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PHD CANDIDATE
COLUMBIA COMPUTER GRAPHICS GROUP (C2G2)
YF2320@COLUMBIA.EDU [CURRICULUM VITAE | LINKEDIN | GOOGLE SCHOLAR]

My research focuses on physics simulation, including elastic rods, fluids, thin shells, and their complex coupling and collision handling. At Columbia I am advised by Prof. Changxi Zheng and Prof. Eitan Grinspun. During my summer time, I had wondrous internship experience at Pixar Research, Weta Digital, Adobe Research, NVIDIA, GE Healthcare, and Microsoft Research Asia. I got my bachelor degree in Tsinghua University where I worked with Prof. Bin Wang on rendering and GPU.

PUBLICATIONS

A Multi-Scale Model for Simulating Liquid-Fabric Interactions
ACM Transactions on Graphics (SIGGRAPH 2018)  simulation
Yun (Raymond) Fei, Christopher Batty, Eitan Grinspun, Changxi Zheng
[Abstract | Project Page | In Press: Deutschlandfunk (in German), 3DVF (in French), Columbia Engineering, CG世界 (in Chinese)]

We propose a method for simulating the complex dynamics of partially and fully saturated woven and knit fabrics interacting with liquid, including the effects of buoyancy, nonlinear drag, pore (capillary) pressure, dripping, and convection-diffusion. Our model evolves the velocity fields of both the liquid and solid relying on mixture theory, as well as tracking a scalar saturation variable that affects the pore pressure forces in the fluid. We consider the porous microstructure implied by the fibers composing individual threads, and use it to derive homogenized drag and pore pressure models that faithfully reflect the anisotropy of fabrics. In addition to the bulk liquid and fabric motion, we derive a quasi-static flow model that accounts for liquid spreading within the fabric itself. Our implementation significantly extends standard numerical cloth and fluid models to support the diverse behaviors of wet fabric, and includes a numerical method tailored to cope with the challenging nonlinearities of the problem. We explore a range of fabric-water interactions to validate our model, including challenging animation scenarios involving splashing, wringing, and collisions with obstacles, along with qualitative comparisons against simple physical experiments.

我们提出了一种模拟部分或完全饱和机织物、针织物与液体相互作用的复杂运动的方法,模拟的效果包括了浮力、非线性拖曳力、孔隙(毛细)压力、滴流和对流扩散。我们的模型基于混合物理论来计算液体和固体的速度场,并同时追踪影响流体孔隙压力的饱和度。我们研究了构成单根纤维的多孔微结构,并用它来推导均匀化的拖曳力和孔隙压力模型,这些模型忠实地反映了织物具有各向异性的特点。在大块液体和织物的运动之外,我们还推导出一个准静态流动模型,用于描述液体在织物内部的传导。我们的实现大大扩展了布料和流体的标准数值模型,从而可以模拟湿织物的各种行为,并且我们的实现囊括了一种用于处理具有挑战性的非线性问题的数值方法。我们做了一系列的织物-水相互作用实验从而验证我们的模型,其中包括一些具有挑战性的动画场景,比如液体飞溅,拧毛巾,以及布料与障碍物的碰撞等,同时与简单的物理实验做了一些定性比较。

A Multi-Scale Model for Simulating Liquid-Hair Interactions
ACM Transactions on Graphics (SIGGRAPH 2017)  simulation
Yun (Raymond) Fei, Henrique Teles Maia, Christopher Batty, Changxi Zheng, Eitan Grinspun
[Abstract | Project Page | In Press: 80.lv, CG Channel, PC Gamer, CG世界 (in Chinese)]

