Indirect-approach method for specified-end points seismic ray tracing in three dimen-sional inhomogeneous media

Generally speaking, the factors of both medium and tectonic that give rise to heterogeneity of the earth crust and mantle structures should be taken into account simultaneously in three dimensional seismic ray tracing. In this paper, the three dimensional structure models are constructed with the model similar to generation system in computer aid design and manufacturing (CAD/CAM). Based on the algorithm proposed by Cerveny et al . for complete seismic ray tracing in complex three dimensional structures, a new technique called the indirect approach method for two point seismic ray tracing in three dimensional laterally heterogeneous media has been put forward, and its numerical computing examples were given.

Measurement and verification of concentration-dependent diffusion coefficient:Ray tracing imagery of diffusion process

Ray tracing method is used to study the propagation of collimated beams in a liquid-core cylindrical lens(LCL),which has dual functions of diffusion cell and image formation.The diffusion images on the focal plane of the used LCL are simulated by establishing and solving both linear and nonlinear ray equations,the calculated results indicate that the complex imaging results of LCL in inhomogeneous media can be treated by the law of ray propagation in homogeneous media under the condition of small refractive index gradient of diffusion solution.Guided by the calculation conditions,the diffusion process of triethylene glycol aqueous solution is experimentally studied at room temperature by using the LCL in this paper.The spatial and temporal concentration profile Ce(z,t)of diffusion solution is obtained by analyzing diffusion image appearing on the focal plane of the LCL;Then,the concentration-dependent diffusion coefficient is assumed to be a polynomial D(C)=D0×(1+α1C+α2C2+α3C3+…).The finite difference method is used to solve the Fick diffusion equation for calculating numerically the concentration profiles Cn(z,t).The D(C)of triethylene glycol aqueous solution is obtained by comparing the Cn(z,t)with Ce(z,t).Finally,the obtained polynomial D(C)is used to calculate the refractive index profiles nn(z,t)s of diffusion solution in the used LCL.Based on the ray propagation law in inhomogeneous media and the calculated n(z,t),the ray tracing method is used again to simulate the dynamic images of the whole experimental diffusion process to varify the correctness of the calculated D(C).The method presented in this work opens up a new way for both measuring and verifying the concentration-dependent liquid diffusion coefficients.

An improved algorithm based on equivalent sound velocity profile method at large incident angle

With the development of ultra-wide coverage technology,multibeam echo-sounder(MBES)system has put forward higher requirements for localization accuracy and computational efficiency of ray tracing method.The classical equivalent sound speed profile(ESSP)method replaces the measured sound velocity profile(SVP)with a simple constant gradient SVP,reducing the computational workload of beam positioning.However,in deep-sea environment,the depth measurement error of this method rapidly increases from the central beam to the edge beam.By analyzing the positioning error of the ESSP method at edge beam,it is discovered that the positioning error increases monotonically with the incident angle,and the relationship between them could be expressed by polynomial function.Therefore,an error correction algorithm based on polynomial fitting is obtained.The simulation experiment conducted on an inclined seafloor shows that the proposed algorithm exhibits comparable efficiency to the original ESSP method,while significantly improving bathymetry accuracy by nearly eight times in the edge beam.

An intersection method for locating earthquakes in complex velocity models

The intersection method is one of the basic approaches for locating earthquakes and is not only robust but also efficient. However, its location accuracy is not high, especially for focal depth because the velocity model used for the conventional intersection method is based on homogeneous or laterally homogeneous media, which is too simple. In order to improve the accuracy, we have modified the existing intersection method. In the modified approach, the earthquake loci are not assumed to be circular or hyperbolic and calculation accuracy is improved using a minimum traveltime tree algorithm for tracing rays. The numerical model shows that the modified method can locate earthquakes in complex velocity models.

