Real-time Finite Element Method Research Articles

A Collapsible Soft Actuator Facilitates Performance in Constrained Environments.

Complex environments, such as those found in surgical and search-and-rescue applications, require soft devices to adapt to minimal space conditions without sacrificing the ability to complete dexterous tasks. Stacked Balloon Actuators (SBAs) are capable of large deformations despite folding nearly flat when deflated, making them ideal candidates for such applications. This paper presents the design, fabrication, modeling, and characterization of monolithic, inflatable, soft SBAs. Modeling is presented using analytical principles based on geometry, and then using conventional and real-time finite element methods. Both one and three degree-of-freedom (DoF) SBAs are fully characterized with regards to stroke, force, and workspace. Finally, three representative demonstrations show the SBA's small-aperture navigation, bracing, and workspace-enhancing capabilities.

Review on generic methods for mechanical modeling, simulation and control of soft robots.

In this review paper, we are interested in the models and algorithms that allow generic simulation and control of a soft robot. First, we start with a quick overview of modeling approaches for soft robots and available methods for calculating the mechanical compliance, and in particular numerical methods, like real-time Finite Element Method (FEM). We also show how these models can be updated based on sensor data. Then, we are interested in the problem of inverse kinematics, under constraints, with generic solutions without assumption on the robot shape, the type, the placement or the redundancy of the actuators, the material behavior… We are also interested by the use of these models and algorithms in case of contact with the environment. Moreover, we refer to dynamic control algorithms based on mechanical models, allowing for robust control of the positioning of the robot. For each of these aspects, this paper gives a quick overview of the existing methods and a focus on the use of FEM. Finally, we discuss the implementation and our contribution in the field for an open soft robotics research.

Online Stress Measurement During Laser-aided Metallic Additive Manufacturing

In situ measurement of residual stress is a challenge, and it is a source of many defects during additive manufacturing (AM). Usually, postmortem measurement is too late to save the product once a defect appears. Most of the existing technologies are predictive simulations and postmortem analysis. However, these technologies cannot directly reflect the stress evolution during the fabrication process. This paper introduces a computer vision-based stress monitoring system combined with finite element method (FEM) technology to estimate the stress development inside of the deposition layer. The system uses a CCD camera and a line laser beam to measure the height of the melt pool and solidified layer, forms a real-time FEM model, and uses the surface displacement between the two states to calculate the stress development during the solidification process. The results show that there is no obvious shape change after solidification. The shape of the melt pool and its solid state is similar. The stress distribution obtained through online monitoring is similar to that from the traditional thermal-stress simulation.

Application of mode superposition to hybrid simulation using Real Time Finite Element Method

The following paper presents methods for application of mode superposition to the analytical part of the hybrid simulation, when Real Time Finite Element Method is used to model the analytical substructure. Introducing mode superposition can bring significant computation time decrease in real time computations, by performing some calculations offline. The paper describes requirements, methods and algorithms for introducing mode superposition to explicit and implicit integration schemes. In explicit schemes mode superposition allows to increase the minimum time step often enabling real time computations that were not possible before. In implicit schemes mode superposition allows to reduce the time step of the analysis (and therefore increase accuracy). Numerical examples proving the effectiveness of the presented algorithms are given.DOI: http://dx.doi.org/10.5755/j01.mech.23.5.14642

Finite Element Method Simulation of 3D Deformable Solids

This book serves as a practical guide to simulation of 3D deformable solids using the Finite Element Method (FEM). It reviews a number of topics related to the theory and implementation of FEM approaches: measures of deformation, constitutive laws of nonlinear materials, tetrahedral discretizations, and model reduction techniques for real-time simulation. Simulations of deformable solids are important in many applications in computer graphics, including film special effects, computer games, and virtual surgery. The Finite Element Method has become a popular tool in many such applications. Variants of FEM catering to both offline and real-time simulation have had a mature presence in computer graphics literature. This book is designed for readers familiar with numerical simulation in computer graphics, who would like to obtain a cohesive picture of the various FEM simulation methods available, their strengths and weaknesses, and their applicability in various simulation scenarios. The book is also a practical implementation guide for the visual effects developer, offering a lean yet adequate synopsis of the underlying mathematical theory. Chapter 1 introduces the quantitative descriptions used to capture the deformation of elastic solids, the concept of strain energy, and discusses how force and stress result as a response to deformation. Chapter 2 reviews a number of constitutive models, i.e., analytical laws linking deformation to the resulting force that has successfully been used in various graphics-oriented simulation tasks. Chapter 3 summarizes how deformation and force can be computed discretely on a tetrahedral mesh, and how an implicit integrator can be structured around this discretization. Finally, chapter 4 presents the state of the art in model reduction techniques for real-time FEM solid simulation and discusses which techniques are suitable for which applications. Topics discussed in this chapter include linear modal analysis, modal warping, subspace simulation, and domain decomposition.

Introducing interactive inverse FEM simulation and its application for adaptive radiotherapy.

We introduce a new methodology for semi-automatic deformable registration of anatomical structures, using interactive inverse simulations. The method relies on non-linear real-time Finite Element Method (FEM) within a constraint-based framework. Given a set of few registered points provided by the user, a real-time optimization adapts the boundary conditions and(/or) some parameters of the FEM in order to obtain the adequate geometrical deformations. To dramatically fasten the process, the method relies on a projection of the model in the space of the optimization variables. In this reduced space, a quadratic programming problem is formulated and solved very quickly. The method is validated with numerical examples for retrieving Young's modulus and some pressures on the boundaries. Then, we apply the approach for the registration of the parotid glands during the radiotherapy of the head and neck cancer. Radiotherapy treatment induces weight loss that modifies the shape and the positions of these structures and they eventually intersect the target volume. We show how we could adapt the planning to limit the radiation of these glands.

A responsive finite element method to aid interactive geometric modeling.

Current computer-aided engineering systems use numerical-simulation methods mainly as offline verification tools to reject designs that don't satisfy the required constraints, rather than as tools to guide users toward better designs. However, integrating real-time finite element method (FEM) into interactive geometric modeling can provide user guidance. During interactive editing, real-time feedback from numerical simulation guides users toward an improved design without tedious trial-and-error iterations. Careful reuse of previous computation results, such as meshes and matrices, on the basis of speed and accuracy trade-offs, have helped produce fast FEM analysis during interactive editing. Several 2D example applications and informal user studies show this approach's effectiveness. Such tools could help nonexpert users design objects that satisfy physical constraints and help those users understand the underlying physical properties.

Real-time FEM Control System for Connected Piezoelectric Actuators

In this paper, the Finite Element Method (FEM) and the previously proposed inverse theory for bimorph piezoelectric actuators are applied into a real time control algorithm of connected piezoelectric actuators. Most control schemes handle an entire system in series, which becomes a drawback when some elements lose their function in a higher redundant system. On the other hand, the FEM can handle the system in parallel by subdividing it into discrete finite elements, and can cope with flexibility in the change of form and material properties. Noncompatible finite elements are used to express the actuators in the control algorithm, and empirical formulae considering time-dependent characteristics such as creep and residual strain, are also implemented. A real-time FEM control system, which consists of a PC, a bipolar DC unit and a signal-distributing controller, is developed. The system is verified by experiments on quasi-static displacement control of connected piezoelectric actuators. The results show the possibility of highly accurate, realtime control of the actuators using the FEM.