Self-adaptive simulation method for sailing flow field of channel boat

Abstract

The invention belongs to the technical field of ship sailing flow field calculation, and provides a channel boat sailing flow field adaptive simulation method comprising the following steps: establishing a fluid model and a channel boat model, and setting a computational domain; setting initial flow field distribution, channel boat navigational speed and an initial grid division scheme; performing grid division on the fluid model based on the initial grid division scheme; capturing the gas-liquid interface form in the navigation process of the channel boat and tracking liquid drops and bubbles; segmenting a liquid drop splashing area and a gas-liquid interaction area based on tracking results of the liquid drops and the bubbles; carrying out self-adaptive grid division on the liquid drop splashing area and the gas-liquid interaction area to obtain a corrected grid division scheme; and carrying out numerical simulation on the time evolution process of the sailing flow field of the channel boat based on the corrected grid division scheme. According to the method provided by the invention, the calculation precision is ensured while the calculation efficiency is optimized, the calculation stability is remarkably improved, and effective support is provided for precise modeling of the gas-liquid two-phase flow and structural optimization of the channel boat.

Description

Technical Field

[0001] The present application belongs to the technical field of ship navigation flow field calculation, and specifically relates to an adaptive simulation method for the navigation flow field of a channel boat. Background Art

[0002] The channel boat is a new type of high-speed ship. Compared with traditional ships, the most significant improvement in its structure is the unique slotted structure of the bow. For example, patents CN108945280A and CN202609027U disclose high-speed ships with bow slots. When the water flow in the slotted area enters the slot, due to pressure changes and flow rate differences, part of the air is sucked into the water flow, enters the underwater area and forms bubbles in the water. These bubbles interact with the water flow and change the flow properties.

[0003] Since the channel boat has a special channel structure at the bow, when it sails at a higher speed, complex water-gas interaction phenomena will occur near the channel. For example, due to the rapid mixing speed of water and air, the bubbles generated near the liquid-gas interface do not remain stable, but will break, split and diffuse, forming a group of small bubbles. These bubbles not only change the flow characteristics of water, but also produce fluctuations in the gas-liquid interface in the water and increase the phenomenon of liquid splashing, so that the channel boat will be affected by fluid, gas and splashing droplets at the same time when sailing at high speed. Obviously, only by comprehensively analyzing the various factors that affect the navigation state of the channel boat can the structure of the channel boat be optimized in a targeted manner, thereby further improving the speed and navigation stability of the channel boat.

[0004] However, there is currently no method for accurate numerical simulation of the navigation flow field of the special structure of the slot boat. The reason is that the bow structure of the slot boat is special, and the water-gas interaction process generated when the water flows into the slot is more complicated than that of conventional ships. In the calculation domain, especially in the calculation area around the slot boat, liquid flow field and bubbles distributed therein, gas flow field and splashing droplets distributed therein will appear simultaneously, and the flow field, bubbles, and droplets interact with each other, which together affect the navigation of the slot boat. Although the accuracy of numerical simulation can be improved by increasing the grid density in the conventional way, this is bound to greatly increase the consumption of computing resources; in addition, from the perspective of the stability of numerical simulation, the liquid splashing phenomenon often causes the simulation process to diverge, which also causes the extension of simulation time and the decrease of simulation accuracy, thereby interfering with the accurate simulation of water-gas interaction phenomenon. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present application provides an adaptive simulation method of the flow field of a channel boat navigation through an embodiment, so as to perform efficient and accurate analysis of the flow field during the navigation of the channel boat.

[0006] The adaptive simulation method of the channel boat navigation flow field provided in the present application comprises the following steps: S1, establishing a fluid model and a channel boat model and setting a calculation domain, wherein the fluid model includes a liquid part and a gas part; S2, setting the initial flow field distribution of the fluid model, the speed of the channel boat and the initial grid division scheme; S3, meshing the fluid model based on the initial meshing scheme; S4, capturing the gas-liquid interface morphology during the navigation of the channel boat based on the initial grid division scheme, and tracking the droplets and bubbles caused by the change of the gas-liquid interface morphology; S5, segmenting the droplet splashing area and the gas-liquid interaction area based on the tracking results of the droplets and bubbles; S6, using the first grid division scheme and the second grid division scheme to perform adaptive grid division on the droplet splash area and the gas-liquid interaction area, respectively, to obtain a revised grid division scheme, wherein the grid density of the droplet splash area divided according to the first grid division scheme is less than the grid density divided according to the initial grid division scheme, and the grid density of the gas-liquid interaction area divided according to the second grid division scheme is greater than the grid density divided according to the initial grid division scheme; S7, numerically simulating the time evolution process of the channel boat navigation flow field based on the modified grid division scheme.

