Ray Tracing Technique Research Articles

Simulation of femtosecond pulse in a Kerr-lens mode-locked Ti:sapphire laser

The Kerr-lens mode-locking (KLM) is known as a suitable method for generation of femtosecond pulses and mode-locked Ti:sapphire laser is now widely used sources of stable, energetic femtosecond pulses. We will present the simulation of KLM in Ti:sapphire laser cavities with a folded-cavity four-mirror by applying the ABCD ray-tracing technique for a Gaussian beam. Simulations will be performed for an asymmetric resonator design. Based on the numerical analysis, we will find the optimum design parameters (slit position, gain cavity spacing, gain medium position) for KLM.

Testing Relativistic Reflection Models with GRMHD Simulations of Accreting Black Holes

X-ray reflection spectroscopy is currently one of the leading techniques for studying the inner part of accretion disks around black holes, measuring black hole spins, and even testing fundamental physics in strong gravitational fields. However, the accuracy of these measurements depends on the reflection models employed for the spectral analysis, which are sometimes questioned. In this work, we use a general relativistic magnetohydrodynamic code to generate a thin accretion disk in Kerr spacetime and ray-tracing techniques to calculate its relativistically broadened reflection spectrum. We simulate NuSTAR observations and we test the capability of current reflection models to recover the correct input parameters. Our study shows that we can measure the correct input parameters in the case of high inclination angle sources, while we find some minor discrepancies when the inclination angle of the disk is low.

Highly Robust Synthetic Aperture Radar Target Recognition Method Based on Simulation Data Training

Sufficient synthetic aperture radar (SAR) data is the key element in achieving excellent target recognition performance for most deep learning algorithms. It is unrealistic to obtain sufficient SAR data from the actual measurements, so SAR simulation based on electromagnetic scattering modeling has become an effective way to obtain sufficient samples. Simulated and measured SAR images are nonhomologous data. Due to the fact that the target geometric model of SAR simulation is not inevitably consistent with the real object, the SAR sensor model in SAR simulation may be different from the actual sensor, the background environment of the object is also inevitably different from that of SAR simulation, the error of electromagnetic modeling method itself, and so on. There are inevitable differences between the simulated and measured SAR images, which will affect the recognition performance. To address this problem, an SAR simulation method based on a high-frequency asymptotic technique and a discrete ray tracing technique is proposed in this paper to obtain SAR simulation images of ground vehicle targets. Next, various convolutional neural networks (CNNs) and AugMix data augmentation methods are proposed to train only on simulated data, and then target recognition on MSTAR measured data is performed. The experiments show that all the CNNs can achieve incredible recognition performance on the nonhomologous SAR data, and the RegNetX-3.2GF achieves state-of-the-art performance, up to 84.81%.

Enhanced ultrasonic total focusing imaging of CFRP corner with ray theory-based homogenization technique

Ultrasonic testing is effective in defect characterization and quality assurance of Carbon Fiber Reinforced Plastic (CFRP) components in the aerospace industry. Due to the coupling between complex shape and elastic anisotropy, the Phased Array Ultrasonic Testing (PAUT) and time-based Total Focusing Method (TFM) face significant challenges in the calculation of wave propagation. A wave velocity distribution model is established for a multidirectional convex corner of CFRP based on a homogenization theory and the above coupling effects are also incorporated. A ray-tracing method is proposed based on Dijkstra’s shortest path search algorithm. The predicted time of flight ensures that this technique, the homogenized TFM, could synthesize a high-quality focused image by post-processing on the full matrix capture data. Experiments on a laminate with three ϕ1.5 mm Side-Drilled Holes (SDHs) in different circumferential directions confirm a successful homogenized TFM imaging that all SDHs can be effectively detected. As compared to the isotropic scenario, the maximum positioning error is reduced to 0.12, 0.08, and 0.38 mm, and the Signal-to-Noise Ratios (SNRs) are increased by 2.1, 1.1, and 11.8 dB, respectively. It is suggested that the ray-tracing assisted TFM technique can effectively improve the imaging of corners in CFRP components.

