Phill-Seung Lee

Towards improving the MITC9 shell element

Abstract Our objective in this paper is to present some results regarding the predictive capabilities of the MITC9 shell element when the tying points in the element are changed. The MITC9 element is a general nine-node shell element based on the formulation approach of using mixed-interpolated tensorial components. Different tying points are very simple to implement and are not decreasing the computational efficiency of the element. Hence, the use of the “best” tying points is clearly of value.

On the asymptotic behavior of shell structures and the evaluation in finite element solutions

The objective of this paper is to demonstrate how the asymptotic behavior of a shell structure, as the thickness (t) approaches zero, can be evaluated numerically. We consider three representative shell structural problems; the original Scordelis–Lo roof shell problem, a herein proposed modified Scordelis–Lo roof shell problem and the partly clamped hyperbolic paraboloid shell problem. The asymptotic behavior gives important insight into the shell load bearing capacity. The behavior should also be known when a shell problem is used to test a shell finite element procedure. We briefly review the fundamental theory of the asymptotic behavior of shells, develop our numerical schemes and perform the numerical experiments with the MITC4 shell finite element. � 2002 Elsevier Science Ltd. All rights reserved.

The quadratic MITC plate and MITC shell elements in plate bending

The analysis of plates can be achieved using the quadratic MITC plate or MITC shell elements. The plate elements have a strong mathematical basis and have been shown to be optimal in their convergence behavior, theoretically and numerically. The shell elements have not (yet) been analyzed mathematically in depth for their rates of convergence, with the plate/shell thickness varying, but have been shown numerically to perform well. Since the shell elements are general and can be used for linear and nonlinear analyses of plates and shells, it is important to identify the differences in the performance of these elements when compared to the plate elements. We briefly review the quadratic quadrilateral and triangular MITC plate and shell elements and study their performances in linear plate analyses.

The MITC4+ shell element and its performance

An effective new 4-node shell element is derived from the MITC4 shell element.A new assumed membrane strain field is developed to alleviate membrane locking.The numerical results show the improved predictive capability. The objective in this paper is to improve the performance of the 4-node MITC quadrilateral shell finite element, referred to as the MITC4 element (Dvorkin and Bathe, 1984). We propose a new MITC4 shell element, the MITC4+ element, in which the mid-surface membrane strain components are assumed using the concept of the MITC method. The tying membrane strains are obtained from four triangular domains which subdivide the mid-surface of the 4-node quadrilateral shell element. This approach alleviates locking that can happen when the MITC4 shell elements are geometrically distorted in curved geometries. Several basic tests including the isotropy, zero energy mode, and patch tests are performed. Through the solution of various shell problems, the convergence behavior of the MITC4+ shell element is studied to show the improvements reached.

Mesh based construction of flat-top partition of unity functions

A novel idea to construct flat-top partition of unity functions in a closed form on a general (structured or unstructured) finite element mesh is presented. An efficient and practical construction method of a flat-top partition of unity function is important in the generalized finite element method (GFEM). Details on how to construct flat-top partition of unity functions on a provided mesh are given. The generalized finite element approximation with the use of the new flat-top partition of unity function is presented with various numerical examples that demonstrate the effectiveness of proposed flat-top partition of unity functions.

Posteriori Error Estimation Method for Flexibility-Based Component Mode Synthesis

The objective of this paper is to develop a simple and robust error estimation method for the flexibility-based component mode synthesis method. The flexibility-based component mode synthesis method is known to provide reliable and improved performance compared to other component mode synthesis methods. However, it is not possible to estimate errors in finite element models reduced by the flexibility-based component mode synthesis method yet. In this study, an a posteriori method is developed to accurately estimate relative errors in individual eigenvalues approximated by the flexibility-based component mode synthesis method without knowing the exact eigenvalues. The excellent performance of this error estimation method is demonstrated through various numerical examples.

Medial preoptic circuit induces hunting-like actions to target objects and prey

As animals forage, they must obtain useful targets by orchestrating appropriate actions that range from searching to chasing, biting and carrying. Here, we reveal that neurons positive for the α subunit of Ca2+/calmodulin-dependent kinase II (CaMKIIα) in the medial preoptic area (MPA) that send projections to the ventral periaqueductal gray (vPAG) mediate these target-directed actions in mice. During photostimulation of the MPA–vPAG circuit, mice vigorously engaged with 3D objects and chased moving objects. When exposed to a cricket, they hunted down the prey and bit it to kill. By applying a head-mounted object control with timely photostimulation of the MPA–vPAG circuit, we found that MPA–vPAG circuit-induced actions occurred only when the target was detected within the binocular visual field. Using this device, we successfully guided mice to navigate specified routes. Our study explains how the brain yields a strong motivation to acquire a target object along the continuum of hunting behavior.This study finds the key neurons that respond to 3D objects in the medial preoptic area (MPA). Their photostimulation induces hunting-like behaviors towards toys and prey, showing how the brain organizes behaviors to acquire useful resources.

Toward Modular Analysis of Supramolecular Protein Assemblies.

Despite recent advances in molecular simulation technologies, analysis of high-molecular-weight structures is still challenging. Here, we propose an automated model reduction procedure aiming to enable modular analysis of these structures. It employs a component mode synthesis for the reduction of finite element protein models. Reduced models may consist of real biological subunits or artificial partitions whose dynamics is described using the degrees of freedom at the substructural interfaces and a small set of dominant vibrational modes only. Notably, the proper number of dominant modes is automatically determined using a novel estimator for eigenvalue errors without calculating the reference eigensolutions of the full model. The performance of the proposed approach is thoroughly investigated by analyzing 50 representative structures including a crystal structure of GroEL and an electron density map of a ribosome.

A MODE SELECTION ALGORITHM FOR THE FLEXIBILITY-BASED COMPONENT MODE SYNTHESIS

Abstract. A major challenge in component mode synthesis (CMS) remains the absence of a robust mode selection algorithm which can provide a measure of accuracy of the reduced model compared to the full model. In order to address this challenge, two concepts have been proposed in tandem: mode selection and error estimation methods. In this paper, we reassess performance of a recently proposed mode selection method and an a posteriori error estimation method, and propose an efficient iterative algorithm that combines these two methods. The flexibility-based component mode synthesis (F-CMS) is used to demonstrate the performance of the above methods. Numerical examples illustrate the effectiveness of the present algorithm.

Remote Navigation of Turtle by Controlling Instinct Behavior via Human Brain-computer Interface

Brain-Computer Interface (BCI) techniques have advanced to a level where it is now eliminating the need for hand-based activation. This paper presents a novel attempt to remotely control an animal’s behavior by human BCI using a hybrid of Event Related Desynchronization (ERD) and Steady-State Visually Evoked Potential (SSVEP) BCI protocols. The turtle was chosen as the target animal, and we developed a head-mounted display, wireless communication, and a specially designed stimulation device for the turtle. These devices could evoke the turtle’s instinctive escape behavior to guide its moving path, and turtles were remotely controlled in both indoor and outdoor environments. The system architecture and design were presented. To demonstrate the feasibility of the system, experimental tests were performed under various conditions. Our system could act as a framework for future human-animal interaction systems.