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Data-driven simulation in fluids animation: A survey

DOI:10.3724/SP.J.2096-5796.20.00099

Accepted Date:2021-02-26

Abstract (4) | PDF (1)

The field of fluid simulation is developing rapidly, and data-driven methods provide many frameworks and techniques for fluid simulation. This paper presents a survey of data-driven methods used in fluid simulation in computer graphics in recent years. First, we provide a brief introduction of physical-based fluid simulation methods based on their spatial discretization, including Lagrangian, Eulerian, and hybrid methods. The characteristics of these underlying structures and their inherent connection with data-driven methodologies are then analyzed. Subsequently, we review studies pertaining to a wide range of applications, including data-driven solvers, detail enhancement, animation synthesis, fluid control, and differentiable simulation. Finally, we discuss some related issues and potential directions in data-driven fluid simulation. We conclude that the fluid simulation combined with data-driven methods has some advantages, such as higher simulation efficiency, rich details and different pattern styles, compared with traditional methods under the same parameters. It can be seen that the data-driven fluid simulation is feasible and has broad prospects.

Affine particle-in-cell method for two-phase liquid simulation

DOI:10.3724/SP.J.2096-5796.20.00051

Accepted Date:2021-02-25

Abstract (4) | PDF (1)

Background  The interaction of gas and liquid can produce many interesting phenomena, such as bubbles rising from the bottom of the liquid. The simulation of two-phase fluids is a challenging topic in computer graphics. To animate the interaction of a gas and liquid, MultiFLIP samples the two types of particles, and a Euler grid is used to track the interface of the liquid and gas. However, MultiFLIP uses the fluid implicit particle (FLIP) method to interpolate the velocities of particles into the Euler grid, which suffer from additional noise and instability. Methods To solve the problem caused by fluid implicit particles (FLIP), we present a novel velocity transport technique for two individual particles based on the affine particle-in-cell (APIC) method. First, we design a weighed coupling method for interpolating the velocities of liquid and gas particles to the Euler grid such that we can apply the APIC method to the simulation of a two-phase fluid. Second, we introduce a narrowband method to our system because MultiFLIP is a time-consuming approach owing to the large number of particles. Results Experiments show that our method is well integrated with the APIC method and provides a visually credible two-phase fluid animation. Conclusions  The proposed method can successfully handle the simulation of a two-phase fluid.

Stains on imperfect textile

DOI:10.3724/SP.J.2096-5796.20.00097

Accepted Date:2021-02-25

Abstract (5) | PDF (2)

Background  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.

Affine transformation of virtual 3D object using 2D localization of fingertips

DOI:10.3724/SP.J.2096-5796.20.00053

Accepted Date:2020-11-01

Abstract (52) | PDF (7)

Background Interactions with virtual 3D objects in the virtual reality (VR) environment using the gesture of fingers captured in a wearable 2D camera have emerging applications in real-life. Method This paper presents an approach of a two-stage convolutional neural network, one for the detection of hand and another for the fingertips. One purpose of VR environments is to transform a virtual 3D object with affine parameters by using the gesture of thumb and index fingers. Results To evaluate the performance of the proposed system, one existing, and another developed egocentric fingertip databases are employed so that learning involves large variations that are common in real-life. Experimental results show that the proposed fingertip detection system outperforms the existing systems in terms of the precision of detection. Conclusion The interaction performance of the proposed system in the VR environment is higher than that of the existing systems in terms of estimation error and correlation between the ground truth and estimated affine parameters.

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

DOI:10.3724/SP.J.2096-5796.20.00048

Accepted Date:2020-09-14

Abstract (77) | PDF (11)

Background In SPH fluid simulation method, the smooth length not only affects the process of neighbor search, but also affects the calculation accuracy of pressure solver. Therefore, it plays an important role in ensuring the accuracy and stability of SPH. Methods In this paper, an adaptive SPH fluid simulation method with variable smooth length is designed, in which the size of smooth length is adaptively adjusted by the ratio of particle density to the weighted average of the density of its neighboring particles. In addition, a neighbor search scheme and kernel function scheme are designed to solve the asymmetry problems caused by variable smooth length. Results Compared with some classical methods, the simulation efficiency of the proposed algorithm is competitive, and the variance of the number of neighbor particles is effectively reduced. As a result, the visual effect is closer to the physical reality. Conclusions In this paper, the precision of interpolation calculation in SPH algorithm is improved by using the adaptive smooth length scheme, so that the stability of the algorithm is enhanced and larger time step is possible.

Survey on lightweighting methods of huge 3D models for online Web3D visualization

DOI:10.3724/SP.J.2096-5796.20.00006

Accepted Date:2020-02-13

Abstract (195) | PDF (23)

Background With the rapid development of Web3D technologies, online Web3D visualization , especially for complex models or scenes, has been a great yet heavy demand. As the serious conflict between Web3D system load and the resource consumption in processing these huge models, the huge 3D model lightweighting methods for online Web3D visualization are reviewed in this paper. Methods Observing the geometry redundance introduced by man-made operations in modeling procedure, several categories of lightweighting related work which aim for reducing the data amount and resource consumption for Web3D visualization are elaborated. Results With comparing perspectives, the characteristics of each method are summarized and within the reviewed methods, the geometric redundance removal which achieves the lightweight goal by detecting and removing the repeated components is an appropriate way for current online Web3D visualization. Meanwhile, the learning algorithm, though not practical at present, is our expected topic. Conclusions Various aspects should be considered in an efficient lightweight method for online Web3D visualization, including characteristics of original data, combination or extended of the existed methods, and even scheduling strategy, cache management, rendering mechanism. Meanwhile, innovation methods, especially the learning algorithm is worth exploring.