Numerical wave generation method based on LS-DYNA velocity boundary

Abstract

The present invention relates to the technical field of numerical wave making, and in particular to a numerical wave making method based on LS-DYNA velocity boundary, comprising the following steps: simulating a wave pool in an actual environment and establishing a finite element model; establishing a numerical wave pool; establishing a single-layer environment unit in LS-DYNA with the *ALE_AMBIENT_HYDROSTATIC keyword to determine the far-field boundary condition to break the wave in the numerical wave pool; determining the time step based on the variance of the error amount of the establishment process of the numerical waves, or determining the number of observation points based on the average establishment time of the numerical waves, or determining the number of grid nodes based on the average actual utilization rate of the grids in the establishment process of the numerical wave pool; and re-determining the number of grid nodes according to the difference in wave wavelengths generated by the numerical wave pool model. The present invention achieves the improvement of the stability of the wave making and breaking process.

Description

Technical Field

[0001] The invention relates to the technical field of numerical wave generation, and in particular to a numerical wave generation method based on LS-DYNA velocity boundary. Background Art

[0002] Amphibious aircraft take off and land more frequently on water than on land, especially when landing under complex meteorological conditions on the sea surface. The complex hydrodynamic loads increase the gliding resistance of the aircraft during landing, increase the overload, and cause drastic changes in pitch and heave motions, which may even cause fatigue damage to the fuselage structure and cause harm to the aircraft and its passengers. The ability to take off and land under specified meteorological and hydrological conditions, namely wavekeeping, is an important factor in determining the performance of amphibious aircraft [Ma Zenghui]. Numerical simulation methods based on relevant experiments are the development trend of research on the wavekeeping performance of amphibious aircraft. Among them, the simulation of waves is the primary condition for conducting numerical tests on the wavekeeping performance of amphibious aircraft. The correctness of wave simulation will directly affect the correctness and reliability of the numerical test results.

[0003] China Patent Publication No.: CN111723532A, discloses a numerical wave generation method coupling POM and OpenFOAM, using POM to simulate a coarse-resolution wave model of the target area, and then obtain the functional relationship between the fluid velocity and height at each grid point by polynomial fitting, and write it into the initial file of OpenFOAM after conversion, drive OpenFOAM to perform side boundary fitting calculation according to the input data, during the calculation, POM continuously updates the data of the target area according to the time change and outputs the corresponding functional relationship, OpenFOAM recalculates once with each update of POM, and generates pool waves similar to the real ocean environment within the specified cycle time. The present invention provides coupling calculation of POM and OpenFOAM, realizes the coupling of large-scale ocean model and small-scale computational fluid dynamics CFD model OpenFOAM, downscaling to finer resolution data, helps to improve the accuracy of virtual tests under the numerical water tank of ships, and improves the accuracy of ship hydrodynamic performance evaluation and prediction. It can be seen that the numerical wave-making method coupling POM and OpenFOAM has the problem that the error of the numerical wave pool establishment process increases due to the large time step, which leads to the decrease of the stability of wave making and wave breaking. Summary of the invention

[0004] To this end, the present invention provides a numerical wave making method based on LS-DYNA velocity boundary, so as to overcome the problem in the prior art that the error in the numerical wave pool establishment process increases due to the excessive time step, thereby causing the stability of wave making and wave breaking to decrease.

[0005] To achieve the above-mentioned purpose, the present invention provides a numerical wave-making method based on LS-DYNA velocity boundary, comprising: determining the control equation of a numerical wave pool model to simulate a wave pool in an actual environment, and establishing a finite element model based on the control equation of the numerical wave pool model; establishing numerical waves according to the wave-making method input by the velocity boundary; establishing a single-layer environmental unit in LS-DYNA with the *ALE_AMBIENT_HYDROSTATIC keyword to determine the far-field boundary condition to eliminate waves in the numerical pool; obtaining the error amount of the establishment process of several numerical waves; determining the time step based on the variance of the error amount of the establishment process of the several numerical waves or, judging whether the stability of the storage space of the wave-making system meets the requirements based on the variance of the error amount of the several numerical wave establishment processes and the average establishment time of the several numerical waves; if it does not meet the requirements, determining the number of observation points, or, determining the number of grid nodes based on the average establishment time of the several numerical waves and the average utilization rate of the grids in the several numerical wave establishment processes; obtaining the wave wavelength difference amount generated by the numerical wave pool model after the number of observation points is determined to redetermine the number of observation points; using the redetermined number of observation points to compare the generated numerical wave pool with the target wave to update the numerical wave pool model.

[0006] Furthermore, the control equations of the numerical wave pool model include an unsteady RANS equation for an incompressible fluid, a continuity equation, a volume fraction equation, and a momentum equation.

[0007] Furthermore, the expression of the unsteady RANS equation of the incompressible fluid is:

[0008]

[0009]

[0010] Among them, U i is the average speed, u i ' is the pulsation speed, u i 'u' j is the Reynolds stress and P is the pressure.