Extension of e^N method to general three-dimensional boundary layers

In order to extend the eN method to general three-dimensional boundary layers, the conservation law of the imaginary parts for the wave parameters with a fixed wave vector is deduced. The compatibility relationship （CR） and the general theory of ray tracing （RT）, which have been extensively used in conservative systems, are applied to a general three-dimensional boundary layer belonging to non-conservative systems. Two kinds of eN methods, i.e., the eN-CR method and the eN-RT method, are established. Both the two kinds of methods can wavenumber and the amplitude of the be used to predict the evolutions of the spanwise disturbances in general three-dimensional boundary layers. The reliability of the proposed methods is verified and validated by performing a direct numerical simulation （DNS） in a hypersonic general three-dimensional boundary layer over an aircraft model. The results are also compared with those obtained by other eN methods, indicating that the proposed methods have great potential applications in improving the transition prediction accuracy in general three-dimensional boundary layers.

Study of a 105 GHz short-pulse dummy load for the electron cyclotron resonance heating system with the quasi-optical method

The accurate power measurement is important for an ECRH system in tokamak.The dummy load is designed and developed for the measurement of the millimeter wave power.This work analyzes the dummy load based on the quasi-optical method and the ray tracing method.The reflectivity and thermal deposition of the dummy load have been considered to ensure the safety of the entire system.High-power tests have been carried out at a 105 GHz/500 kW ECRH system.The results of the tests indicate that the designed dummy load is stable and valid.

A numerical and experimental comparison of heat transfer in a quasi two-dimensional packed bed

Heat transfer plays a major role in many industrial processes taking place in packed beds.An accurate and reliable simulation of the heat exchange between particles is therefore crucial for a reliable operation and to optimize the processes in the bed.The discrete ordinates method(DOM)provides an established numerical technique to model radiative heat transfer in granular media that offers the possibility to consider the directional dependence of the radiation propagation.In this work,DOM is compared with Monte Carlo ray tracing,which provides an alternative method for heat transfer simulations.Geomet-rically simple configurations are used to investigate the influence of the angular discretization on the accuracy of the results and the computation time in both methods.The obtained insights are then transferred to a more complex configuration of a quasi two-dimensional test rig consisting of metal rods for which also experimental results are available.Our results show that both DOM and Monte Carlo ray tracing allow for an accurate simulation of heat transfer in packed beds.Monte Carlo ray tracing requires thereby computation times that are surprisingly competitive(although still somewhat slower)compared to DOM and allows for an easier computation of highly accurate reference solutions.In our preliminary comparison to the experimental test rig,Monte Carlo ray tracing also provides the advantage that it can more easily model highly specular materials such as stainless steel.Both methods are comparable for diffuse materials such as magnesium oxide.

光线跟踪法在某太阳能集热元件光线分析中的应用

基于复合抛物面型集热器(CPC)的光学特性,介绍了一种新型的选择性太阳光隧道,采用光线跟踪法分析并计算其冬夏两种工况下的光学特性。结果表明,选择性太阳光隧道利用冬夏两季太阳高度角的差异可实现不同的吸热效果,为设计改进太阳能集热器提供了理论依据。

An efficient adaptive space partitioning algorithm for electromagnetic scattering calculation of complex 3D models

The space partitioning algorithm based on the rounding and addressing operations has been proved to be an efficient space partitioning algorithm with the potential for real-time calculation.An improvement on this kind of space partitioning algorithms for solving complex 3D models is presented.Numerical examples show that the efficiency of the improved algorithm is better than that of the original method.When the size of most target elements is smaller than the size of spatial grids,the efficiency of the improved method can be more than four times of that of the original method.An adaptive method of space partitioning based on the improved algorithm is developed by taking the surface element density or the curvature as the threshold for deep partitioning and conducting the deep partitioning using the octree method.A computer program implementation for applying the method in some typical applications is discussed,and the performance in terms of the efficiency,reliability,and resource use is evaluated.Application testing shows that the results of the adaptive spacing partitioning are more convenient for the follow-up use than that of the basic uniform space partitioning.Furthermore,when it is used to calculate the electromagnetic scattering of complex targets by the ray tracing(RT)method,the adaptive space partitioning algorithm can reduce the calculation time of the RT process by more than 40%compared with the uniform space segmentation algorithm.

