Numerical simulation research method for watertight air chamber device based on LBM

Abstract

The invention discloses an LBM-based numerical simulation research method for a watertight air chamber device, and the method comprises the steps: S1, constructing an LBM-based wave numerical water tank, and simulating a process that waves enter an OWC air chamber; s2, according to the volume and the mass of air in the OWC air chamber at the initial moment in the simulation process, the initial condition of the gas state is obtained; s3, based on the gas state initial condition, updating the volume of air in the gas chamber at each time step, and based on the updated volume and the gas mass at the previous moment, calculating the current gas mass; s4, calculating the pressure intensity in the gas chamber according to the current gas mass and the updated volume, substituting the pressure intensity in the gas chamber into a free surface boundary condition of an LBM model, and updating a density distribution function; and S5, repeating the steps S2-S4 until a time termination condition is met, and completing numerical simulation of the wave energy conversion process in the OWC air chamber.

Description

Technical Field

[0001] This invention belongs to the field of marine engineering technology, and in particular relates to a numerical simulation research method for a watertight air chamber device based on LBM. Background Technology

[0002] Wave energy technology is in a stage of rapid development, among which oscillating water column wave energy conversion devices (OWC devices) are widely used. The energy conversion efficiency of OWC devices is directly affected by the oscillation characteristics of the water column and the pressure changes in the air chamber. Therefore, conducting research on the power generation process of OWC devices is of great significance for improving device performance. With the continuous development of computational fluid dynamics technology, numerical simulation has become an important means of studying the power generation performance of OWC. Common numerical models include single-phase flow models, two-phase flow models, etc. Single-phase flow models omit the simulation of orifice airflow, resulting in higher computational efficiency. However, traditional single-phase flow OWC models rely on damping coefficients that have no physical meaning, making it difficult to adapt to the numerical simulation needs of different types of OWC devices and resulting in poor versatility. The Lattice Boltzmann Method (LBM method) has higher computational efficiency and excellent parallel scalability compared to other CFD models. Therefore, it has unique advantages in simulating multi-OWC systems or OWCs with complex shapes and can handle complex boundaries. At present, research on OWC based on the LBM method is still relatively limited, lacking consideration of air compressibility and different air chamber orifice shapes. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a numerical simulation method for watertight air chamber devices based on LBM, which can simulate the wave energy conversion process inside the OWC air chamber without calibrating the damping coefficient, has a wider range of applications, and higher computational efficiency.

[0004] To achieve the above objectives, this invention provides a numerical simulation research method for a watertight air chamber device based on LBM, comprising:

[0005] S1. Construct a wave numerical flume based on LBM to simulate the process of waves entering the air chamber of the OWC oscillating water column wave energy conversion device.

[0006] S2. Based on the air volume and mass in the OWC chamber at the initial moment during the simulation, obtain the initial conditions of the gas state.

[0007] S3. Based on the initial conditions of the gas state, update the air volume in the gas chamber at each time step, and calculate the current gas mass based on the updated volume and the gas mass at the previous moment.

[0008] S4. Calculate the pressure inside the gas chamber based on the current gas mass and the updated volume, and substitute the pressure inside the gas chamber into the free surface boundary conditions of the LBM model to update the density distribution function;

[0009] S5. Repeat S2-S4 until the time termination condition is met to complete the numerical simulation of the wave energy conversion process in the OWC chamber.

[0010] Optionally, constructing an LBM-based wave numerical flume includes setting the flume boundary conditions, air chamber geometry parameters, and wave parameters.

[0011] Optionally, the initial conditions of the gas state include:

[0012] The volume and mass of air in the chamber at the initial moment are statistically analyzed and used as the initial input for the gas state evolution at time step S3.

[0013] Optionally, calculating the current gas mass includes: based on the gas mass m(t) from the previous moment, the updated volume V(t+Δt), and the orifice coefficient β, solving for the current gas mass m(t+Δt) by introducing a gas compressibility model.

