CN108108569B - A fast modeling method of ship hull based on buoyancy surface element - Google Patents

Abstract

The invention discloses a hull rapid modeling method based on a buoyancy surface element, which mainly comprises the following steps: designing main parameters of a ship body, and establishing a rough three-dimensional model of the ship body; arranging a centroid position and dividing buoyancy surface elements on the rough three-dimensional model of the ship body, performing preliminary simulation according to the buoyancy sum of the buoyancy bodies corresponding to each buoyancy surface element, and establishing a physical model of the ship body; the buoyancy surface element is used for dividing the ship body into a plurality of discrete planes, and each discrete plane is called as a buoyancy surface element; establishing a visual model of a ship body; carrying out parameter association on a physical model of a ship body and a visual model of the ship body; rendering and visual simulation are carried out, and a hull refinement model is established. The invention provides a modeling method which is based on a virtual reality technology, can realize parameter matching design and stress calculation of ship bodies with different shapes and sizes, and can adjust the design of the ship body shape at any time according to design requirements, so that designers can quickly establish a ship body model.

Description

A fast modeling method of ship hull based on buoyancy surface element

technical field

The invention relates to the technical field of virtual simulation, in particular to a method for rapid modeling of ship hulls based on buoyancy surface elements.

Background technique

The buoyancy dynamics modeling of the hull is an important part of the hull design. In the current iteration of hull design, the main testing methods are the experimental method and the Computational Fluid Dynamics (CFD) method.

The experimental method is the most reliable method to study the manoeuvrability of the hull under wave conditions. This method conducts experiments in the tank by constructing a scaled model of the ship type. However, the experimental method has high cost and low efficiency due to the production of its solid model and the tank, and it occupies an area of space.

The CFD method is one of the most mainstream methods in current engineering applications. The target project of this modeling method is relatively single. After replacing the project, it is often necessary to completely redesign the modeling. When multiple models are required, the reuse rate between the models is low, and the overall The design iteration process is slow; and the traditional fluid calculation is an extremely complex program. The virtual fluid calculation of large hulls often requires large workstations to do operations for hours or even days. Coupling effects may cause erroneous results for mesh simplification. In the early stage of design, the design of the hull often pays more attention to the overall control rather than individual details. Therefore, the CFD method is lacking in the calculation efficiency of the macro-control stage in the early design stage, and cannot meet the rapid modification plan in the early stage of the design stage. efficiency requirements.

The dynamic modeling of the hull by means of virtual simulation can reduce to a certain extent the repeated modeling caused by the different size and shape of the hull in the traditional dynamic modeling, thereby improving the efficiency of the design iteration process.

The application of virtual reality technology started late, especially for ordinary hulls, real-time calculation of sway is not important, and the wave resistance of the ship can be estimated according to the empirical formula. However, for special ship types, such as aircraft carriers that need to undertake carrier-based aircraft take-off and landing tasks, it is very important to calculate the sway of the hull under different wave levels in real time, otherwise it will cause great difficulties for the pilots to take off and land, and my country's aircraft carriers have just started in 2012. , the research on the construction of the aircraft carrier is still preliminary. Therefore, it is urgent to realize the rapid modeling of the hull in the virtual reality environment on the aircraft carrier.

SUMMARY OF THE INVENTION

Aiming at the above-mentioned technical problems in the related art, the present invention relies on the virtual reality technology, uses the PhysX physics engine to establish a physical model of the hull, and uses the Unity3D engine to establish a visual model, so as to provide a kind of parameter matching design and Force calculation, and the modeling method that can adjust the hull shape design at any time according to the design requirements, so that designers can quickly build a hull model, which can be used for early iterative design of designers, virtual training of personnel on board, etc.

