The paper deals with a solution of radiation heat transfer problems in enclosures filled with nonparticipating medium using ray tracing on hierarchical ortho-Cartesian meshes. The idea behind the approach is that radiative heat transfer problems can be solved on much coarser grids than their counterparts from computational fluid dynamics (CFD). The resulting code is designed as an add-on to OpenFOAM, an open-source CFD program. Ortho-Cartesian mesh involving boundary elements is created based upon CFD mesh. Parametric non-uniform rational basis spline (NURBS) surfaces are used to define boundaries of the enclosure, allowing for dealing with domains of complex shapes. Algorithm for determining random, uniformly distributed locations of rays leaving NURBS surfaces is described. The paper presents results of test cases assuming gray diffusive walls. In the current version of the model the radiation is not absorbed within gases. However, the ultimate aim of the work is to upgrade the functionality of the model, to problems in absorbing, emitting and scattering medium projecting iteratively the results of radiative analysis on CFD mesh and CFD solution on radiative mesh.

Ray tracing simulation of sound field in rooms is a common tool in room acoustic design for predicting impulse response. There are numerous commercial engineering tools utilising ray tracing simulation. A specific problem in the simulation is the modelling of diffuse reflections when contribution of individual surface is prevailing. The paper introduces modelling of scattering which is interesting when the whole impulse response of a room is not a goal but contribution of certain surface. The main goal of the project is to shape directivity characteristics of scattered reflection. Also, an innovative approach is suggested for converting the energy histogram information obtained by ray tracing into an “equivalent impulse response”. The proposed algorithm is tested by comparing the results with measurements in a real sound field, realised in a scaled model where a diffusing surface is hardware-implemented.

Using the tunderwater corner reflector (CR) to simulate the acoustic scattering characteristics of the military target is a new technology to counter active sonar detection. Existing underwater CRs only have the ability to interfere with the acoustic field, but have limitations in acoustic wave modulation. Therefore, acoustic metasurfaces applied on CRs to enhance the ability of acoustic wave modulation has a great application prospect. A fast prediction method based on the Kirchhoff approximation (KA) and the ray tracing theory is proposed to calculate the acoustic scattering characteristics of CR with acoustic metasurfaces in grooves array type. The accuracy of the method is verified by the finite element method (FEM) simulation. The modulation effect of CR with grooves array in different gradient combinations on the structural scattering acoustic field is analyzed. The research shows that the CR with different combinations of the acoustic metasurface has an obvious modulation effect on the amplitude of the acoustic waves and the deflection of acoustic field. In particular, the grooves array in combination with positive and negative gradients has an obvious deflection impact on the scattering acoustic field.

External light outcoupling structures provide a cost-effective and highly efficient solution for light extraction in organic light-emitting diodes. Among them, different microtextures, mainly optimized for devices with isotopically oriented emission dipoles, have been proposed as an efficient light extraction solution. In the paper, the outcoupling for a preferential orientation of emission dipoles is studied for the case of a red bottom-emitting organic light-emitting diode. Optical simulations are used to analyse the preferential orientation of dipoles in combination with three different textures, namely hexagonal array of sine-textures, three-sided pyramids, and random pyramids. It is shown that while there are minimal differences between the optimized textures, the highest external quantum efficiency of 51% is predicted by using the three-sided pyramid texture. Further improvements, by employing highly oriented dipole sources, are examined. In this case, the results show that the top outcoupling efficiencies can be achieved with the same texture shape and size, regardless of the preferred orientation of the emission dipoles. Using an optimized three-sided pyramid in combination with ideally parallel oriented dipoles, an efficiency of 62% is achievable. A detailed analysis of the optical situation inside the glass substrate, dominating external light outcoupling, is presented. Depicted results and their analysis offer a simplified further research and development of external light extraction for organic light-emitting devices with highly oriented dipole emission sources.

Fibre optic microlenses are small optical elements formed on the end-faces of optical fibres. Their dimensions range from a few tens to hundreds of micrometres. In the article, four optical fibre microlenses are modelled and analysed. Microlenses are used for light beam manipulation and quantitative metrics are needed to evaluate the results, for example, the size of focusing spot or intensity distribution. All four lenses tested are made of rods of the same refractive index; they were welded to a single-mode fibre. Two modelling methods were used to analyse the lenses: ray-tracing and finite-difference time-domain. The ray-tracing algorithm moves rays from one plane to another and refracts them on the surfaces. Finite-difference time-domain consists of calculating Maxwell’s equations by replacing spatial and temporal derivatives by quotients of finite differences. In this paper, the results of the microlenses analyses obtained from ray-tracing and finite-difference time-domain methods were compared. Both methods of analysis showed the presence of undesirable side lobes related to lens design, namely rods too long for lens fabrication. The test results were compared with the measurements made with the knife-edge method. The use of a single tool to determine parameters of an optical fibre lens does not allow for precise determination of its properties. It is necessary to use different tools and programs. This allows a complete analysis of the beam parameters, letting us find the causes of technical issues that limit the performance of the lenses.

The present work is aimed at geometrical optimization and optical analysis of a small-sized parabolic trough collector (PTC). Improving the performance of parabolic trough collectors can greatly justify the use of solar energy. An optimized curvature geometry, the location of the absorber tube, and the heat flux distribution along the circumference of the absorber tube are major features in the geometric optimization and optical modelling of parabolic trough collectors. Rim angle, aperture width, the diameter of the absorber tube, receiver position, and the optimum value of heat flux are the major parameters considered in this work for geometrical and optical analysis. The Monte Carlo ray tracing method has been adopted for analysis. The non-uniform heat flux distribution profile obtained from optical analysis of the proposed parabolic trough collector has been compared with the profile available in the literature, and good agreement has been obtained, which proves the feasibility and reliability of the model and method used for this study. An experimental new small-sized parabolic trough collector has been fabricated for the optimized rim angle of 90 deg after a successful laser light feasibility test. The effect of the absorber tube position along the optical axis on the heat flux profile was analysed and found to be substantial. Furthermore, the sensitivity analysis of the parabolic trough collector using the software applied has been discussed separately.