三维图形引擎中流体类似物的仿真方法研究
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摘要
三维图形引擎中对流体类似物的仿真方法一直是国内外研究机构及相关人员关注的焦点。多年来，大量研究学者对这类仿真问题在运动建模、行为建模、绘制方法等方面，不断提出新的解决办法，也使得这类仿真方法在大量的军事态势、模拟训练、灾难应急、城市仿真、展览展示等等应用中推广开来。
为满足各类三维图形应用和仿真的需求，本文以纳维-斯托克斯流体动力学体系为理论基础，对实时群体行为仿真、快速粒子动力学模拟和基于空气动力学的大规模云场模拟等几个关键技术进行了深入研究。本文取得的创新研究成果包括：
(1)针对大规模群体行为的细节层次问题，提出了群体的渐进层次框架，将流体动力学和自主智能代理混合建模，并实现了两种技术之间的平滑过渡。基于欧拉形式的Navier-Stokes方程和连续性方程，解决了群体行为的仿真约束、路径规划、动力学模拟等问题。提出了混合GLOD和Impostors的高效绘制，在不同的观察距离上使用多种精度的角色模型表达方式，有效地降低了大规模群体的实时绘制多边形数。
(2)对基于Navier-Stokes方程的光滑粒子动力学方程作一系列的理论推导，对密度和力场的计算给出了详细的数值分析；特别在光滑核函数的选择上，达到紧支撑、归一化等仿真要求。提出了基于空间哈希的快速邻域查询方法，极大的提高了数万个粒子数量级的邻域查询效率，并且无需维护全局空间信息。实现了基于顶点变形的快速表面重建，采用基于预设表面几何的顶点变形法提取流体表面，该方法比传统的Marching Cube方法计算速度提高数倍。
(3)提出了一种基于空气动力学原理改进的三维云场模拟方法，考虑大气运动条件下云的特性，建立云场的动力学模型。提出了基于基础纹理的云粒子近景绘制、基于正八边形环Impostor的云场远景绘制方法，提高大范围云层的渲染速度，达到降低面片数、加速绘制的目标。提出了基于大气散射原理的简化云场光照模型，仅计算单一散射光照模型对单个粒子的散射作用，在基本达到云场外观着色效果的前提下，大大减少了云粒子的光照计算量。对云场模拟在实验及应用中遇到的实际问题进行了讨论、分析，并提出了有效的解决方案，包括：卷云的建模、“穿云”时的“鸿沟”问题；云的流动性效果、着色和阴影处理、云层光晕效果；烟、雾的模拟效果以及战场爆炸特效等。
The fluid simulation method in the3D graphics engine has been the focus ofdomestic and foreign research institutions. In recent years, a large number of researcherscontinue to propose new solutions for such simulation problems in motion modeling,behavioral modeling, rendering methods, etc. It makes this type of simulation methodsto promote in many applications, including Military Situation, Simulation Training,Disaster Response, Urban Simulation, and Exhibition.
To meet the needs of various types of three-dimensional graphics applications andsimulations, this dissertation based on the Navier-Stokes equations, made an in-depthstudy of several key technologies, such as Real-time Crowd Behavior Simulation, theFast Particle Dynamics and Large-scale Cloud Simulation Based on the Aerodynamics.Main contributions of this dissertation include:
(1) To solve the problem of level of detail for a large-scale crowd behaviors, aprogressive-level model of large crowd has been proposed, which combines fluiddynamics with autonomous agents and achieves a smooth transition between the twotechnologies. Based on the Euler form of the Navier-Stokes equations and the continuityequation, several problems of crowd simulation have been solved, including constraints,path planning, and dynamics simulation. An efficient rendering method of mixed GLODand Impostors is proposed, which adopts multiple representations of the role model indifferent observation distances, and effectively reduces the polygon number of real-timerendering.
(2) Based on the smoothed particle hydrodynamics equations, a detailednumerical analysis is given for the calculation of density and force fields, and anadvisable choice of smooth kernels is made to meet the needs of Compact Support andnormalizable kernel. A neighbor query method based on spatial hashing is presented,which greatly improves the query efficiency of the tens of thousands of particles,without the maintenance of global spatial information. A fast surface reconstructionmethod based on the vertex deformation is realized. It extracts the fluid surface usingvertex deformation of the predefined geometry, and it is several times faster than the traditional Marching Cube.
(3) A Three-dimensional cloud simulation method is proposed based on theprinciple of aerodynamics improved. The close-range rendering of cloud particles basedon elemental textures and the distance rendering using Impostors of the regular octagonring are proposed, which improves the speed when rendering a wide range of cloud,reaches the target to reduce the number of polygons, accelerate draw. A simplifiedillumination model of cloud is presented based on the atmospheric scattering, whichcalculates single scattering light model on the single particle, and greatly reduces thecalculations of cloud particles lighting. Effective solutions are given for the cloudsimulation in experiments and applications, such as cirrus modeling,"hard lines"problems of in-clouds experience; cloud flowing effect, coloring and shading process,clouds halo; simulations of smoke, fog and battlefield explosion.