[0007] Preferably, in the initial grid division scheme, the grid density of the gas-liquid interface area and the interface area between the fluid and the channel boat is greater than the grid density of other areas.

[0008] Furthermore, step S4 is implemented by a Level Set algorithm, which specifically includes the following steps: S41, defining a labeling function, wherein the zero isosurface of the labeling function is a gas-liquid interface; S42, solving the evolution equation of the labeling function and capturing the gas-liquid interface morphology and the real-time flow field distribution of the fluid model at a plurality of sampling moments; S43, by reconstructing the gas-liquid interface and evolving the flow field, bubbles and droplet structures are generated in the liquid part and the gas part respectively based on the interface instability mechanism, and their distribution at several sampling moments is tracked.

[0009] Further, step S5 includes the following steps: S51, dividing an initial grid correction area in the calculation domain around the channel boat according to the tracking results of the bubble and droplet structures, the initial grid correction area being the union of the areas where at least one bubble structure and at least one droplet structure appear at the plurality of sampling moments; S52, dividing a plurality of statistical grids in the initial grid correction area according to a preset statistical grid density; S53, based on the tracking results of the droplet structure at a plurality of sampling moments, counting the droplet splashing trend in each statistical grid; S54, dividing a droplet splashing area from the initial grid correction area based on the statistical result of the droplet splashing trend; S55, based on the division result of the droplet splashing area, a gas-liquid interaction area is divided from the initial grid correction area.

[0010] Preferably, for each statistical grid, its droplet splashing trend is statistically calculated based on the following formula: , in, is the splash separation index, is the total number of sampling moments, For the The total number of droplets that appear in the statistical grid at the sampling moment, For the The sampling time appears in the statistical grid The velocity vector of the droplet, For the The sampling time appears in the statistical grid The unit vector of a droplet relative to the channel boat is directed from the center of mass of the bow of the channel boat to the droplet position. is the maximum value function, Is a null value.

[0011] Furthermore, the droplet splashing area is divided from the initial grid correction area based on the statistical result of the droplet splashing trend, specifically: The statistical grids with values ​​greater than the preset threshold are divided into droplet splash areas.

[0012] Preferably, the preset threshold increases with the increase of the relative speed of the channel boat, and the maximum value limit that can be reached is 1.

[0013] Furthermore, the gas-liquid interaction area is divided from the initial grid correction area based on the division result of the droplet splash area, specifically: the gas-liquid interaction area is divided from the remaining area after the droplet splash area is removed from the initial grid correction area.

[0014] Preferably, the initial grid correction area is larger than the combination of the droplet splash area and the gas-liquid interaction area, and the remaining area of ​​the initial grid correction area after excluding the droplet splash area and the gas-liquid interaction area is located behind the channel boat.

[0015] Preferably, the gas-liquid interaction zone is further divided into a first gas-liquid interaction zone and a second gas-liquid interaction zone; The first gas-liquid interaction zone is Value is not and is less than or equal to the preset threshold, the second gas-liquid interaction area is Value is area; The grid density of the first gas-liquid interaction zone divided according to the second grid division scheme is greater than the grid density of the second gas-liquid interaction zone divided according to the second grid division scheme.

[0016] Preferably, the modified grid division scheme further includes a step of performing a grid density smoothing operation on the droplet splash area and other areas or on the gas-liquid interaction area and other areas.