Thermal performance enhancement in parabolic trough solar collectors by using an absorber tube with spherical pins

ABSTRACT Improving the overall performance of parabolic trough collectors (PTCs) represents the best method to reduce the cost of energy produced. The goal is to increase their potential to generate more useful heat, particularly at high ranges of temperatures. Therefore, various techniques have been thoroughly examined in the literature. Indeed, the non-uniform heat flux on the PTC receivers induces overheating of the absorber tube and significant thermal stress, which requires the use of expensive materials. It also reduces the overall thermal performance of the system. To overcome these issues, practical solutions must be introduced. In this paper, integrated spherical pins are used and different configurations have been proposed and investigated. To do so, a numerical model that combines optical and thermal aspects has been developed. For this, the Monte Carlo ray tracing technique (MCRT) is coupled with the finite volume method (FVM). Also, experimental tests on the MicroSol-R platform have been used to validate the numerical models. A number of energetic and exergetic performance indices are used to analyze the potential improvements due to the use of spherical pins. The analysis showed that the use of pins increases the heat transfer coefficient by up to 27.2% and reduces the heat loss by up to 9.32% compared with conventional smooth tubes. Moreover, it is found that the performance evaluation criterion (PEC) can be enhanced by up to 24.92%. Consequently, when using a solar receiver with five pins (which was selected as the best configuration among the examined configurations), the overall efficiency and the exergetic efficiency are increased by up to 4.1% and 2.2%, respectively. Indeed, the use of pins inside the solar receiver is a practical solution to improve the efficiency of the PTC system and has the potential to reduce the thermal stress on the receiver thanks to the high heat transfer coefficient. It also helps prevent overheating and reduce thermal losses by keeping the maximum temperature within a suitable operational range.

Acoustic radiation from random waves on plates

Controlling and simulating the sound radiating from complex structures is of importance in many engineering applications. We calculate the radiated acoustic power from plates with diffuse bending vibrations. We characterise the diffuse field by a two-point correlation function (CF) of normal velocities. Given the relation between field–field CFs and ray-dynamical phase space densities, the approach taken here offers a basis for coupling structure borne ray-tracing techniques with acoustic radiation. At the same time, it caters for stochastic, noisy driving of such systems. The results for the radiation efficiency of a plate are presented in an asymptotic form analogous to the Weyl formula for the density of states. Leading contributions from the plate interior and its boundary are derived, with corner corrections also being given for particular boundary conditions and right-angled corners. A notable feature of this analysis is that the bulk contribution vanishes below a critical frequency, and the asymptotic estimate of radiated power then leads with a boundary contribution. This is shown to agree well with a more traditional calculation based on modal analysis in the special case of a rectangular plate.

Simulating invisible light: a model for exploring radiant cooling’s impact on the human body using ray tracing

Radiant systems are an energy-efficient method for providing cooling to building occupants through active surfaces. To assess the impact of the radiant environment on occupants in space, we develop a ray-tracing simulation, which accounts for longwave radiation. Thermal radiation shares many characteristics with visible light, and thus is highly dependent on surface geometry. Much research effort has been dedicated to characterizing the behavior of visible light in the built environment and its impact on the human experience of space. However, longwave infrared radiation’s effect on the human perception of heat is still not well characterized or understood within the design community. In order to make the embodied effect of radiant surfaces’ geometry and configuration legible, we have developed a Mean Radiant Temperature (MRT) simulation method, which is based on a ray-tracing technique. It accounts for the detailed geometry of the human body and its surrounding environment. We use a case study of a pavilion built with an envelope consisting of active cooling panels in Singapore. Using measured data for the surrounding surface temperatures in the pavilion, we explore the impact of both the active panels and the surrounding passive elements and thermal environment on a person’s radiant heat exchange in different postures. The reflectivity and emissivity values of different surfaces are taken into account, and the ray-tracing process allows for multiple-bounce simulation. The model accounts for both longwave and shortwave radiation, and the simulation results are compared with field measurements for validation. The results are expressed both numerically and as spatial radiant-heat-maps. These show a variation of up to 11°C in MRT across the space studied. Furthermore, a digital manikin is used to assess the impact of the radiant cooling panels across the human body. The results show a 10°C variation in radiant temperature perceived by different regions of the body in one position. The findings reveal a significant heterogeneity of radiant heat transfer that current analysis methods typically overlook for both architectural space and the geometry of the human body.

RTPLTool: a software tool for path loss modeling in 5G outdoor systems

The increase in the required bandwidth along with the global growth of existing wireless communication systems is one of the major reasons why research and industry communities are exploring 5G and millimeter-wave frequencies. The advantages of millimeter wave frequencies for 5G applications are a wide range of accessible and unlicensed spectrum, the use of small antennas in RF applications with increasing frequency, and low losses due to the interference effects compared to the currently used frequency bands. However, due to some computational challenges especially at millimeter waves (i.e. in FR2 frequency band), it is necessary to develop efficient software tools or to adapt new approaches in existing models for efficient propagation modeling. In this work, a web-based software tool has been developed to calculate propagation or path loss for 5G outdoor systems. Terrain profile and environmental data were obtained through web-based mapping services and digital elevation data. Two different ray-tracing techniques were applied with respect to the type of area, i.e. urban and rural areas. Quasi-3D ray-tracing techniques were used by using the data obtained from OpenStreetMap (OSM) for urban microcellular environments, whereas the shooting and bouncing ray (SBR) method was employed for rural terrain profiles gathered from the digital elevation data. The results of the developed software tool were compared with some measurement results and some results obtained from a commercial software program (i.e. WinProp) by considering real propagation scenarios. The software tool was developed as an ASP.NET web application on Microsoft Visual Studio via the MATLAB SDK Compiler.