[0014] m(t+Δt)=[ρ a βV(t+Δt)] / [β+V(t+Δt)-V(t)]+[m(t)-[ρ a βV(t)] / [β+V(t+Δt)-V(t)]]·[V(t) / V(t+Δt)]^[β / (V(t+Δt)-V(t))];

[0015] Where, ρ a Let V(t) be the atmospheric pressure, and V(t) be the air volume in the chamber before the update.

[0016] Optionally, obtaining the aperture coefficient β includes:

[0017] Based on whether the opening shape is circular or rectangular, and combined with the Reynolds number Re, friction g, γ, c, and pipe geometric parameters, the opening coefficient β value for the corresponding shape is calculated.

[0018] Optionally, calculating the pressure inside the air chamber includes:

[0019] Based on the current gas mass m(t+Δt) and volume V(t+Δt), and considering the air adiabatic coefficient γ and the speed of sound c in the air, calculate the pressure p(t+Δt) inside the gas chamber:

[0020] p(t+Δt)=[c² / γ]·ρ(t+Δt)=[c² / γ]·[m(t+Δt) / V(t+Δt)];

[0021] Where ρ(t+Δt) is the pressure inside the air chamber at the new moment.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] This invention is based on the LBM method, taking into account air compressibility and the shape of the orifice pipe. It introduces calculation methods for the length-to-diameter ratio α, friction g, and orifice coefficient β to calculate the mass and pressure of the gas in the OWC chamber and update the pressure on the free surface inside the chamber. This allows for a more realistic simulation of wave changes and flow field characteristics within the OWC chamber. It eliminates the need for calibrating the damping coefficient and is applicable to OWC chambers with different orifice shapes. Because the calculation process is based on a single-phase flow model, it can significantly improve computational efficiency and save computational costs. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This is a flowchart of a numerical simulation research method for a watertight air chamber device based on LBM according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the OWC device structure according to an embodiment of the present invention;

[0027] Figure 3 This is a simulation result diagram of a conventional single-phase flow according to an embodiment of the present invention;

[0028] Figure 4 This is a simulation result diagram of an embodiment of the present invention;

[0029] Figure 5 This is a comparison chart of numerical simulation results and experimental results from an embodiment of the present invention. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0032] This embodiment proposes a numerical simulation research method for a watertight air chamber device based on LBM, such as... Figure 1 As shown, the specific steps include:

[0033] S1. Construct a wave numerical flume based on LBM to simulate the process of waves entering the OWC chamber;

[0034] S2. Obtain the initial gas state conditions based on the air volume and mass in the OWC air chamber at the initial moment during the simulation process;

[0035] S3. Based on the initial gas state conditions, update the air volume in the air chamber at each time step, and calculate the current gas mass based on the updated volume and the gas mass at the previous moment;

[0036] S4. Calculate the pressure in the air chamber according to the current gas mass and the updated volume, and substitute the pressure in the air chamber into the free surface boundary condition of the LBM model to update the density distribution function;

[0037] S5. Repeat S2 - S4 until the time termination condition is satisfied to complete the numerical simulation of the wave energy conversion process in the OWC air chamber.

[0038] Specifically, as Figure 1 shown, this embodiment specifically includes the following steps:

[0039] Step (1). Establish a wave numerical flume to simulate the waves entering the air chamber;

[0040] Step (2). Statistically analyze the air volume V(t) and mass m(t) in the OWC air chamber;

[0041] Step (3). Enter a new moment and re - statistically analyze the air volume V(t + Δt) in the OWC air chamber;

[0042] Step (4). Calculate the friction resistance g = Re / 64·1 / C 2 D· = α + g LT (Re), where CD is taken as 0.85. When 0 < Re < 2000, g LT (Re) = 1. When 4000 < Re < 10000, g LT (Re) = Re / 64·0.3164 / Re0.25, Re = DhU / ν, Dh is the hydraulic diameter of the pipe. For a pipe with width W, length L, area A, and the x - coordinate of the pipe cross - section is [-W / 2, W / 2], the hydraulic diameter of a circular pipe is taken as W, and the hydraulic diameter of a rectangular pipe is taken as 2WH / (W + H), where H is the cross - section height of the square pipe;

