Adaptive smoothing length method based on weighted average of neighboring particle density for SPH fluid simulation

Background In the smoothed particle hydrodynamics(SPH)fluid simulation method,the smoothing length affects not only the process of neighbor search but also the calculation accuracy of the pressure solver.Therefore,it plays a crucial role in ensuring the accuracy and stability of SPH.Methods In this study,an adaptive SPH fluid simulation method with a variable smoothing length is designed.In this method,the smoothing length is adaptively adjusted according to the ratio of the particle density to the weighted average of the density of the neighboring particles.Additionally,a neighbor search scheme and kernel function scheme are designed to solve the asymmetry problems caused by the variable smoothing length.Results The simulation efficiency of the proposed algorithm is comparable to that of some classical methods,and the variance of the number of neighboring particles is reduced.Thus,the visual effect is more similar to the corresponding physical reality.Conclusions The precision of the interpolation calculation performed in the SPH algorithm is improved using the adaptive-smoothing length scheme;thus,the stability of the algorithm is enhanced,and a larger timestep is possible.

Study of ghost image suppression in polarized catadioptric virtual reality optical systems

Backgrounds This paper introduces a polarized catadioptric virtual reality optical system.With a focus on the issue of serious ghost image in the system,root causes are analyzed based on design principles and optical structure.Methods The distribution of stray light is simulated using Lighttools,and three major ghost paths are selected using the area of the diffuse spot,S d and the energy ratio of the stray light,K as evaluation means.A method to restrain the ghost image through optimization of the structure of the optical system by controlling the focal power of the ghost image path is proposed.Results/Conclusions The results show that the S_(d) for the ghost image path increases by 40%and K decreases by 40%after optimization.Ghost image is effectively suppressed,which provides the theoretical basis and technical support for ghost suppression in a virtual reality optical system.

Stains on imperfect textile

The imperfect material effect is one of the most important themes to obtain photo-realistic results in rendering.Textile material rendering has always been a key area in the field of computer graphics.So far,a great deal of effort has been invested in its unique appearance and physics-based simulation.The appearance of the dyeing effect commonly found in textiles has received little attention.This paper introduces techniques for simulation of staining effects on textiles.Pulling,wearing,squeezing,tearing,and breaking effects are more common imperfect effects of fabrics,these external forces will cause changes in the fabric structure,thus affecting the diffusion effect of stains.Based on the microstructure of yarn,we handle the effect of the stain on the imperfect textile surface.Our simulation results can achieve a photo-realistic effect.

Freeform OST-HMD system with large exit pupil diameter and vision correction capability

Compactness and light weight,large exit pupil diameter and distance,small distortion for virtual image,and see-through light paths are pivotal factors to achieve a better,wearable experience of optical see-through headmounted displays(OST-HMDs).In addition,light efficiency of the virtual image light path is an important factor for heat dissipation in HMD devices.This paper presents a new type of OST-HMD optical system that includes three wedge-shaped freeform prisms and two symmetric lenses.Based on a 0.71 in.microdisplay,an OST-HMD prototype with a diagonal field of view(FOV)of 45.3°,an F-number(F/#)of 1.8,an exit pupil size of 12 mm×8 mm,and an eye relief of 18 mm is demonstrated.The maximum value of distortion of the final system is 0.6%and 0.4%for virtual image and see-through light path,respectively.The overall dimension of the optical system per eye is no larger than 30 mm(width)×40 mm(height)×14 mm(thickness),and the weight of the optical module including lenses,holder,and microdisplay is 12.8 g.The light efficiency of the virtual image light path is up to 50%higher than those of other OST-HMD optical solutions.