Improved viscous flow non-reflection numerical value wave water tank

Abstract

An improved viscous flow non-reflection numerical value wave water tank relates to the technical field of computational fluid mechanics and comprises a computational domain, a flow field solving module, a liquid-liquid two-phase VOF module, a wave making module, a wave absorbing module, a solid-liquid boundary processing module and a data acquisition and analysis module, and the wave making module and the wave absorbing module are used for generating target waves to absorb emergent wave energy; the liquid-liquid two-phase VOF module realizes synchronous acquisition of an internal interface and a mixing ratio; the solid-liquid boundary processing module applies a complex / moving boundary condition on the fixed grid; the data acquisition and analysis module extracts information of a free surface and an internal interface, calculates characteristic quantities such as waves and mass transfer, feeds back indexes such as a reflection coefficient and a conservation error for damping and time step self-adaptive adjustment, realizes high-precision capturing of large deformation of the free surface, synchronously obtains mass transfer and flow information in liquid, and realizes high-precision capturing of large deformation of the free surface. And the influence of the reflected wave on the calculation precision is effectively suppressed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of computational fluid dynamics, in particular to an improved viscous flow non-reflective numerical wave tank. BACKGROUND

[0002] In the simulation of nearshore waves, the design of coastal engineering and the research of disaster prevention and mitigation, accurately reproducing the characteristics of wave propagation, breaking and internal flow is an important goal of numerical tank technology.

[0003] The existing numerical tank is mostly based on a single liquid-gas VOF method, which can only capture the changes of the free surface, but lacks effective means to obtain the movement of the liquid inside the water body of different sources.

[0004] In addition, long-time wave propagation is prone to secondary reflection waves, affecting the calculation accuracy; the processing of complex terrain or structural boundaries also affects the numerical stability.

[0005] Therefore, a high-precision numerical tank system is needed that can capture large deformation of the free surface and simultaneously obtain internal water movement information. SUMMARY

[0006] The embodiments of the present application provide an improved viscous flow non-reflective numerical wave tank, which can capture large deformation of the free surface with high precision, simultaneously obtain mass transport and flow information inside the liquid, and effectively suppress the influence of reflected waves on calculation accuracy.

[0007] An improved viscous flow non-reflective numerical wave tank, comprising: A computational domain adapted to construct a parameterized virtual fluid space to provide geometric constraints and discrete solution carriers for wave evolution; A flow field solving module adapted to solve the internal flow field, based on the mass conservation equation and Navier-Stokes equation of fluid mechanics, using a step-by-step algorithm to finally solve the hydrodynamic information of each grid; A wave generation module adapted to introduce a force source term in the momentum equation to generate target waves; A wave absorption module adapted to use a sponge layer damping method to absorb reflected waves, wherein the damping coefficient increases with position; A liquid-liquid two-phase VOF module adapted to track the interface of liquid of different sources; A solid-liquid boundary processing module adapted to use an immersed boundary method to process complex solid boundaries; A data acquisition and analysis module adapted to simultaneously output the free surface and liquid-liquid internal interface position and flow information, and perform flow field visualization processing.

[0008] Further, the target waves include linear waves, Stokes waves, irregular waves, focused waves, elliptical cosine waves and solitary waves.

[0009] Further, the damping wave-eliminating module realizes damping wave-elimination by adding a dissipation source term to the momentum equation, wherein the damping term is defined only in the wave-eliminating region, and its value is zero outside the wave-eliminating region.

[0010] Further, the dissipation source term in the momentum source wave-eliminating method is calculated in the following manner:

[0011] In the formula, is an absorption coefficient (dissipation source term); is a starting position of the absorption region; is a length of the absorption region; is a current position coordinate; is a damping spatial distribution form index , is a maximum damping strength coefficient (Dmax) , wherein, is a calculation time step.

