基于改进的水力侵蚀算法的腐蚀化地形生成

提出一种新颖的计算机游戏场景地形生成技术.通过引入水量图和沉积物图来改进传统的水力侵蚀算法,以仿真自然地形因风化因素造成的腐蚀化现象,从而增强地形模拟真实感;为了保证游戏实时性,采取四种加速策略进行整体算法优化.实验结果证明,算法适用于为计算机游戏和动画生成实时的真实感地形效果.     

顾及沟谷结构特征的数字地形模拟生成方法

利用计算机模拟生成的数字地形,其真实感很大程度上来源于其包含的与真实地形相似的结构特征和空间关系。为了使模拟生成的随机地形具有流水地貌中水系与地形相互套合的空间形态关系,引入一种新的数字地形模拟生成方法。该方法利用受粘结系数和平均场参数控制的受限扩散凝聚（DLA）模型生成谷底线,并在此基础上利用逐级膨胀操作模拟生成数字地形。实验结果证明,使用该方法生成数字地形在过程上具有良好的可控性,在形态结构上具有随机性,且具有类似于自然环境中的树状沟谷结构特征。     

大规模地形建模的研究

针对目前各种大规模地形建模的优缺点,并结合目前流行的地形建模方法,提出一种较为真实的地形建模方案。为达到更真实的模拟,对地形泥土腐蚀现象做了研究,提出了一种基于细胞自动机的腐蚀模拟方法。     

应用分形仿真水墨扩散轮廓

针对水墨在宣纸上扩散后会出现较明显的具有自相似特性的轮廓线这一特点,提出一种仿真中国水墨画扩散边界的实现方法．该方法通过流体仿真模型产生扩散笔迹,利用分形在扩散笔迹的最外层模拟一条不规则的扩散边界,并填充两者之间的空隙,使得扩散效果更自然、逼真．实验结果表明,借助分形模拟的扩散效果接近真实的水墨画效果．     

大规模真实感固流交互实时绘制方法

针对大规模水面固流交互模拟过程中物体运动和水波扩散不真实且实时性差的问题,提出一种大规模水环境实时交互绘制方法.首先采用分区模拟的方法取代传统的整体高度细节方法,实时模拟大型水域环境,降低计算复杂度;然后在物体运动过程中引入波浪力,结合自定义风力因子实现物体随波逐流的运动效果;在交互波生成过程中,引入正态分布函数对物体三角形面片进行计算,以增强水面波生成的真实感;最后采用结合流体黏度和表面污染形成的衰减公式来改进波动方程,使水波扩散效果更加平滑稳定.实验结果表明,在保证实时性的基础上,该方法能更真实地模拟物体在水面上的运动,同时有效地表现交互过程中水波的生成与扩散过程.     

基于参考图像的彩墨画快速渲染法

通过对彩墨画创作过程的模拟,提出一种基于参考图像的彩墨画快速渲染算法,其模拟过程分为铺底模拟和细节刻画两个阶段。在铺底阶段,利用平均曲率流与冲击滤波的组合对图像进行细节简化,并通过对颜色空间的截取和拉伸数字模拟彩墨画的留白特征,同时提供基于PatchMatch算法的颜色学习着色方法;在细节刻画阶段,针对墨水的扩散现象提出一个随机模拟扩散的公式,并给出模拟彩墨画描边手法的边界处理方法,最后进行纸张效果合成。实验结果表明,该算法能够快速地将参考图像渲染成具有彩墨画风格的艺术作品。     

基于MapReduce模型的侵蚀地形因子计算方法研究

针对传统侵蚀地形因子提取方法在处理海量数据时出现的瓶颈,提出一种基于MapReduce模型的侵蚀地形因子计算方法。该方法将并行计算模型MapReduce与改进的通用土壤流失方程（revised universal soil loss equation,RUSLE）相结合。利用最大坡降原理和B+树建立流向关系查找树来表现地形数据的相关性;利用MapReduce模型进行流路查找与栅格汇聚来替代传统正反向遍历算法,解决侵蚀地形因子计算过程中汇水和累计坡长的计算效率问题。实验结果表明,对于基于海量数字高程模型数据的地形因子提取,该方法能够在计算精度允许的范围内有效提高效率。     

WCDMA随机呼叫冲击测试模型研究

真实的环境下,呼叫是随机发生的,并且有着自己的分布规律.测试环境要尽可能的接近真实环境,在冲击测试中,各个UE的行为也要尽可能的接近商用环境,这样的测试结果才具有可信度.提出一种随机冲击测试模型,该随机冲击测试模型可以有效模拟真实商用环境下UE的行为,对NodeB进行信令和数据冲击测试,可以有效验证基站的反应速度和性能,以及协议的正确性.     