[0017] The embodiment of the present application provides an adaptive simulation method for the flow field of a channel boat navigation. First, by comprehensively considering the bubble bursting, droplet splashing and their influence on the navigation process of the channel boat during the high-speed navigation of the channel boat, the gas-liquid interface is tracked to accurately obtain the dynamic process of the two-phase flow. Then, an adaptive meshing technology based on the splash separation index (SSI) is used to dynamically adjust the mesh size according to the flow field changes, coarsen the mesh in the droplet splashing area far away from the hull to achieve the purpose of dissipating unnecessary droplets, and refine the mesh in the water-gas intensive interaction areas such as the slotted area, thereby optimizing the calculation efficiency and ensuring the calculation accuracy, and significantly improving the calculation stability, providing effective support for the accurate modeling of gas-liquid two-phase flow and the optimization of the channel boat structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of an adaptive simulation method for a channel boat navigation flow field provided in an embodiment of the present application; Figure 2 It is a structural schematic diagram of the channel boat model in the embodiment of the present application; Figure 3 This is a specific implementation flow chart of step S4 in the embodiment of the present application; Figure 4 This is a specific implementation flow chart of step S5 in the embodiment of the present application; Figure 5 It is a schematic diagram of the change of the preset threshold value with the relative speed in the embodiment of the present application; Figure 6 A schematic diagram of meshing a fluid model using an initial meshing scheme in a specific embodiment of the present application; Figure 7 A schematic diagram of meshing a fluid model using a modified meshing scheme in a specific embodiment of the present application; Figure 8A side view of the channel boat navigation flow field obtained by meshing the fluid model using a modified meshing scheme in a specific embodiment of the present application; Fig. 9 This is a top view of the channel boat navigation flow field obtained by meshing the fluid model using a modified meshing scheme in a specific embodiment of the present application. DETAILED DESCRIPTION

[0019] Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.

[0020] As analyzed in the background technology, there is currently no method for accurately simulating the flow field of a channel boat. Therefore, it is difficult to optimize the structure of the channel boat in a targeted manner based on the simulation results. To this end, the present application provides an adaptive simulation method for the flow field of a channel boat through an embodiment. Figure 1 , the simulation method comprises the following steps: S1, establishing a fluid model and a channel boat model and setting a calculation domain, wherein the fluid model includes a liquid part and a gas part; S2, setting the initial flow field distribution of the fluid model, the speed of the channel boat and the initial grid division scheme; S3, meshing the fluid model based on the initial meshing scheme; S4, capturing the gas-liquid interface morphology during the navigation of the channel boat based on the initial grid division scheme, and tracking the droplets and bubbles caused by the change of the gas-liquid interface morphology; S5, segmenting the droplet splashing area and the gas-liquid interaction area based on the tracking results of the droplets and bubbles; S6, using the first grid division scheme and the second grid division scheme to perform adaptive grid division on the droplet splash area and the gas-liquid interaction area, respectively, to obtain a revised grid division scheme, wherein the grid density of the droplet splash area divided according to the first grid division scheme is less than the grid density divided according to the initial grid division scheme, and the grid density of the gas-liquid interaction area divided according to the second grid division scheme is greater than the grid density divided according to the initial grid division scheme; S7, numerically simulating the time evolution process of the channel boat navigation flow field based on the modified grid division scheme.

[0021] The steps of the method are described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0022] Step S1: Step S1 is used to establish a relevant model for numerical simulation of the navigation flow field and set the environment for numerical simulation.

[0023] In some embodiments, a fluid model can be established based on indicators such as simulation accuracy requirements, wherein the fluid model includes a liquid part located below and a gas part located above, and the interface between the two parts is called a gas-liquid interface. The gas-liquid interface continuously changes according to the navigation conditions of the channel boat during subsequent numerical simulations.

[0024] In some embodiments, a channel boat model can be established based on the structural parameters of the channel boat used for analysis. Obviously, the channel boat model used for numerical simulation only needs to finely characterize the shape of the hull shell located in the liquid part and near the gas-liquid interface, and set the hull shell in the above-mentioned part as a rigid body to provide rigid constraints at the interface between the hull and the fluid. In this way, the complexity of the model can be greatly simplified without losing the accuracy of numerical simulation. Figure 2 A schematic diagram of a channel boat model for numerical simulation in some specific embodiments is shown. Figure 2 As shown, the structure of the lower shell of the channel boat model is relatively fine, which can accurately characterize the M-type double channel structure located at the bow of the boat, while the upper part is simply set up with a flat top structure.

[0025] After obtaining the fluid model and the channel boat model, the calculation domain can be further set. The size of the calculation domain can be determined according to the simulation accuracy, the flow rate of the fluid used for simulation, the ship speed and other information. For example, when the flow rate or the ship speed of the liquid part is large, the size of the calculation domain can be appropriately expanded, and vice versa. The size of the calculation domain can be reduced. The above setting methods are all known to those skilled in the art and will not be repeated here.

[0026] Steps S2-S3: Step S2 is used to initialize the numerical simulation. Specifically, in this step, the initial flow field distribution can be set for the liquid part and the gas part of the fluid model respectively, wherein the flow field distribution can include the fluid flow rate at each position of the fluid model. Obviously, the flow field distribution of the liquid part corresponds to the speed of the water flow, and the flow field distribution of the gas part corresponds to the wind speed. In addition, the flow field distribution of the fluid model can also include information such as pressure or pressure at each position of the fluid model, and the water resistance and wind resistance encountered by the channel boat during navigation can be calculated through the above information.

