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I am a PhD student specialized in physics simulation, currently working with Prof. Eitan Grinspun and Prof. Changxi Zheng.

Previously, I got my M. Sc. in computer science from Columbia University, and B. Eng. in computer software from Tsinghua University.

FYUN@ACM.ORG, +1(347)-226-8785 [CURRICULUM VITAE | LINKEDIN | WECHAT]

PRESS RELEASE

Researchers Develop Algorithm to 3D Print Vibrational Sounds
[National Science Foundation]

PHYSICS SIMULATION

Yun (Raymond) Fei, Henrique Teles Maia, Christopher Batty, Changxi Zheng, Eitan Grinspun, A Multi-Scale Model for Simulating Liquid-Hair Interactions, ACM Transactions on Graphics (SIGGRAPH 2017), Volume 36 Issue 4, July 2017.
[Abstract | Project Page]

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。

Dingzeyu Li, Yun Fei, Changxi Zheng. Interactive Acoustic Transfer Approximation for Modal Sound, ACM Transactions on Graphics (SIGGRAPH 2016), Volume 35 Issue 1, December 2015.
[Abstract | Preprint: High, Low | 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。

Gaurav Bharaj, David Levin, James Tompkin, Yun Fei, Hanspeter Pfister, Wojciech Matusik, Changxi Zheng. Computational Design of Metallophone Contact Sounds, ACM Transactions on Graphics (Proc. of SIGGRAPH Asia 2015), 2015.
[Abstract | Preprint | ACM Digital Library | Supplementary | Video: YouTube, bilibili | Project page | Industrial Reproduction]

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。

GPU

Mesh2Centroids: SPH-based Lloyd's Relaxation on GPU inside 3D Meshes, 2012
[GitHub]

Yun Fei, Guodong Rong, Bin Wang, Wenping Wang, Parallel L-BFGS-B algorithm on GPU, Computers and Graphics, Volume 40, May 2014, Pages 1-9.
[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.

Yun Fei, Bin Wang, and Jiating Chen. Point-Tessellated Voxelization. In proceedings of Graphics Interface 2012, May 28-30, 2012 1-9.
[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.

Real-time Stereo Matching on GPU with Hierarchical AD-Census, 2011
[YouTube | Source (Direct3D)]

RENDERING

Miaoyi Wang, Bin Wang, Yun Fei, Kang-Lai Qian, Wenping Wang, Jiating Chen, Jun-Hai Yong. Towards Photo Watercolorization with Artistic Verisimilitude, IEEE Transactions on Visualization and Computer Graphics, 2014.
[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.

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). Bilateral Blue Noise Sampling. ACM Transactions on Graphics (Proc. of SIGGRAPH Asia 2013)
[Abstract | Preprint, Low (1.9MB) , High (23.0MB) | Video: YouTube, bilibili | Image Stippling | Source | 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.

Yun Fei, Bin Wang. Fast Multi-image-based Photon Tracing with Grid-based Gathering. In posters of SIGGRAPH 2012, selected as the Student Research Competition Semi-finalist Star, Aug 5-9, 2012 1-1.
[Abstract | ACM digital library | Preprint | Brief | YouTube | Poster]

We developed a real-time solution for approximate global illumination, where the temporal cost in complex scenes is dramatically reduced. Our approach initially traces photon-rays with multiple cube-maps, and then gathers the irradiance of photons using uniform grids filled with low-order spherical harmonics. Numerous global illumination effects can be rendered efficiently in our framework.

MOBILE COMPUTING

Xi Xiong, Zheng Yang, Longfei Shangguan, Yun Fei, Milos Stojmenovic, and Yunhao Liu. SmartGuide: Towards Single-image Building Localization with Smartphone. In proceedings of MobiHoc 2015, June 24, 2015 1-10.
[Abstract | ACM Digital Library | Preprint]

We introduce SmartGuide, a light-weighted and efficient approach to localize and recognize a distant unknown building. Our approach relies on shooting only a single photo of a target building via a smartphone and a local 2D Google map. SmartGuide first extracts a partial top view contour of a building from its side-view photo by applying vanishing point and the Manhattan World Assumption, and then fetches a candidate building set from a local 2D Google map based on smartphone's GPS readings. Partial top view shape, orientation and distance relative to the camera are used as input parameters in a probability model, which adversely recognizes the best candidate building in the local map. Our model is developed based on kernel density estimation that helps reduce noise in the smartphone sensors, such as GPS readings and camera ray direction reported by noisy accelerometer and compass. Experimental results demonstrate that our approach recognizes buildings ranging from 20m to 520m and achieves 92.7% accuracy in downtown areas where the Manhattan World Assumption is applicable. In addition, the processing time is no more than 6 seconds for 87% of cases. Compared with existing building localization schemes, SmartGuide offers numerous advantages. Our method avoids taking multiple photos, intricate 3D reconstruction or any initial deployment cost of database construction, making it faster and less labor-intensive than existing solutions.

MISCELLANEOUS

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

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

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

4 Minutes for 40 Years: A Brief Review of Modern Computer Graphics, Jan. 2014
[YouTube]

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), selected as the Excellent Graduation Thesis, rank 1st in department
[Preprint | Tsinghua University Library | Source (Direct3D) | Video: Youku, YouTube]

Compatibility Patch for using GLFW 3 with AntTweakBar
[Header File]

PRESENTATION

The Lagrangian: Art of Smoothed Particle Hydrodynamics (SPH)
[PDF (4.7MB)]