Collaborative Research: HCC: Small: Understanding Human Hair With Type 4 Simulation

了解人类头发的机制在视觉媒体中有着广泛的应用，对于忠实地描绘虚拟人类至关重要，因为在面部之后，头发是我们在建立一个人的身份时所关注的下一个特征。然而，几乎所有现有的研究都集中在对直发或卷发的描述上，这是沃克头发类型系统中的1到3种类型，而第4种类型的头发，也被称为非洲质感或卷曲的头发，几乎没有得到关注。这种知识差距是不幸的，因为美国数百万人的自然发型，以及全球10亿人的自然发型是4型；因此，在数字媒体中表示和模拟虚拟的4型头发是困难的，因为现有的算法在设计时没有考虑到它的具体计算挑战。更广泛地说，如果没有对4型头发的全面研究，就不可能全面了解人类的头发。本项目将通过开发新的力学模型和有效的计算方法来解决这些缺陷。固体的基本力学行为是由它的应变能决定的，而能量通常是根据实际固体的特定行为定制的。利用团队的互补专业知识和先前为体积固体设计强大的新能量的经验，将定义一种新的、各向异性的弹塑性4型头发能量，并将根据实际测量结果和广泛的大规模模拟数据验证所得模型。此外，对类型4头发的详细了解将为跨越所有头发类型的表示指明道路；为了跨越这些类型，本研究将开发跨链（1D），壳（2D）和体积（3D）体系的应变能的通用特征分析方法。项目成果将包括有效的方法，能够为人类头发产生逼真的运动，在所有的多样性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding the mechanics of human hair has wide applications in visual media and is critical to faithfully depicting virtual humans, because after the face, hair is the next characteristic that we look to when establishing a person's identity. However, almost all existing research has focused on the depiction of straight or curly hair, which spans Types 1 to 3 in the Walker hair typing system, whereas Type 4 hair, also known as afro-textured or kinky hair, has received almost no attention. This knowledge gap is unfortunate, because the naturally occurring hair type of millions of people in the United States, and a billion people worldwide, is Type 4; consequently, representing and simulating virtual Type 4 hair in digital media is difficult, because existing algorithms were not designed with its specific computational challenges in mind. More broadly, a comprehensive understanding of human hair is not possible without a complete investigation of Type 4. This project will address these deficiencies by developing new mechanical models and efficient computational methods for Type 4 hair. The fundamental mechanical behavior of a solid is determined by its strain energy, and energies are usually custom-tailored to the behavior of specific real-world solids. Leveraging the team's complementary expertise and prior experience designing robust new energies for volumetric solids, a new, anisotropic, elasto-plastic energy for Type 4 hair will be defined, and the resulting model will be validated against real-world measurements as well as extensive large-scale simulation data. Moreover, a detailed understanding of Type 4 hair will point the way toward representations that span all hair types; to bridge these types, this research will develop general eigenanalysis methods for strain energies that span the strand (1D), shell (2D), and volumetric (3D) regimes. Project outcomes will include efficient methods that are capable of generating realistic motion for human hair, in all of its diversity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.