Motion simulation method for underwater unmanned vehicle in shallow water under influence of ocean current

Abstract

The invention belongs to the field of underwater unmanned vehicles, and particularly relates to a motion simulation method of an underwater unmanned vehicle in a shallow water area under the influence of ocean current. The method specifically comprises the following steps: establishing a motion equation set of the underwater unmanned vehicle, and calculating the change of the ocean current speed along with the depth; calculating ocean current speed change caused by wind; judging whether the ocean current is in a turbulent state; the ocean current speed in the turbulent flow state is calculated; according to the ocean current speed change condition in the navigation process of the underwater vehicle in the shallow water area, more real navigation of the underwater unmanned vehicle is simulated. Compared with the prior art, according to ocean current calculation of the shallow water area where the underwater unmanned vehicle is located, ocean current is no longer regarded as steady flow of a uniform flow field and is regarded as superposition of steady flow, wind ocean current and turbulent flow, and therefore real ocean current calculation of the underwater unmanned vehicle when the underwater unmanned vehicle sails in the shallow water area is achieved; and the calculated ocean current is substituted into the motion equation set of the underwater unmanned vehicle to obtain a more real motion curve.

Description

Technical Field

[0001] The invention belongs to the field of underwater unmanned vehicles, and in particular to a method for simulating the movement of underwater unmanned vehicles in shallow waters under the influence of ocean currents. Background Art

[0002] The underwater unmanned vehicle will be affected by many factors during its navigation, and the ocean current is one of the most influential factors. Especially in shallow waters, the impact of the ocean current on the navigation status of the underwater unmanned vehicle increases significantly.

[0003] Ocean current is a very complex phenomenon of seawater flow. Many scholars are committed to studying the navigation of underwater unmanned vehicles. However, in the existing known research, ocean current is often regarded as a steady flow state of uniform flow field. However, for shallow water areas of the ocean, the ocean current changes violently and cannot be regarded as a steady flow of uniform flow field as before. The reasons are:

[0004] Shallow waters of the ocean are affected by wind, and the speed changes caused by advection winds on ocean currents are uniform and constant. However, there are also gusts on the sea surface, which can cause a short-term and drastic change in the speed of the ocean current, making the ocean current no longer in a steady state, so it needs to be taken into account.

[0005] The ocean currents in shallow water areas are sometimes in a turbulent state, which makes the ocean currents show strong time-varying characteristics. During the diving movement and horizontal rotation movement of the underwater unmanned vehicle, the turbulence will cause the speed and position of the UUV to change dramatically in a short time. Turbulence needs to be taken into account during the analysis process.

[0006] Therefore, it is necessary to comprehensively consider the factors that affect the ocean currents to calculate the ocean currents and obtain the actual changes in ocean currents in shallow waters, so as to fully reflect the impact of ocean currents on underwater unmanned vehicles when sailing in shallow waters, thereby obtaining a more realistic movement state of underwater unmanned navigation in shallow waters. Summary of the invention

[0007] The purpose of the present invention is to provide a method for simulating the movement of underwater unmanned vehicles in shallow waters under the influence of ocean currents. In the simulation of the movement of underwater unmanned vehicles in shallow waters, ocean currents are regarded as the superposition of steady flow, wind currents, and turbulent flow. Among them, wind currents are divided into ocean current changes caused by advection winds and ocean current changes caused by gusts. And it is judged whether the ocean current is in a turbulent state. If it is in a turbulent state, the ocean current calculation is performed for the turbulent state. In this way, the changes in ocean currents in shallow waters are fully described, so as to realize the real ocean current calculation when the underwater unmanned vehicle is sailing in shallow waters, thereby obtaining a more realistic motion state curve diagram of underwater unmanned navigation in shallow waters.

[0008] The technical solution to achieve the purpose of the present invention is: a method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean currents, characterized in that the specific steps are as follows:

[0009] Establish the equations of motion for underwater unmanned vehicles;

[0010] Calculate the change in ocean current speed with depth;

[0011] Calculate changes in ocean current speed caused by wind;

[0012] Determine whether the ocean current is in a turbulent state;

[0013] Calculate the current speed in turbulent conditions;

[0014] The ocean current velocity is solved comprehensively and brought into the underwater unmanned vehicle motion equations to obtain the motion state of underwater unmanned navigation in shallow waters.