LBVH 순회를 이용한 거대 도체 구조의 레이다 단면적 분석

In this study, the radar cross-section (RCS) of a large structure is analyzed using the linear bounding volume hierarchy (LBVH), which is a representative acceleration algorithm of the ray-tracing technique. A ray-tracing technique, which is a high-frequency method, is used to analyze the electromagnetic properties of large structures, and bounding volume hierarchy (BVH), a binary tree structure, is applied to reduce the intersection search time. The improvement in the calculation speed is quantitatively analyzed by dividing an arbitrary scatterer into several triangles. The calculation results are compared with those of multilevel fast multipole method (MLFMM) and ray-launching geometrical optics (RL-GO) using the Feko commercial software to verify the accuracy. The proposed technique can be utilized for the efficient RCS calculations of large structures.

Digital-Twin-Enabled City-Model-Aware Deep Learning for Dynamic Channel Estimation in Urban Vehicular Environments

Most of the existing works on vehicle-to-everything (V2X) communications assume some deterministic or stochastic channel models, which is unrealistic for highly-dynamic vehicular channels in urban environments under the influence of high-speed vehicle motion, intermittent connectivity, and signal attenuation in urban canyon. Enabled by the concept of digital twin, the digital replica of a real-world physical system, this paper proposes a city-model-aware deep learning algorithm for dynamic channel estimation in urban vehicular environments. Specifically, the digital twin simulation allows us to accurately model radio ray reflection and attenuation in urban canyon, and the data can be supplemented and validated with empirical measurements. Our results indicates that the city-model-aware deep neural network (CMA DNN) estimator performs much better than conventional methods and has more than 32% improvement in BER when compared with generic DNN approaches that do not take the 3D city model into account. Since some geometry-based models like ray-tracing techniques used in the digital twin simulation for dynamic channel modeling could be computational expensive, we also propose a basis expansion model (BEM) approach to simplify the computation load of the overall methodology to gain a good balance between accuracy and timeliness.

Ray tracing method applied in the annual evaluation of reflectors integrated to an evacuated tube solar collector

A method to evaluate the performance of annual solar concentrators is presented. The ray-tracing technique is regularly used to assess the solar concentrator's performance; however, most of the works in this area simplify the simulation process by considering representative scenarios throughout the year, such as solar tracking studies in summer and winter solstices or monthly averages to evaluate the annual system performance. The presented method develops annual simulations using dynamic data exchange protocol to allow communication between TracePro® and MATLAB with defined time intervals, applied to assess the integration of a reflector system to evacuated tube collectors under three configurations: rear reflector plate, compound parabolic concentrator, and parabolic concentrator; the finding that the latter presents the most favorable results, increasing the incident radiation on the outside of the tubes up to 36%.

Analysis of Ray Tracing Methodology and Techniques and its Distinction from other Render Models

Abstract: In 3D computer-generated graphics, ray tracing is a form of rendering technique for calculating light transport for the purpose of giving a photo-realistic image. This survey paper mainly focuses on the brief working of ray tracing methodology and various techniques available to achieve this. This helps to understand one how ray tracing can be applied in the field of computer graphics to produce stunning realistic renders. At present time ray tracing is primarily available for gaming (real-time ray tracing) and also for visual effects in cinema industry. This paper also gives a detailed study about hardware and software components used for ray tracing

Resolving Radiant: Combining Spatially Resolved Longwave and Shortwave Measurements to Improve the Understanding of Radiant Heat Flux Reflections and Heterogeneity