[0011] Furthermore, the step of establishing the finite element model includes:

[0012] Define the upper surface of the air domain as a non-reflecting boundary condition;

[0013] Apply velocity disturbance boundary at the fluid inlet section;

[0014] Use environmental units at the flow field outlet to simulate far-field boundary conditions;

[0015] The mesh is refined in the area where the free liquid surface appears.

[0016] Furthermore, the steps of establishing the numerical wave pool include:

[0017] The left boundary of the numerical wave tank model is defined as a periodic fluid disturbance;

[0018] Set the free surface to vary as a function of time.

[0019] Furthermore, the function expression that changes with time is:

[0020]

[0021] The velocity at the entrance is:

[0022]

[0023]

[0024] Where A is the amplitude, d is the water depth, k is the wave number, ω is the frequency, is the initial phase angle, u is the horizontal velocity, and w is the vertical velocity.

[0025] Furthermore, the step of determining the time step includes:

[0026] The variances of the error amounts of the several numerical wave establishment processes are compared with the preset first variance and the preset second variance respectively;

[0027] If the variance of the error amount of the several numerical wave establishment processes is greater than the preset first variance and less than or equal to the preset second variance, it is determined that the stability of the wave making and wave breaking process is lower than the allowable range, and the time step is determined;

[0028] The time step is determined by the difference between the variance of the error amount of the several numerical wave establishment processes and the preset first variance.

[0029] Furthermore, the step of determining the number of observation points includes:

[0030] If the variance of the error amount in the process of establishing the plurality of numerical waves is greater than a preset second variance, it is preliminarily determined that the storage space of the wave-making system does not meet the requirements;

[0031] and comparing the average establishment time of the plurality of numerical waves with the preset first time and the preset second time;

[0032] If the average establishment time of the several numerical waves is greater than the preset first time length and less than or equal to the preset second time length, it is determined for the second time that the storage space of the wave-making system does not meet the requirements, and the number of observation points is determined according to the difference between the average establishment time of the several numerical waves and the preset first time length to output the first corresponding number.

[0033] Furthermore, the step of determining the number of the grid nodes includes:

[0034] If the average establishment time of the plurality of numerical waves is greater than the preset second time, it is preliminarily determined that the grid division accuracy is lower than the allowable range;

[0035] and comparing the average utilization rate of the grids in the several numerical wave establishment processes with a preset utilization rate;

[0036] If the average utilization rate of the grid in the process of establishing the several numerical waves is less than the preset utilization rate, the grid division accuracy is secondarily determined to be lower than the allowable range, and the number of the grid nodes is determined based on the difference between the preset utilization rate and the average utilization rate of the grid in the process of establishing the several numerical waves.

[0037] Further, the step of re-determining the number of the observation points includes:

[0038] Comparing the wave wavelength difference amount generated by the numerical wave tank model after the number of observation points is determined with a preset difference amount;

[0039] If the difference in wave wavelengths generated by the numerical wave tank model is greater than a preset difference, it is determined that the interference degree of the observation point on the wave breaking result exceeds an allowable range, and the number of observation points is redetermined to output a second corresponding number;

[0040] The second corresponding quantity is re-determined by the difference between the wave wavelength difference amount generated by the numerical wave pool model and the preset difference amount.

[0041] Compared with the prior art, the beneficial effect of the present invention is that the wave-making method of the present invention generates waves by adopting the velocity boundary method, and applies a periodic displacement load curve at the inlet boundary to generate target waves. In the water area of ​​the wave-making area, the keyword *INITIAL_HYDROSTATIC_ALE is used to initialize the hydrostatic pressure under the action of gravity. The environment unit is set at the outlet of the flow field to simulate the far-field boundary conditions to eliminate the interference of the boundary reflection of the waves on the effective waves. *ALE_AMBIENT_HYDROSTATIC is set as the corresponding keyword. The time step is determined according to the variance of the error amount of the establishment process of several numerical waves, which reduces the influence of the excessive time step on the stability of wave making and absorbing. The number of observation points is determined according to the average establishment time of several numerical waves, which reduces the jamming caused by excessive water at the observation point and the influence on the stability of memory supply, and further improves the stability of the wave-making and absorbing process.

[0042] Furthermore, the wave-making method of the present invention sets the control equation of the numerical wave pool model. In order to truly simulate the various functions of the physical experimental wave pool in the actual environment, in the constructed numerical wave pool model, the wave flow is treated as a two-phase (water and air) flow, and the free surface is the interface between the water domain and the air domain. Moreover, since the speed of sound in the flow field is larger than the fluid flow speed, both water and air are treated as incompressible fluids, so that the control equation of the numerical wave pool can effectively reflect the actual situation of the fluid movement in the physical water pool, thereby further improving the stability of the wave-making and wave-breaking process.