[0043] Step (5). Calculate Re≈|[DV(t + Δt)] / [νAm(t + Δt)]·[m(t + Δt) - m(t)] / Δt| at the new moment, and calculate the opening coefficient β. When the opening shape is circular, β = [πW 4 c²Δt] / [32γg(Re, α)νL]. When the opening shape is rectangular, β = [HW³c²Δt] / [8γg(Re, α)νL];

[0044] Step (6), calculate the gas mass m(t+Δt) at the new moment = [ρ a βV(t+Δt)] / [β+V(t+Δt)-V(t)]+[m(t)-[ρ a βV(t)] / [β+V(t+Δt)-V(t)]]·[V(t) / V(t+Δt)]^[β / (V(t+Δt)-V(t))];

[0045] Step (7): Calculate the pressure inside the OWC chamber using the gas mass m(t+Δt) and volume V(t+Δt) as p(t+Δt) = [c² / γ]·ρ(t+Δt) = [c² / γ]·[m(t+Δt) / V(t+Δt)].

[0046] Step (8): Substitute the pressure p(t+Δt) inside the air chamber at the new moment into the boundary conditions of the free surface to update the density distribution function;

[0047] Step (9): Determine whether the time termination condition t>tend is met. If it is met, the calculation ends; if it is not met, t=t+Δt, and return to step (3).

[0048] The wave numerical flume was established based on the LBM method.

[0049] The length-to-diameter ratio α of an open pipe is a finitely large number.

[0050] Frictional resistance g is obtained based on local friction, laminar friction along the flow, and turbulent friction along the flow.

[0051] The orifice coefficient β is obtained based on whether the exhaust pipe is rectangular or circular.

[0052] Furthermore, constructing a wave numerical flume based on LBM includes setting the flume boundary conditions, air chamber geometry parameters, and wave parameters.

[0053] Furthermore, the initial conditions for the gas state include:

[0054] The volume and mass of air in the chamber at the initial moment are statistically analyzed and used as the initial input for the gas state evolution at time step S3.

[0055] Furthermore, the calculation of the current gas mass includes: based on the gas mass m(t) at the previous moment, the updated volume V(t+Δt), and the orifice coefficient β, the gas mass m(t+Δt) at the current moment is solved by introducing a gas compressibility model.

[0056] Furthermore, obtaining the aperture coefficient β includes:

[0057] Based on whether the opening shape is circular or rectangular, and combined with the Reynolds number Re, friction g, γ, c, and pipe geometric parameters, the opening coefficient β value for the corresponding shape is calculated.

[0058] Furthermore, calculating the pressure inside the air chamber includes:

[0059] Calculate the pressure p(t+Δt) inside the gas chamber based on the current gas mass m(t+Δt) and volume V(t+Δt), the air adiabatic coefficient γ, and the speed of sound c in the air.

[0060] This implementation uses a single-chamber OWC device as an example to specifically describe the numerical simulation research method for OWC devices based on the LBM method, as follows:

[0061] The OWC device uses waves to oscillate up and down in the air chamber, pushing the air in the upper part to move, creating a pressure difference between the inside and outside of the air chamber. This drives the air to reciprocate and impact the air turbine, thereby generating electricity. The initial air volume V(t) and mass m(t) in the air chamber are calculated. At a new time, the air volume V(t+Δt) in the OWC air chamber is recalculated. The frictional resistance g is calculated based on the Reynolds number Re and the aspect ratio α. The opening coefficient β is calculated based on the frictional resistance g. The gas mass m(t+Δt) at the new time is calculated. The pressure p(t+Δt) in the OWC air chamber is calculated from the gas mass m(t+Δt) and volume V(t+Δt). The pressure p(t+Δt) in the air chamber at the new time is substituted into the free surface boundary conditions to update the density distribution function and Reynolds number Re. After one cycle, the process continues to the next cycle, repeating the above calculation process until the termination condition is met.