We introduce and demonstrate new measurement and modeling techniques to fully resolve the spatial variation in shortwave and longwave radiant heat transfer in the outdoor environment. We demonstrate for the first time a way to directly resolve the shortwave radiant heat transfer from terrestrial reflected and diffuse sky components along with the standard direct solar radiation using an adapted thermopile array and ray-tracing modeling techniques validated by 6-direction net radiometer. Radiant heat transfer is a major component of heat experienced in cities. It has significant spatial variability that is most easily noticed as one moves between shade and direct solar exposure. But even on a cloudy and warm day the invisible longwave infrared thermal radiation from warm surfaces makes up a larger fraction of heat experienced than that caused by convection with surrounding air. Under warm or hot climate conditions in cities, radiant heat transfer generally accounts for the majority of heat transfer to people. Both the shortwave (visible/solar) and the longwave (infrared/thermal) have significant spatial variation. We demonstrate sensor methods and data analysis techniques to resolve how these radiant fluxes can change the heat experienced by >1 kWm−2 across small distances. The intense solar shortwave radiation is easily recognized outdoors, but longwave is often considered negligible. Longwave radiation from heat stored in urban surfaces is more insidious as it can cause changes invisible to the eye. We show how it changes heat experienced by >200 Wm−2. These variations are very common and also occur at the scale of a few meters.

Acoustic neutrino detection in a Adriatic multidisciplinary observatory (ANDIAMO)

The existence of cosmic accelerators able to emit charged particles up to ZeV energies has been confirmed by the observations made in the last years by experiments such as Auger and Telescope Array. The interaction of such energetic cosmic-rays with gas or low energy photons, surrounding the astrophysical sources or present in the intergalactic medium, guarantee an ultra-high-energy neutrino related emission. When these energetic neutrinos interact in a medium produce a thermo-acoustic process where the energy of generated particle cascades can be conveyed in a pressure pulse propagating into the same medium. The kilometric attenuation length as well as the well-defined shape of the expected pulse suggest a large-area-undersea-array of acoustic sensors as an ideal observatory. For this scope, we propose to exploit the existing and no more operative offshore (oil rigs) powered platforms in the Adriatic sea as the main infrastructure to build an acoustic submarine array of dedicated hydrophones covering a surface area up to 10000 km2 and a volume up to 500 km3. In this work we describe the advantages of this detector concept using a ray tracing technique as well as the scientific goals linked to the challenging purpose of observing for the first time ultra-high-energy cosmic neutrinos. This observatory will be complementary to the dedicated radio array detectors with the advantages of avoiding any possible thermo-acoustic noise from the atmospheric muons.

Determination of uncertainty profiles in neutral atmospheric properties measured by radio occultation experiments

Radio occultations are commonly used to assess remotely the thermodynamic properties of planets or satellites’ atmospheres within the solar system. The data processing usually involves the so-called Abel inversion method or the numerical ray-tracing technique. Both these approaches are now well established, however, they do not allow to easily determine the uncertainty profiles in the atmospheric properties, and this makes the results difficult to interpret statistically. Recently, a purely analytical approach based on the time transfer functions formalism was proposed for modeling radio occultation data. Using this formulation, we derive uncertainty relationships between the frequency shift and the thermodynamic properties of the neutral atmosphere such as the temperature, pressure, and neutral number density. These expressions are important for interpreting previous results from past radio occultation experiments. They are especially relevant for deriving the system requirements for future missions in a rigorous manner and consistently with the scientific requirements about the atmospheric properties retrieval.

Optical design optimization for improved lamp-reflector units in high-flux solar simulators.

High flux solar simulators are artificial solar facilities developed to imitate the on-sun operations of concentrating solar power technologies but under a well-controlled lab-scale environment. We report the optical enhancement of different high flux solar simulators for solar thermal and thermochemical applications. The solar simulator enhancement is numerically conducted by optimizing the geometry of ellipsoidal reflectors at focal lengths of 1600, 1800, and 2000 mm. The Monte Carlo ray-tracing technique is employed to evaluate the optical performance of different reflector designs. The typical seven-lamp solar simulator arrangement in hexagonal configuration is modeled to analyze the optical performance at different focal lengths. In addition, different xenon arc lamps are modeled with rated powers of 3000, 4000, 4500, and 5000 W for assessing the radiative flux characteristics of the proposed solar simulators. After the optimization, theoretical results show that peak fluxes and radiative powers of 7.2-14.3MW/m2 and 5.06-10.4 kW, respectively, can be achieved with the proposed designs of solar simulators for the different rated powers. Compared with a commercial reflector, theoretical peak flux and power can be improved up to 36% and 17.9%, respectively, with the proper combination of lamp-reflector units. We provide design alternatives to select a more suitable light source at low-rated powers (≤5000W) and different focal lengths of the reflector, which simplifies the complexity of the design and improves the performance of solar simulators.

