Flume test system for determining the hydrodynamic parameters of the swaying motion of floating structures

Abstract

The invention discloses a water tank test system for measuring the hydrodynamic parameters of the swaying motion of a floating structure, comprising a plurality of force balances, a horizontal movable base, a swaying base and a contactless measuring device. The model is connected to the swaying base through the plurality of force balances, the swaying base is rotatably connected to the horizontal movable base, the movement of the horizontal movable base and the swaying base realizes the coupled motion mode of simulating the swing and shaking in water, the force balance is used to measure the total load of the model in the body coordinate system, the contactless measuring device is used to record the displacement of the key points of the model and obtain the acceleration data, the invention calibrates the mass matrix and calculates the inertial force part, combines the dynamic response time history data and the hydrostatic force change time history data, and finally converts the force vectors in different coordinate systems into a unified coordinate system, thereby determining the hydrodynamic force exerted on the model when it is swaying in water. The invention can accurately obtain the hydrodynamic force exerted on the model when it is swaying in water.

Description

Technical Field

[0001] The invention belongs to the field of marine engineering and hydrodynamic tests, and in particular relates to a water tank test system for measuring hydrodynamic parameters of swaying motion of a floating structure. Background Art

[0002] With the increasing demand for the development of marine resources, the research on marine structures has become increasingly critical. In a complex marine environment, floating structures such as offshore platforms and floating wind turbines are subject to forces and moments from all directions, which not only significantly affects the comfort of personnel, but may also endanger life and property safety. Therefore, in actual engineering projects, it is particularly important to accurately evaluate the possible motion responses of floating structures and their impacts. In order to deeply understand and accurately predict the behavior of floating structures (such as offshore platforms, floating wind turbines, etc.) in a fluid environment, it is crucial to determine their hydrodynamic parameters and real-time wave and flow loads. These key data can be obtained through a variety of means, including theoretical analysis, numerical simulation, and model tests, and play a decisive role in the design and evaluation of the performance of structures in complex fluid environments. For example, in the field of marine engineering, these parameters can help engineers evaluate and design the performance and safety of offshore platforms, ships, underwater equipment, etc. under the action of waves and currents.

[0003] For simpler structures, theoretical analysis combined with semi-empirical formulas can quickly estimate the hydrodynamic characteristics under specific conditions. Although this method is simple and fast, its practical value is limited due to its approximation and limitations. For complex structures, it relies more on numerical simulation technology, especially computational fluid dynamics (CFD), which can provide detailed information about the flow field around the structure, and then predict the forces and the swaying motion caused by them, so as to obtain the hydrodynamic parameters of the corresponding swaying motion. However, high-precision simulations require a lot of computing resources, especially when dealing with complex situations in actual waters, and also need to solve the challenges brought by meshing, such as divergence and negative volume.

[0004] As a direct and effective means, physical tests are still indispensable for obtaining hydrodynamic parameters. A scaled-down physical model is constructed in a laboratory tank or open water, and the structure is forced to perform prescribed motions through restrained model tests to obtain the corresponding hydrodynamic parameters. Subsequently, artificial waves are applied to simulate the real ocean environment in order to collect measured hydrodynamic data. For linear motion (such as sway and surge), towing tests can often be simply arranged and implemented, and the torque changes during the motion can be effectively measured and recorded using equipment such as force balances, thereby determining the relevant hydrodynamic coefficients. However, for rotational motions such as roll and pitch, a dedicated six-degree-of-freedom motion platform is relied upon to achieve the swaying of the model at a specific frequency and amplitude.

[0005] At present, the existing restrained model test devices are usually fixed on the upper part of the structure, which is suitable for testing linear motion. However, for rotational motion, especially for simulating the swing of the structure in the marine environment, the swing center of these devices is located at the upper part of the structure, which does not conform to the actual situation and it is difficult to accurately simulate the real swing of the structure in the marine environment. In addition, the dedicated six-degree-of-freedom motion device used to measure the swaying motion of the structure is often expensive, usually needs to be installed in the early stage of the water tank construction, and the operation is also more complicated. In view of these problems, it has become particularly necessary to develop new experimental devices and methods to serve the hydrodynamic measurement of the swaying motion, while reducing the test cost and simplifying the operation process. Summary of the invention

[0006] In view of the above shortcomings, the purpose of the present invention is to provide a water tank test system for measuring the hydrodynamic parameters of the swaying motion of a floating structure, so as to solve the problems existing in the prior art of high device cost, complex operation and difficulty in accurately simulating the structural swaying in the real marine environment.

