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In-plane free vibration analysis of combined ring-beam structural systems by wave propagation

JOURNAL OF SOUND AND VIBRATION 2010年第24期329卷 5087-5104页

作者： Chouvion, B. Fox, C. H. J. McWilliam, S. Popov, A. A. Univ Nottingham Fac Engn Mat Mech & Struct Div Nottingham NG7 2RD England

This paper presents a systematic, wave propagation approach for the free vibration analysis of networks consisting of slender, straight and curved beam elements and complete rings. The analysis is based on a ray tracing method and a procedure to predict the natural frequencies and mode shapes of complex ring/beam networks is demonstrated. In the wave approach, the elements are coupled using reflection and transmission coefficients, and these are derived for discontinuities encountered in a MEMS rate sensor consisting of a ring supported on an array of folded beams. These are combined, taking into account wave propagation and decay, to provide a concise and efficient method for studying the free vibration problem. A simplification of the analysis that exploits cyclic symmetry in the structure is also presented. The effects of decaying near-field wave components are included in the formulation, ensuring that the solutions are exact. To illustrate the effectiveness of the approach, several numerical examples are presented. The predictions made using the proposed approach are shown to be in excellent agreement with a conventional FE analysis. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： FREE vibration ELASTIC wave propagation MICROELECTROMECHANICAL systems NEAR-fields NUMERICAL analysis FINITE element method ray tracing algorithms

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Seismic refraction traveltime inversion for static corrections in a glaciated shield rock environment: a case study

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GEOPHYSICAL PROSPECTING 2009年第6期57卷 997-1008页

作者： Schijns, Heather Heinonen, Suvi Schmitt, Douglas R. Heikkinen, Pekka Kukkonen, Ilmo T. Univ Alberta Dept Phys Inst Geophys Res Edmonton AB T6G 2J1 Canada Univ Helsinki Inst Seismol FIN-00014 Helsinki Finland Geol Survey Finland Espoo 02151 Finland

A traveltime inversion technique is applied to model the upper similar to 40 m of the subsurface of a glaciated shield rock area in order to calculate static corrections for a multi-azimuth multi-depth walk-away vertical seismic profile and a surface seismic reflection profile. First break information from a seismic refraction survey is used in conjunction with a ray-tracing program and an iterative damped least-squares inversion algorithm to create a two-dimensional model of the subsurface. The layout of the seismic survey required crooked seismic lines and substantial gaps in the source and receiver coverage to be accounted for. Additionally, there is substantial topographical variation and a complex geology consisting of glaciofluvial sediment and glacial till overlying a crystalline bedrock. The resolution and reliability of the models is measured through a parameter perturbation technique, normalized chi 2 values, root means square traveltime residuals and comparison to known geology.

关键词： INVERSION (Geophysics) EARTHQUAKE resistant design SEISMIC refraction method ray tracing algorithms SHIELDS (Geology)

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Photocatalytic Mineralization of Commercial Herbicides in a Pilot-Scale Solar CPC Reactor: Photoreactor Modeling and Reaction Kinetics Constants Independent of Radiation Field

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ENVIRONMENTAL SCIENCE & TECHNOLOGY 2009年第23期43卷 8953-8960页

作者： Colina-Marquez, Jose Machuca-Martinez, Fiderman Puma, Gianluca Li Univ Nottingham Dept Chem & Environm Engn Nottingham NG7 2RD England Univ Valle Sch Chem Engn Cali Colombia

The six-flux absorption-scatte ring model (SFM) of the radiation field in the photoreactor, combined with reaction kinetics and fluid-dynamic models, has proved to be suitable to describe the degradation of water pollutants in heterogeneous photocatalytic reactors, combining simplicity and accuracy. In this study, the above approach was extended to model the photocatalytic mineralization of a commercial herbicides mixture (2,4-D, diuron, and ametryne used in Colombian sugar cane crops) in a solar, pilot-scale, compound parabolic collector (CPC) photoreactor using a slurry suspension of TiO2. The ray-tracing technique was used jointly with the SFM to determine the direction of both the direct and diffuse solar photon fluxes and the spatial profile of the local volumetric rate of photon absorption (LVRPA) in the CPC reactor. Herbicides mineralization kinetics with explicit photon absorption effects were utilized to remove the dependence of the observed rate constants from the reactor geometry and radiation field in the photoreactor. The results showed that the overall model fitted the experimental data of herbicides mineralization in the solar CPC reactor satisfactorily for both cloudy and sunny days. Using the above approach kinetic parameters independent of the radiation field in the reactor can be estimated directly from the results of experiments carried out in a solar CPC reactor. The SFM combined with reaction kinetics and fluid-dynamic models proved to be a simple, but reliable model, for solar photocatalytic applications.