[0043] Furthermore, the wave-making method of the present invention treats the wave flow as a two-phase flow by setting up a finite element model, and the free surface is the interface between the water domain and the air domain. Since the speed of sound in the flow field is larger than the fluid flow speed, both water and air are treated as incompressible fluids, so that the control equation of the numerical wave pool can effectively reflect the actual situation of the fluid movement in the physical water pool, reducing the impact of the inaccurate reflection of the actual situation of the fluid movement in the physical water pool on the wave-making method, and further achieving the improvement of the stability of the wave-making and wave-breaking process.

[0044] Furthermore, the wave-making method of the present invention establishes a numerical wave pool by setting a velocity boundary input type wave-making, and obtains the corresponding numerical wave by inputting a velocity function at the wave-making boundary. The velocity boundary does not need to consider the fluid-solid coupling effect between the wave-making plate and the fluid, so there is no convergence problem of the dynamic grid, and there is no leakage problem of the immersion fluid-solid coupling interaction. In addition, the wave-making effect is good in the initial stage, and a stable target wave can be obtained in a short time. The length of the wave-making area is small, and it has good wave-making ability and higher calculation efficiency, which further improves the stability of the wave-making and wave-breaking process.

[0045] Furthermore, the wave-making method of the present invention reduces the number of grids and nodes by adding the keyword *ALE_AMBIENT_HYDROSTATIC at the far-reaching boundary, verifies the wave-making performance of the numerical water pool through simulation experiments on regular waves and comparative analysis of the numerical wave pool, improves the propagation stability of linear regular waves, reduces and eliminates the numerical reflection of the wave and the attenuation over time through waveform error analysis at the far-reaching boundary at the left end, performs grid encryption in the area where the wave height is located, adopts sparse grid division inside the water pool, and uses large grids to divide the width to improve the quality of wave making, thereby further achieving the improvement of the stability of the wave-making and wave-breaking process.

[0046] Furthermore, the wave-making method of the present invention determines the time step by setting a preset first variance and a preset second variance, through the variance of the error amount of several numerical wave establishment processes, thereby reducing the influence on the stability of the wave-making and wave-breaking process caused by the increase of simulation error amount due to excessive time step, and further achieving the improvement of the stability of the wave-making and wave-breaking process.

[0047] Furthermore, the wave-making method of the present invention sets a preset first time length and a preset second time length, and determines the number of observation points by the average establishment time of several numerical waves, thereby reducing the jamming in the numerical wave pool establishment process caused by an excessive number of observation points, thereby reducing the impact on the stability of the storage space, and further achieving the improvement of the stability of the wave-making and wave-breaking process.

[0048] Furthermore, the wave-making method of the present invention determines the number of grid nodes by setting a preset utilization rate and the actual utilization rate of the network in the process of establishing a numerical wave pool, thereby reducing the problem of waste caused by too many grid nodes, which in turn leads to a decrease in the accuracy of grid division, and further improves the stability of the wave-making and wave-breaking process.

[0049] Furthermore, the wave-making method of the present invention sets a preset difference and redetermines the number of observation points through the wave wavelength difference generated by the numerical wave tank model, thereby reducing the deviation in observation results caused by an excessive number of observation points, which in turn leads to a decrease in observation effectiveness, and further improves the stability of the wave-making and wave-breaking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is an overall flow chart of the numerical wave making method based on LS-DYNA velocity boundary according to an embodiment of the present invention;

[0051] Figure 2 It is a schematic diagram of a numerical model of a numerical wave making method based on LS-DYNA velocity boundary according to an embodiment of the present invention;

[0052] Figure 3 A schematic diagram of a finite element mesh of a numerical wave-making method based on LS-DYNA velocity boundary according to an embodiment of the present invention;

[0053] Figure 4 It is a schematic diagram of wave generation results at a stable moment in a numerical water tank of a numerical wave generation method based on LS-DYNA velocity boundary according to an embodiment of the present invention;

[0054] Figure 5 A wave diagram generated in a water pool at the wave stability moment of a numerical wave generation method based on LS-DYNA velocity boundary according to an embodiment of the present invention;

[0055] Figure 6 It is a schematic diagram of the target wave theoretical wave attenuation result of the numerical wave making method based on LS-DYNA velocity boundary in an embodiment of the present invention;

[0056] Figure 7 It is a schematic diagram of the wave breaking results of the wave breaking zone at the initial moment of the numerical wave making method based on the LS-DYNA velocity boundary in an embodiment of the present invention;

[0057] Figure 8 It is a schematic diagram of wave generation and wave elimination results near the end of the numerical wave generation method based on LS-DYNA velocity boundary in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0059] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0060] See also Figure 1 , Figure 2 , Figure 3 as well as Figure 4 As shown, they are respectively an overall flow chart of the numerical wave making method based on LS-DYNA velocity boundary, a schematic diagram of the numerical model, a schematic diagram of the finite element mesh, a schematic diagram of the wave generation result in the numerical water tank at the stable moment, a wave diagram generated in the water tank at the wave stable moment, a schematic diagram of the target wave theoretical wave breaking result, a schematic diagram of the wave breaking result in the wave breaking zone at the initial moment, and a schematic diagram of the wave making and wave breaking result near the end moment; the present invention provides a numerical wave making method based on LS-DYNA velocity boundary, comprising the following steps:

[0061] Determining the governing equations of the numerical wave pool model to simulate the wave pool in the actual environment, and establishing a finite element model based on the governing equations of the numerical wave pool model;

[0062] The numerical wave is established according to the wave-making method input by the velocity boundary;

[0063] In LS-DYNA, a single-layer environmental unit is created with the *ALE_AMBIENT_HYDROSTATIC keyword to determine the far-field boundary conditions to eliminate waves in the numerical water pool;

[0064] Get the error amount of several numerical wave building processes;

[0065] Determining the time step based on the variance of the error amount of the several numerical wave establishment processes, or determining whether the stability of the storage space of the wave-making system meets the requirements based on the variance of the error amount of the several numerical wave establishment processes and the average establishment time of the several numerical waves;

[0066] If the requirements are not met, the number of observation points is determined, or the number of grid nodes is determined based on the average establishment time of the plurality of numerical waves and the average utilization rate of the grid in the establishment process of the plurality of numerical waves;

[0067] Obtain the difference in wave wavelengths generated by the numerical wave tank model after the number of observation points is determined to redefine the number of observation points;

[0068] The generated numerical wave pool is compared with the target wave using the re-determined number of observation points to update the numerical wave pool model.

[0069] Specifically, starting from t=9.0 seconds, observation points are set according to the number of re-determined observation points at 3 times the wavelength of the left boundary entrance, and the generated numerical wave pool is compared with the target wave. If the similarity between the generated numerical wave pool and the target wave is less than 85%, the numerical wave pool model is updated.

[0070] Specifically, the free surface is the interface between the air domain and the water domain.

[0071] Specifically, the horizontal direction is the wave propagation direction, and the vertical direction is the wave fluctuation direction.

[0072] Specifically, the environmental unit is (*SECTION_SOLID in AET=4.

[0073] Specifically, the time step refers to the difference or time interval between each time point in the numerical wave pool model process. Adjusting the time step can achieve the adjustment of the fineness of the numerical wave pool simulation.

[0074] The wave-making method of the present invention generates waves by adopting the velocity boundary method, and applies a periodic displacement load curve at the inlet boundary to generate target waves. In the water area of ​​the wave-making area, the keyword *INITIAL_HYDROSTATIC_ALE is used to initialize the hydrostatic pressure of gravity. The flow field outlet is set with an environmental unit to simulate the far-field boundary condition to eliminate the interference of the boundary reflection of the wave on the effective wave. *ALE_AMBIENT_HYDROSTATIC is set as the corresponding keyword. The time step is determined according to the variance of the error amount of the establishment process of several numerical waves, which reduces the influence of the excessive time step on the stability of wave making and absorbing. The number of observation points is determined according to the average establishment time of several numerical waves, which reduces the jamming caused by the excessive water volume at the observation point and the influence on the stability of the memory supply, and further improves the stability of the wave-making and absorbing process.

[0075] Specifically, the velocity disturbance boundary is defined by adding the following two keywords to the solution file k file of LS-DYNA to define the disturbance of the left inlet boundary: *BOUNDARY_PRESCRIED_MOTIOBN and *DEFINE_CURVE_FUNCTION.

[0076] Specifically, the comparison of the numerical wave pool generation results with the target waves includes: if the similarity between the wave generation results at the stable moment in the numerical pool and the wave graph generated in the pool at the wave stable moment and the target wave reaches 90%, the wave height of the waves generated by the numerical pool is basically maintained at 0.02m, the wavelength is basically maintained at 1m, and the wave height error at the far-reaching boundary is less than 0.3, indicating that the regular waves simulated by the numerical pool can be continuously generated and stably propagated.

[0077] Specifically, the observation of the wave-breaking capacity of the far-reaching boundary includes that when the wave energy is completely absorbed by the numerical wave pool and no numerical reflection occurs, the wave generation is not disturbed, and the wave shape is stable at the initial moment, the wave height is maintained at 0.01 meters, and the wavelength is maintained at 1 meter, and it gradually propagates forward. When the error is less than 0.3, the similarity between the wave-breaking results of the initial moment and the wave-making and wave-breaking results near the end and the theoretical wave-breaking results of the target wave reaches 90%.

[0078] Specifically, the variance of the error amount in the process of establishing the several numerical waves is the variance of the error amount between the wave height generated by the numerical pool and the wave height generated by the target numerical pool in the process of establishing the several numerical wave pools. The calculation method of the variance of the error amount in the process of establishing the several numerical waves is a conventional technical means well known to those skilled in the art. Therefore, the calculation process of the variance of the error amount in the process of establishing the several numerical waves will not be repeated here.

[0079] Specifically, the average utilization rate of the grid in the process of establishing several numerical waves is calculated as follows:

[0080]

[0081] Wherein, W is the average utilization rate of the grids in the process of establishing several numerical waves, C1 is the number of grids used in the simulation process, C2 is the number of grids not used in the simulation process, L is the number of simulations, and L is a natural number greater than or equal to 1.