The diverse interactions between hair and liquid are complex and span multiple length scales, yet are central to the appearance of humans and animals in many situations. We therefore propose a novel multi-component simulation framework that treats many of the key physical mechanisms governing the dynamics of wet hair. The foundations of our approach are a discrete rod model for hair and a particle-in-cell model for fluids. To treat the thin layer of liquid that clings to the hair, we augment each hair strand with a height field representation. Our contribution is to develop the necessary physical and numerical models to evolve this new system and the interactions among its components. We develop a new reduced-dimensional liquid model to solve the motion of the liquid along the length of each hair, while accounting for its moving reference frame and influence on the hair dynamics. We derive a faithful model for surface tension-induced cohesion effects between adjacent hairs, based on the geometry of the liquid bridges that connect them. We adopt an empirically-validated drag model to treat the effects of coarse-scale interactions between hair and surrounding fluid, and propose new volume-conserving dripping and absorption strategies to transfer liquid between the reduced and particle-in-cell liquid representations. The synthesis of these techniques yields an effective wet hair simulator, which we use to animate hair flipping, an animal shaking itself dry, a spinning car wash roller brush dunked in liquid, and intricate hair coalescence effects, among several additional scenarios.

头发和液体之间多样的相互作用十分复杂,并且跨越多个长度尺度,这种复杂交互在许多情况下对于有人类和动物出现的场景是至关重要的。为此,我们提出了一种新颖的多组分模拟框架,该框架用于处理湿头发动态过程中所涉及的关键物理机制。本文采用的两大基础模型分别是:用于头发的离散杆模型,及用于流体的粒子胞元模型。为了处理粘附在头发上的薄层液体,我们在每根头发上附加了一个高度场。本文的贡献在于,开发了必要的物理和数值模型来运作这个新系统及其组件之间的相互作用。我们开发了一种新的降维液体模型,以解算沿着每根毛发流动的液体运动状态,同时考虑其运动参考系和对毛发动力学的影响。基于连接它们的液体桥的几何形状,我们推导了相邻毛发之间的表面张力引起的内聚效应的模型。我们采用拖曳模型来处理头发和周围液体之间较粗糙的相互作用,并提出了新的滴液和液滴捕获方法,能够维持液体体积不变,从而在降维模型和粒子模型之间转移液体。综合以上方法,我们开发了一种有效的湿毛发模拟器,用于模拟头发翻转、动物甩毛、旋转的洗车筒,以及其他几种场景中复杂的头发聚结效应。

Interactive Acoustic Transfer Approximation for Modal Sound
ACM Transactions on Graphics (SIGGRAPH 2016)  simulation
Dingzeyu Li, Yun Fei, Changxi Zheng
[Abstract | Preprint: Compressed, Regular | ACM Digital Library | Video: YouTube, bilibili | Fast Forward | Project Page]

Current linear modal sound models are tightly coupled with their frequency content. Both the modal vibration of object surfaces and the resulting sound radiation depend on the vibration frequency. Whenever the user tweaks modal parameters to adjust frequencies the modal sound model changes completely, necessitating expensive recomputation of modal vibration and sound radiation.

We propose a new method for interactive and continuous editing as well as exploration of modal sound parameters. We start by sampling a number of key points around a vibrating object, and then devise a compact, low-memory representation of frequency-varying acoustic transfer values at each key point using Prony series. We efficiently precompute these series using an adaptive frequency sweeping algorithm and volume-velocity-preserving mesh simplification. At runtime, we approximate acoustic transfer values using standard multipole expansions. Given user-specified modal frequencies, we solve a small least-squares system to estimate the expansion coefficients, and thereby quickly compute the resulting sound pressure value at arbitrary listening locations. We demonstrate the numerical accuracy, the runtime performance of our method on a set of comparisons and examples, and evaluate sound quality with user perception studies.

当前线性模态声音模型与它们的频率成分紧密耦合,因此物体表面的模态振动和由此产生的声音辐射取决于振动频率。每当用户通过调整模态参数来调整频率时,模态声音模型将完全改变,迫使用户重新计算模态振动和声音辐射,这些计算非常耗时。

我们提出了一种新方法可以互动式地持续编辑模态声音参数以及探索这些参数。我们首先在振动的物体周围采样一些关键点,然后在每个关键点使用Prony序列设计出一套紧致的,不需要太多内存的结构来表示频率变化的声音传输方程的数据。我们通过使用自适应的频率扫描算法和保持体积速度的网格简化算法,有效地预先计算这些序列。在运行时,我们使用标准的多极扩张来近似声音传输方程的数据。给定用户指定的模态频率,我们解一个最小二乘系统来估计序列展开的系数,并由此快速计算在任意收听位置所得的声压值。我们展示了这套方法计算的准确性,通过对一组实验的比较以及运行时性能分析,我们还研究了不同声音质量对于用户感知的影响。