[0007] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a test system for measuring the hydrodynamic parameters of a model during rocking motion, comprising a plurality of force balances, a horizontal movable base, a rocking base and a contactless measuring device, wherein the model to be tested is connected to the rocking base via the plurality of force balances, the rocking base is rotatably connected to the horizontal movable base, the horizontal movable base is mounted on two parallel slide rails and can move laterally along the slide rails, the rocking base is driven by a rocker mechanism to perform reciprocating rocking motion in the longitudinal direction, thereby simulating a coupled motion mode of swinging and shaking in water, the force balance is used to measure the total load of the model to be tested in the body coordinate system, and the contactless measuring device is used to record the displacement of key points of the model to be tested and obtain acceleration data; the implementation method of the system comprises the following steps:

[0008] Step S1: Place the test system on water, drive the rocking base through the rocker mechanism to make the model to be tested move in a predetermined rocking mode, and record the resultant force and motion state under the dynamic coordinates at this time; rotate the installation direction of the rocking base by 90° clockwise or counterclockwise, and then move the model to be tested in the predetermined rocking mode again, so as to obtain multiple sets of data; before the model to be tested moves, the collected data are: The force balance collects data F sensor ={F x ,F y ,F z}, where x, y, and z are the body coordinate systems of the force balance, and the non-contact measurement device obtains the coordinates of n key nodes P n ={x n ,y n ,z n}, when the model to be tested moves, the key node coordinates are marked as P′ n={x′ n ,y′ n ,z′ n}, there is the following relationship: {x n ′,y n ′,z n ′}={x n ,y n ,z n}R+{ξ1,ξ2,ξ3}, where ξ1,ξ2,ξ3 are the rigid body translation displacements of the model to be tested in the x, y, and z directions respectively. The rotation matrix R is a matrix containing 9 unknown quantities. In the rotation matrix, α, β, and γ are the Euler angles of rotation. The formula of the rotation matrix R is as follows:

[0009]

[0010] Through the position relationship of multiple sets of key nodes, the least squares method is used to fit the rotation matrix R and the translation displacement, and then the spatial position x = {ξ1,ξ2,ξ3,α,β,γ} of the model to be tested is determined, and then the corresponding velocity is obtained by two differences and acceleration data;

[0011] Step S2: Based on the data collected in step S1, the following equation is established: Where {G} is gravity, [M] is the mass matrix, and the mass matrix is ​​assumed to be a 6×6 matrix of unknown numbers, that is, [M] = [m ij ] 6×6 , use the least squares method to solve the unknown coefficients m of the mass matrix ij , complete the calibration of the mass matrix of the model to be tested;

[0012] Step S3: Place the test system in water and adjust it to a predetermined initial position, drive the horizontal moving base to move horizontally, and drive the swing base to swing back and forth, so that the model to be tested starts to move according to the preset swing mode. The following motion equation is established: The spatial position {x} of the model is continuously monitored and tracked in real time using a force balance;

[0013] Step S4: Solve the motion equation, where {F b} is the change of buoyancy, which is calculated by integrating the hydrostatic pressure on the surface of the model to be tested, that is, Where ρ is the density of water, g is the acceleration due to gravity, and n i is the normal vector of the surface of the model to be tested, and the radiation force {F r};

[0014] Step S5: Displacement {x} by different frequencies ω and radiation force {Fr} ω , and the corresponding radiation force is Among them, the additional mass matrix [M add ] and the additional damping matrix [C add ] are all 6×6 unknown matrix, through the radiation force of a certain frequency oscillation motion {F r} ω Perform phase decomposition and obtain the corresponding additional mass matrix [M add ] and the additional damping matrix [C add ];