[0082] Specifically, the calculation formula for the difference in wave wavelengths generated by the numerical wave pool model is:

[0083] M=|B2-B1|

[0084] Among them, M is the difference in wave wavelength generated by the numerical wave pool model, B2 is the wave wavelength generated by the numerical pool, and B1 is the wave wavelength generated by the target numerical pool.

[0085] Specifically, the calculation formula for the average establishment time of several numerical waves is:

[0086]

[0087] Among them, R is the average establishment time of several numerical waves, V a is the duration of establishing the a-th numerical wave, S is the number of times the numerical wave is established, and S is a natural number greater than or equal to 1.

[0088] The wave-making method of the present invention reduces the number of grids and nodes by adding the keyword *ALE_AMBIENT_HYDROSTATIC at the far-reaching boundary, verifies the wave-making performance of the numerical water pool through simulation experiments on regular waves and comparative analysis of the numerical wave water pool, improves the propagation stability of linear regular waves, reduces and eliminates the numerical reflection of the wave and the attenuation over time through waveform error analysis at the far-reaching boundary at the left end, performs grid encryption division in the area where the wave height is located, adopts sparse grid division inside the water pool, and uses large grids to divide the width to improve the quality of wave making, and further achieves the improvement of the stability of the wave making and wave absorbing process.

[0089] See also Figure 2 As shown, the control equations of the numerical wave pool model include the unsteady RANS equations of incompressible fluid, the continuity equation, the volume fraction equation and the momentum equation.

[0090] See also Figure 2 As shown, the expression of the unsteady RANS equation of the incompressible fluid is:

[0091]

[0092]

[0093] Among them, U i is the average speed, u i ' is the pulsation speed, u i 'u' j is the Reynolds stress and P is the pressure.

[0094] Specifically, the continuity equation is the continuity equation of an incompressible fluid, wherein the expression of the continuity equation of an incompressible fluid is:

[0095]

[0096] Where v is the velocity vector.

[0097] Specifically, for waves, a two-phase flow of water and air, a volume fraction is introduced (q = 1 for air, q = 2 for water). q The volume fraction equation should be satisfied, where the volume fraction equation is expressed as:

[0098]

[0099]

[0100] Specifically, the free liquid surface changes with time. Ignoring the influence of air density and viscosity, the water surface is regarded as a free liquid surface. Both air and water must satisfy the momentum conservation equation, where the momentum conservation equation is expressed as:

[0101]

[0102] Among them, ρ is the fluid density, μ is the viscosity coefficient, g is the gravitational acceleration, P is the pressure, and F is the mass force other than gravity.

[0103] Specifically, is the distance function from any point in the flow field to the free surface. At any time, the free surface is The zero isovalue surface, that is, at any point on the free liquid surface at any time, there is always Therefore, it satisfies:

[0104]

[0105] Where v is the velocity vector in the flow basin.

[0106] exist The flow of liquid is solved in the local water area, and the free liquid surface position is obtained by interpolation method

[0107]

[0108]

[0109] Where nj is the control body surface normal.

[0110] The wave making method of the present invention sets the control equation of the numerical wave pool model. In order to truly simulate various functions of the physical experimental wave pool in the actual environment, in the constructed numerical wave pool model, the wave flow is treated as a two-phase (water and air) flow, the free surface is the interface between the water area and the air domain, and because the sound speed in the flow field is larger than the fluid flow speed, both water and air are treated as incompressible fluids, so that the control equation of the numerical wave pool can effectively reflect the actual situation of the fluid movement in the physical water pool, and further improve the stability of the wave making and absorbing process.

[0111] See also Figure 3 As shown, the steps of establishing the finite element model include:

[0112] Define the upper surface of the air domain as a non-reflecting boundary condition;

[0113] Apply velocity disturbance boundary at the fluid inlet section;

[0114] Use environmental units at the flow field outlet to simulate far-field boundary conditions;

[0115] The mesh is refined in the area where the free liquid surface appears.

[0116] See also Figure 2 As shown, the steps of establishing the numerical wave pool include:

[0117] The left boundary of the numerical wave tank model is defined as a periodic fluid disturbance;

[0118] Set the free surface to vary as a function of time.

[0119] See also Figure 2 As shown, the function expression that changes with time is:

[0120]

[0121] The velocity at the entrance is:

[0122]

[0123]

[0124] Where A is the amplitude, d is the water depth, k is the wave number, ω is the frequency, is the initial phase angle, u is the horizontal velocity, and w is the vertical velocity.

[0125] Specifically, the steps of encrypting the grid of the key area are:

[0126] Encrypt the fluid height within the range of 0.9m to 1.1m;

[0127] In the wave transmission direction, a uniform finite element mesh is used.