流体动画模拟的一种新方法

近年来基于物理的流体模拟成为计算机动画领域中的一个极具有挑战性的问题,针对有限差分方法和有限元方法对流体动画模拟的局限性,利用光滑流体动力学方法实现了流体的动画模拟,该方法不依赖网格,适合于计算具有极大变形的流体计算,溃坝坍塌现象的模拟实验表明：方法既能模拟流体的整体演进特征,又能表现流体飞溅、破碎的现象,能够真实有效地模拟水流运动情况。     

基于物理动力学的烟雾建模与渲染

为了提高三维场景中烟雾模拟的真实性,以粒子系统为基础,对烟雾的运动模型与渲染方法进行了研究.为模拟烟雾扩散特性,提出预定义扩散范围的方法来近似控制烟雾的整体扩散区域,并通过线性增大粒子半径来模拟烟雾粒子的自身扩散.在烟雾运动过程中,基于动力学原理,建立了一种较准确的烟雾运动模型,并分析了烟雾粒子扩散过程中风对粒子的影响.在渲染时,为避免传统粒子系统渲染出的颜色过于平滑,利用图形处理器可编程特性,引入法线贴图计算粒子表面的散射光叠加到粒子本身颜色上,增加了烟雾的层次感和颗粒感.实验结果表明,该实现方法粒子运动更加真实,视觉效果更加逼真.     

Real-time simulation of physically based on-surface flow

Although many papers have been published in the field of fluid simulation, little attention has been paid to on-surface flow involving wetting and stain transportation as well as erosion and deposition phenomena. In this paper, we introduce nonzero divergence in the mass equation of Navier–Stokes equations to simulate water penetration from on-surface flow into substrate material. Also, the volume of fluid method is adopted to track the free surface. With a computation of the actual amount of absorbed water we render the wetting effects with fully dry and fully wet texture images simultaneously. Using our model, the on-surface flow that accompanies water absorption can be simulated realistically in real time with OpenGL preview rendering. Experimental results illustrate that our model can be widely applied to solve various problems related to on-surface flow.     

A new,flexible and widely applicable software package for the simulation of one-dimensional moisture flow: SoWaM

Most one-dimensional soil moisture flow simulation models have restricted applicability due to (amongst other things): i) insufficient user flexibility; ii) a lack of user friendliness; iii) dependency on scale, temporal and/or spatial, and iv) fixed boundary conditions. Therefore, we developed a simple and highly flexible software package to simulate, visualize and analyze 1-D moisture flow in soils: SoWaM (Soil Water Model). The package has a modular setup and consists of a range of tools to visualize, analyze and compare input data and results. Soil hydraulic properties for each specified soil layer can be defined by either Van Genuchten parameters or cubical splines. Since the model does not impose limits on element size or time interval, it is possible to perform simulations in very high detail, both spatially and temporally. Furthermore, four different criteria for irrigation scheduling have been implemented. The SoWaM package provides an accurate, simple and highly flexible tool to simulate soil moisture flow and to evaluate the effects of various factors on soil water movement, such as timing and amount of irrigation, soil hydraulic properties and soil layering. Results of a case study are presented to illustrate model performance.     

Hydraulic erosion

This paper presents a generalized solution to modelling hydraulic erosion using ideas from fluid mechanics. The model is based on the Navier–Stokes equations, which provide the dynamics of velocity and pressure. These equations form the basis for the model to balance erosion and deposition that determine changes in the layers between water and erosion material. The eroded material is captured and relocated by water according to a material transport equation. The resulting model is fully 3D and is able to simulate a variety of phenomena including river meanders, low hill sediment wash, natural water springs and receding waterfalls. The simulations show the terrain morphogenesis and can be used for animations as well as for static scene generation. Copyright © 2006 John Wiley & Sons, Ltd.     

SOILPSI: a potential-driven three-dimensional soil water redistribution model—description and comparative evaluation

ECOPHYS, an individual-based process model for poplar, requires a three-dimensional soil water redistribution model to simulate soil water dynamics, plant uptake, and root growth. SOILPSI is a potential-driven water redistribution model based on the RHIZOS rhizosphere simulator. It expands on RHIZOS by calculating water flux based on water potential, and has a macropore flow mode to allow rapid drainage of the soil. SOILPSI simulates water flux in three dimensions and accounts for slope. SOILPSI was evaluated by comparing model output to soil moisture data collected under bare soil conditions. AMMI analysis of a date×depth matrix of differences between simulated and observed soil moisture content showed that excluding the two shallowest soil layers resulted in a difference matrix that conformed to an additive model. The grand mean predicted values were within 2% of the observed values, and 50 of 56 predicted values were within 5% of the observed values. Better agreements between simulated and observed soil moisture content were observed deeper in the soil profile and later in the season. Agreement between SOILPSI and field conditions was consistently more accurate than RHIZOS. Improving simulation of evaporative flux at the soil surface would improve simulation accuracy in the upper horizons.     