[0015] Step S6: Adjust the model to be tested to a predetermined initial position, wait for the water surface to be completely still, and then generate waves, so that the model to be tested is forced to swing under the action of the waves, and continuously collect force {F sensor} and the spatial position {x} data of the model to be tested, and solve the equation of motion The fluid force {F i +F d +F r +F b}, further separation of wave incident force and diffraction force components {F i +F d}, in order to solve the equation of motion, we first need to unify the gravity, fluid force, and inertia force into the balance force F sensor The body coordinate system where the balance force is located is the vector F m The form in the fixed coordinate system of space Existence relationship

[0016] Step S7: According to the data collected in step S6 and the mass matrix calibrated in step S2, the inertial force and the hydrostatic force are obtained, and the instantaneous rotation matrix R is calculated, the force is converted into a unified coordinate system, and the fluid dynamic force is output;

[0017] Step S8: Further calculate the fluid force {F i +F d +F r +F b}, extract the wave incident force and diffraction force components {F i +F d}, repeat the test, and then store and analyze all the data collected during the test to accurately obtain the fluid dynamic forces acting on the model when it sways in the water.

[0018] The beneficial effects and advantages of the present invention are as follows: the present invention can reduce the difficulty of experimental operation, can accurately obtain the fluid dynamic force exerted on the model when it sways in water, and provides reliable experimental data support for the design and evaluation of marine structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a three-dimensional schematic diagram of the test system of the present invention;

[0020] Figure 2 is a side view of the test system of the present invention;

[0021] Figure 3 A top view of the test system of the present invention;

[0022] Figure 4 A schematic diagram of the arrangement of the test system of the present invention for installing the model to be tested;

[0023] Figure 5 This is a flow chart of the test system of the present invention for determining the rocking hydrodynamic force of the model to be tested. DETAILED DESCRIPTION

[0024] like Figure 1-4 As shown, a test system for measuring the hydrodynamic parameters of a model during swaying motion comprises four groups of force balances 1, a horizontal movable base 2, a swaying base 3 and a contactless measuring device. The model 4 to be tested is connected to the swaying base 3 via the four groups of force balances 1. The swaying base 3 is rotatably connected to the horizontal movable base 2. The horizontal movable base 2 is mounted on two parallel slide rails 5 and can move laterally along the slide rails 5. The swaying base 3 is driven by a rocker mechanism 6 to perform a reciprocating swaying motion in the longitudinal direction, thereby simulating a coupled motion mode of swaying and shaking in water. The force balance 1 is used to measure the total load of the model 4 to be tested in the body coordinate system. The contactless measuring device is used to record the displacement of key points of the model 4 to be tested and obtain acceleration data. The two bases can be selected as needed. The optional installation and locking device components are made of high-strength stainless steel and aluminum alloy to ensure the stability of the entire device. The base platform is provided with fine-tuning screws, allowing the user to adjust the swing position according to different models. The system receives data from four sets of force balances and contactless measurement equipment, calibrates the mass matrix and calculates the inertial force part, combines the dynamic response time history data and the hydrostatic force change time history data, and finally converts the force vectors in different coordinate systems into a unified coordinate system, thereby determining the fluid dynamic force exerted on the model when it swings in the water. The contactless measurement equipment described in this embodiment includes a laser rangefinder, an industrial camera array or an image analysis system. When the model 4 to be measured needs to swing freely in waves and water currents, the rocker mechanism 6 is removed;

[0025] like Figure 5 As shown, the implementation steps of the system are as follows:

[0026] Step S1: Place the test system on water, drive the rocking base through the rocker mechanism to make the model to be tested move in a predetermined rocking mode, and record the resultant force and motion state under the dynamic coordinates at this time; rotate the installation direction of the rocking base by 90° clockwise or counterclockwise, and then move the model to be tested in the predetermined rocking mode again, so as to obtain multiple sets of data; before the model to be tested moves, the collected data are: The force balance collects data F sens or={F x ,F y ,F z}, where x, y, and z are the body coordinate systems of the force balance, and the non-contact measurement device obtains the coordinates of n key nodes P n ={x n ,y n ,z n}, when the model to be tested moves, the key node coordinates are marked as P n ′={x n ′,y n ′,z n ′}, there is the following relationship: {x n ′,y n ′,z n ′}={x n ,y n ,z n}R+{ξ1,ξ2,ξ3}, where ξ1,ξ2,ξ3 are the rigid body translation displacements of the model to be tested in the x, y, and z directions respectively. The rotation matrix R is a matrix containing 9 unknown quantities. In the rotation matrix, α, β, and γ are the Euler angles of rotation. The formula of the rotation matrix R is as follows:

[0027]

[0028] Through the position relationship of multiple sets of key nodes, the least squares method is used to fit the rotation matrix R and the translation displacement, and then the spatial position x = {ξ1,ξ2,ξ3,α,β,γ} of the model to be tested is determined, and then the corresponding velocity is obtained by two differences and acceleration data;

[0029] Step S2: Based on the data collected in step S1, the following equation is established: Where {G} is gravity, [M] is the mass matrix, and the mass matrix is ​​assumed to be a 6×6 matrix of unknown numbers, that is, [M] = [m ij ] 6×6 , use the least squares method to solve the unknown coefficients m of the mass matrix ij , complete the calibration of the mass matrix of the model to be tested;

[0030] Step S3: Place the test system in water and adjust it to a predetermined initial position, drive the horizontal moving base to move horizontally, and drive the swing base to swing back and forth, so that the model to be tested starts to move according to the preset swing mode. The following motion equation is established: The spatial position {x} of the model is continuously monitored and tracked in real time using a force balance;

[0031] Step S4: Solve the motion equation, where {F b} is the change of buoyancy, which is calculated by integrating the hydrostatic pressure on the surface of the model to be tested, that is, Where ρ is the density of water, g is the acceleration due to gravity, and n i is the normal vector of the surface of the model to be tested, and the radiation force {F r};

[0032] Step S5: Displacement {x} by different frequencies ω and radiation force {F r} ω , and the corresponding radiation force is Among them, the additional mass matrix [M add ] and the additional damping matrix [C add ] are all 6×6 unknown matrix, through the radiation force of a certain frequency oscillation motion {F r} ω Perform phase decomposition and obtain the corresponding additional mass matrix [M add ] and the additional damping matrix [C add ];

[0033] Step S6: Adjust the model to be tested to a predetermined initial position, wait for the water surface to be completely still, and then generate waves, so that the model to be tested is forced to swing under the action of the waves, and continuously collect force {F sensor} and the spatial position {x} data of the model to be tested, and solve the equation of motion The fluid force {F i +F d +F r +F b}, further separation of wave incident force and diffraction force components {F i +F d}, in order to solve the equation of motion, we first need to unify the gravity, fluid force, and inertia force into the balance force F sensor The coordinate system of the body where the balance force is located is the vector F m The form in the fixed coordinate system of space Existence relationship

[0034] Step S7: According to the data collected in step S6 and the mass matrix calibrated in step S2, the inertial force and the hydrostatic force are obtained, and the instantaneous rotation matrix R is calculated, the force is converted into a unified coordinate system, and the fluid dynamic force is output;

[0035] Step S8: Further calculate the fluid force {F i +F d +F r +F b}, extract the wave incident force and diffraction force components {F i +F d}, repeat the test, and then store and analyze all the data collected during the test to accurately obtain the fluid dynamic forces acting on the model when it sways in the water.

