Kensuke Hara

Improvement in modeling of Walking Assist Machine Using Crutches for dynamic analysis

In a previous study, a gait assistive device embodying actuators, known as Walking Assist Machine Using Crutches (WAMC), was proposed for people who suffer from lower limb disabilities. Experiments with healthy subjects show that WAMC can provide upright stance position and assisted forward gait to the user. However, the simplistic kinetostatic model used in gait analysis does not permit to obtain forces and torques acting on the system (user and WAMC) in detail. In this paper, an anthropometric 2D model which can investigate the gait characteristics of the system is proposed. Force and torques acting on the system parts can be guessed prior to the experiments if the users height and weight are specified. This will also help increasing the consistency between the dynamic simulation results and the input parameters required for experiments. Results of the gait analysis show that the model can successfully reproduce the kinematics of the system joints derived from experiments. In addition, it is shown by dynamics analysis that WAMC provides a comfortable ride as the forces and torques acting on the system are in admissible limits.

Simulation and Measurement of a Nonlinear Hydrodynamic Sloshing Force on a Rectangular Tank With Shallow Water Depth

This paper deals with a hydrodynamic sloshing force on a rectangular tank. In particular, we focus on a contribution of the nonlinear sloshing in shallow water depth to the hydrodynamic force. It is well known that the water wave in shallow water depth shows the characteristic behaviors such as the solitary wave by inherent nonlinearities. Therefore, the effect of nonlinearity is crucial for the estimation of the hydrodynamic sloshing force. Although these behaviors arises from the typical feature of the sloshing in shallow water depth, the theoretical analysis is essentially difficult because a lot of higher order nonlinear terms and eigenmodes have to be taken into account for accurate numerical predictions. Consequently, it yields complicated algebraic procedures. This study presents a formulation based on the Hamiltonian dynamics. In addition, the Dirichlet-Neumann operators (DNO) developed by Craig and Sulem was introduced to obtain an asymptotic description for the kinematic boundary condition of the liquid surface. The proposed approach facilitates the consideration of the nonlinearity for the formulation. Moreover, experiments were conducted to measure time histories of the wave height and the nonlinear fluid force due to the sloshing in a rectangular tank subjected to a horizontal excitation. As the results of frequency analyses for the time histories of the hydrodynamic force, many frequency spectra with the odd multiple of the dominant frequency were observed. These features were also obtained by the theoretical predictions by the proposed method.Copyright

Formulation of the Aeroelastic Instability Problem of Rectangular Plates in Uniform Flow Based on the Hamiltonian Mechanics for the Constrained System

This paper addresses a formulation and an aeroelastic instability analysis of a plate in a uniform incompressible and irrotational flow based on the classical variational principle framework. Because of an intrinsic algebraic relation between the plate displacement and the velocity potential, this system has to be formulated as the constrained system. In this study, we tried to apply the Hamiltonian mechanics to the formulation of the fluid-structure interaction problem with mixed boundary condition. As a result, we obtain the canonical equations, that consist of the evolution equations for the plate displacement, the velocity potential, the Lagrange multiplier and canonically conjugate momenta for those physical quantities. In particular, it was found that the Lagrange multiplier was just the pressure. In other words, the equations of time evolution could be derived for not only the plate displacement and the velocity potential but also the pressure (the Lagrange multiplier). The stability of this system was analyzed by the eigenvalue analysis. Then, flutter modes, their frequencies and growth rates were discussed. The proposed technique has the advantage that it can reduce iteration procedures in the stability analysis. As a consequence, it can be expected that the stability of this system can be evaluated efficiently. This paper introduces a formulation of the only two dimensional problem, and the stability analysis of a clamped-free plate is implemented as an numerical example. Howerver, this formulation can be applied to three dimensional problems without intrinsic difficulties.Copyright