial intersection point is calculated;

d. according to the method, the possibility of collision or winding between every two dragging wet ends is screened, and the result of the co-dragging safety evaluation of the multiple dragging wet ends under the given overall layout scheme can be obtained.

The invention has the beneficial effects that:

the method can predict the underwater space formation of the multi-towing wet end under different working conditions, and according to the prediction result, the multi-towing wet end co-towing safety under the given overall scheme layout is evaluated through the collision or winding possibility analysis of every two wet ends, so that the overall compatibility layout optimization of the multi-towing wet end of the water surface platform can be supported.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a schematic drawing of a drag wet end system.

Fig. 2 shows the general layout of the two towed wet ends of a surface vessel (plan view).

FIG. 3 shows exemplary output point locations for left-drag and right-drag (PL for left-drag, PR for right-drag).

FIG. 4 shows streamer amplitude variation for a left drag and drop cable length of 500m, a velocity of 30kn, and a wave height of 4 m.

FIG. 5 shows streamer amplitude variation for a left drag and drop cable length of 500m, a velocity of 18kn, and a wave height of 4 m.

FIG. 6 shows streamer amplitude variation for a left drag and drop cable length of 500m, velocity of 8kn, and wave height of 4 m.

FIG. 7 shows streamer amplitude variation for a right drag-and-drop cable length of 500m, a velocity of 30kn, and a wave height of 4 m.

FIG. 8 shows streamer amplitude variation for a right drag-and-drop cable length of 500m, a velocity of 18kn, and a wave height of 4 m.

FIG. 9 shows streamer amplitude variation for a right drag-and-drop cable length of 500m, velocity of 8kn, and wave height of 4 m.

Fig. 10 is a depth difference change curve of two trailing wet ends in uniform rotation (speed 8kn, rudder angle of 15 degrees, right turn 180 degrees, straight sailing 200 s).

Fig. 11 is a depth difference change curve of two trailing wet ends in uniform rotation (speed 8kn, rudder angle of 25 degrees, right turn 180 degrees, straight sailing 200 s).

Fig. 12 is a depth difference change curve of two trailing wet ends in uniform rotation (speed 8kn, rudder angle of 35 degrees, right turn 180 degrees, straight sailing 200 s).

Fig. 13 is a depth difference change curve of two trailing wet ends in uniform rotation (speed 18kn, rudder angle of 15 degrees, right turn 180 degrees, straight sailing 100 s).

Fig. 14 is a depth difference change curve of two trailing wet ends in uniform rotation (speed 18kn, rudder angle of 25 degrees, right turning 90 degrees and straight sailing 100 s).

Fig. 15 is a depth difference change curve of two trailing wet ends in uniform rotation (speed 18kn, rudder angle of 35 degrees, right turning 90 degrees, straight sailing 100 s).

Fig. 16 is a depth difference change curve of two trailing wet ends in uniform rotation (30 kn speed, 15 degree rudder angle, 180 degree right turn, 100s straight voyage).

Fig. 17 is a depth difference change curve of two trailing wet ends in uniform rotation (30 kn speed, 25 degrees rudder angle, 180 degrees right turn, 100s straight voyage).

Fig. 18 is a depth difference change curve of two trailing wet ends in uniform rotation (30 kn, 35 degree rudder angle, 180 degree right turn and 100s straight voyage).

Detailed Description

The following further describes the specific implementation of the intellectual achievement aiming at the two-towing wet-end system of a certain surface vessel and combining the attached drawings.

S1 hydrodynamic analysis of towed wet end

For two towed wet ends (left tow and right tow) as shown in fig. 2, a towed wet end system as shown in fig. 1 is set up with the forward end points of the streamers connected to a point a on the surface vessel. According to the dynamics theory of the cable system, a matrix equation, namely an equation (1), is established.

S2, calculating towing wet end underwater formation numerical value

For the overall arrangement condition of the surface ship, the layout of the retraction system and the towing points of the two towing wet ends is determined as shown in fig. 2, and meanwhile, the coordinate parameters of the towing points of the two towing wet ends can be determined. The horizontal distance between the tow wet end tow points is 8.3 m.

The parameters of the two towed wet ends and the general characteristics of the surface vessel are shown in table one, table two and table three, respectively.

Table-left hydrodynamic characteristic parameter

Table two right drag power characteristic parameter

Parameter name	Towing cable	Dragging line array	Tail rope
				Length (m)	650	68	18
Diameter (m)	0.0305	0.092	0.025
				Density (kg/m)3)	1682.5	1027	713
Coefficient of tangential force Ct	0.023	0.015	0.023
				Coefficient of normal force Cn	1.6	1.8	1.8
Modulus of elasticity (. times.10)-10)	21	21	21

Corresponding relation between ship speed, rudder angle turning radius and ship length ratio of surface ship

And (3) carrying out steady state solution according to boundary conditions, and further carrying out unsteady state solution to obtain an amplitude change curve of the two-towing wet-end streamer under the conditions of the cable laying length of 500m, the speed of 30kn/18kn/8kn, the wave height of 4m and the like, as shown in fig. 4-9, wherein the abscissa s represents the projection of the streamer on a horizontal plane after straightening, and the ordinate dz represents the depth change amplitude of the streamer in the vertical direction.