In order to realize the above-mentioned technical purpose, the technical scheme of the present invention comprises the following steps:

S1: Design the main parameters of the hull, and establish a rough three-dimensional model of the hull;

S2: Arrange the position of the center of mass and divide the buoyancy surface elements on the rough three-dimensional model of the hull, and perform preliminary simulation according to the sum of the buoyancy of the buoyancy bodies corresponding to each of the buoyancy surface elements to establish a physical model of the hull; The buoyancy surface element refers to dividing the hull into a plurality of discrete planes, and each of the discrete planes is called a buoyancy surface element;

S3: adjust parameters according to the simulation result of the physical model of the hull;

S4: determine whether the physical model of the hull reaches the expected target, if so, skip to S5, otherwise, skip to S1;

S5: establish a visual model of the hull;

S6: Perform parameter association between the physical model of the hull and the visual model of the hull;

S7: determine whether the physical model of the hull and the visual model of the hull are correctly associated, if so, skip to S8, otherwise, skip to S6;

S8: Rendering and visual simulation are performed, and a detailed model of the hull is established;

S9: Determine whether the refined model of the hull achieves the expected target, and if so, save the design scheme, otherwise, skip to S5.

Further, in S2, the position of the center of mass and the division of buoyancy surface elements are arranged on the rough three-dimensional model of the hull, and a preliminary simulation is performed according to the sum of the buoyancy of the buoyancy bodies corresponding to each of the buoyancy surface elements to establish the The specific steps for the physical model of the hull include:

S21: Determine the number n of the buoyancy panel, and divide the area of the buoyancy panel according to the shape of the bottom of the hull;

S22: Judging the calculation requirements, whether the calculation speed is required to be greater than the calculation accuracy, if so, skip to S23, otherwise, skip to S24;

S23: Perform random sampling calculation on the buoyancy surface element;

S24: Perform fixed panel sampling calculation on the buoyancy panel;

S25: Scan the plumb bob of each buoyancy surface element upward to generate each buoyant body corresponding to each of the buoyancy surface elements, and obtain the characteristic volume of each of the buoyancy bodies, so as to calculate each of the buoyancy bodies The water immersion ratio δ;

S26: Calculate the buoyancy F _buoyancy of each of the buoyancy bodies, and obtain the sum of the buoyancy of all the buoyancy bodies;

S27: Perform a visual simulation to establish a physical model of the hull; the performing visual simulation to establish a physical model of the hull is realized by using the Unity3D engine and the PhysX engine.

Further, in S21, the number n of the buoyancy surface elements satisfies: 50<n<500.

Further, in S21, the area of the buoyancy surface element should cover all parts of the hull immersed in the water surface, and be a closed area; for a symmetrical hull, the area of the buoyancy surface element includes a symmetrical area.

Further, in S23, the random surface element sampling is to randomly select some of the buoyancy surface elements for sampling calculation, so as to reduce the amount of calculation.

Further, in S24, the sampling of the fixed surface elements may be calculated by sampling all the buoyancy surface elements at a fixed step size.

Further, in S24, the sampling of the fixed panel may also be a sampling calculation performed on a preselected part of the buoyancy panel from all the buoyancy panels.

Further, in S25, the calculation formula of the water immersion ratio δ of the buoyant body is:

Wherein, H ₁ is the wave height at the point where the plumb weight of the geometric center of the buoyancy surface element is upward; H ₂ is the edge height of the buoyant body at the point where the plumb weight of the geometric center of the buoyancy surface element is upward; H ₃ is the buoyancy force The height of the geometric center of the surfel.

Further, in S26, the calculation formula of the buoyancy F _buoyancy of the buoyant body is:

Among them, C _B is the global buoyancy adjustment constant, ideally the value of C _B is 1; ρ _water is the density of water; g is the gravity constant; V _volume is the volume of the hull; C _count is the selection of each frame in the Unity3D engine the number of buoyancy panels.

Preferably, in S6, the parameter association is mainly reflected in the position of the center of mass, the geometric center position of the buoyancy surface element, and the position and direction of the propeller thrust.

Beneficial effects of the present invention:

1) The present invention is based on virtual reality technology, has short cycle and low cost, and does not have high requirements on site and physical model by experimental method. Using PhysX to quickly complete the engineering calculation of dynamics in the early stage of design, and using Unity3D to visualize it, allows designers to perform realistic and reliable task simulations through computers in the early stage, which has far-reaching significance for the entire design cycle and future training exercises .