基于波环粒子的实时水波仿真方法

为了降低水波模拟过程中的计算成本并提高其扩散现象的逼真度,提出一种基于波环粒子包的实时二维平面水波仿真方法。该方法采用波环粒子为基本计算单元,粒子内部继承“波包”的概念,使用多个频段水波叠加的方式再现水波视觉效果。在计算水波反射过程时,通过添加镜像波源的形式减少碰撞计算,避免复杂几何判定。为适应不同硬件的计算性能差异,该方法提供额外的计算精度参数,可针对不同硬件计算能力调节水波反射计算复杂度。实验结果表明,该方法可使用较少的粒子模拟出较为真实的水波运动,且避免了碰撞反射后水波断裂的问题。在相同硬件平台上的性能测试显示,所提波环仿真方法的渲染帧率比传统波包算法高出至少60%,在一些水波状态特别复杂的情况下可达到400%以上的加速效果。     

控压钻井井下气侵工况的自适应参数及状态估计

针对控压钻井过程中井下可能发生气侵的特殊工况,提出一种可在异常工况下估计井底压力,并借此判断异常工况的方法.首先,基于简化的漂移通量模型,在传统控压钻井水力学模型中添加气体膨胀项,建立控压钻井气液两相流模型;其次,将井下环空摩擦积分和井底气侵量视为未知参数,将井底流量视为未知状态,设计一种可对未知参数以及未知状态进行联合估计的自适应观测器,并以此为基础估计井底压力;最后,通过仿真实验验证所提方法的有效性.仿真结果表明,所建气液两相流模型可在井下发生气侵时模拟井底压力变化,且所提观测器能实时准确地跟踪井底流量及压力变化.     

虚拟肝脏手术中的美兰注射实现技术研究

肝脏肿瘤切割手术中美兰注射过程是准确找到肿瘤所在位置的关键步骤之一。真实地模拟出美兰注射过程对虚拟肝脏肿瘤切割手术而言至关重要。针对虚拟手术中真实感的需求,提出了一种结合纹理映射技术的美兰注射模拟算法。运用扩散方程模拟了美兰在纹理表面的扩散过程,并结合保角映射算法将变化的纹理映射到虚拟手术中的三维网格表面。扩散方程能够真实地模拟出液体在物体表面扩散的过程,保角的纹理映射算法能够得到三维网格点的纹理坐标。实验结果表明,美兰注射过程的模拟算法能够模拟出虚拟肝脏肿瘤切割手术过程中的肿瘤标定,满足虚拟手术中的真实感需求。     

Document image binarization based on topographic analysis using a water flow model

This paper proposes a local adaptive thresholding method based on a water flow model, in which an image surface is considered as a three-dimensional (3-D) terrain. To extract characters from backgrounds, we pour water onto the terrain surface. Water flows down to the lower regions of the terrain and fills valleys. Then, the thresholding process is applied to the amount of filled water for character extraction, in which the proposed thresholding method is applied to gray level document images consisting of characters and backgrounds. The proposed method based on a water flow model shows the property of locally adaptive thresholding. Computer simulation with synthetic and real document images shows that the proposed method yields effective adaptive thresholding results for binarization of document images.     

一种面向虚拟环境的真实感水波面建模算法

给出了一种新型的模拟真实感水波面的建模算法．引入Perlin噪声作为水面高度场动态变化的激励源,依靠噪声的平滑特性来模拟水面连续动荡变化的效果．为了避免对每个水面网格点进行噪声计算,使用了准均匀B样条曲面来构造水波面,将噪声施加于B样条曲面的特征控制点,间接地控制水面高度场,这样在不增加噪声计算量的情况下可以对水面进行高分辨率的细分,而B样条曲面的生成速度依靠图形硬件的加速功能得以保证．用独立于视点的Cube Map纹理映射技术模拟了水面的反射效果,用跟踪视向量对应的折射向量的方法模拟了折射效果．实践证明,用该算法模型在普通PC平台上即可实时模拟真实感水波面．