Particle-based Ice Freezing Simulation

Physics-based modeling of nature scene is a challenging topic in research of computer graphics.Ice Freezing Scenes are one of the most important natural scenes which are useful in virtual reality and digital entertainments.As a complex natural material,ice is rich in visual details including air bubbles,cracks and volume expansion.To manually model the freezing process with complex details in a CG representation would be a daunting task.Recently,researchers have made great efforts on simulating freezing of specific type of ice,such as icicle and frost with physics-based methods.And freezing applied on volume of ice with rich details and the underlying physical processes are also well studied.However,current ice freezing simulation algorithms are not capable to deal with dynamic freezing phenomenon occur on flowing water,where the dynamics of water play an important role.In order to reduce the modeling cost and simulate the complex freezing scenes efficiently,a physical particle-based dynamic ice freezing model is presented in this paper.At first,we represent water as fluid and construct a particle-based freezing simulation framework.Then,on that basis,we improve the heat conduction equation to solve temperature varying problem.For the opacity character of ice,we simulate the air bubble diffusion depending on particle distance in a well-distributed way.Besides,we adopted a hybrid solidification approach to simulate the stable phase transition process.At last,we focus on the simulation of various freezing phenomenon,such as rigid fluid collision,surface adhesion and melting on the basis of particle-based framework.The result demonstrates that the proposed method is effective and robust for simulation of dynamic freezing on flowing water with realistic visual appearance,convincing animation process and easily controlled freezing conditions.Our contributions are as follows:(1)Propose a set of particle-based methods for ice freezing.We represent water and ice as particles and model the water as fluids dynamics.Fluids dynamics introduce flexible representation of water movement and final ice volume shape after freezing.Volume expansion can also be captured with this approach.Particle-based method is free from space limitation and realistic animation of freezing is possible.Besides,particle-based fluid simulation is convenient for various interactive freezing scenes.More importantly,physical-based freezing sub process can be well coupled with particle-based method and it builds a suitable and extendible freezing framework.(2)Propose an accurate and reasonable physics-based ice freezing process model.We solve the heat transfer and air bubble diffusion process in the particle-based framework.By adopting an advanced heat transfer equation involving the thermal diffusion difference between ice and water,a correct heat transfer process is achieved and the computation complexity is also reduced.In addition,various freezing speed and direction can be controlled due to user-specified parameters.Air bubble diffusion is solved by taking into consideration the relative distance of particles to achieve convincing dissolved air distribution.(3)Propose a robust hybrid solidification model.Our method divides phase transition process into two states according to particle phases.We firstly use phase-dependent viscosity in near solid states.Then we adopt shape matching constraints in fully solid state by making use of stability of position based method.This method makes solidification simple,robust and efficient.(4)Simulation of various freezing scene with particle-based methods.A unified particle model is used to simulate the phenomenon of rigid-fluid collision,friction,surface adhesion and melting,which improves the variety of freezing scene and as well validate our methods adequately.