Claims

1. A test system for measuring hydrodynamic parameters of a model during rocking motion, characterized in that: The invention comprises a plurality of force balances, a horizontal movable base, a rocking base and a contactless measuring device. The model to be tested is connected to the rocking base through the plurality of force balances. The rocking base is rotatably connected to the horizontal movable base. The horizontal movable base is installed on two parallel slide rails and can move laterally along the slide rails. The rocking base is driven by a rocker mechanism to perform reciprocating rocking motion in the longitudinal direction, thereby realizing a coupled motion mode of simulating swinging and shaking in water. The force balance is used to measure the total load of the model to be tested in the body coordinate system. The contactless measuring device is used to record the displacement of key points of the model to be tested and obtain acceleration data. The implementation method of the system is as follows: Step S1: Place the test system on water, drive the rocking base through the rocker mechanism to make the model to be tested move in a predetermined rocking mode, and record the resultant force and motion state under the dynamic coordinates at this time; rotate the installation direction of the rocking base by 90° clockwise or counterclockwise, and then move the model to be tested in the predetermined rocking mode again, so as to obtain multiple sets of data; before the model to be tested moves, the collected data are: The force balance collects data F sensor ={F x ,F y ,F z }, where x, y, and z are the body coordinate systems of the force balance, and the non-contact measurement device obtains the coordinates of n key nodes P n ={x n ,y n ,z n }, when the model to be tested moves, the key node coordinates are marked as Pn′={x n ′,y n ′,z n ′}, there is the following relationship: {x n ′,y n ′,z n ′}={x n ,y n ,z n }R+{ξ1,ξ2,ξ3}, where ξ1,ξ2,ξ3 are the rigid body translation displacements of the model to be tested in the x, y, and z directions respectively. In the rotation matrix, α, β, and γ are the Euler angles of rotation. The formula of the rotation matrix R is as follows: Through the position relationship of multiple sets of key nodes, the least squares method is used to fit the rotation matrix R and the translation displacement, and then the spatial position x = {ξ1,ξ2,ξ3,α,β,γ} of the model to be tested is determined, and then the corresponding velocity is obtained by two differences and acceleration data; Step S2: Based on the data collected in step S1, the following equation is established: Where {G} is gravity, [M] is the mass matrix, and the mass matrix is ​​assumed to be a 6×6 matrix of unknown numbers, that is, [M] = [m ij ] 6×6 , use the least squares method to solve the unknown coefficients m of the mass matrix ij , complete the calibration of the mass matrix of the model to be tested; Step S3: Place the test system in water and adjust it to a predetermined initial position, drive the horizontal moving base to move horizontally, and drive the swing base to swing back and forth, so that the model to be tested starts to move according to the preset swing mode. The following motion equation is established: The spatial position {x} of the model is continuously monitored using a force balance and tracked in real time; Step S4: Solve the motion equation, where {F b } is the change of buoyancy, which is calculated by integrating the hydrostatic pressure on the surface of the model to be tested, that is, Where ρ is the density of water, g is the acceleration due to gravity, and n i is the normal vector of the surface of the model to be tested, and the radiation force {F r }; Step S5: Displacement {x} by different frequencies ω and radiation force {F r } ω , and the corresponding radiation force is Among them, the additional mass matrix [M add ] and the additional damping matrix [C add ] are all 6×6 unknown matrix, through the radiation force of a certain frequency oscillation motion {F r } ω Perform phase decomposition and obtain the corresponding additional mass matrix [M add ] and the additional damping matrix [C add ]; Step S6: Adjust the model to be tested to a predetermined initial position, wait for the water surface to be completely still, and then generate waves, so that the model to be tested is forced to swing under the action of the waves, and continuously collect force {F sensor } and the spatial position {x} data of the model to be tested, and solve the equation of motion The fluid force {F i +F d +F r +F b }, further separation of wave incident force and diffraction force components {F i +F d }, in order to solve the equation of motion, we first need to unify the gravity, fluid force, and inertia force into the balance force F sensor The body coordinate system where the balance force is located is the vector F m The form in the fixed coordinate system of space Existence relationship Step S7: According to the data collected in step S6 and the mass matrix calibrated in step S2, the inertial force and the hydrostatic force are obtained, and the instantaneous rotation matrix R is calculated, the force is converted into a unified coordinate system, and the fluid dynamic force is output; Step S8: Further calculate the fluid force {F i +F d +F r +F b }, extract the wave incident force and diffraction force components {F i +F d }, repeat the test, and then store and analyze all the data collected during the test to accurately obtain the fluid dynamic forces acting on the model when it sways in the water.

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