Three dimensional velocity structure beneath the Kunming Telemetered Seismic Network

Based on the P wave first arrival time data of 275 local earthquakes recorded by Kunming Telemetered Seismic Network from 1982 to 1989, a 3-D velocity structure beneath the network was obtained by the separationmethod of focal parameter and medium structure parameter and 3-D approximate ray tracing. In view of 'thesituation that the intervals between stations in the network is relatively long, and the local first arrival phasemay be Pn instead of P, so we simulated Pn as the diving wave from the layer beneath Moho and using approximate ray tracing method on the grid model. The final 3-D velocity structure is basically consistent withthe result from the deep seismic sounding and the anomaly inversion of Bouguer gravity. The Dianzhong area(in the vicinity of Dukou and Chuxiong) shows an obvious high velocity zone at depth of 45 km, which canbe interpreted as the uplift of Moho discontinuity. The upper crust in this area displays lower velocity zone,so the uplift of Moho discontinuity is considered as the result of isostatic compensation. The configuration ofvelocity contours indicates that the upper crust and lower crust are complicated, while the middle crust is relatively simple. This feature reveals that Yunnan area belongs to modern tectonically active region. As themain boundary of the major tectonic units in the study area, although there is no obvious evidence about lowvelocity anomaly zone along the Red River Fault, the fault shows up th feature of sturctural divide on themid-lower crustal velocity contours, and it is inferred that the fault passes through the Moho-discontinuity atleast.

Study on the Propagation Characteristics of Radio Wave for Indoor Non-Line-of-Sight

The propagation characteristics of radio wave have been an important topic in wireless communications. Based on the ray tracing method, the propagation of radio wave for indoor NLOS environment is simulated and analyzed. In this paper, the received power is obtained by simulation, and we will analyze the impact of various factors on the received power. Later, the study can be used to simplify indoor radio wave propagation model and provide a theoretical basis, which is in favor of indoor wireless communication network planning and optimization and can lay the foundation of the development of future technology.

Improving a Hybrid Method of Indoor Propagation Modeling for Wireless Communications Systems

Propagation prediction is very important in the design of wirelesscommunication systems. A combined ray tracing and Finite-Difference Time-Domain (FDTD) method isimproved on modeling the indoor radio propagation by applying Perfectly Matched Layer (PML)Absorbing Boundary Conditions (ABCs) to FDTD grid. Thus, more accurate propagation prediction can beobtained.

Uniform Deterministic Discrete Method for Three Dimensional Systems

For radiative direct exchange areas in three dimensional system, the Uniform Deterministic Discrete Method (UDDM) was adopted. The spherical surface dividing method for sending area element and the regular icosahedron for sending volume element can meet with the direct exchange area computation of any kind of zone pairs. The numerical examples of direct exchange area in three dimensional system with nonhomogeneous attenuation coefficients indicated that the UDDM can give very high numerical accuracy.

Investigation of laser diode face-pumped high average power heat capacity laser

The three-dimensional （3D） pump intensity distribution in medium of the laser diode （LD） pumped high average power heat capacity laser is simulated by the ray tracing method, and the divergence characteristics of fast axis and slow axis of LD are simultaneously considered. The transient 3D temperature and stress distributions are also simulated by the finite dement method （FEM） with considering the uneven heat source distribution in medium. A LD face-pumped Nd：GGG heat capacity laser is designed. The average output power is 1.49 kW with an optical-optical efficiency of 24.1%. OCIS codes： 140.3480, 140.6810, 120.6810, 000.4430.