[0012] Further, the liquid-liquid two-phase VOF module introduces and on the basis of the original liquid volume fraction , wherein and respectively represent different sources of liquid, and the interface tracking process of different sources of liquid includes: independently solving the convection equations of and , and performing mass correction at each time step to maintain +

[0013] The above technical solutions provided by the embodiments of the present application have at least the following beneficial effects: 1. Double-interface information is synchronously acquired: while capturing the large deformation of the free surface, the internal water flow information is also acquired, and the data is more comprehensive.

[0014] 2. Good reflection wave suppression effect: the momentum source wave generation and the sponge layer damping wave-elimination are combined, and the secondary reflection wave interference is effectively reduced.

[0015] 3. Strong adaptability to complex boundaries: the interaction with structures such as breakwaters, pile foundations, and wave-eliminating blocks can be simulated.

[0016] Other features and advantages of the present application will be described in the following specification, and some will become apparent from the specification, or will be understood from the practice of the present application. The purposes and other advantages of the present application can be achieved and obtained by the structures specifically pointed out in the written specification, claims, and drawings.

[0017] The technical solutions of the present application will be further described in detail below with the aid of drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this specification, illustrate embodiments of the present application and are used to explain the present application, but are not intended to limit the present application. In the drawings: Figure 1 The structural schematic diagram of the viscous flow non-reflective numerical wave tank disclosed in the embodiments of the present application is shown. Figure 2 The main solution flow chart of the established non-reflective viscous flow numerical model disclosed in the embodiments of the present application is shown.

[0019] Reference signs: 1, calculation domain; 2, liquid-liquid two-phase VOF module; 3, wave generation module; 4, wave absorption module; 5, solid-liquid boundary processing module; 6, data acquisition and analysis module; 7, flow field solving module. DETAILED DESCRIPTION

[0020] Exemplary embodiments of the present disclosure will be described in greater detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be accurately conveyed to those skilled in the art.

[0021] Figure 1 The structural schematic diagram of the viscous flow non-reflective numerical wave tank disclosed in the embodiments of the present application is shown, wherein the numerical wave tank is composed of a calculation domain 1, a liquid-liquid two-phase VOF module 2, a wave generation module 3, a wave absorption module 4, a solid-liquid boundary processing module 5, a data acquisition and analysis module 6, and a flow field solving module 7.

[0022] The calculation domain 1 provides geometric constraints, grid discretization, and region labels; the wave generation module 3 applies a momentum source to the momentum equation in the source area to generate target waves; the wave absorption module 4 applies position-dependent damping in the sponge layer to absorb outgoing wave energy; the liquid-liquid two-phase VOF module 2 introduces and keeps and keeps and keeps to independently obtain the internal interface and mixing ratio simultaneously; the solid-liquid boundary processing module 5 applies complex / moving boundary conditions on a fixed grid using the immersed boundary method; the data acquisition and analysis module 6 acquires velocity, pressure, and The free surface extracts the interface information and calculates the wave and mass transport characteristics, and the reflection coefficient and conservation error can be fed back to adjust the damping and time step.

[0023] Specifically, the calculation domain 1 is used to construct a parameterized virtual fluid space to provide a geometric constraint and a discrete solving carrier for wave evolution, including a geometric range, a grid, a region label (a wave making area, a sponge layer, a structure domain, etc.), and a time step advancing control.

[0024] The flow field solving module is suitable for internal flow field solving, based on the mass conservation equation and Navier-Stokes equation of fluid mechanics, and adopts a step-by-step algorithm to solve the hydrodynamic information of each grid.

[0025] The internal flow field is solved, and the control equations of the numerical water tank are the mass conservation equation and the Navier-Stokes equation, and the expressions are as follows: ; ; In the formula, is the coordinate axis in the Cartesian rectangular coordinate system, is the velocity component, is the time, is the fluid density, is the pressure, is the body force, such as gravity, is the dynamic viscosity coefficient, is the wave making momentum source term function, is the damping wave absorbing source term.