[0027] In step S2, the speed of the channel boat can also be set. In some embodiments, a coordinate system can be established with the channel boat as the origin, and the calculation domain can be bound to the channel boat so that the channel boat remains stationary relative to the calculation domain. The fluid model is driven to move in the calculation domain by the combined speed of the flow rate of the liquid part and the gas part and the ship speed to facilitate subsequent numerical calculations.

[0028] Step S2 is also used to set a grid division scheme for performing initial grid division on the fluid model in the computational domain. In an embodiment of the present application, the grid division scheme set in step S2 is referred to as an initial grid division scheme.

[0029] An initial grid division scheme can be formulated according to a grid setting scheme familiar to those skilled in the art. For example, in some preferred embodiments, grid encryption is performed on the gas-liquid interface area (i.e., the gas-liquid interface and the area within a certain distance above and below it), and the interface area between the fluid and the channel boat, respectively, to ensure the accuracy of the numerical simulation in the above-mentioned area.

[0030] After the initial grid division scheme is set, in step S3, the fluid model in the calculation domain can be grid divided according to the initial grid division scheme.

[0031] Step S4: Step S4 is used to perform a preliminary simulation of the navigation flow field of the channel boat on the fluid model divided by the initial grid division scheme, so as to obtain the gas-liquid interface changes caused by the navigation of the channel boat and track the bubbles and droplets caused by the gas-liquid interface changes. The results of this preliminary simulation will serve as the basis for modifying the grid division scheme in the subsequent step S5.

[0032] like Figure 3 As shown, in an embodiment of the present application, step S4 can be implemented by a Level Set algorithm, which specifically includes the following steps: S41, defining a labeling function, wherein the zero isosurface of the labeling function is the gas-liquid interface.

[0033] In the Level Set algorithm, by defining a marking function It describes the interface between different phases of fluid and can accurately handle the shape change of the interface. It is suitable for simulating complex fluid dynamics, especially in phenomena such as splashing droplets and bubble bursting. The part < 0 is regarded as the liquid phase area. The region >0 is considered as the gas phase region. Obviously, the marking function The zero isosurface of =0) indicates the gas-liquid interface.

[0034] S42, solving the evolution equation of the labeling function and capturing the gas-liquid interface morphology and the real-time flow field distribution of the fluid model at a number of sampling moments.

[0035] The Level Set algorithm captures the dynamic changes of the interface by solving the evolution equation of the marking function. The evolution equation of the marking function is shown as follows: (1) In the above formula, is the velocity field of the fluid, is the time variable, is the gradient operator, and the equation represents the labeling function Evolves as the fluid motion changes.

[0036] By solving the evolution equation shown in formula (1) during a preset sampling period, we can obtain the corresponding values ​​of several sampling moments: , thereby capturing the shape of its zero isosurface (i.e., gas-liquid interface), and at the same time, the real-time distribution of the flow field at each sampling moment can be obtained.

[0037] S43, by reconstructing the gas-liquid interface and evolving the flow field, bubbles and droplet structures are generated in the liquid part and the gas part respectively based on the interface instability mechanism, and their distribution at several sampling moments is tracked.

[0038] When the interface is disturbed enough and the distance changes, instability will occur at the gas-liquid interface. The above instability mechanism causes the gas phase components to enter the liquid phase components, thereby generating multiple bubbles in the liquid area. The bubbles may also burst and generate multiple droplets. In the Level Set algorithm, by reconstructing the gas-liquid interface and evolving the flow field, the dynamic evolution of the interface can be accurately captured, and the bubble bursting process can be accurately simulated.

[0039] In some specific embodiments, the process of simulating the dynamic changes of the interface between droplets and bubbles in the gas-liquid two-phase flow by the Level Set algorithm includes the following operations: Interface deformation tracking: Calculate the normal velocity of the gas-liquid interface through the evolution of the marker function and update the zero isosurface position; Topological change processing: When the interface curvature exceeds a critical value, the interface breaks to generate bubbles in the liquid part of the fluid model and droplets in the gas part of the fluid model.

[0040] UI refactoring: periodically reinitialize marker functions to maintain numerical stability.