为满足各类三维图形应用和仿真的需求，本文以纳维-斯托克斯流体动力学体系为理论基础，对实时群体行为仿真、快速粒子动力学模拟和基于空气动力学的大规模云场模拟等几个关键技术进行了深入研究。本文取得的创新研究成果包括：
(1)针对大规模群体行为的细节层次问题，提出了群体的渐进层次框架，将流体动力学和自主智能代理混合建模，并实现了两种技术之间的平滑过渡。基于欧拉形式的Navier-Stokes方程和连续性方程，解决了群体行为的仿真约束、路径规划、动力学模拟等问题。提出了混合GLOD和Impostors的高效绘制，在不同的观察距离上使用多种精度的角色模型表达方式，有效地降低了大规模群体的实时绘制多边形数。
(2)对基于Navier-Stokes方程的光滑粒子动力学方程作一系列的理论推导，对密度和力场的计算给出了详细的数值分析；特别在光滑核函数的选择上，达到紧支撑、归一化等仿真要求。提出了基于空间哈希的快速邻域查询方法，极大的提高了数万个粒子数量级的邻域查询效率，并且无需维护全局空间信息。实现了基于顶点变形的快速表面重建，采用基于预设表面几何的顶点变形法提取流体表面，该方法比传统的Marching Cube方法计算速度提高数倍。
(3)提出了一种基于空气动力学原理改进的三维云场模拟方法，考虑大气运动条件下云的特性，建立云场的动力学模型。提出了基于基础纹理的云粒子近景绘制、基于正八边形环Impostor的云场远景绘制方法，提高大范围云层的渲染速度，达到降低面片数、加速绘制的目标。提出了基于大气散射原理的简化云场光照模型，仅计算单一散射光照模型对单个粒子的散射作用，在基本达到云场外观着色效果的前提下，大大减少了云粒子的光照计算量。对云场模拟在实验及应用中遇到的实际问题进行了讨论、分析，并提出了有效的解决方案，包括：卷云的建模、“穿云”时的“鸿沟”问题；云的流动性效果、着色和阴影处理、云层光晕效果；烟、雾的模拟效果以及战场爆炸特效等。
The fluid simulation method in the3D graphics engine has been the focus ofdomestic and foreign research institutions. In recent years, a large number of researcherscontinue to propose new solutions for such simulation problems in motion modeling,behavioral modeling, rendering methods, etc. It makes this type of simulation methodsto promote in many applications, including Military Situation, Simulation Training,Disaster Response, Urban Simulation, and Exhibition.
To meet the needs of various types of three-dimensional graphics applications andsimulations, this dissertation based on the Navier-Stokes equations, made an in-depthstudy of several key technologies, such as Real-time Crowd Behavior Simulation, theFast Particle Dynamics and Large-scale Cloud Simulation Based on the Aerodynamics.Main contributions of this dissertation include:
(1) To solve the problem of level of detail for a large-scale crowd behaviors, aprogressive-level model of large crowd has been proposed, which combines fluiddynamics with autonomous agents and achieves a smooth transition between the twotechnologies. Based on the Euler form of the Navier-Stokes equations and the continuityequation, several problems of crowd simulation have been solved, including constraints,path planning, and dynamics simulation. An efficient rendering method of mixed GLODand Impostors is proposed, which adopts multiple representations of the role model indifferent observation distances, and effectively reduces the polygon number of real-timerendering.
(2) Based on the smoothed particle hydrodynamics equations, a detailednumerical analysis is given for the calculation of density and force fields, and anadvisable choice of smooth kernels is made to meet the needs of Compact Support andnormalizable kernel. A neighbor query method based on spatial hashing is presented,which greatly improves the query efficiency of the tens of thousands of particles,without the maintenance of global spatial information. A fast surface reconstructionmethod based on the vertex deformation is realized. It extracts the fluid surface usingvertex deformation of the predefined geometry, and it is several times faster than the traditional Marching Cube.
(3) A Three-dimensional cloud simulation method is proposed based on theprinciple of aerodynamics improved. The close-range rendering of cloud particles basedon elemental textures and the distance rendering using Impostors of the regular octagonring are proposed, which improves the speed when rendering a wide range of cloud,reaches the target to reduce the number of polygons, accelerate draw. A simplifiedillumination model of cloud is presented based on the atmospheric scattering, whichcalculates single scattering light model on the single particle, and greatly reduces thecalculations of cloud particles lighting. Effective solutions are given for the cloudsimulation in experiments and applications, such as cirrus modeling,"hard lines"problems of in-clouds experience; cloud flowing effect, coloring and shading process,clouds halo; simulations of smoke, fog and battlefield explosion.
引文
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