[0026] The flow field is solved by a step-by-step algorithm, and the control equation is time-integrated based on the Euler method. The flow field time integration adopts a step-by-step projection method, which divides the equation into a convection term and a non-convection term (diffusion term and pressure term).

[0027] First, a high-order compact difference method is used as a basic solver for the flow field to solve the convection term; then an explicit central difference method is used to solve the diffusion term; a red-black SOR iteration method is used to solve the pressure Poisson equation for pressure-velocity coupling calculation, to complete the update and solution of the velocity and pressure field; finally, an improved THINC-SW method of VOF type is used to reconstruct the free surface.

[0028] The wave making module 3 and the wave absorbing module 4 are suitable for applying sources (wave making) / sinks (damping) to the momentum equation in the source area to generate target waves and suppress reflections.

[0029] Among them, the wave generation module 3 is suitable for introducing a force source term into the momentum equation to generate target waves, including adding a momentum source term to the momentum equation in the sub-region source region of the computation domain 1, and generating target waves such as linear waves / Stokes waves / irregular waves / focused waves / elliptical cosine waves and isolated waves according to the target signal.

[0030] Wave generation module 3 operates in the source region of computational domain 1; provides momentum input to the NS solution; provides a consistent phase and amplitude baseline for the VOF free surface; and is used in conjunction with wave suppression to reduce reflection.

[0031] Wave-absorbing module 4 uses a sponge layer damping method to absorb reflected waves. The damping coefficient increases with position, including applying a damping term to the momentum in the end sponge layer to absorb the energy of the outgoing wave. This is used to reduce the reflection coefficient and create a "reflection-free" propagation environment.

[0032] Wave damping module 4 depends on the sponge layer label of computation domain 1; together with wave generation module 3, it determines the global reflection level; and it has a positive effect on the numerical stability of VOF free surface and dual interface.

[0033] Wave damping module 4 achieves damping wave reduction by adding a dissipation source term to the momentum equation. The damping term is defined only inside the wave reduction region and has a value of zero outside the wave reduction region.

[0034] The calculation method for the dissipation source term in the momentum source wave elimination method is as follows:

[0035] In the formula, This is the absorption coefficient (dissipation source term); This indicates the starting position of the absorption region; The length of the absorption region; The coordinates of the current position; Damping spatial distribution pattern index , The maximum damping strength coefficient ( ,in, (For calculating the time step).

[0036] The liquid-liquid two-phase VOF module 2 is suitable for interface tracking of liquids from different sources, based on the original liquid phase volume fraction. Based on and These represent liquids from different sources. and Representing different sources / initial regions of the same liquid phase to track internal liquid-liquid interfaces and mixing, the interface tracking process for liquids from different sources includes: independent solution and The convection equations are calculated, and mass corrections are made at each time step to maintain... + .

[0037] The liquid-liquid two-phase VOF module 2 functions include: Free surface: with volume fraction Capturing gas-liquid interface; Internal interface: with volume fraction And volume fraction Capturing liquid-liquid interface and mixing ratio; Property coupling: according to volume fraction Mixing density / viscosity into N-S equation; Analysis output: providing mixing ratio, mass transfer rate, etc. for data module.

[0038] The working process of the liquid-liquid two-phase VOF module 2 includes: Conservation coupling: keep + ; Convection update: respectively advancing the convection equations of 、 And With the same velocity field; Wherein, The evolution process of ; In the formula, Indicates the time rate of change of ; Indicates the fluid velocity field; Indicates the spatial gradient of .

[0039] The evolution process of ; In the formula, Indicates the time rate of change of ; Indicates the fluid velocity field; Indicates the spatial gradient of .

[0040] Interface reconstruction: using THINC / SW method to keep interface sharpness and phase accuracy; Mass correction: wherein the mass correction formula is: ; ; ; In the formula, represents another intermediate time value; , represents the corrected sub-phase volume fraction; , represents the uncorrected prediction value obtained by solving the transport equation; is an independent prediction value of the total liquid phase volume fraction; represents the total liquid phase volume fraction; represents the volume fraction of ; represents the volume fraction of .

