Physical Model-Based Ocean Scene Modeling In Marine Simulator

Marine simulator is an important application of virtual reality technology in the field of traffic and transportation engineering.Since its development,it has played an important role in many fields such as nautical education,engineering demonstration,and academic research.In order to further improve the physical reality of the ocean scenes in marine simulator,enrich the application scope of marine simulator,and improve the integration of the ocean scene models in the visual system,this paper focuses on the in-depth theoretical research and exploration around key technologies of the physics-based motion and interaction modeling of ocean scenes in marine simulator,aiming to provide theoretical basis and guidance for improving the performance of the marine simulator.In order to improve the physical realism of the ocean scene in marine simulator,in this paper,the Lagrangian form Navier-Stokes equations are adopted as the governing equations of ocean waves,and the governing equations are discretely solved based on the Smoothed Particle Hydrodynamics(SPH)method.This paper mainly focuses five key issues,including incompressibility,boundary treatment and fluid-rigid coupling,oil spill modeling,stochastic fluctuating wind field modeling,and particle based ocean surface reconstruction.It aims to propose a multi-scene modeling method based on SPH framework to unify the ocean scene modeling,reduce the difficulty of coupling different scene models,and enhance the system scalability.In order to further enhance the incompressibility of SPH framework,a novel hybrid incompressible SPH framework is proposed by combining the PPE with velocity divergence as the source term and the nonlinear density constraint based on position based dynamics.The framework first adjusts the particle distribution at the position layer by solving the density constraint to maintain the density invariance,and then the divergence-free velocity field is obtained by solving the PPE to ensure that the density change rate is zero.The hybrid SPH model achieves more ideal incompressibility by limiting the amount and rate of density change.In order to solve the problem of difficulty in modeling of complex fluid-righd coupling scenes in marine simulator,an adaptive single-layer non-uniformly sampled boundary particle model is proposed based on the hybrid SPH framework.The three-dimensional Poisson disk sampling algorithm is used to sample the rigid body object as single-layer boundary particles.The contribution of the boundary particles is taken into account when the physical quantities of ocean particles are computed.By introducing the artificial mass,the contribution of boundary particles is adaptively adjusted according to the shape of the rigid body,and the correction factor is used to correct the contribution of the missing layer boundary particles to ensure the stability of the calculation of the physical quantities of ocean particles at the boundary and the effectiveness of the interaction.The proposed boundary model is naturally coupled with the hybrid SPH framework,and can deal with various types of complex boundaries adaptively.The interaction between fluids and fluids is an important part of ocean interaction scene modeling.Based on the hybrid SPH framework,an improved particle number density model is proposed for modeling offshore oil spill scenes.The model assumes the equal rest density within the support domain,which can uniformly process all neighboring particles including non-uniformly sampled boundary particles,handle density discontinuities at interfaces between multiple fluids,and can simulate the spreading,drifting,and broken of offshore oil spills.In order to simulate rough sea such as heavy wind and waves,this paper proposes a three-dimensional stochastic fluctuating wind field model.The model disturbs the initial wind field based on Perlin noise.The modified wind profile equation is used to simulate the vertical attenuation of wind velocity in the vertical direction.The intensity of the wind field can be flexibly controlled by adjusting the pulse period and pulse width.The wind field model can effectively simulate the complex ocean scenes such as wave overturns.In order to improve the efficiency and realism of ocean surface reconstruction based on SPH framework,this paper proposes an improved anisotropic screen space fluid rendering algorithm.The algorithm constructs the covariance matrix for each ocean particle based on the weighted version Principal Component Analysis(WPCA),and uses the bilateral Jacobi method to perform singular value decomposition(SVD)on the covariance matrix to generate an anisotropic transformation matrix for each ocean particle.A novel anisotropic piecewise function is derived to alleviate the deformation and discontinuity of ocean particle shape at the boundary.Compared with the traditional screen space fluid algorithm,the improved anisotropic algorithm can not only produce smoother ocean surfaces,but also retain the anisotropy to the maximum extent at the boundary,and can maintain sharper features.In this paper,the ocean scene motion and interaction modeling method based on the hybrid SPH framework has broad applicability.The modeling process is unified,and the system is highly integrated and has flexible configuration.It can simulate a variety of typical virtual ocean scenes using a unified framework,which has important practical significance for improving the performance of marine simulator,and lays down the theoretical foundation for physics-based modeling of ocean scenes in marine simulator.