[0041] Through the above steps, the reconstructed gas-liquid interface, as well as the shape and trajectory of the generated bubbles and droplets can be accurately tracked at each sampling moment.

[0042] Steps S5-S6: In an embodiment of the present application, step S5 further divides the calculation domain into a droplet splash zone and a gas-liquid interaction zone by statistically analyzing the droplet and bubble structures tracked at multiple sampling moments, and step S6 performs grid thinning and grid encryption processing on the droplet splash zone and the gas-liquid interaction zone, respectively, thereby realizing the correction of the initial grid division scheme.

[0043] The reasons for further dividing the droplet splash zone and the gas-liquid interaction zone in the computational domain and performing mesh sparseness and mesh encryption respectively are: First, when the channel boat is sailing at a high speed, the bubbles formed by the compressed gas entering the channel do not remain stable, but will continue to break, split and diffuse to form a group of small bubbles. These bubbles not only affect the dynamic characteristics of water, but also increase the phenomenon of liquid splashing, resulting in the simultaneous existence of liquid phase fluid, gas phase fluid, bubbles in the liquid phase fluid and droplets in the gas phase fluid in some areas. Since the bubbles generated by the interaction of this part of gas and liquid can further lift the hull and achieve the effect of drag reduction, it is necessary to conduct a more accurate analysis of its evolution; secondly, the applicant found in the simulation process that when calculating the interaction between splashing droplets, bubbles and the hull, the large-scale droplet evolution calculation will bring certain instability to the numerical simulation, often causing the simulation process to diverge. Although the mesh can be encrypted in all areas where bubbles or droplets exist, this method will cause a huge increase in the amount of calculation, resulting in a significant increase in calculation time and cost.

[0044] To this end, the present application adopts a different grid construction method to solve the above problem: first, an initial area is delineated based on the distribution of droplets and bubbles at several sampling moments, and then the evolution behavior of the droplets in the area is statistically analyzed to determine the distribution area of ​​the droplets away from the hull. For this part of the area, since the movement and evolution of its droplets have no effect on the navigation of the channel boat, there is no need to consider its interaction with the channel boat, so its grid is coarsened, which on the one hand reduces the calculation complexity of this part of the area, and on the other hand can further ensure that it will not affect the calculation stability; for areas where there are droplets whose motion state is not much different from that of the channel boat, and areas where there are droplets mixed with bubbles, since the droplets therein involve complex interactive calculations, it is necessary to encrypt the grid to improve the calculation accuracy and avoid numerical divergence.

[0045] refer to Figure 4 In an embodiment of the present application, step S5 includes the following steps: S51, dividing an initial grid correction area in the calculation domain around the channel boat according to the tracking results of the bubble and droplet structures, the initial grid correction area is the union of the areas where at least one bubble structure and at least one droplet structure appear in the several sampling moments.

[0046] S52, dividing a plurality of statistical grids in the initial grid correction area according to a preset statistical grid density.

[0047] S53, based on the tracking results of the droplet structure at several sampling moments, the droplet splashing trend is counted in each statistical grid.

[0048] In some embodiments, the splash separation index may be expressed as follows: Characterize the statistical results of droplet splash trends in each statistical grid: (2) in, is the total number of sampling moments, For the The total number of droplets that appear in the statistical grid at the sampling moment, For the The sampling time appears in the statistical grid The velocity vector of the droplet, For the The sampling time appears in the statistical grid The unit vector of a droplet relative to the channel boat is directed from the center of mass of the bow of the channel boat to the droplet position. is the maximum value function, Is a null value.

[0049] According to the meaning of the above variables, for any statistical grid, Represents the component of each droplet's velocity and the bow direction. This component is used to measure the velocity of the droplet away from the hull. The index represents the ratio of the component of the droplet moving away from the hull in the statistical grid to the total velocity of the droplet: when When it approaches 1, it means that most of the droplets move away from the hull, that is, most of the splashing droplets are away from the hull, which shows that the splashing phenomenon is in progress and the droplets have an obvious splashing tendency; when When it approaches 0, it means that the droplet has no obvious tendency to move away from the hull. It may be due to water-gas interaction or other disturbances that the droplet still remains near the hull, or the movement direction is not obvious. when When it is between 0 and 1, it means that the droplet has a tendency to move away from the hull, and may also have a movement component close to the hull. This situation may involve complex water-air interaction or partial droplet backflow phenomenon; when , it means that at each sampling moment, no droplets appeared in the statistical grid, only bubbles existed. In this case, The value of .