S3, multi-wet-end common-towing safety analysis and judgment

On the basis of the numerical simulation, the safety of the two dragging wet ends is analyzed and judged by utilizing the relative relation of the space array of the dragging wet ends.

During the slewing maneuver, the surface ship calculates the time-dependent change curve of the depth difference dz between the two towed wet ends, i.e., z (left towing) -z (right towing), as shown in fig. 10 to 18. According to the calculation result, the distance between the two dragging wet ends is large enough (8.3m) and the difference in depth is large, although the space is crossed (vertical line in the figure), the sign of dz is kept unchanged, which indicates that the two do not collide. The general layout scheme of the surface ship is feasible.

While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (9)

1. A multi-wet-end common-dragging safety analysis method based on formation calculation is characterized by comprising the following steps:

s1 hydrodynamic analysis of the towed wet end: taking the dynamic parameters of each towing wet end as input, considering the navigational speed, the turning radius and the heave of the movement of the surface ship and the influence of the environmental parameters of sea waves and ocean currents, and establishing a cable system dynamic model;

s2, calculating the towing wet end underwater formation numerical value: determining a preliminary overall layout scheme, inputting relevant parameters by using the dynamic model, and carrying out the calculation of underwater space formations of the towing wet ends by adopting a numerical calculation method;

s3, multi-wet-end common-dragging safety analysis and judgment: screening the space intersection conditions of the dragging wet ends under different working conditions, comparing the depth change trend of the wet ends at the intersection points, evaluating the collision and winding risks of the dragging of the multiple dragging wet ends together, and determining the feasibility of the overall layout scheme.

2. The method for analyzing the safety of the multi-wet-end co-trailing based on the formation calculation according to claim 1, wherein the step S1 specifically includes the following steps:

s1.1, establishing a towing wet end system, wherein a front end point of a towing cable is connected with a point A on a surface ship; there are 3 coordinate systems in the towed wet end system: space fixed coordinate system O-xyz, surface ship coordinate system O₁-x₁y₁z₁Dragging a local coordinate system (t, n, b) of the wet end, wherein an xy plane of a fixed coordinate system O-xyz is taken as a still water surface, and each coordinate system is a right-handed screw; for an orthonormal unit vector (i, j, k) of a fixed coordinate system (x, y, z), the two can be related by the euler angle (α, β, γ), i.e. (t, n, b) ═ i, j, k) a, if b is kept parallel to the plane formed by i, j but perpendicular to k, then there is a coordinate transformation matrix

S1.2, according to the dynamics theory of the cable system, in a local coordinate system (t, n, b) of a towing wet end, the following matrix equation exists:

My′＝Ny&+q (1)

wherein y (s, T) [ T, V ]_t,V_n,V_b,α,γ]^T,

The meaning of the physical quantities in the formula is as follows:

s: the arc length measured from the trailing point a;

t: time;

t: tension on the cable;

V(s,t)＝(V_t,V_n,V_b): a velocity vector represented by a local coordinate system (t, n, b);

m: the mass of the streamer per unit length;

a: cross-sectional area of the streamer;

ρ: density of seawater;

m₁: m + ρ a (virtual mass of streamer per unit length);

g: acceleration of gravity;

w: (m- ρ A) g (weight in water per unit length of streamer) or mg (weight in air per unit length of streamer);

e: 1/EA (E is the modulus of elasticity of the streamer);

C_t,C_n: the tangential and normal resistance coefficients of the towing cable are determined by experiments;

d: the diameter of the streamer;

J＝(J_t,J_n,J_b): a water or air velocity vector represented by a local coordinate system (t, n, b);

partial derivation of water or air velocity vector J versus time；

U＝(U_t,U_n,U_b): V-J (relative to the velocity of the water or air stream).

3. The method for analyzing the safety of the multi-wet-end co-trailing based on the formation calculation according to claim 2, wherein the step S2 specifically includes the following steps:

s2.1, determining a preliminary layout scheme and motion parameters at a dragging point;

s2.2, determining boundary conditions;

s2.3, performing steady state solution according to boundary conditions to obtain the attitude of the towing cable in a space fixed coordinate system O-xyz;

and S2.4, further carrying out unsteady state solution according to the steady state solution to obtain the attitude of the streamer at each moment.

4. The method for multi-wet-end-drag-common security analysis based on formation calculation according to claim 3, wherein in step S2.1, the preliminary layout scheme is determined by: the retraction system of the towing wet end is arranged on a tail deck of the surface ship, when a plurality of towing wet end retraction systems are arranged, the distance between two towing cables is not less than 3m, then the arrangement of the towing mooring device and the gangway ladder of the tail deck is comprehensively considered, and the overall layout scheme is preliminarily determined.