关键词： PHOTOCATALYSIS RESEARCH ABSORPTION CHEMICAL models FLUID dynamics -- Mathematical models CHEMICAL kinetics HERBICIDES -- Environmental aspects DIURON ray tracing algorithms POLLUTION -- Experiments MATHEMATICAL models

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Assessment of an unstructured exponential scheme discrete ordinates radiation model for non-gray media

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HEAT AND MASS TRANSFER 2011年第11期47卷 1349-1362页

作者： Dembele, S. Lima, K. L. M. Wen, J. X. Kingston Univ Fac Engn London SW15 3DW England

For radiative transfer in complex geometries, Sakami and his co-workers have developed a discrete ordinates method (DOM) exponential scheme for unstructured meshes which was mainly applied to graymedia. The present study investigates the application of the unstructured exponential scheme to a wider range of non-gray scenarios found in fire and combustion applications, with the goal to implement it in an in-house Computational Fluid Dynamics (CFD) code for fire simulations. The original unstructured gray exponential scheme is adapted to non-gray applications by employing a statistical narrow-band/correlated-k (SNB-CK) gasmodel and meshes generated using the authors' own mesh generator. Different non-gray scenarios involving spectral gas absorption by H(2)O and CO(2) are investigated and a comparative analysis is carried out between heat flux and radiative source terms predicted and literature data based on ray-tracing and Monte Carlo methods. The maximum discrepancies for total radiative heat flux do not typically exceed 5%.

关键词： RADIATIVE transfer TRANSPORT theory (Mathematics) -- Discrete ordinates method COMPUTATIONAL fluid dynamics HEAT flux ray tracing algorithms MONTE Carlo method

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Environment modeling in a flight simulator

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PROGRAMMING AND COMPUTER SOFTWARE 2017年第4期43卷 234-242页

作者： Sapronov, R. V. Tupolev Natl Res Tech Univ Ul K Marksa 10 Kazan 420111 Tatarstan Russia

An approach is proposed to the height and displacement maps normalization from the spectra described by J. Tessendorf. Techniques are considered to avoid some rendering artefacts with projected grids when the viewer is (1) far from the origin of a coordinate system and (2) near the waterline. Modeling and lighting of the water surface is described. Techniques based on volumetric models using screen-space raytracing for rendering various atmospheric effects (clouds, fog, rain, snow, etc.) are proposed. Approaches to implementing these techniques applicable to a wide range of real-time applications are described.

关键词： FLIGHT simulators RENDERING (Computer graphics) VOLUMETRIC analysis ray tracing algorithms SPECTRUM analysis

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Sampling gap fraction and size for estimating leaf area and clumping indices from hemispherical photographs

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CANADIAN JOURNAL OF FOREST RESEARCH 2010年第8期40卷 1588-1603页

作者： Gonsamo, Alemu Walter, Jean-Michel N. Pellikka, Petri Univ Helsinki Dept Geog FIN-00014 Helsinki Finland Univ Strasbourg Inst Bot Fac Sci Vie F-67083 Strasbourg France

Hemispherical photography is becoming a popular technique for gap fraction measurements to characterize biophysical parameters and solar radiation in plant canopies. One of the crucial steps in the measurement of canopy gap fraction using hemispherical photography is determining the resolution of the sampling grid. In this work, the effects of varying resolutions of sampling grids by modifying the angle widths of zenithal annuli and azimuthal sectors were evaluated for leaf area and clumping indices computations. Sensitivity analysis was performed to test these effects using artificial photographs simulating ideal canopies with varying leaf area index and aggregation levels of foliage elements. Contrasting forest types, including natural tropical cloud forest and exotic plantations, were tested as real canopies. Results indicate that leaf area and clumping indices estimates are significantly affected by the variation of sampling grids. A new approach to solve the problem of null-gap segments, obscured completely by foliage, is proposed. However, the determination of optimal combinations of zenithal annuli and azimuthal sector angular widths that suit all canopy types remains a difficult practical problem that is often overlooked. Finally, theoretically sound gap fraction and size sampling regions were demonstrated for reliable estimates of canopy biophysical parameters.