Computational Design of Metallophone Contact Sounds
ACM Transactions on Graphics (SIGGRAPH Asia 2015)  simulation fabrication
Gaurav Bharaj, David Levin, James Tompkin, Yun Fei, Hanspeter Pfister, Wojciech Matusik, Changxi Zheng
[Abstract | Preprint | ACM Digital Library | Supplementary | Video: YouTube, bilibili | Project page | Industrial Reproduction | In Press: Science 360, Wired, Popular Science, Gizmodo, Inverse, Columbia Engineering, Science Daily, Gizmag, TechRadar, 3DFab+Print]

Metallophones such as glockenspiels produce sounds in response to contact. Building these instruments is a complicated process, limiting their shapes to well-understood designs such as bars. We automatically optimize the shape of arbitrary 2D and 3D objects through deformation and perforation to produce sounds when struck which match user-supplied frequency and amplitude spectra. This optimization requires navigating a complex energy landscape, for which we develop Latin Complement Sampling to both speed up finding minima and provide probabilistic bounds on landscape exploration. Our method produces instruments which perform similarly to those that have been professionally-manufactured, while also expanding the scope of shape and sound that can be realized, e.g., single object chords. Furthermore, we can optimize sound spectra to create overtones and to dampen specific frequencies. Thus our technique allows even novices to design metallophones with unique sound and appearance.

钟琴等铁器在被碰触时会产生响应的声音。构建这些乐器是一个复杂的过程,因此它们的形状被限制于易于理解的设计,如条形等。我们可以自动优化任意二维和三维形状,并通过变形,穿孔等方式,使得这些乐器被敲击时能匹配用户提供的频率和幅度谱产生的声音。这种优化需要探索复杂的能量分布,为此我们设计了拉丁补采样算法,这种算法既加快了寻找极小值的过程,又可以提供能量分布探索的概率范围。我们的方法可以用来生产性能近似于专业制造的乐器,同时也拓宽了这些乐器能够产生的形状和声音,例如,单个物体产生和弦的种类。此外,我们可以优化声音频谱来产生泛音,并抑制特定频率的产生。因此,我们的技术甚至允许非专业人员来设计铁器,并使得这些铁器拥有独特的声音和外观。

On the Hessian of Shape Matching Energy
Technical Report, 2015  simulation
Yun Fei
[PDF | arXiv]

SmartGuide: Towards Single-image Building Localization with Smartphone
Proceedings of MobiHoc 2015  mobile computing
Xi Xiong, Yang Zheng, Longfei Shangguan, Yun Fei, Miloš Stojmenović, Yunhao Liu
[Preprint]

Parallel L-BFGS-B algorithm on GPU
Computers and Graphics, 2014  GPU geometry
Yun Fei, Guodong Rong, Bin Wang, Wenping Wang
[Abstract | ScienceDirect | Preprint | Github]

Due to the rapid advance of general-purpose graphics processing unit (GPU), it is an active research topic to study performance improvement of non-linear optimization with parallel implementation on GPU, as attested by the much research on parallel implementation of relatively simple optimization methods, such as the conjugate gradient method. We study in this context the L-BFGS-B method, or the limited memory Broyden–Fletcher–Goldfarb–Shanno with boundaries, which is a sophisticated yet efficient optimization method widely used in computer graphics as well as general scientific computation. By analyzing and resolving the inherent dependencies of some of its search steps, we propose an efficient GPU-based parallel implementation of L-BFGS-B on the GPU. We justify our design decisions and demonstrate significant speed-up by our parallel implementation in solving the centroidal Voronoi tessellation (CVT) problem as well as some typical computing problems.

