Yuk-Ming Tang

Human foot modeling towards footwear design

Comfort test of footwear is mainly based on subjective perception of the wearer and a large number of subjects are required to obtain a reliable result. Therefore, the subjective comfort test is expensive and time consuming. Although the foot size and shape of a subject can be obtained by using a three-dimensional (3D) foot scanner, it is still difficult to create foot motion animations of each subject suitable for computer simulation. In this paper, we propose a fast approach to model foot deformation and present its application in simulating interaction with footwear towards footwear design. The simulation determines deformation of foot and footwear models. It can also determine stress distribution in the footwear. Given an initial foot model and a captured foot motion, human foot animation is created first. Then, the footwear model is fitted to the foot to compute the deformation and stress in the footwear. In this article, the boundary element method (BEM) is adopted. We demonstrate the results by conducting simulation of a captured gait motion. Experimental results showed that the method can be used to simulate human gait motion, and can determine deformation of footwear.

The effect of tendons on foot skin deformation

Anatomical human models are usually divided into layers including skin, muscle and skeleton. In spite of the realistic animation of the models that can be achieved, and the realistic appearance of the model determined by the underlying muscles and skeleton, the role of tendons in determining the deformation of skin surface has not been well addressed. This paper presents an approach for modeling human foot tendons and determines their influence on the skin layer deformation. Our goal is to model deformation of the tendons such that a realistic foot simulation can be obtained. An anatomical foot model including skin, muscle, tendon and skeleton layers is adopted. The appearance of the skin layer is determined based on the underlying layers. To allow interactive deformation of the tendon models, the axial deformation technique is adopted. Given the position of the foot and the basis function, the position of the data points that control the axial curve is updated. To allow more accurate computation of the data point positions, a method that estimates the basis function based on real data obtained from foot images is also presented. Experimental results showed that the axial deformation technique can model deformation of the foot tendons with satisfactory visual realism. With the tendon deformation, the visual realism on the skin deformation is also enhanced.

Comparison of FEM and BEM for interactive object simulation

Abstract There are two major approaches for real-time object simulation namely, the geometry (non-physically) based and the physically based approaches. Geometry based approaches such as free-form deformation (FFD) employ purely geometric techniques to model deformation. Physically based approaches usually adopt mass–spring system, finite element method (FEM) or boundary element method (BEM) for simulation. The mass–spring system is simple and only gives a coarse estimation of object deformation. Recently, FEM and BEM have been extensively used in object simulation because of the demand for more realistic simulation. However, a major drawback of FEM and BEM is their difficulty to achieve real-time deformation. In this article, we compare two different physically based approaches, FEM and BEM, according to their accuracy and computational complexity. Several experiments were conducted to compare the time required for the pre-computation process and the deformation process. In addition, the BEM with linear boundary elements is implemented and tested. At the current state of investigation, for the meshes with triangular elements, BEM with linear boundary elements is significantly faster than BEM with constant boundary elements under most of the circumstances. With the band matrix of FEM, the pre-computation process is faster than the BEM for a model with small mesh size. However if the mesh size of the model is large, the pre-computation process of BEM with linear boundary elements is the fastest.

Education: Simulating tendon motion with axial mass-spring system

Computer simulations provide an interactive platform for exploring the biomechanics of animal movement. Despite the substantial amount of work that has been devoted to simulate human models, simulation of human tendons and its effect on the deformation of skin layer has not been well addressed. In this paper, a graphical model is developed for simulating tendon motions with axial mass-spring system. Based on the deformation of tendons, the skin layer attached to the tendon is deformed accordingly. In the proposed model, the geometry of the tendon is defined by an axial curve. The appearance of the skin layer is determined based on the deformation of the underlying tendons. Given a human model in a motion, the axial curve is adjusted according to the relative position of the foot skeleton. The shape of the axial curve of the tendon that is used to control the deformation of the tendons is computed with a mass-spring system. In this article, simulation of human hand and foot models is demonstrated. A validation method is proposed to compare the tendon deformation between the simulated and the real data captured from the motion analysis system. Experimental results showed that the axial deformation technique can deform the hand and foot tendons with satisfactory accuracy in comparison with the real data. Besides, the models are simulated at an interactive frame rate. With the deformation of the tendons, the visual realism of human foot and hand simulation is enhanced.