Transient radiative heat transfer in an inhomogeneous participating medium with Fresnel’s surfaces

This paper studies the radiative heat transfer within an inhomogeneous and isot- ropically scattering medium with reflecting Fresnel's surfaces. Thermal radiation transfers in a curve inside a medium with an inhomogeneous distribution of a re- fractive index. The inhomogenous medium is divided into n homogenous isother- mal sub-layers and in each sub-layer the radiation transfers in a straight line. By adopting a multilayer radiative transfer model and using a ray-tracing/nodal- ana- lyzing method, a radiative transfer model is built for the inhomogenous participat- ing medium. In the multilayer model, a criterion for refraction / total reflection at the interfaces between neighboring sub-layers is introduced, avoiding the integral singularity and reflection at physically inexistent interfaces (only the total reflection is considered). Transient thermal behavior is examined when the parameters of the radiative properties such as refractive indexes, extinction coefficients, and sin- gle-scattering albedoes vary continually along the thickness direction.

Optical performance analysis of an innovative linear focus secondary trough solar concentrating system

The parabolic trough solar concentrating system has been well developed and widely used in commercial solar thermal power plants. However, the conventional system has its drawbacks when connecting receiver tube parts and enhancing the concentration ratio. To overcome those inherent disadvantages, in this paper, an innovative concept of linear focus secondary trough concentrating system was proposed, which consists of a fixed parabolic trough concentrator, one or more heliostats, and a fixed tube receiver. The proposed system not only avoids the end loss and connection problem on the receiver during the tracking process but also opens up the possibility to increase the concentration ratio by enlarging aperture. The design scheme of the proposed system was elaborated in detail in this paper.Besides, the optical performance of the semi and the whole secondary solar trough concentrator was evaluated by using the ray tracing method. This innovative solar concentrating system shows a high application value as a solar energy experimental device.

Transient Coupled Radiative and Conductive Heat Transferin a Composite of Semitransparent Media

The transient coupled radiative and conductive heat transfer in a semitransparent composite under the complexboundary conditidns is investigated by the ray tracing method in combination with Hottel’s zonal method and thecontrol-volume method. The composite is composed of tWo plane layers of nonscattering sendtransparent media withthe different thermophysical Properties in each layer. Both boundals surfaces and the internal interface aresemitransparent. The reflections are assUmed diffuse or specular. The transient temperature distributions in thecomposite are Obtained for the combined thermal boundary conditions of incident radiation and convective heat transfer.Under diffuse reflection, the resultS in this paper are separately compared with the steady and transient results ofPrevious work. The comparison shows the reliability and the high calculating accuracy of the formulas derived in thespaper. The Present analysis includes the effeCts of the optical thickness, the conduchon-radiation parameter, the spectralproperty and the renechve mode on the transient temperature distributions.

Thermal Emission of a Disc Body of SemitransparentMaterial

By introducing the concept of radiosity intensity to diffuse surfaces, the ray tracing method is improved to analyze the thermal emission of a disc body of gray semitransparent material. The two plane sur-faces of the disc body are both specularly reflecting, and the fiank surface is either diffusely reflecting or specularly reflecting. The apparent thermal emission from one plane sllrface is investigated with considering the infiuences of the characteristic optical thickness, the dimensionless radius, the refrac-tive index of the material and the reflecting characteristics of the flank surface. The directional and hemispherical emissions show considerable differences under different refiecting characteristics of the flank surface. Moreover, in some cases, the emission not only varies with the viewing direction but also with the apparent emitting position on the plane surface. Some interesting results are presented and discussed.

Variance reduction using interframe coherence for animated scenes

In an animated scene,geometry and lighting often change in an unpredictable way. Rendering algorithms based on Monte Carlo methods are usually employed to precisely capture all features of an animated scene. However,Monte Carlo methods typically take a long time to produce a noise-free image. In this paper,we propose a variance reduction technique for Monte Carlo methods which exploits coherence between frames. Firstly,we introduce a dual cone model to measure the incident coherence intersecting camera rays in object space. Secondly,we allocate multiple frame buffers to store image samples from consecutive frames. Finally,the color of a pixel in one frame is computed by borrowing samples from neighboring pixels in current,previous,and subsequent frames. Our experiments show that noise is greatly reduced by our method since the number of effective samples is increased by use of borrowed samples.