2) The present invention has low requirements for computer computing power, and the single-step computing time is less than 0.02 seconds, which meets the real-time requirements of virtual reality. Through the method provided by the present invention, designers can quickly adjust different parameters according to different hull sizes and shapes, and quickly obtain intuitive force calculation, evaluate and modify the design method at an early stage, so as to iteratively modify the hull design, which greatly improves the design. work efficiency.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. In the embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

1 is a flowchart of a modeling method according to an embodiment of the present invention;

Fig. 2 is the flow chart of establishing the physical model of the hull according to the embodiment of the present invention;

Fig. 3 is the crude three-dimensional model of the hull of the embodiment of the present invention;

4 is a schematic diagram of the division of the buoyancy surface element of the hull according to the embodiment of the present invention;

5 is a schematic diagram of a single buoyancy body according to an embodiment of the present invention;

6 is a schematic diagram of the calculation of the water immersion ratio of a single buoyancy body according to an embodiment of the present invention;

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the protection scope of the present invention.

Referring to FIG. 1, an embodiment of the present invention provides a method for rapid modeling of hull based on buoyancy surface elements, including the following steps:

S1: Design the main parameters of the hull and establish a rough 3D model of the hull;

The main parameters of the hull include: overall length, length between vertical lines, moulded width, moulded depth, draft, displacement, propeller position, rudder surface position, etc. The rough three-dimensional model of the hull is established as shown in Figure 3.

S2: Arrange the position of the center of mass and divide the buoyancy surface elements on the rough 3D model of the hull, and conduct preliminary simulation according to the sum of the buoyancy of the buoyancy bodies corresponding to each buoyancy surface element to establish the physical model of the hull; the buoyancy surface element refers to the It is divided into multiple discrete planes, each discrete plane is called a buoyancy surface element, and the buoyancy condition of the hull is calculated in real time according to the buoyancy surface element; the sum of the buoyancy provided by all the buoyancy surface elements should be equal to the hull displacement;

The specific steps for establishing the physical model of the hull are shown in Figure 2:

S21: Determine the number n of buoyancy surface elements, and divide the area of buoyancy surface elements according to the shape of the bottom of the hull;

The division of buoyancy surface elements should follow the principle of uniformity and rationality, and should meet the following specific requirements:

(1) The number of buoyancy surface elements is reasonable;

(2) Symmetrical hulls require symmetrical buoyancy surface elements;

(3) The buoyancy panel should cover all parts of the hull that may be submerged in the water;

(4) The buoyancy surface elements are assembled into a closed body and can reflect the complete basic shape of the hull.

The more buoyancy surface elements are divided, the more realistic the visualization results are, but the computing power of the computer or workstation is also higher, and 50-500 buoyancy surface elements can be divided according to the size of the hull. In the embodiment of the present invention, 350 buoyancy surface elements are taken to obtain a schematic diagram of the division of the buoyancy surface elements of the hull as shown in FIG. 4 .

S22: Judging the calculation requirements, whether the calculation speed is required to be greater than the calculation accuracy, if so, skip to S23, otherwise, skip to S24;

According to the actual hull modeling requirements, if it is required to realize the modeling quickly, in the case of ensuring a certain accuracy, skip to step S23 to perform random sampling calculation on the buoyancy surface element; otherwise, skip to step S24 to calculate the buoyancy surface element The surfel performs fixed surfel sampling calculation.

S23: Perform random sampling calculation on the buoyancy surface;

For the complex shape of the hull, the division of buoyancy surface elements can be as many as several hundred, and it is a burden for the computer to let them participate in the calculation of each step length at the same time. Based on the principle of virtual reality optimization, in order to reduce the amount of calculation, some random positions are selected for calculation in each frame, instead of all participating in the calculation, which is called the random panel sampling method.