[0015] Compared with the prior art, the present invention has the following significant advantages:

[0016] (1) The present invention regards the ocean current in shallow waters as the superposition of steady flow, wind current and turbulence, and comprehensively calculates the changes of the ocean current in shallow waters. Compared with the current calculation method commonly used nowadays, which regards the ocean current as a steady flow in a uniform flow field, the ocean current calculation method in the present invention can more accurately reflect the changes of ocean current velocity in a real environment, and provide more realistic ocean current velocity data for underwater unmanned vehicles during navigation, thereby more realistically simulating the movement of underwater unmanned vehicles in shallow waters.

[0017] (2) Dividing wind-driven ocean currents into changes in ocean current speed caused by advection wind and changes in ocean current speed caused by gusts can better reflect the impact of wind on ocean current speed.

[0018] (3) A first-order Markov process is used to describe the random motion characteristics of turbulence in the ocean environment and a linear filter is used to generate turbulent velocity components to solve the velocity change of turbulence. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : Flow chart of underwater unmanned vehicle motion simulation in the present invention;

[0020] Figure 2 : The current velocity in the present invention varies with depth;

[0021] Figure 3 : The change in sea current velocity caused by the gusts in the present invention;

[0022] Figure 4 : Turbulent velocity in the present invention, wherein (a) turbulent velocity in three directions, (b) total turbulent velocity;

[0023] Figure 5 : The total ocean current velocity in the present invention;

[0024] Figure 6 : The underwater unmanned vehicle in the present invention navigates in shallow waters. DETAILED DESCRIPTION

[0025] The following will be combined with the attached embodiment of the present invention Figure 1-6 , the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] S1: Establish the motion equations of underwater unmanned vehicle:

[0027] S1.1: Ignore the rolling channel kinematics and establish the kinematic equations of the underwater unmanned vehicle:

[0028]

[0029] Where x, y, and z represent the spatial position coordinates of the underwater unmanned vehicle in the inertial system; u, v, and w represent the speed of the underwater unmanned vehicle in the x, y, and z directions in the body coordinate system; θ is the pitch angle; ψ is the yaw angle; q is the pitch angular velocity; and r is the yaw angular velocity.

[0030] S1.2: Ignore the rolling channel dynamics and establish the underwater unmanned vehicle dynamics equation:

[0031]

[0032] In the formula, {m 11 ,m 22 ,m 33 ,m 55 ,m 66} represents the inertia term including the effect of additional mass; {X u ,Y v ,Z w ,M q ,N r} represents the fluid mechanics parameter of the linear resistance term; {X u|u| ,Y v|v| ,Z w|w| ,M q|q| ,N r|r|} represents the fluid mechanics parameter of the secondary resistance term, τ 1 is the thrust of the underwater unmanned vehicle, τ 2 is the pitching moment, τ 3 is the yaw moment.

[0033] S2: Calculate the change of ocean current speed with depth:

[0034] S2.1: Consider the ocean current as laminar flow and calculate the change of ocean current velocity with depth in shallow waters based on the known surface current velocity:

[0035] V z =V s (z / d) 1 / 7 (3)

[0036] Where V z is the laminar current velocity at the current depth, V s is the sea surface velocity, and d is the current water depth of the UAV.

[0037] S2.2: Calculate the change in ocean current velocity caused by advection winds:

[0038]

[0039] Where, d 0 is the reference depth of the ocean current caused by wind, generally 50m; H is the depth of sea water; V w V is the ocean current speed caused by the advection wind. w The calculation formula of (0) is:

[0040] V w (0) = 0.02 V 10 (5)

[0041] Where: V 10 It is the wind speed at 10m above sea level, generally 6.5 to 11m / s.

[0042] S3: Calculate the change in ocean current speed caused by gusts:

[0043]

[0044] Where: τ gust is the wind stress caused by gusts, ρ w is the density of seawater, α is the damping coefficient of the ocean current. The damping coefficient of the ocean current in shallow water is close to 0.1, V is the ocean current speed caused by gusts, and t is time.

[0045] S4: Determine whether the ocean current is in a turbulent state;

[0046] S4.1: The Reynolds number is a dimensionless number used to characterize the flow of a fluid. The Reynolds number can be used to determine whether an ocean current is in a turbulent state. The Reynolds number Re of an ocean current can be calculated as:

[0047]

[0048] Where ρ is the fluid density, v is the characteristic fluid velocity, L is the characteristic length (such as the depth of the fluid or the size of the obstacle), and μ is the dynamic viscosity of the fluid.

[0049] S4.2: Determine whether the ocean current is in a turbulent state by the Reynolds number. When the Reynolds number Re exceeds a certain value (usually Re>4000), the fluid enters a turbulent state. If the ocean current is in a turbulent state, continue to S5, otherwise jump to S6.