[0050] S54, based on the statistical result of the droplet splashing trend, dividing the droplet splashing area from the initial grid correction area.

[0051] Specifically, the statistics of each grid are obtained by step S53. After the value is obtained, in step S54, a preset threshold between 0 and 1, such as 0.7, can be set to The statistical grids with values ​​greater than a preset threshold are determined as droplet splash areas.

[0052] In some preferred embodiments, the preset threshold will increase with the increase of the relative speed of the channel boat (i.e., the result of the vector synthesis of the flow velocity and the speed). This is because as the speed continues to increase, more droplets may participate in the interaction with the boat body. For this reason, the threshold should be increased to reduce the size of the area where the grid is coarsened. This is also in line with the requirement that more areas need to be calculated in detail with high-speed movement. However, it is obvious that no matter how it is increased, the maximum value that the preset threshold can reach is limited to 1.

[0053] To this end, a preset threshold function such as the one shown in the following formula may be constructed to determine the preset thresholds corresponding to different relative speeds: (3) in, is the preset threshold, is the relative speed (in knots), is the proportional coefficient. The above formula indicates that the minimum value of the preset threshold is 0.7. As the relative speed increases, the preset threshold gradually increases, and its upper limit is 1. The change of the preset threshold with the increase of relative speed can be referred to Figure 5 , where the proportionality coefficient The value of is 0.1. It should be noted that formula (3) is only an optional form of the preset threshold function. Under the condition that the preset threshold increases with the relative speed of the channel boat and is subject to the maximum value constraint, other preset threshold functions that meet the conditions can also be constructed.

[0054] S55, based on the division result of the droplet splashing area, a gas-liquid interaction area is divided from the initial grid correction area.

[0055] In step S55, the gas-liquid interaction area can be divided from the remaining area after the droplet splashing area is removed from the initial grid correction area.

[0056] In some embodiments, the remaining area after removing the droplet splash area from the initial grid correction area can be directly divided into the gas-liquid interaction area, that is, the initial grid correction area is equal to the combination of the droplet splash area and the gas-liquid interaction area.

[0057] Taking into account that during the navigation of the slot boat, the area where bubbles exist may extend from the slot of the slot boat to a considerable area behind the slot boat, these areas where bubbles exist behind the slot boat do not actually affect the navigation of the slot boat. Therefore, in some preferred embodiments, the initial grid correction area is larger than the combination of the droplet splash area and the gas-liquid interaction area, that is, it is only necessary to divide the area located on the slot boat hull and in front of it in the remaining area after the droplet splash area is eliminated from the initial grid correction area into the gas-liquid interaction area. In this case, the remaining area in the initial grid correction area after the droplet splash area and the gas-liquid interaction area are eliminated is located behind the slot boat. For this part of the area, there is no need to modify its grid division scheme, and the initial grid division scheme can be used for grid division.

[0058] After completing the division of the droplet splash zone and the gas-liquid interaction zone, the droplet splash zone and the gas-liquid interaction zone can be adaptively meshed again in step S6 according to the first meshing scheme and the second meshing scheme, so as to obtain a modified meshing scheme. As analyzed above, the first meshing scheme performs mesh sparse processing on the droplet splash zone, and by simplifying the simulation of the evolution process of droplets that do not interact with the channel boat, it effectively alleviates the problem of divergence of calculation results in the numerical simulation process while reducing the amount of calculation; for the gas-liquid interaction zone, the second meshing scheme performs mesh encryption processing on it, so as to maximize the simulation accuracy of the interaction process between bubbles, droplets and the channel boat body in the region, so as to ensure the accuracy of the overall numerical simulation results.

[0059] In some preferred embodiments, after the droplet splash zone and the gas-liquid interaction zone are respectively re-divided into grids to obtain a revised grid division scheme, the revised grid division scheme can be further optimized. For example, a step of smoothing the grid density between the droplet splash zone and other areas, or between the gas-liquid interaction zone and other areas, can be added to the revised grid division scheme to ensure that the grids in different areas can transition naturally.

[0060] Step S7: After completing step S6, the time evolution process of the channel boat navigation flow field can be numerically simulated in step S7. Obviously, in this step, the modified grid division scheme will be used to grid the fluid model in the calculation domain, and then the operation basically consistent with step S4 will be adopted. At each numerical simulation moment, the gas-liquid interface is captured by the Level Set algorithm, bubbles and droplets are tracked, and the flow field distribution of the liquid part and the gas part at the numerical simulation moment is calculated. According to the numerical simulation results of the navigation flow field, the flow field evolution around the hull of the channel boat during navigation, the gas-liquid interaction, etc. can be effectively obtained, thereby providing a reliable basis for optimizing the hull structure and further improving the drag reduction effect.