S24: Perform fixed panel sampling calculation on the buoyancy panel;

Fixed panel sampling is to sample and calculate all buoyancy panels in a single step, or to preselect some buoyancy panels that can represent the properties of the buoyant body from all buoyancy panels for sampling and calculation.

S25: Scan the plumb bob of each buoyancy surface element upward to generate a buoyant body corresponding to each buoyancy surface element, and obtain the characteristic volume of each buoyancy body, thereby calculating the flooding ratio δ of each buoyancy body;

Scan the plumb bob of each buoyant surface element selected in step S24 or S25 upward to generate a buoyant body corresponding to each buoyancy surface element. The schematic diagram of a single buoyant body is shown in Figure 5, and the characteristic volume of each buoyant body is denoted as V _cell , see Fig. 6, further calculate the flooding ratio of a single buoyant body. In Fig. 6, V ₁ and V ₂ are both buoyancy bodies. After dividing the smooth bottom surface of the hull into the sum of multiple buoyancy surface elements, the Take a reference point from the geometric center, read the height H ₃ of the geometric center of the buoyancy surface element, and shoot the ray vertically upward from the reference point. The height of the edge is recorded as H ₂ , and the height of the ocean surface that hits is the height of the wave at the point where the plumb weight of the geometric center of the buoyancy surface element is upwards, recorded as H ₁ . Here, _H1 is the local dynamic value generated by wave modeling and varies with the local sea surface height. In order to meet the requirements of real-time, define the water immersion ratio δ of a single buoyant body:

If the buoyant body is completely submerged in water, that is, H ₂ <H ₁ , then δ=1; if the buoyant body is completely out of the water, that is, H ₃ >H ₁ , then δ=0.

S26: Calculate the buoyancy F _buoyancy of each buoyant body, and obtain the buoyancy F of the hull;

According to the selected buoyancy surface element, the buoyancy calculation is performed on the hull. The force on the hull is simplified as: buoyancy, resistance, and buoyancy and resistance are independent of each other. Here, the flow force generated by waves is not calculated for the time being.

1) Buoyancy

According to the buoyancy formula:

F _buoyancy = ρ _water gV _dis (3)

Among them, ρ _water is the density of water, g is the gravitational constant, and V _dis is the drainage volume. Therefore, it is necessary to convert the area of each buoyancy panel into a drainage volume.

An intuitive solution is V _dis =S _cell *h, where S _cell is the projection of the area of a single buoyancy panel on the horizontal plane, and h is the water entry depth# of a single buoyancy panel area, but S _cell is a quantity that is not easy to solve. , the bottom normal of each buoyancy surface element changes every frame, which means that each buoyancy surface element needs to solve one more normal three-dimensional vector in each frame.

In order to further meet the requirements of real-time, this method simplifies all other parts except the water entry depth as constants, combined with the water immersion ratio δ, there are:

V _dis =S _cell h = V _cell δ (4)

In formula (5), V _volume is the volume of the hull, and C _count is the number of buoyancy surface elements taken in each frame.

Then, the buoyancy F _buoyancy of the buoyancy body corresponding to a single buoyancy surface element can be simplified as:

Among them, _CB is the global buoyancy adjustment constant, ideally the value of _CB is 1; in formula (2), only the water immersion ratio δ can be obtained to obtain the buoyancy F _buoyancy of a single buoyant body, which reduces the calculation steps and speeds up the the speed of modeling.

Summing the F _buoyancy of all buoyancy panels provides the sum of the buoyancy of the hull, F _{buoyancy(total)} :

F _{buoyancy(total)} =C _B ρ _water gV _volume δ _total (6)

2) Resistance

According to the resistance formula:

F _drag = -0.5ρ _water SV ² (7)

Among them, S is the characteristic area of the buoyancy surface element, and V is the speed of the object motion.

Similar to the solution of buoyancy, the characteristic area S of the buoyancy surface element is a variable affected by the velocity V direction of the buoyancy surface element. In order to simplify the calculation, this paper avoids solving the characteristic area S of each buoyancy surface element, and adopts the same method as in the buoyancy solution. method, introducing the flooding ratio δ to estimate the characteristic area S of the buoyancy surface element.