[0128] Specifically, the finite element model has a length, width and height of 5.1, 0.1 and 1.1 m respectively. The length of 5.1 m consists of two parts, namely, an effective wave-making area with a length of 5 m and a far-field boundary unit with a length of 0.1 m; the height of 1.1 m also consists of two parts, including an air domain with an initial length of 0.1 m and a water domain with an initial length of 1 m. The dotted line is a dividing line of 0.1 m in width between air and water in the initial field.

[0129] Specifically, the method of encrypting the grid includes adding dense node distribution using the encrypted grid division method near the free liquid surface from z = 0.9m to z = 1.1m in the height direction; using the sparse grid division method inside the water pool from z = 0 to z = 0.9m and the air domain above 1.1m. In the length direction of the wave-making area, the grid division method of uniformly distributed nodes is adopted, in which the nodes and grids are evenly arranged.

[0130] The wave making method of the present invention treats wave flow as two-phase flow by setting up a finite element model, and the free surface is the interface between the water area and the air area. Since the speed of sound in the flow field is larger than the flow speed of the fluid, both water and air are treated as incompressible fluids, so that the control equation of the numerical wave pool can effectively reflect the real situation of the fluid movement in the physical water pool, reducing the influence of the inaccurate reflection of the real situation of the fluid movement in the physical water pool on the wave making method, and further realizing the improvement of the stability of the wave making and wave absorbing process.

[0131] See also Figure 1 As shown, the step of determining the time step includes:

[0132] The variances of the error amounts of the several numerical wave establishment processes are compared with the preset first variance and the preset second variance respectively;

[0133] If the variance of the error amount of the several numerical wave establishment processes is greater than the preset first variance and less than or equal to the preset second variance, it is determined that the stability of the wave making and wave breaking process is lower than the allowable range, and the time step is determined;

[0134] The time step is determined by the difference between the variance of the error amount of the several numerical wave establishment processes and the preset first variance.

[0135] Specifically, the step of determining the time step includes:

[0136] Specifically, if ΔQ≤ΔQ0, the time step is adjusted to the first time step using the preset second time step adjustment coefficient;

[0137] If ΔQ>ΔQ0, the time step is adjusted to the second step using the preset first time step adjustment coefficient.

[0138] Specifically, the variance of the error amount in the process of establishing several numerical waves is recorded as Q, the preset first variance is recorded as Q1, the preset second variance is recorded as Q2, the difference between the variance of the error amount in the process of establishing several numerical waves and the preset first variance is recorded as △Q, △Q is set as Q-Q1, the preset variance difference is recorded as △Q0, the preset first time step adjustment coefficient is recorded as β1, and the preset second time step adjustment coefficient is recorded as β2, wherein 0<β1<β2<1, Q1<Q2, the time step is recorded as T, and the adjusted time step is recorded as T', and T'=T×βi is set, wherein βi is the preset i-th time step adjustment coefficient, and i=1,2.

[0139] The wave-making method of the present invention sets a preset first variance and a preset second variance, and determines the time step by the variance of the error amount of several numerical wave establishment processes, thereby reducing the influence on the stability of the wave-making and wave-breaking process caused by the increase of simulation error amount due to excessive time step, and further realizing the improvement of the stability of the wave-making and wave-breaking process.

[0140] See also Figure 1 As shown, the step of determining the number of observation points includes:

[0141] If the variance of the error amount in the process of establishing the plurality of numerical waves is greater than a preset second variance, it is preliminarily determined that the storage space of the wave-making system does not meet the requirements;

[0142] and comparing the average establishment time of the plurality of numerical waves with the preset first time and the preset second time;

[0143] If the average establishment time of the several numerical waves is greater than the preset first time length and less than or equal to the preset second time length, it is determined for the second time that the storage space of the wave-making system does not meet the requirements, and the number of observation points is determined according to the difference between the average establishment time of the several numerical waves and the preset first time length to output the first corresponding number.

[0144] Specifically, the first corresponding quantity includes a first quantity and a second quantity.

[0145] Specifically, the step of determining the number of observation points includes:

[0146] Specifically, if ΔR≤ΔR0, the number of the observation points is adjusted to a first number using a preset second number adjustment coefficient;

[0147] If ΔR>ΔR0, a preset quantity adjustment coefficient is used to adjust the quantity of the observation points to a second quantity.

[0148] Specifically, the average establishment time of several numerical waves is recorded as R, the preset first time is recorded as R1, the preset second time is recorded as R2, the difference between the average establishment time of several numerical waves and the preset first time is recorded as △R, △R is set as R-R1, the preset time difference is recorded as △R0, the preset first quantity adjustment coefficient is recorded as α1, the preset second quantity adjustment coefficient is recorded as α2, wherein 0<α1<α2<1, R1<R2, the number of observation points is recorded as E, the number of observation points after adjustment is recorded as E', and E'=E×(1+αp) is set, wherein αp is the preset pth quantity adjustment coefficient, and p is set as 1,2.