[0061] In some preferred embodiments, the stress conditions of the channel boat hull during navigation can be further calculated based on the flow field distribution at each simulation moment. The above-mentioned hull stress conditions can further provide effective information for optimizing the hull operation.

[0062] In some preferred embodiments, the duration of the numerical simulation of step S7 is greater than the duration covered by each sampling moment in step S4, that is, the grid division scheme can be corrected based on the sampling results within a shorter time period, and then the numerical simulation of the long-term navigation flow field can be carried out based on the corrected grid division scheme.

[0063] In addition, due to the gas-liquid interaction area generated in step S55, there is still an area containing both bubbles and droplets (i.e. The value is less than or equal to the preset threshold, but not ), and the area containing only bubbles (i.e. Value is ), therefore, in some preferred embodiments, the grid division scheme can be further optimized. Specifically, the gas-liquid interaction area can be further divided into a first gas-liquid interaction area and a second gas-liquid interaction area, wherein the first gas-liquid interaction area is Value is not and is less than or equal to the preset threshold, the second gas-liquid interaction area is Value is area.

[0064] Different grid division densities can be further set for the first gas-liquid interaction zone and the second gas-liquid interaction zone: the grid density of the first gas-liquid interaction zone divided according to the second grid division scheme is greater than the grid density of the second gas-liquid interaction zone divided according to the second grid division scheme. Through the above settings, three different areas are actually formed in the second grid division scheme: for the droplet splashing area that does not interact with the hull, a coarser grid is used for division; for the area where bubbles and droplets exist at the same time and interact with the hull, the densest grid is used for division; for the area where only bubbles exist, since this area does not need to consider the problem of numerical divergence, its grid density is between the first two.

[0065] Figures 6 to 9 The figure shows the results of various steps of calculating the channel boat navigation flow field using the adaptive simulation method of the channel boat navigation flow field provided in the present application in a specific embodiment. The embodiment is a channel boat wave resistance test. The channel boat has a speed of 25 knots. The fluid model contains waves with a period of 5.5s. The wave height, wavelength and wave speed are 1.2m, 47.23m and 8.59m / s respectively.

[0066] in, Figure 6A schematic diagram of meshing a fluid model using the initial meshing scheme. Figure 7 Schematic diagram of meshing the fluid model using the modified meshing scheme. Figure 6 and Figure 7 It can be seen that the grid is thickened in the area in front of the slot boat where there is splashing liquid but not in contact with the slot boat, so as to reduce the amount of numerical simulation calculation and improve the speed of numerical simulation. The grid is encrypted in the area in front of the slot boat and inside the slot where there is complex gas-liquid interaction and splashing droplets in contact with the slot boat, so as to ensure the accuracy of numerical simulation in the above-mentioned complex interaction areas. Figure 8 and Fig. 9 The side view and top view of the flow field distribution at the 11th second obtained by simulating the evolution of the flow field of the channel boat navigation using the modified grid division scheme are shown respectively. It can be seen from the above figures that by using the method provided by the present application, a more reasonable adaptive grid division is performed on the key areas that affect the flow field analysis results during the simulation of the channel boat navigation flow field, and a balance between the accuracy and speed of the channel boat navigation flow field analysis is achieved.

[0067] The above is a detailed introduction to the specific implementation methods of the present application. For those skilled in the art, several improvements and modifications may be made to the present application without departing from the principles of the present application. These improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. An adaptive simulation method for the flow field of a channel boat, characterized in that: The following steps are involved: S1, establishing a fluid model and a channel boat model and setting a calculation domain, wherein the fluid model includes a liquid part and a gas part; S2, setting the initial flow field distribution of the fluid model, the speed of the channel boat and the initial grid division scheme; S3, meshing the fluid model based on the initial meshing scheme; S4, capturing the gas-liquid interface morphology during the navigation of the channel boat based on the initial grid division scheme, and tracking the droplets and bubbles caused by the change of the gas-liquid interface morphology; S5, segmenting the droplet splashing area and the gas-liquid interaction area based on the tracking results of the droplets and bubbles; S6, using the first grid division scheme and the second grid division scheme to perform adaptive grid division on the droplet splash area and the gas-liquid interaction area, respectively, to obtain a revised grid division scheme, wherein the grid density of the droplet splash area divided according to the first grid division scheme is less than the grid density divided according to the initial grid division scheme, and the grid density of the gas-liquid interaction area divided according to the second grid division scheme is greater than the grid density divided according to the initial grid division scheme; S7, numerically simulating the time evolution process of the channel boat navigation flow field based on the modified grid division scheme.