Among them, S _area is the total surface area of the set of buoyancy surface elements of the hull, and its value can be directly obtained by the software in 3D modeling.

Then when a single buoyant surface moves at V _local speed in water, the resistance F _drag generated can be simplified as:

where _CD is the global resistance adjustment constant, which should ideally be 1.

The sum of F _drag of each buoyancy surface element provides the sum of the resistance of the hull F _drag(total) :

F _drag(total) =-0.5C _D ρ _water S _area δ _total |V _local | ² (10)

According to the sum of buoyancy and resistance, the buoyancy F of the hull is calculated by the PhysX engine.

S27: Perform a visual simulation to establish a physical model of the hull; the performing visual simulation to establish a physical model of the hull is realized by using the Unity3D engine and the PhysX engine.

Unity3D is one of the most widely used game engines at present. Its realistic visual effects and excellent built-in physical property calculation function make it favored by many developers in the field of virtual simulation. At the same time, its personal version is free and open source code makes it easy to upload. Developers can use Unity3D to quickly and easily modify different physical modeling, and display their visual models more intuitively, greatly improving the speed of the process.

PhysX is a relatively well-known physical simulation software. It performs operations through CPU or independent floating-point processor to simulate real physical effects, so that in virtual simulation, the motion of virtual objects is consistent with the laws of real world physics, and virtual simulation is increased. The realism of the simulation.

Through PhysX and Unity3D two engines, you can create a visual simulation in the computer, and at the same time meet the requirements of realistic visual effects and reliable physical motion.

S3: Adjust the parameters according to the simulation results of the physical model of the hull;

S4: Determine whether the physical model of the hull reaches the expected target, if so, skip to S5, otherwise, skip to S1;

S5: Establish a visual model of the hull;

S6: Parameter association between the physical model of the hull and the visual model of the hull;

The parameter association is mainly reflected in the position of the center of mass, the geometric center of the buoyancy surface element, and the position and direction of the propeller thrust.

S7: Determine whether the physical model of the hull and the visual model of the hull are correctly related, if so, skip to S8, otherwise, skip to S6;

S8: Rendering and visual simulation are performed, and a detailed model of the hull is established;

Refine the texture, lighting, complete the rendering of the model, and enhance the realism of the visual model.

S9: Determine whether the refined model of the hull achieves the expected goal, and if so, save the design scheme, otherwise, skip to S5.

It should be understood by those skilled in the art that the sequence of the method steps provided in the above embodiments may be adaptively adjusted according to actual conditions, or may be performed concurrently according to actual conditions.

All or part of the steps in the methods involved in the above embodiments may be completed by instructing the relevant hardware through a program, and the program may be stored in a storage medium readable by a computer device for executing the methods described in the above embodiments. all or part of the steps. The computer equipment includes: personal computer, server, network equipment, intelligent mobile terminal, smart home equipment, wearable intelligent equipment, vehicle-mounted intelligent equipment, etc.; the storage medium includes: RAM, ROM, magnetic disk, magnetic tape, optical disk, Flash memory, U disk, mobile hard disk, memory card, memory stick, network server storage, network cloud storage, etc.

The "frame" is the operation unit of the Unity3D engine, which means that several pictures are displayed per second, and each frame is calculated once. For example, 30 frames means that 30 pictures are displayed per second.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (7)