Towards Photo Watercolorization with Artistic Verisimilitude
IEEE Transactions on Visualization and Computer Graphics, 2014  image rendering
Miaoyi Wang, Bin Wang, Yun Fei, Kang-Lai Qian, Wenping Wang, Jiating Chen, Jun-Hai Yong
[Abstract | Preprint | IEEE Xplore | Gallery]

We present a novel artistic-verisimilitude driven system for watercolor rendering of images and photos. Our system achieves realistic simulation of a set of important characteristics of watercolor paintings that have not been well implemented before. Specifically, we designed several image filters to achieve: 1) watercolor-specified color transferring; 2) saliency-based level-of-detail drawing; 3) hand tremor effect due to human neural noise; and 4) an artistically controlled wet-in-wet effect in the border regions of different wet pigments. A user study indicates that our method can produce watercolor results of artistic verisimilitude better than previous filter-based or physical-based methods. Furthermore, our algorithm is efficient and can easily be parallelized, making it suitable for interactive image watercolorization.

Bilateral Blue Noise Sampling
ACM Transactions on Graphics (SIGGRAPH Asia 2013)  geometry rendering
Jiating Chen*, Xiaoyin Ge*, Li-Yi Wei, Bin Wang, Yusu Wang, Huamin Wang, Yun Fei, Kang-Lai Qian, Jun-Hai Yong, Wenping Wang (*Joint 1st authors)
[Abstract | Preprint, Compressed (1.9MB) , Regular (23.0MB) | Video: YouTube, bilibili | Image Stippling | GitHub | Project Page]

Blue noise sampling is an important component in many graphics applications, but existing techniques consider mainly the spatial positions of samples, making them less effective when handling problems with non-spatial features. Examples include biological distribution in which plant spacing is influenced by non-positional factors such as tree type and size, photon mapping in which photon flux and direction are not a direct function of the attached surface, and point cloud sampling in which the underlying surface is unknown a priori. These scenarios can benefit from blue noise sample distributions, but cannot be adequately handled by prior art.

Inspired by bilateral filtering, we propose a bilateral blue noise sampling strategy. Our key idea is a general formulation to modulate the traditional sample distance measures, which are determined by sample position in spatial domain, with a similarity measure that considers arbitrary per sample attributes. This modulation leads to the notion of bilateral blue noise whose properties are influenced by not only the uniformity of the sample positions but also the similarity of the sample attributes. We describe how to incorporate our modulation into various sample analysis and synthesis methods, and demonstrate applications in object distribution, photon density estimation, and point cloud sub-sampling.

Research on GPU Acceleration of Incompressible Smoothed Particle Hydrodynamics and Applications
不可压平滑粒子流体动力学算法GPU并行加速及其应用研究
Bachelor Thesis of Tsinghua University (in Chinese), 2013  simulation GPU
[Preprint | Tsinghua University Library | Source (Direct3D) | Video: Youku, YouTube]

Point-Tessellated Voxelization
Proceedings of Graphics Interface 2012  GPU geometry rendering
Yun Fei, Bin Wang, and Jiating Chen
[Abstract | ACM digital library | Preprint | Video: YouTube, bilibili | Source (Direct3D)]

Applications such as shape matching, visibility processing, rapid manufacturing, and 360 degree display usually require the generation of a voxel representation from a triangle mesh interactively or in real-time. In this paper, we describe a novel framework that uses the hardware tessellation support on the graphics processing unit (GPU) for surface voxelization. To generate gap-free voxelization results with superior performance, our framework uses three stages: triangle subdivision, point generation, and point injection. For even higher temporal efficiency we introduce PN-triangles and displacement mapping to voxelize meshes with rugged surfaces in high resolution.

Our framework can be implemented with simple shader programming, making it readily applicable to a number of real-time applications where both development and runtime efficiencies are of concern.

Fast multi-image-based photon tracing with grid-based gathering
SIGGRAPH 2012 Poster
Yun Fei, Bin Wang
[Brief Report | Poster | Technical Report | YouTube]

DEMO & SHORT FILMS

Mesh2Centroids: SPH-based Lloyd's Relaxation on GPU inside 3D Meshes
Technical Demo
[GitHub]

Affine Particle-in-Cell in 2D
Educational Demo
[GitHub]

A Single C++ Header Generating 3D Triangulated Rounded Corner Box
[GitHub]

4 Minutes for 40 Years: A Brief Review of Modern Computer Graphics
[YouTube]