[0149] The wave making method of the present invention sets a preset first time length and a preset second time length, and determines the number of observation points by the average establishment time length of several numerical waves, thereby reducing the jamming in the numerical wave pool establishment process caused by too many observation points, thereby reducing the impact on the stability of the storage space, and further improving the stability of the wave making and absorbing process.

[0150] See also Figure 1 As shown, the step of determining the number of the grid nodes includes:

[0151] If the average establishment time of the plurality of numerical waves is greater than the preset second time, it is preliminarily determined that the grid division accuracy is lower than the allowable range;

[0152] and comparing the average utilization rate of the grids in the several numerical wave establishment processes with a preset utilization rate;

[0153] If the average utilization rate of the grid in the process of establishing the several numerical waves is less than the preset utilization rate, the grid division accuracy is secondarily determined to be lower than the allowable range, and the number of the grid nodes is determined based on the difference between the preset utilization rate and the average utilization rate of the grid in the process of establishing the several numerical waves.

[0154] Specifically, the step of determining the number of observation points includes:

[0155] Specifically, if ΔW≤ΔW0, the number of grid nodes is adjusted to the first number of nodes using a preset second node number adjustment coefficient;

[0156] If ΔW>ΔW0, the number of grid nodes is adjusted to a second number of nodes using a preset first number of node adjustment coefficient.

[0157] Specifically, the average utilization rate of the grid in the process of establishing several numerical waves is recorded as W, the preset utilization rate is recorded as W0, the difference between the preset utilization rate and the average utilization rate of the grid in the process of establishing several numerical waves is recorded as △W, and △W is set as W0-W. The preset time difference is recorded as △W0, the preset first node quantity adjustment coefficient is recorded as γ1, and the preset second node quantity adjustment coefficient is recorded as γ2, wherein 0<γ1<γ2<1, the number of grid nodes is recorded as G, and the adjusted number of grid nodes is recorded as G', and G'=G×(1+γu), wherein γu is the preset u-th node quantity adjustment coefficient, and u is set as 1,2.

[0158] The wave making method of the present invention determines the number of grid nodes by setting a preset usage rate and the actual usage rate of the network in the process of establishing a numerical wave pool, thereby reducing the problem of waste caused by too many grid nodes leading to a decrease in grid usage rate and further reducing the accuracy of grid division, and further achieving the improvement of the stability of the wave making and absorbing process.

[0159] See also Figure 1 As shown, the step of re-determining the number of observation points includes:

[0160] Comparing the wave wavelength difference amount generated by the numerical wave tank model after the number of observation points is determined with a preset difference amount;

[0161] If the difference in wave wavelengths generated by the numerical wave tank model is greater than a preset difference, it is determined that the interference degree of the observation point on the wave breaking result exceeds an allowable range, and the number of observation points is redetermined to output a second corresponding number;

[0162] The second corresponding quantity is re-determined by the difference between the wave wavelength difference amount generated by the numerical wave pool model and the preset difference amount.

[0163] Specifically, the second corresponding quantity includes a third quantity and a fourth quantity.

[0164] Specifically, the step of re-determining the number of observation points includes:

[0165] Specifically, if ΔM≤ΔM0, the number of the observation points is adjusted to a fourth number using the preset three-number adjustment coefficient;

[0166] If ΔM>ΔM0, the number of the observation points is adjusted to a fourth number using the preset four-number adjustment coefficients.

[0167] Specifically, the wave wavelength difference generated by the numerical wave pool model is recorded as M, the preset difference is recorded as M0, the difference between the wave wavelength difference generated by the numerical wave pool model and the preset difference is recorded as △M, △M=M-M0 is set, the preset difference is recorded as △M0, the preset third quantity adjustment coefficient is recorded as α3, the preset fourth quantity adjustment coefficient is recorded as α4, wherein 1<α3<α4, the number of observation points after the secondary adjustment is recorded as E”, and E”=E'×(1+αe), wherein αe is the preset e-th quantity adjustment coefficient, and e=3,4 is set.

[0168] The wave making method of the present invention sets a preset difference and redetermines the number of observation points through the wave wavelength difference generated by the numerical wave tank model, thereby reducing the deviation of the observation results caused by the excessive number of observation points, thereby reducing the effectiveness of the observation, and further improving the stability of the wave making and absorbing process.

[0169] Example 1

[0170] In this embodiment 1, when R>R0, the number of observation points E is adjusted according to the difference △R between the average establishment time of several numerical waves and the preset first time; the average establishment time of several numerical waves is recorded as R, the preset first time is recorded as R1, the preset second time is recorded as R2, the difference between the average establishment time of several numerical waves and the preset first time is recorded as △R, △R=R-R1 is set, the preset time difference is recorded as △R0, a preset number adjustment coefficient is recorded as α1, and a preset number adjustment coefficient is recorded as α2, wherein 0<α1<α2<1, R1<R2, the number of observation points is recorded as E, and the number of observation points after adjustment is recorded as E', R1=2s, R2=3S, α1=0.6, α2=0.8, △R0=3s, E=5, R=5s in this embodiment 1,

[0171] In the present embodiment 1, ΔR=5s-2s=3s, it is determined that ΔR>ΔR0 and the number of observation points is adjusted to E' using the preset second quantity adjustment coefficient α2, and it is calculated that E=5×0.8=4.