Comparison between FEM and BEM for Real-time Simulation

AbstractComputer simulation of object deformation has wide applications in areas such as movies, computer graphics, computer games, etc. Numerous methods have been proposed to simulate deformable objects. A common practice of simulating deformable objects is to use physically-based approaches which include the mass-spring system and the finite element method (FEM). The mass-spring system only gives a coarse estimation of object deformation whereas the FEM requires generating solid volumetric elements which is a tedious and time consuming process. The use of boundary element method (BEM) allows objects to be deformed without generating solid volumetric elements.In order to achieve real-time deformation, all these methods require time-consuming pre-computation process. In this paper, a comparison is made between the FEM and the BEM techniques. We propose to adopt linear elements of boundary element technique for real-time applications. The method not only allows physically-based and real-time deformation, i...

An Accelerated BEM Approach for the Simulation of Deformable Objects

AbstractThis paper introduces an approach for speeding up the simulation on deformable objects with the boundary element method (BEM). According to the relationship between a matrix and its inverse, the inverse operation on an objective matrix can be completed by calculating the inverse of another matrix with smaller dimension. An update procedure on inverse calculation for three cases is analyzed to avoid directly computing the matrix inverse every time when the boundary condition changes. Besides, a fast matrix-matrix multiplication (MMM) method is conducted to further improve the computational speed.

Development and evaluation of a mobile platform for teaching mathematics of CAD subjects

ABSTRACTNowadays, Hong Kong has adopted a new 3-3-4 academic structure for senior secondary education and higher education since 2012. Students can admit to most of the university programme without compulsory subject requirement. It means that students can admit to a programme without sufficient background on the underpinning subjects. Recently, it was found that a number of students were admitted to the engineering programmes without sufficient mathematical background, and it is a great challenge for the students study future engineering subjects, especially for the computer-aided product design (CAD) and other subjects that requires demanding mathematical background knowledge. In this project, a mobile learning platform is developed intend to provide a convenient and attractive channel for students to review and study the mathematics concepts and equations that need to be used in class. The platform encourages students’ self-learning and facilitating them to learn other engineering subjects easily. Two ...

Voxel-based approach to generate entire human metacarpal bone with microscopic architecture for finite element analysis

With the development of micro-computed tomography (micro-CT) technology, it is possible to construct three-dimensional (3D) models of human bone without destruction of samples and predict mechanical behavior of bone using finite element analysis (FEA). However, due to large number of elements required for constructing the FE models of entire bone, this demands a substantial computational effort and the analysis usually needs a high level of computer. In this article, a voxel-based approach for generation of FE models of entire bone with microscopic architecture from micro-CT image data is proposed. To enable the FE analyses of entire bone to be run even on a general personal computer, grayscale intensity thresholds were adopted to reduce the amount of elements. Human metacarpal bone (MCP) bone was used as an example for demonstrating the applicability of the proposed method. The micro-CT images of the MCP bone were combined and converted into 3D array of pixels. Dual grayscale intensity threshold parameters were used to distinguish the pixels of bone tissues from those of surrounding soft tissues and improve predictive accuracy for the FE analyses with different sizes of elements. The method of selecting an appropriate value of the second grayscale intensity threshold was also suggested to minimize the area error for the reconstructed cross-sections of a FE structure. Experimental results showed that the entire FE MCP bone with microscopic architecture could be modeled and analyzed on a personal computer with reasonable accuracy.

The development of a virtual cycling simulator

Cycling is one of the current thirteen elite sports in Hong Kong. Despite cycling is one of the well known activities in the world and has numerous advantages for health, it is still far from popular in Hong Kong. In this research, a virtual cycling simulator is developed for exercise and entertainment purpose, and for promoting the cycling activity. The hardware of the cycling simulator consists of four major units including a bike platform, an actuation unit, a sensing unit and a display unit. The control system receives signals from the sensing unit and controls the motions of the actuation unit. It also computes and renders the virtual environment in real-time thereby providing the experience of cycling on different terrain models.