关键词： HEMISPHERICAL photography SOLAR radiation PLANT canopies SENSITIVITY analysis LEAF area index CLOUD forests ray tracing algorithms PLANTATIONS ZENITH distance

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Stereotactic Body Radiation Therapy (SBRT) Using Robotic Radiosurgery for Lung Cancer: Comparison of Treatment Plans Using ray tracing (RT) and Monte Carlo (MC) Algorithm

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INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 2014年第1-Sup期90卷 S913-S914页

作者： Pennington, A. Selvaraj, R. Leventouri, T. 21st Century Oncol Deerfield Beach FL USA Florida Atlantic Univ Boca Raton FL 33431 USA

3785

关键词： STEREOTACTIC radiotherapy LUNG cancer -- Treatment LUNG cancer -- Patients ray tracing algorithms PROTON therapy TOXICITY testing CLINICAL trials

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Electromagnetic detection of a perfect cloak based on the material nonlinear response

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APPLIED PHYSICS B-LASERS AND OPTICS 2011年第2期105卷 225-229页

作者： Shi, J. Wang, Z. Liu, D. Gong, W. Su, Y. Beijing Normal Univ Dept Phys Appl Opt Beijing Area Major Lab Beijing 100875 Peoples R China Nanchang Hang Kong Univ Key Lab Nondestruct Test Minist Educ Nanchang 330063 Peoples R China

Methods of detecting a perfect invisible cloak are analyzed. A classical frequency-domain method of detection is proposed. It is based on the detection of the difference between the nonlinear responses of the materials of the cloak and the background. The cloak treated here is perfect working within any frequency. The method for detecting the cloak in the frequency domain is demonstrated numerically for an example.

关键词： ELECTROMAGNETIC waves NONLINEAR theories NUMERICAL analysis FINITE element method QUANTUM theory TRANSFORMATIONS (Mathematics) ray tracing algorithms

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Double directional characterisation of radio wave propagation through metallic watertight doors on board ships

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ELECTRONICS LETTERS 2012年第6期48卷 307-308页

作者： Kdouh, H. Farhat, H. Tenoux, T. Zaharia, G. Brousseau, C. Grunfelder, G. Lostanlen, Y. El Zein, G. IETR Rennes France Siradel Rennes France

The objective of this reported work was to characterise electromagnetic wave propagation between adjacent rooms in the lower deck areas of ships. A wideband multiple-input multiple-output channel sounder has been used to realise double directional propagation measurements at 2.2 GHz. The antenna configuration was a linear array at the transmission side and a rectangular one at the reception. The measurement data are first processed with a classic beamforming technique, then with a high resolution algorithm to extract the dominant paths. A ray-tracing based simulation tool is used to understand the measurement results. It is observed that, in spite of the metallic structure of watertight doors, wireless communication remains possible between adjacent rooms after door closure. Results show that electromagnetic waves mainly propagate through door edges openings.

关键词： BROADBAND communication systems WIRELESS communication systems RADIO wave propagation ELECTROMAGNETIC waves BEAMFORMING ray tracing algorithms

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Simplified analytical propagation model for railway environments based on uniform theory of diffraction

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ELECTRONICS LETTERS 2013年第6期49卷 397-399页

作者： He, R. Zhong, Z. Ai, B. Guan, K. Chen, R. Beijing Jiaotong Univ State Key Lab Rail Traff Control & Safety Beijing 100044 Peoples R China

Proposed is a simplified analytical propagation model in railway environments. A heuristic ray tracing with geometrical optics and uniform theory of diffraction are adopted. Four typical and dominating ray paths that undergo reflections from ground and train roof and diffraction from the corner of the train are considered. The measurements verify that the analytical propagation model works very well in typical railway environments.

关键词： HEURISTIC ray tracing algorithms BEAM tracing algorithms GEOMETRICAL diffraction RAILROADS

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