[0172] The applicant of the present invention has described the specific implementation of the present invention in conjunction with the drawings of the specification. The technicians in the industry should understand that the above specific implementation and description are only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A numerical wave generation method based on LS-DYNA velocity boundary, characterized in that: The following steps are involved: Determining the governing equations of the numerical wave pool model to simulate the wave pool in the actual environment, and establishing a finite element model based on the governing equations of the numerical wave pool model; The numerical wave is established according to the wave-making method input by the velocity boundary; In LS-DYNA, a single-layer environmental unit is created with the *ALE_AMBIENT_HYDROSTATIC keyword to determine the far-field boundary conditions to eliminate waves in the numerical water pool; Get the error amount of several numerical wave building processes; Obtain the difference in wave wavelengths generated by the numerical wave tank model after the number of observation points is determined to redefine the number of observation points; comparing the generated numerical wave pool with the target wave using the re-determined number of observation points to update the numerical wave pool model; The variances of the error amounts of the several numerical wave establishment processes are compared with the preset first variance and the preset second variance respectively; If the variance of the error amount of the several numerical wave establishment processes is greater than the preset first variance and less than or equal to the preset second variance, it is determined that the stability of the wave making and wave breaking process is lower than the allowable range, and the time step is determined; Wherein, the time step is determined by the difference between the variance of the error amount of the several numerical wave establishment processes and the preset first variance; If the variance of the error amount in the process of establishing the plurality of numerical waves is greater than a preset second variance, it is preliminarily determined that the storage space of the wave-making system does not meet the requirements; and comparing the average establishment time of the plurality of numerical waves with the preset first time and the preset second time; if the average establishment time of the plurality of numerical waves is greater than the preset first time and less than or equal to the preset second time a second duration, secondarily determining that the storage space of the wave-making system does not meet the requirements, and determining the number of observation points according to the difference between the average establishment duration of the plurality of numerical waves and the preset first duration to output a first corresponding number; If the average establishment time of the plurality of numerical waves is greater than the preset second time, it is preliminarily determined that the grid division accuracy is lower than the allowable range; and comparing the average utilization rate of the grids in the several numerical wave establishment processes with a preset utilization rate; If the average utilization rate of the grid in the process of establishing the several numerical waves is less than the preset utilization rate, the grid division accuracy is secondarily determined to be lower than the allowable range, and the number of grid nodes is determined based on the difference between the preset utilization rate and the average utilization rate of the grid in the process of establishing the several numerical waves.

2. The numerical wave generation method based on LS-DYNA velocity boundary according to claim 1 is characterized in that: The control equations of the numerical wave pool model include the unsteady RANS equations of incompressible fluid, the continuity equation, the volume fraction equation and the momentum equation.

3. The numerical wave generation method based on LS-DYNA velocity boundary according to claim 2 is characterized in that: The expression of the unsteady RANS equation of the incompressible fluid is: Among them, Ui is the time-averaged velocity in the i direction, uj is the time-averaged velocity in the j direction, Xi is the coordinate of i, Xj is the coordinate of j, t is time, ui' is the pulsating velocity, ui'u'j is the Reynolds stress, and P is the pressure.

4. The numerical wave generation method based on LS-DYNA velocity boundary according to claim 3 is characterized in that: The steps of establishing the finite element model include: Define the upper surface of the air domain as a non-reflecting boundary condition; Apply velocity disturbance boundary at the fluid inlet section; Use environmental units at the flow field outlet to simulate far-field boundary conditions; The mesh is refined in the area where the free liquid surface appears.

5. The numerical wave generation method based on LS-DYNA velocity boundary according to claim 4 is characterized in that: The steps of establishing the numerical wave pool include: The left boundary of the numerical wave tank model is defined as a periodic fluid disturbance; Set the free surface to vary as a function of time.

6. The numerical wave generation method based on LS-DYNA velocity boundary according to claim 5 is characterized in that: The expression of the function that changes with time is: The velocity at the entrance is: Where A is the amplitude, d is the water depth, k is the wave number, and ω is the frequency is the initial phase angle, u is the horizontal velocity, w is the vertical velocity, z=0 is the still water surface position, and x is the wavelength.

7. The numerical wave generation method based on LS-DYNA velocity boundary according to claim 6 is characterized in that: The step of re-determining the number of observation points comprises: Comparing the wave wavelength difference amount generated by the numerical wave tank model after the number of observation points is determined with a preset difference amount; If the wave wavelength difference amount generated by the numerical wave tank model is greater than the preset difference amount, it is determined that the interference degree of the observation point on the wave breaking result exceeds the allowable range, and the number of observation points is redetermined to output a second corresponding number; wherein the second corresponding number is redetermined by the difference between the wave wavelength difference amount generated by the numerical wave tank model and the preset difference amount.

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