Papers by Keyword: Energy Method

Abstract: The inverted pendulum is one of the most common experimental devices used to illustrate nonlinear control techniques, and various studies have been conducted on its swing-up and stabilization control from different perspectives. In real-world inverted pendulums, there are limitations on the displacement and velocity of the fulcrum, making it crucial to consider these constraints in control strategies.In this study, we propose a new swing-up and stabilization control method for the inverted pendulum that allows independent setting of the displacement and velocity limits of the fulcrum. The effectiveness of this method is verified through simulations and experimental tests.

Abstract: In this paper, we propose a swing-up control law for the Pendubot, a type of two-joint, two-link, underactuated robot in which the shoulder joint is actuated and the elbow joint is unactuated, maintaining the elbow joint fully extended as much as possible. The proposed control law is designed by the energy-based method. Using the phase plane trajectories obtained from the angular and angular velocity oscillatory motion of the forearm, the target trajectory of the shoulder joint is calculated so that the trajectory is a small phase advance from the forearm. We design a tracking control law for the shoulder joint so that the forearm and the upper arm behave as a single pendulum. The effectiveness of the proposed method is verified by numerical simulation and actual experiments.

Abstract: In this paper, we propose a swing-up control law for the Pendubot, a type of two-joint, two-link, underactuated robot in which the shoulder joint is actuated and the elbow joint is unactuated, considering the restricted angular movement of the shoulder joint. The proposed control law is designed by the energy-based method. Using the phase plane trajectories obtained from the angular and angular velocity oscillatory motion of the forearm, a target trajectory of the shoulder joint is calculated such that the mechanical energy of the forearm motion increases. We design a tracking control law for the shoulder joint with respect to a target trajectory. The maximum amplitude of the target trajectory directly restricts the angular motion of the actuator. The effectiveness of the proposed method is verified by numerical simulation and actual experiments.

Abstract: The effect of fiber cross-section on effective elastic and piezoelectric coefficients of piezoelectric fiber reinforced composites (PFRC) is investigated through two micromechanical analyzes viz. modified strength of materials (MSM) approach and energy approach. Results are verified with that of strength of materials (SM) approach available in the literature. A constant electric field is considered in the direction transverse to the fiber direction and is assumed to be same both in the fiber and matrix phases. It is observed that MSM and strength of materials (SM) approach predictions for the effective piezoelectric coefficient of the PFRC assessing the actuating capability in the fiber direction are in excellent agreement and also when the fiber volume fraction exceeds a critical value, this effective piezoelectric coefficient becomes significantly larger than the corresponding coefficient of the piezoelectric material of the fiber as investigated by both SM and MSM approaches. However, results of energy approach differ from both MSM and SM results and effective piezoelectric constant never exceeds to that of fiber as obtained by energy approach. It has been found for the piezoelectric fibers, cross-section of fiber has insignificant effect on the effective properties as predicted by MSM and energy approaches. Nomenclature

Abstract: It is calculated the effective anisotropic stiffness tensor of the representative volume element in 2.5D woven composites by energy method. The Multi-point constraints are applied to periodic boundary conditions. Compared with the static tensile tests, the validity of present method is verified.

Abstract: The mechanical properties of KD-II type silicon carbide fiber braided three-dimensional four-directional (3D4d) SiC_f/SiC woven composites fabricated by PIP method were studied in this paper. The computed tomography (CT) technology was used to observe the cross section shape and orientation of the fiber bundles inside woven composite materials, and digital image correlation (DIC) method was used to measure deformation, during the tensile tests of the composites. Theoretical and numerical methods were adopted to predict mechanical properties of the 3D4d SiC_f/SiC woven composites, and effectiveness of different methods was discussed based on the comparison of results obtained from the experiments and prediction model.

Abstract: Transverse compaction and in-plane shear deformartion are the dominative deformation mode for woven preform during forming process. A full finite element model of the 2.5D woven composites has been established by the computed tomography (CT) in this paper. Based on the energy method, the effective orthotropic/anisotropic stiffness coefficients C_ij are calculated by performing a finite element analysis (FEA) of this full cell model. Using this model, the effects of the compaction and shear deformation of the 2.5D woven preform on the composites stiffness are investigated in detail. Compared the results of the static tensile tests, the rationality of the model and the method is verified.

Abstract: The problem of natural oscillations of an elastic thin non-circular cylindrical wavy shell of an open profile is considered. The problem is based on the Rayleigh-Ritz energy method. On the basis of the proposed method for determining the lowest frequencies and forms of natural vibrations of shells of complicated shape, the numerical convergence of the developed algorithm is investigated. The evaluation of the results of this numerical experiment is given.

Abstract: We previously presented an energy method for predicting the bounds of fracture toughness of brittle films on a soft substrate from nanoindentation. The method is now further improved by minimizing elastic-plastic work from the measured energy during ring crack formation. Then, we applied this method to determine the limits of fracture toughness of alumina films with a thickness of 100 nm. It was found that fracture toughness of the films is in the range of 1.8-2.2 MPa.m^0.5, which is consistent with those measured by the conventional method.

Abstract: Based on the energy method and beam-element theory, the nonlinear strain are considered, non-stress length and non-stress curvature of element of geometry control method are introducted in the integration process of stain energy. The static equilibrium equation of the geometry control method is established. Take the impacts of structural geometric profile induced by temporary loads and temperature field during the construction procedure are investigated, the correctness of the geometry control method is verified by the numerical simulation analysis.