1. A hull rapid modeling method based on a buoyancy surface element is characterized by comprising the following steps:

s1: designing main parameters of the ship body, and establishing a rough three-dimensional model of the ship body;

s2: arranging a centroid position and dividing buoyancy surface elements on the rough three-dimensional model of the ship body, performing preliminary simulation according to the buoyancy sum of the buoyancy bodies corresponding to each buoyancy surface element, and establishing a physical model of the ship body; the buoyancy surface element is used for dividing the ship body into a plurality of discrete planes, and each discrete plane is called as a buoyancy surface element;

s3: adjusting parameters according to a simulation result of the physical model of the ship body;

s4: judging whether the physical model of the ship body reaches an expected target or not, if so, jumping to S5, otherwise, jumping to S1;

s5: establishing a visual model of the ship body;

s6: performing parameter association on the physical model of the ship body and the visual model of the ship body;

s7: judging whether the physical model of the ship body is correctly associated with the visual model of the ship body, if so, jumping to S8, otherwise, jumping to S6;

s8: rendering and visual simulation are carried out, and a detailed model of the ship body is established;

s9: judging whether the hull refinement model reaches an expected target or not, if so, saving the design scheme, otherwise, jumping to S5;

in S2, the step of arranging a centroid position and dividing buoyancy surface elements on the rough three-dimensional model of the ship body, and performing preliminary simulation according to the sum of buoyancy of the buoyancy bodies corresponding to each buoyancy surface element, and the step of establishing the physical model of the ship body specifically includes:

s21: determining the number n of the buoyancy surface elements, and dividing the area of the buoyancy surface elements according to the shape of the bottom of the ship body;

s22: judging the calculation requirement, judging whether the calculation speed is required to be greater than the calculation precision, if so, jumping to S23, otherwise, jumping to S24;

s23: carrying out random surface element sampling calculation on the buoyancy surface element;

s24: carrying out fixed surface element sampling calculation on the buoyancy surface element;

s25: scanning each buoyancy surface element upwards in a plumb mode to generate each buoyancy body corresponding to each buoyancy surface element, and acquiring the characteristic volume of each buoyancy body, so that the soaking proportion delta of each buoyancy body is calculated;

s26: meterCalculating the buoyancy F of each buoyancy body_buoyancyAnd the sum of the buoyancy of all the buoyancy bodies is obtained, namely the buoyancy F of the ship body;

s27: carrying out visual simulation, and establishing a physical model of the ship body; performing visual simulation, and establishing a physical model of the ship body by using a Unity3D engine and a Physx engine;

in S25, the formula for calculating the immersion ratio δ of the buoyant body is:

wherein H₁The height of the sea wave at the upper part of the plumb bob of the geometric center of the buoyancy surface element; h₂The height of the edge of the buoyancy body at the geometric center of the buoyancy surface element and above the plumb direction is defined; h₃The height of the geometric center of the buoyancy surface element is defined as the height of the geometric center of the buoyancy surface element;

in S26, the buoyancy F of the buoyant body_buoyancyThe calculation formula of (2) is as follows:

wherein, C_BThe value of CB is ideally 1 for a global buoyancy adjustment constant; rho_waterIs the density of water; g is a gravity constant; v_volumeIs the volume of the hull; c_countThe number of buoyancy bins chosen for each frame in the Unity3D engine.

2. The hull rapid modeling method based on buoyancy surface elements according to claim 1, characterized in that in S21, the number n of buoyancy surface elements satisfies: 50< n < 500.

3. The method for rapidly modeling a hull based on buoyancy panels according to claim 2, wherein in S21, the area of the buoyancy panel should cover all parts of the hull immersed in the water surface and is a closed area; for a symmetrical hull, the area of the buoyancy surface element comprises a symmetrical area.

4. The hull rapid modeling method based on buoyancy surface elements according to claim 3, characterized in that in S23, the random surface element sampling is to randomly select part of the buoyancy surface elements for sampling calculation, so as to reduce the calculation amount.

5. The hull rapid modeling method based on buoyancy bins according to claim 4, characterized in that in S24, the fixed bin sampling is a sampling calculation for all the buoyancy bins by a fixed step.

6. The method according to claim 4, wherein in S24, the fixed bin sampling is a sampling calculation from a preselected portion of all the buoyancy bins.

7. The method for rapidly modeling a hull based on a buoyancy bin according to any one of claims 1 to 6, wherein in S6, the parameter association is mainly embodied in the position of a centroid, the position of a geometric center of the buoyancy bin, the position of thrust of a propeller and the direction.

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