[0050] S5: Calculate the current velocity under turbulent conditions;

[0051] S5.1: A random process model (based on a first-order Markov process) is used to simulate the random motion characteristics of turbulence in the marine environment. The random motion characteristic equation of the turbulence is:

[0052]

[0053] In the formula, U represents the average speed of the turbulent current, t represents the time, U(i) represents the average speed of the turbulent current at the current moment, U(i-1) represents the average speed of the turbulent current at the previous moment, T U is the time constant, σ U is the standard deviation of turbulent velocity, W U (i) is white noise.

[0054] S5.2: Set the velocity standard deviation, integral scale length and average velocity U of the ocean current, and generate the turbulent velocity component of the ocean current through a linear filter:

[0055]

[0056] Where U is the average velocity of the turbulent current; u′ is the turbulent velocity in the x direction, v′ is the turbulent velocity in the y direction, w′ is the turbulent velocity in the z direction, and W is u (t), W v (t), W w (t) are standard normally distributed white noise in the x, y and z directions respectively; σ u is the standard deviation of turbulent velocity in the x direction, σ v is the standard deviation of turbulent velocity in the y direction, σ w is the standard deviation of turbulent velocity in the z direction; L u is the integral scale length in the x direction, L v is the integral scale length in the y direction, L w is the integral scale length in the z direction.

[0057] S6: Integrate S2 to S5 to comprehensively solve the change of ocean current velocity during the navigation process of the underwater vehicle in shallow waters, bring it into the kinematic equation, obtain the motion equation group of the underwater unmanned vehicle in shallow waters under the influence of ocean currents, and simulate a more realistic navigation movement of the underwater unmanned vehicle.

[0058] The kinematic equation of the underwater unmanned vehicle under the influence of ocean current is as follows:

[0059]

[0060] Where: They represent the velocity components of the front depth laminar current in the x, y and z directions respectively; They represent the velocity components of the ocean current in the x, y and z directions caused by the advection wind respectively; V x 、V y 、V z They represent the velocity components of the ocean current in the x, y and z directions caused by the gusts.

[0061] By integrating the kinematic equations and dynamic equations of the underwater unmanned vehicle under the influence of ocean currents, a group of motion equations of the underwater unmanned vehicle in shallow waters under the influence of ocean currents is obtained, thereby obtaining a more realistic navigation motion curve of the underwater unmanned vehicle.

[0062] Example

[0063] Assume that the sea surface velocity is 0.5m / s and the wind speed at 10m above the sea surface is 8m / s. The sea current velocity changes with depth as follows: Figure 2 Assume that the underwater unmanned vehicle is in shallow water at a depth of 10m and the gust stress is 1.2N / m 2 The gusts acted in the first 10 seconds and from the 50th to the 55th second respectively, and the changes in the ocean current speed caused by the gusts were obtained as follows: Figure 3 Assume that the ocean current is in a turbulent state from the 20th to the 80th second, and the ocean current velocity in the turbulent state is obtained as Figure 4 The total ocean current velocity obtained by comprehensive calculation is shown in Figure 5 The calculated ocean current is introduced into the underwater unmanned vehicle motion equations to obtain the underwater unmanned vehicle rotation motion under the influence of ocean current as shown in Figure 6 As shown. Figure 2-5 It can be seen that the method mentioned in the present invention can more realistically describe the changes in ocean currents when an underwater unmanned vehicle is sailing in shallow waters.

[0064] analyze Figure 6, because the sea current in shallow waters is affected by many factors, it is not a steady flow or a uniform change. Therefore, the underwater vehicle sailing in shallow waters is affected by the sea current, and its motion curve has an oscillation phenomenon. Therefore, the motion curve of the underwater unmanned vehicle simulated based on the shallow water current changes described in the present invention is closer to the actual situation.

Claims

1. A method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean currents, characterized in that: The steps include: S1: establishing a group of motion equations of the underwater unmanned vehicle; S2: Calculate the change of ocean current speed with depth; S3: Calculate the change in ocean current speed caused by gusts; S4: Determine whether the ocean current is in a turbulent state; S5: Calculate the current velocity under turbulent conditions; S6: According to the change of ocean current speed during the navigation of underwater vehicles in shallow waters, the motion equations of underwater unmanned vehicles in shallow waters under the influence of ocean currents are obtained to simulate more realistic navigation motion of underwater unmanned vehicles.

2. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 1, characterized in that: In S1, the kinematic equation of the underwater unmanned vehicle is established as: Where x, y, z represent the spatial position coordinates of the underwater unmanned vehicle in the inertial system; u, v, w represent the speed of the underwater unmanned vehicle in the x, y, and z directions in the body coordinate system; θ is the pitch angle; ψ is the yaw angle; q is the pitch angular velocity; r is the yaw angular velocity; The dynamic equation of the underwater unmanned vehicle is established as: In the formula, {m 11 ,m 22 ,m 33 ,m 55 ,m 66 } represents the inertia term including the effect of additional mass; {X u ,Y v ,Z w ,M q ,N r } represents the fluid mechanics parameter of the linear resistance term; {X u|u| ,Y v|v| ,Z w|w| ,M q|q| ,N r|r| } represents the fluid mechanics parameters of the secondary resistance term, τ1 is the thrust of the underwater unmanned vehicle, τ2 is the pitch moment, and τ3 is the yaw moment.

3. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 1, characterized in that: S2 specifically includes: S2.1: Consider the ocean current as laminar flow and calculate the change of ocean current velocity with depth in shallow waters based on the known surface current velocity: In z =V s (f / d) 1 / 7 ; Where V z is the laminar current velocity at the current depth, V s is the sea surface velocity, d is the current water depth of the unmanned vehicle; z represents the height coordinate of the spatial position of the underwater unmanned vehicle in the inertial system; S2.2: Calculate the change in ocean current velocity caused by advection winds: Where d0 is the reference depth of the ocean current caused by wind; H is the depth of sea water; V w The speed of the ocean current caused by the advection wind.

4. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 1, characterized in that: In S3, the formula for the change in ocean current speed caused by gusts is: Where: τ gust is the wind stress caused by gusts, ρ w is the density of seawater, α is the damping coefficient of the ocean current, V is the ocean current speed caused by gusts, and t is time.

5. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 1, characterized in that: In S4, the Reynolds number is used to determine whether the ocean current is in a turbulent state, and the Reynolds number Re of the ocean current is calculated: Where ρ is the fluid density, v is the characteristic fluid velocity, L is the characteristic length (such as the depth of the fluid or the size of the obstacle), and μ is the fluid dynamic viscosity; When the Reynolds number Re exceeds the set value, it is determined that the fluid enters a turbulent state; if the ocean current is in a turbulent state, continue to S5; if it is not in a turbulent state, jump to S6.

6. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 5, characterized in that: In S5, the step of calculating the ocean current velocity under turbulent state is: S5.1: Use stochastic process models to simulate the random motion characteristics of turbulence in the marine environment: S5.2: Set the velocity standard deviation, integral scale length and average velocity U of the ocean current, and generate the turbulent velocity component of the ocean current through a linear filter.

7. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 6, characterized in that: The random motion characteristic equation of turbulence is: In the formula, U represents the average speed of the turbulent current, t represents the time, U(i) represents the average speed of the turbulent current at the current moment, U(i-1) represents the average speed of the turbulent current at the previous moment, T U is the time constant, σ U is the standard deviation of turbulent velocity, W U (i) is white noise.

8. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 6, characterized in that: The turbulent velocity component of the ocean current is: Where U is the average velocity of the turbulent current; u′ is the turbulent velocity in the x direction, v′ is the turbulent velocity in the y direction, w′ is the turbulent velocity in the z direction, and W is u (t), W v (t), W w (t) are standard normally distributed white noise in the x, y and z directions respectively; σ u is the standard deviation of turbulent velocity in the x direction, σ v is the standard deviation of turbulent velocity in the y direction, σ w is the standard deviation of turbulent velocity in the z direction; L u is the integral scale length in the x direction, L v is the integral scale length in the y direction, L w is the integral scale length in the z direction.

9. The method for simulating the motion of an underwater unmanned vehicle in shallow water under the influence of ocean current according to claim 6, characterized in that: In S6, the kinematic equation of the underwater unmanned vehicle under the influence of ocean current is as follows: Where: x, y, z represent the spatial position coordinates of the underwater unmanned vehicle in the inertial system; u, v, w represent the speed of the underwater unmanned vehicle in the x, y, and z directions in the body coordinate system; θ is the pitch angle; ψ is the yaw angle; q is the pitch angular velocity; r is the yaw angular velocity, They represent the velocity components of the front depth laminar current in the x, y and z directions respectively; They represent the velocity components of the ocean current in the x, y and z directions caused by the advection wind respectively; V x 、V y 、V z They represent the velocity components of the ocean current in the x, y and z directions caused by the gusts.

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