[0041] The liquid-liquid two-phase VOF module 2 is used to receive the velocity of the N-S for convection, the free surface defined is consistent with the wave making / absorbing phase, and is also used to exchange the interface and mixing information with the data acquisition and analysis module 6 for analysis.

[0042] The solid-liquid boundary processing module 5 uses the immersed boundary method to process complex solid boundaries, and is used to accurately realize the no-slip / impervious conditions of complex geometry and moving structures, and is compatible with the VOF interface, and its working process includes: Geometric embedding: the solid and fluid regions are represented by a mask / distance function; Boundary condition application: add a correction term in the solid adjacent grid; Motion update: if the structure is moving, update the geometry / mask according to the given kinematics or fluid-structure coupling; Interface consistency: limit , , Non-physical penetration in the solid, maintain volume conservation.

[0043] The solid-liquid boundary processing module 5 runs in all cells intersecting the solid in the calculation domain 1, which affects the local velocity / pressure of the N-S solution, and at the same time, it is consistent with the reconstruction cell of VOF, avoiding the interface to pass through the solid wall, and the data acquisition and analysis module 6 can output the shear / pressure engineering quantities near the wall.

[0044] The data acquisition and analysis module 6 simultaneously outputs the free surface and the liquid-liquid internal interface position and flow information.

[0045] Among them, the free surface information is the interface between the gas phase and the liquid phase, including the free surface instantaneous height field (the water surface height at each position at a certain time), the free surface time sequence curve (the water surface height of a measuring point changes with time), the wave parameters (wave height, wavelength, period, phase velocity, etc.) and the free surface shape (such as wave crest, wave trough, broken zone shape), which is used to verify the wave propagation characteristics, wave making / absorbing effect, and free surface large deformation process.

[0046] ​Liquid-liquid internal interface position is the interface formed by different sources of liquid (liquid 1 and liquid 2) inside the liquid phase, including internal interface position field, mixing ratio distribution (the ratio of liquid source 1 to source 2 at a certain position, such as 、 ), mass transfer rate (derived from the change of interface position with time), interface evolution form (the curling and diffusion of the interface with time), which is used to study internal mixing process, pollutant diffusion, cold and hot flow mixing, etc. 、

[0047] Flow information is the velocity field, pressure field and derived turbulent characteristic quantities in the whole calculation domain 1, including instantaneous velocity vector field, pressure distribution field, vorticity, strain rate, turbulent kinetic energy.

[0048] The working process of the data acquisition and analysis module 6 includes: Data extraction, respectively extracting volume fraction field , volume fraction field , volume fraction field , velocity field and pressure field; Interface identification, including extracting isopach to determine the free surface; extracting or isopach near 0.5 to determine the liquid-liquid interface; Characteristic parameter calculation, for the free surface: calculating wave height, wave length, wave speed, breaking index; for the liquid-liquid interface: calculating mixing ratio field, interface length / area, mass transfer rate; for the flow field: calculating velocity vector, pressure gradient, vorticity; Data storage and visualization, stored as a grid file, while visualizing output profile, isopach and time series curve; Statistics and analysis, free surface statistics: maximum wave height, effective wave height, spectral analysis; internal interface statistics: mixing zone volume change rate, interface growth rate; flow statistics: average flow, vortex distribution.

[0049] In the embodiment of the present application, the main steps for solving the non-reflecting viscous flow numerical model established are as follows: Step 1, selecting the dimension of calculation.

[0050] Step 2, according to the requirements of the research object, carrying out grid division.

[0051] Step 3, setting initial conditions and boundary conditions according to the research object.

[0052] Step 4, solving N-S equation by using step-by-step projection method, updating the velocity field and pressure field in the fluid motion process.

[0053] Step 5, updating the free surface by using VOF method.​

[0054] Step 6, update the internal fluid interface by using the liquid-liquid two- phase VOF method.