2. The adaptive simulation method of the channel boat navigation flow field according to claim 1 is characterized in that: In the initial meshing scheme, the mesh density in the gas-liquid interface region and the interface region between the fluid and the channel boat is greater than the mesh density in other regions.

3. The adaptive simulation method of the channel boat navigation flow field according to claim 1 is characterized in that: Step S4 is implemented by the Level Set algorithm, which specifically includes the following steps: S41, defining a labeling function, wherein the zero isosurface of the labeling function is a gas-liquid interface; S42, solving the evolution equation of the labeling function and capturing the gas-liquid interface morphology and the real-time flow field distribution of the fluid model at a plurality of sampling moments; S43, by reconstructing the gas-liquid interface and evolving the flow field, bubbles and droplet structures are generated in the liquid part and the gas part respectively based on the interface instability mechanism, and their distribution at several sampling moments is tracked.

4. The adaptive simulation method of the channel boat navigation flow field according to claim 3 is characterized in that: Step S5 includes the following steps: S51, dividing an initial grid correction area in the calculation domain around the channel boat according to the tracking results of the bubble and droplet structures, the initial grid correction area being the union of the areas where at least one bubble structure and at least one droplet structure appear at the plurality of sampling moments; S52, dividing a plurality of statistical grids in the initial grid correction area according to a preset statistical grid density; S53, based on the tracking results of the droplet structure at a plurality of sampling moments, counting the droplet splashing trend in each statistical grid; S54, dividing a droplet splashing area from the initial grid correction area based on the statistical result of the droplet splashing trend; S55, based on the division result of the droplet splashing area, a gas-liquid interaction area is divided from the initial grid correction area.

5. The adaptive simulation method of the channel boat navigation flow field according to claim 4 is characterized in that: For each statistical grid, its droplet splashing trend is calculated based on the following formula: ， in, is the splash separation index, is the total number of sampling moments, For the The total number of droplets that appear in the statistical grid at the sampling moment, For the The sampling time appears in the statistical grid The velocity vector of the droplet, For the The sampling time appears in the statistical grid The unit vector of a droplet relative to the channel boat is directed from the center of mass of the bow of the channel boat to the droplet position. is the maximum value function, Is a null value.

6. The adaptive simulation method of the channel boat navigation flow field according to claim 5 is characterized in that: The droplet splashing area is divided from the initial grid correction area based on the statistical results of the droplet splashing trend, specifically: The initial mesh correction area The statistical grids with values ​​greater than the preset threshold are divided into droplet splash areas.

7. The adaptive simulation method of the channel boat navigation flow field according to claim 6 is characterized in that: The preset threshold value increases with the increase of the relative speed of the channel boat, and the maximum value limit that can be reached is 1.

8. The adaptive simulation method for the flow field of a channel boat according to claim 6 is characterized in that: The gas-liquid interaction area is divided from the initial grid correction area based on the division result of the droplet splash area, specifically: The gas-liquid interaction area is divided into a remaining area after the droplet splashing area is removed from the initial grid correction area.

9. The adaptive simulation method of the channel boat navigation flow field according to claim 8 is characterized in that: The initial grid correction area is larger than the combination of the droplet splash area and the gas-liquid interaction area, and the remaining area of ​​the initial grid correction area after excluding the droplet splash area and the gas-liquid interaction area is located behind the channel boat.

10. The adaptive simulation method of channel boat navigation flow field according to claim 8, characterized in that: The gas-liquid interaction zone is further divided into a first gas-liquid interaction zone and a second gas-liquid interaction zone; The first gas-liquid interaction zone is Value is not and is less than or equal to the preset threshold, the second gas-liquid interaction area is Value is area; The grid density of the first gas-liquid interaction zone divided according to the second grid division scheme is greater than the grid density of the second gas-liquid interaction zone divided according to the second grid division scheme.

11. The adaptive simulation method of channel boat navigation flow field according to claim 1 is characterized by: The modified grid division scheme also includes a step of performing a grid density smoothing operation on the droplet splashing area and other areas or on the gas-liquid interaction area and other areas.

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