Direct stiffness method

About: Direct stiffness method is a research topic. Over the lifetime, 2584 publications have been published within this topic receiving 53131 citations.

Simulate intersecting 3D hydraulic cracks using a hybrid “FE-Meshfree” method

Abstract: In this work, a discontinuous hybrid “FE-Meshfree” method is developed to simulate three-dimensional (3D) cracking. Then, an algorithm of Local Adaptive Background Sub-element (LABS-element) is developed in the context of hybrid “FE-Meshfree” method to simulate intersecting cracks. Compared to the extended finite element method (XFEM), the present hybrid “FE-Meshfree” method is not required to increase the size of global stiffness matrix, introduce extra unknowns, and construct special enrichment functions. The present algorithms of LABS-element and “FE-Meshfree” method are validated by intensive numerical tests, which achieves the balance between accuracy and flexibility. Additionally, a hydraulic and mechanical (H-M) coupling model is generated, in which the deformation of rocks and the propagation of cracks are solved by the hybrid “FE-Meshfree” method, meanwhile the fluid flow in cracks is solved by a fluid simulator based on the principle of parallel-plate flow model. This H-M coupling model is then used to investigate the propagation of fluid-driven cracks in rock mass with multiple pre-existing cracks, and the observed fluid pressure feedback is potentially useful during shale oil/gas well simulation.

Research on the low frequency band gap properties of periodically composite stiffened thin-plate with fillers

Abstract: In this paper, a new composite stiffened thin-plate (CSTP) is developed, the filler is distributed periodically in the viscoelastic damping material (VDM), and the simplified-super-finite-element (SSFM) is employed in the analysis. According to the periodical properties of the CSTP, a primitive cell is extracted, which is divided into six parts according to n-order Lagrangian element (LgE). After each parts’ mass, stiffness and damping matrices are obtained, the global matrices are assembled by standard direct stiffness method (SDSM). The filler's mass is considered as lump mass loaded on the defined LgE's nodes, and the filler's number is determined by the LgE's order. Then, the element matrices are simplified and compressed by Bloch's theorem. Finally, the band gap properties of the CSTP are determined according to the eigenvalues problems, and the parameters of the structures (such as the filler's mass, the VDM's damping ratio and the lattice constant, etc.) which affect the band gaps are examined thoroughly. The results show the existence of full band gap (FBG) in low frequency. Meanwhile, the results are validated by the finite element method (FEM), which show good consistency.

Constraint-based equilibrium and stiffness control of variable stiffness actuators

Abstract: Considerable research effort has gone into the design of variable passive stiffness actuators (VSAs). A number of different mechanical designs have been proposed, aimed at either a biomorphic (i.e., antagonistic) design, compactness, or simplified modelling and control. In this paper, we propose a (model-based) unified control methodology that is able to exploit the benefits of variable stiffness independent of the specifics of the mechanical design. Our approach is based on forming constraints on commands sent to the VSA to ensure that the equilibrium position and stiffness of the VSA are tracked to the desired values. We outline how our approach can be used for tracking stiffness and equilibrium position both in joint and task space, and how it may be used in the context of constrained local optimal control. In our experiments we illustrate the utility of our approach in the context of online teleoperation, to transfer compliant human behaviour to a variable stiffness device.

General parametric stiffness excitation – anti-resonance frequency and symmetry

Abstract: Stability investigations on vibration cancelling employing the concept of actuators with general stiffness elements are presented Systems with an arbitrary number of degrees of freedom with linear spring- and damping elements are considered, that are subject to self-excitation as well as parametric excitation by stiffness variations with arbitrary phase relations General conditions for full vibration suppression are derived analytically by applying a singular perturbation technique These conditions naturally lead to the terms of parametric resonance and anti-resonance and enable a stability classification with respect to the parametric excitation matrices and their symmetry properties The results are compared to former investigations of systems with a single or synchronous stiffness variation in time and geometrical interpretations are given These basic results obtained can be used for design of a control strategy for actuators with periodically actuated stiffness elements and arbitrary phase relations