地震波模拟中多轴复频移近似完全匹配层的吸收效果及稳定性

在进行地震波模拟计算的过程中用有限的计算区域模拟地下无限空间,需要进行边界截断.为了在边界处不产生虚假反射影响模拟结果,需要引入吸收边界条件.本文采用的近似完全匹配层是一种新型非分裂完全匹配层,计算效率较高.同时相比于其他非分裂完全匹配层,其还具有不改变方程的形式、易于实现等优势.但是当入射波角度较大,边界吸收效果变弱,且残留在边界中的能量使近似完全匹配层变得极其不稳定.多轴复频移近似完全匹配层的提出就是为了改善对大角度入射波的吸收并且提高边界的稳定性.通过实验模拟和矩阵特征值灵敏度来研究多轴复频移近似完全匹配层的吸收效果及稳定性.结果表明该方法不仅能够吸收掠入波,而且对常规入射波的吸收也得到提升,同时拥有更好的稳定性.     

基于小波变换和高斯函数的影像去噪方法研究

提出了小波变换与高斯函数相结合进行影像去噪的方法,在去除高斯白噪声的同时能够有效去除椒盐噪声。此方法是在小波域内结合小波变换的特点对高频子带分别进行高斯低通滤波,将滤波后的小波系数经过反变换后即可得到经过去噪后的影像。实验表明该方法不仅对高斯噪声和椒盐噪声去噪效果明显,而且保留了影像的细节信息,其滤波效果优于中值滤波和小波软阈值法。     

裸地蒸发过程的数值模拟

本文以能量平衡为基础,研究了裸地蒸发过程,并提出一个用Fonran语言编写的,在IBM-PC微机上通过的裸地蒸发过程的模拟程序。这一程序能根据地表红外温度或辐射资料计算裸地蒸发量,并分析能量分配过程与土壤中的含水量、温度分布。初步的田间试验说明,计算值与实测值是比较一致的。     

虚拟现实及其在军事测绘与作训模拟中的应用

虚拟现实是由计算机生成的人造环境或对象,它可以与操作者交互,构成一个封闭的系统,使人有身临其境之感。这一技术扩展了人的认知手段和范围,改变了传统的仿真与模拟方式,已引起了各个专业领域的重视。测绘工程为虚拟现实技术提供了理论、方法和数据基础,并应把这一技术作为下一世纪测绘保障的新手段而给予重视和开发。     

MHD simulations of solar and interplanetary phenomena

Workers in the field of magnetohydrodynamics (MHD) have been interested in the hypothesis that observed solar activities can be utilized in a deterministic way to predict the bulk flow consequences of these activities in the three-dimensional heliosphere. Exploration of this hypothesis, using the conventional/classic initial boundary value approach, will be reviewed against the background of basic, ideal (except for shocks) one-fluid approximations. This work has been divided into two parts: near-Sun simulations in two dimensions of coronal mass ejections (CMEs) as well as interplanetary simulations in 2D and 3D of propagating shocks. In the latter case, the flows behind the shocks should be thought of as interplanetary ICMEs, i.e., the interplanetary, evolutionary consequences of the near-Sun simulations.Initialization of these simulations has been based on observations (optical, soft X-ray, radio) from both ground-and space-based instruments. Simulation outputs have been compared within situ plasma and field observations and interplanetary scintillations (IPS). Improvements in the initialization procedures — spatial/temporal variations of solar plasma and field parameters at the coronal base — are expected from YOHKOH, SOHO, CORONAS-I, and TRACE experiments. Ground truth observations from WIND, SOHO, ACE, and INTERBALL experiments should then be compared with three-dimensional MHD outputs in tests of the fluid hypothesis noted above.     

Simulation of the asian monsoon by IAP AGCM coupled with an advanced land surface model (IAP94)

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用三维运动学模式研究太阳暗条消失与行星际扰动

本文用19个行星际扰动事件为样本,采用三维运动学模式研究暗条消失事件（简称FD事件）与行星际瞬变扰动间的关系．太阳上的扰动源取行星际扰动前2-5d以内的所有FD事件,用势场模式计算得到的源表面磁场为背景,模拟每个扰动在行星际中的传播及其相互作用过程,观察扰动到达地球的时间和扰动大小．从模拟的结果来看,FD事件与行星际扰动事件有较好的对应关系,说明FD事件是行星际瞬变事件的一类重要的太阳源．19个事件中有2个没有对应的FD事件,5个模拟结果与观测结果相差较大,其余12个模拟结果与实际观测符合很好．这与过去这方面的工作有所不同,我们具体模拟了每个扰动事件的传播过程,同时考虑了扰动间的相互作用,包括扰动与共转流之间的相互作用,为太阳-行星际-地磁链天气过程的预报奠定了基础．     

A model to couple overland flow and infiltration into macroporous vadose zone

Most vegetated land surfaces contain macropores that may have a significant effect on the rate of infiltration of water under ponded conditions on the ground surface. Owing to the small-scale variations of the land topography (microtopography), only portions of the land area may get ponded during the process of overland flow. As the macropores transmit water at much higher rates than the primary soil matrix, higher macropore activation in ponded areas produces larger effective infiltration rates into the soil. Therefore, overland flow and infiltration into the macroporous vadose zone are interrelated. Representing the microtopographic variation of the land surface by a simple sine wave function, a method was developed to relate the ponding area to the average ponding depth which was determined by overland flow. A numerical model coupling overland flow and infiltration into the macroporous vadose zone was developed. Overland flow was simulated using the St. Venant equations with the inertia terms neglected. A single macropore model was used to simulate the infiltration into the macroporous vadose zone. The interaction between overland flow and the infiltration into the macroporous vadose zone was analyzed for a hypothetical watershed. The sensitivity analysis revealed that the interaction of macropore flow and overland flow is significant. For the conditions tested, the macropore flow and the overland flow were found to be more sensitive to the macroporosity and less sensitive to the microtopographic surface variation.     

Impacts of multiple stressors on mountain communities: Insights from an agent-based model of a Nepalese village

Mountain communities in developing and transitioning countries are experiencing a period of rapid social, economic, and environmental change. While change has long been a feature of mountain life, the rate, magnitude, nature, and number of the transformations now taking place is unprecedented, with profound implications for the sustainability and welfare of mountain communities in the coming years. It is therefore vital that their potential impacts be understood. Considering stressors in isolation can give a false picture as each stressor alters the context within which the other stressors are operating. Holistic approaches are needed. In this paper, a variety of stressors are concurrently simulated within an empirically informed agent-based model of a rural Nepalese mountain community so that their combined impact can be studied. The potential effect of changing fertility rates, increasing crop yield variability, and earthquakes on household finances is considered for the period 2015–2030. Results show that higher fertility rates, increased crop yield variability, and earthquakes all have negative long-term effects on household finances, and that each of these stressors compounds the effect of the other stressors in an additive fashion. Results further highlight heterogeneity in the capacity of households to cope with stressors and demonstrate the important role that happenstance can play in exacerbating the effect of stressors. Our findings suggest that development practitioners should explicitly take multiple stressors into account when considering interventions. They should also contemplate improved microtargeting of households to increase aid effectiveness over the longer term, while recognising that household vulnerability is often dynamic.     

Third-Order Moments for Shear Driven Boundary Layer

A new third-order model for shear driven boundary layer is presented and tested against large-eddy simulation (LES) data. Numerical solutions are obtained using mean flow components and second-order moments as input. The calculated vertical profiles of the variances and turbulent kinetic energy fluxes and those provided by a LES experiment are compared and discussed