[0062] The simulation results of the conventional single-phase flow model of the OWC device and the simulation results of the present invention are as follows: Figure 3-4 As shown, the simulation results are compared with the experimental results. Figure 5 .

[0063] from Figure 3 and Figure 4 It can be seen that the traditional single-phase flow model ( Figure 3 Because the turbulent frictional resistance was ignored, the calculated pressure change curve was rounded and symmetrical, exhibiting an approximate sine wave pattern. However, when the turbulent frictional resistance was included in the frictional resistance g calculation in this invention, the pressure change curve showed a steeper transition between peaks and valleys, exhibiting a narrower waist and sharper peaks, which is closer to the calculation results of the two-phase flow model. Figure 5 Comparing the simulation results of the traditional single-phase flow model with the experimental results of this invention, it can be found that: there are deviations between the simulation results of the traditional single-phase flow model and the experimental results; the simulation results of this invention are almost consistent with the experimental results, and this invention can effectively simulate the pressure changes in the OWC chamber.

[0064] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A numerical simulation method for a watertight air chamber device based on LBM, characterized in that, include: S1. Construct a wave numerical flume based on LBM to simulate the process of waves entering the OWC chamber; S2. Based on the air volume and mass in the OWC chamber at the initial moment during the simulation, obtain the initial conditions of the gas state. S3. Based on the initial conditions of the gas state, update the air volume in the gas chamber at each time step, and calculate the current gas mass based on the updated volume and the gas mass at the previous moment. S4. Calculate the pressure inside the gas chamber based on the current gas mass and the updated volume, and substitute the pressure inside the gas chamber into the free surface boundary conditions of the LBM model to update the density distribution function; S5. Repeat S2-S4 until the time termination condition is met to complete the numerical simulation of the wave energy conversion process in the OWC chamber.

2. The numerical simulation research method for a watertight air chamber device based on LBM according to claim 1, characterized in that, Constructing a wave numerical flume based on LBM involves setting the flume boundary conditions, air chamber geometry parameters, and wave parameters.

3. The numerical simulation research method for a watertight air chamber device based on LBM according to claim 1, characterized in that, The initial conditions for the gas state include: The volume and mass of air in the chamber at the initial moment are statistically analyzed and used as the initial input for the gas state evolution at time step S3.

4. The numerical simulation research method for a watertight air chamber device based on LBM according to claim 1, characterized in that, Calculating the current gas mass involves: based on the gas mass m(t) from the previous moment, the updated volume V(t+Δt), and the orifice coefficient β, solving for the current gas mass m(t+Δt) by introducing a gas compressibility model. m(t+Δt)=[ρ a βV(t+Δt)] / [β+V(t+Δt)-V(t)]+[m(t)-[ρ a βV(t)] / [β+V(t+Δt)-V(t)]]·[V(t) / V(t+Δt)]^[β / (V(t+Δt)-V(t))]; Where, ρ a Let V(t) be the atmospheric pressure, and V(t) be the air volume in the chamber before the update.

5. The numerical simulation research method for a watertight air chamber device based on LBM according to claim 4, characterized in that, The acquisition of the aperture coefficient β includes: Based on whether the opening shape is circular or rectangular, and combined with the Reynolds number Re, friction g, air adiabatic coefficient γ, sound velocity c in air, and pipe geometric parameters, the opening coefficient β value for the corresponding shape is calculated.

6. The numerical simulation research method for a watertight air chamber device based on LBM according to claim 5, characterized in that, Calculating the pressure inside the air chamber includes: Based on the current gas mass m(t+Δt) and volume V(t+Δt), and using c and γ, calculate the pressure inside the gas chamber: p(t+Δt)=[c² / γ]·ρ(t+Δt)=[c² / γ]·[m(t+Δt) / V(t+Δt)]; Where ρ(t+Δt) is the pressure inside the air chamber at the new moment.

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