헤드 마운티드 디스플레이를 위한 시간 제약 렌더링을 이용한 적응적 포비티드 광선 추적법

Ray tracing-based rendering creates by far more realistic images than the traditional rasterization-based rendering. However, it is still burdensome when implemented for a Head-Mounted Display (HMD) system that demands a wide field of view and a high display refresh rate. Furthermore, for presenting high-quality images on the HMD screen, a sufficient number of ray sampling should be carried out per pixel to alleviate visually annoying spatial and temporal aliases. In this paper, we extend the recent selective foveated ray tracing technique by Kim et al. [<xref ref-type="bibr" rid="B1">1</xref>], and propose an improved real-time rendering technique that realizes the rendering effect of the classic Whitted-style ray tracing on the HMD system. In particular, by combining the ray tracing hardware-based acceleration technique and time-constrained rendering scheme, we show that fast HMD ray tracing is possible that is well suited to human visual systems.

High Frequency Land Backscatter Coefficients Over Northern Australia and the Effects of Various Surface Properties

Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate targets beyond the Earth’s horizon. Consequently, the performance of this type of radar is highly dependent on the ionosphere. Reliable models of the radar ground backscatter are required to accurately assess the ionospheric propagation conditions and, thus, the expected performance of OTHRs. The ground backscatter coefficient characterizes the amount of radiation scattered back from a surface toward a receiver per unit area. While the backscatter coefficient of the sea is well understood and may be calculated from theory if the sea state is known, the backscatter coefficient of land at high frequencies is not well understood. To calculate the land backscatter coefficients over Northern Australia, a methodology that compares observed backscatter ionograms to those synthesized using high-frequency (HF) radio wave ray-tracing techniques through model ionospheres was developed. Maps of the backscatter coefficients across Northern Australia were produced. The effects of surface properties, including topography, soil moisture, and vegetation cover on the backscatter coefficients, were investigated. A weak positive correlation between the backscatter coefficient and the soil moisture and surface roughness was observed; however, it was found that the vegetation had the largest effect on the backscatter coefficient.

Feasibility of a finite-difference time-domain model in large-scale acoustic simulations.

Wave-based techniques for room acoustics simulations are commonly applied to low frequency analysis and small-sized simplified environments. The constraints are generally the inherent computational cost and the challenging implementation of proper complex boundary conditions. Nevertheless, the application field of wave-based simulation methods has been extended in the latest research decades. With the aim of testing this potential, this work investigates the feasibility of a finite-difference time-domain (FDTD) code simulating large non-trivial geometries in wide frequency ranges. A representative sample of large coupled-volume opera houses allowed demonstration of the capability of the selected FDTD model to tackle such composite geometries up to 4 kHz. For such a demanding task, efficient calculation schemes and frequency-dependent boundary admittances are implemented in the simulation framework. The results of in situ acoustic measurements were used as benchmarks during the calibration process of three-dimensional virtual models. In parallel, acoustic simulations performed on the same halls through standard ray-tracing techniques enabled a systematic comparison between the two numerical approaches highlighting significant differences in terms of input data. The ability of the FDTD code to detect the typical acoustic scenarios occurring in coupled-volume halls is confirmed through multi-slope decay analysis and impulse responses' spectral content.

Numerical Simulation of Ionospheric Disturbances Due to Rocket Plume and Its Influence on HF Radio Waves Propagation

In this paper, the ionospheric disturbances of CO2, which is released by rocket exhaust plumes, was simulated. The effect of this disturbance on the propagation of high-frequency (HF) radio waves at different incident frequencies was also simulated by using three-dimensional digital ray tracing technique. The results show that CO2 can effectively dissipate the background electrons and form ionospheric holes after being released in the ionosphere. At the peak height of ionospheric electron density (about 300 km), the electrons are dissipated fastest and the radius of ionospheric hole is also largest. This is due to the fact that the diffusion coefficient of CO2 usually increases with height while the electron density just increases before reaching its peak height and then decreases with height, and the chemical reaction rate between ions and CO2 also becomes largest at the peak height of electron density (about 300 km). Around 100 s after the release of CO2, when the radio waves at a frequency of 8 MHz pass through the ionosphere with an elevation range of 85~95°, the “secondary focusing effect” can occur, and we believe that this is due to the reflection of HF shortwaves on the walls of the ionospheric holes. With time going on, this phenomenon disappears at 300 s and only one focus is left at this time. For the HF shortwaves at same incident frequency, the focusing effect of waves displays a weakening trend with time increasing, and the height of focus center also ascends gradually. At the same time after CO2 releasing, with the increasing of radio waves frequency, the focusing effect also becomes weaker and the focus center displays an ascending trend.