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.

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 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.

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.

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.

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.