5. The formation-calculation-based multi-wet-end-drag-sharing security analysis method according to claim 3, wherein in step S2.1, the motion parameters at the drag point are determined by: when the surface ship moves on the water surface, the mathematical model is a 4-degree-of-freedom manipulation motion equation of the water surface, and the origin O of the surface ship is set₁And (4) acquiring the speed and the position at the dragging point A through the overall layout scheme.

6. The method for multi-wet-end-to-end-drag security analysis based on formation calculation according to claim 3, wherein in step S2.2, the boundary condition exists at the drag point A,

the absolute velocity of the streamer at this point is the same as the surface vessel velocity, i.e.:

V(0,t)＝v(t) (2)

or written as:

Cy(0,t)＝v(t) (3)

wherein:

v(t)＝(v_t,v_n,v_b) And represents the speed of the surface vessel represented by the local coordinate system (t, n, b) as a known quantity.

7. The method for analyzing the safety of the multi-wet-end co-towing based on the formation calculation according to claim 3, wherein in the step S2.3, the steady state refers to a state that the surface ship moves linearly at a constant speed, and the whole towing wet end is in a constant attitude relative to the fluid, and at this time, the partial derivative of any physical quantity to the time t is zero, and then:

where ε represents streamer strain;

note (U)_t,U_n,U_b)＝(U_x,U_y,U_z) And A, the three formulas are a ternary ordinary differential equation set about T, alpha and gamma, the equation set is calculated by a Longdan-Kutta method (Runge-Kutta), and a specific solution method of a steady state is as follows: press formula (4) E taking intersection point B of towing cable and towing line array as initial point(6) Starting to perform integration along the reverse direction of the cable length until the integration reaches the dragging point A, and then obtaining T, alpha and gamma at each position along the cable length;

respectively solving the partial derivatives of the cable length s and the time t by the vector r ═ xi + yj + zk of any point on the towing cable to obtain

r′＝(1+ε)t＝x′i+y′j+z′k (7)

The position coordinates (x, y, z) of the streamer in a spatially-fixed coordinate system are then given by:

after T, alpha and gamma are obtained, integration is carried out along the forward direction of the cable length according to the formula (8), and the attitude of the streamer in a space fixed coordinate system O-xyz can be obtained.

8. The method for multi-wet-end co-trailing security analysis based on formation calculation according to claim 7, wherein in step S2.4, the concrete steps of the unsteady state solution are as follows:

firstly, setting a steady-state calculation result as an initial value of unsteady-state calculation: the steady state calculation can obtain T, alpha and gamma at each point of the cable length, and the speed at each point on the cable is the same as that at the dragging point A, so that V at each point of the cable length can be obtained through a coordinate transformation matrix A_t、V_nAnd V_bThus, each point of the cable length has 6 unknowns; the cable is divided into N sections from A point to B point, and N +1 end points are provided, and T, alpha, gamma and V are provided for each end point_t、V_n、V_bThese 6 unknowns, there are 6(N +1) unknowns in total;

in the second step, the equation for the unsteady state calculation is listed: the midpoint of each segment is listed as 6 equations according to equation (1), for a total of 6N equations; adding 6 boundary conditions, and totally 6(N +1) equations; solving by adopting a Newton iteration method, and obtaining a value at the t (i +1) moment from a value at the t (i) moment;

thirdly, after T, alpha and gamma of each position of the cable length are obtained, giving the position of the towing point A in the fixed coordinate system, integrating along the forward direction of the cable length according to the formula (8) until the position reaches the towing point B, and thus obtaining the attitude of the towing cable in the fixed coordinate system;

and fourthly, giving the value of the time t (i +1) as an initial value to t (i), and repeating the second step and the third step to obtain the attitude of the streamer at any time.

9. The method for analyzing the safety of the multi-wet-end co-trailing based on the formation calculation in the claim 1, wherein in the step S3, the safety of the multi-trailing wet end is analyzed by using the spatial formation relative relationship of the trailing wet ends based on the numerical simulation; the premise that the two dragging wet ends are twisted is judged to be collision, and the method for judging whether the two dragging ends are collided is as follows:

a. firstly, judging whether the postures of the two objects have an intersection point (called space intersection) on a horizontal plane, if the postures of the two objects do not have the intersection point, the two objects do not collide with each other;

b. if there is an intersection, the vertical distance dz (algebraic value) between the two at this intersection is calculated, and the sign of this distance is determined, for example, by assuming that dz is equal to z (left-dragging) -z (right-dragging), and if left-dragging-up and right-dragging-down are present at this intersection, then dz is <0, whereas if left-dragging-up and left-dragging-down are present, then dz > 0. If the left drag and the right drag have spatial intersection in two adjacent steps of calculation and the sign of dz is opposite, it indicates that the two drags collide at the moment;

c. when a collision occurs between the two towed wet ends and the tension of the cable at the collision point is sufficiently small, the possibility of entanglement between the two tows exists, so that the most dangerous situation is that the two tows collide at the tail, and therefore the judgment is generally started from the tail when the spatial intersection point is calculated;

d. according to the method, the possibility of collision or winding between every two dragging wet ends is screened, and the result of the co-dragging safety evaluation of the multiple dragging wet ends under the given overall layout scheme can be obtained.

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