[0055] Step 7, update the structure motion information by using the immersed boundary method.

[0056] Step 8, judge the stability condition and convergence condition, and adjust the time step.

[0057] Step 9, repeat steps 4-8 until the calculation is completed.

[0058] It should be understood that the particular order or hierarchy of steps in the processes disclosed is an example. Based upon design preferences, the particular order or hierarchy of steps in the processes can be re-arranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and as such the order is recited should not be deemed to limit the scope of the corresponding methods. The methods of the present disclosure can be implemented with more, fewer, or even zero of the described elements for performing the described functions. Additionally, it should be understood that not all elements in the processes need to be performed in the specific order presented in the implementations.

[0059] In the above detailed description, various features are grouped together in single embodiments for the purpose of streamlining the disclosure. This disclosed approach is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are explicitly recited in each claim. Rather, as the following claims reflect, inventive subject matter can lie in fewer than all features of a single disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate preferred embodiment.

[0060] Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans can implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0061] The steps of a method or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an ASIC. The ASIC can reside in a user terminal. In the alternative, the processor and the storage medium can reside as discrete components in a user terminal.

[0062] For a software implementation, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes can be stored in memory units and executed by processors. The memory unit can be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

[0063] The foregoing description includes example embodiments of the application. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art will recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either the detailed description or the claims, such term is intended to be interpreted as "comprising" rather than "consisting of." Also, the use of the term "about" in describing the application is intended to be interpreted in a non-limiting sense, meaning that the term "about" is used to allow for variations in the specified quantity due to such factors as variations in manufacturing or other processes, or variations that occur during the use of a product or system. Furthermore, any reference to claim interpretation is made solely to U.S. patent law, nothing herein being intended to mean or suggest that the scope of the application in any way bears on claim interpretation in any other country or jurisdiction.

Claims

1. An improved viscous fluid non-reflecting numerical wave tank characterized by, Comprise: A calculation domain, suitable for constructing a parameterized virtual fluid space to provide geometric constraints and discrete solving carriers for wave evolution; A flow field solving module, suitable for internal flow field solving, based on the mass conservation equation and Navier-Stokes equation of fluid mechanics, using a step-by-step algorithm to solve, finally solving the hydrodynamic information of each grid; A wave generating module, suitable for introducing a force source term in the momentum equation to generate target waves; A wave absorbing module, suitable for using a sponge layer damping method to absorb reflected waves, wherein the damping coefficient increases with position; A liquid-liquid two-phase VOF module, suitable for interface tracking of different source liquids; A solid-liquid boundary processing module, suitable for processing complex solid boundaries using the immersed boundary method; A data acquisition and analysis module, suitable for simultaneously outputting free surface and liquid-liquid internal interface positions and flow information, and performing flow field visualization processing.

2. The improved viscous fluid non-reflecting numerical wave tank of claim 1, wherein, The target waves include linear waves, Stokes waves, irregular waves, focused waves, elliptical cosine waves, and solitary waves.

3. The improved viscous fluid non-reflecting numerical wave tank of claim 1, wherein, The wave absorbing module realizes damping wave absorption by adding a dissipation source term to the momentum equation, wherein the damping term is only defined inside the wave absorbing area, and its value is zero outside the wave absorbing area.

4. The improved viscous fluid non-reflecting numerical wave tank of claim 3, wherein, The calculation method of the dissipation source term in the momentum source wave absorbing method is: 。 5. where, is the absorption coefficient (dissipation source term); is the absorption region start position; is the absorption region length; is the current position coordinate; is the damping spatial profile shape index , is the maximum damping strength coefficient (Dmax) where, to compute the time step).

6. The improved viscous fluid non-reflecting numerical wave tank of claim 1, wherein, wherein, The liquid-liquid two-phase VOF module introduces and to represent different source liquids on the basis of the original liquid volume fraction The interface tracking process for different source liquids includes: independently solving the convection equations of and and performing mass correction at each time step to maintain + .

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