• Journal of Mechanical Science and Technology
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• v.16 no.1
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• pp.13-23
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• 2002

This paper presents inverse kinematic and dynamic analyses of HexaSlide type six degree-of-freedom parallel manipulators. The HexaSlide type parallel manipulators (HSM) can be characterized as an architecture with constant link lengths that are attached to moving sliders on the ground and to a mobile platform. In the inverse kinematic analyses, the slider and link motion (position, velocity, and acceleration) is computed given the desired mobile platform motion. Based on the inverse kinematic analysis, in order to compute the required actuator forces given the desired platform motion, inverse dynamic equations of motion of a parallel manipulator is derived by the Newton-Euler approach. In this derivation, the joint friction as well as all link inertia are included. Relative importance of the link inertia and joint frictions on the computed torque is investigated by computer simulations. It is expected that the inverse kinematic and dynamic equations can be used in the computed torque control and model-based adaptive control strategies.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.33.1-33
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• 2001

We address a novel approach to identify a nonlinear dynamic system for Wiener models, which are composed of a linear dynamic system part followed by a nonlinear static part. The aim of system identification here is to provide the optimal mathematical model of both the linear dynamic and the nonlinear static parts in some appropriate sense. Assuming the nonlinear static part is invertible, we approximate the inverse function by a piecewise linear function. We estimate the piecewise linear inverse function by using the evolutionary computation approach such as genetic algorithm (GA) and evolution strategies (ES), while we estimate the linear dynamic system part by the least squares method. The results of numerical simulation studies indicate the usefulness of proposed approach to the Wiener model identification.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2007.11a
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• pp.159-162
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• 2007

The inverse kinematics problem in robotics is an essential work for grasping and manipulation tasks by robotic and humanoid hands. In this paper, an intelligent neural learning scheme for solving such inverse kinematics of humanoid fingers is presented. Specifically, a multi-layered neural network is utilized for effective inverse kinematics, where a dynamic neural learning algorithm is employed. Also, a bio-mimetic feature of general human fingers is incorporated to the learning scheme. The usefulness of the proposed approach is verified by simulations.

• International Journal of Precision Engineering and Manufacturing
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• v.7 no.3
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• pp.66-71
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• 2006

Some wheelchair users with neuromuscular disorders experience involuntary extensor thrusts, which may cause injuries via impact with the wheelchair, cause the user to slide out of the wheelchair seat, and damage the wheelchair. Knowledge of the human-generated forces during an extensor thrust is of great importance in devising safer, more comfortable wheelchairs. This paper presents an efficient method for identifying human-generated forces during an extensor thrust. We used an inverse dynamic approach with a three-link human body model and a system for measuring human body motion. We developed an experimental system that determines the angular motion of each human body segment and the force at the footrest, which was used to overcome the mathematical indeterminacy of the problem. The proposed method was validated experimentally, illustrating the force-identification process during an extensor thrust.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.5
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• pp.393-399
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• 2013

In this paper, a novel approach to estimate cohesive laws for the mode I fracture of the graphene is presented by combining molecular dynamic simulations and an inverse algorithm based on field projection method and finite element method. The determination of crack-tip cohesive laws of the graphene based on continuum mechanics is a non-trivial inverse problem of finding unknown tractions and separations from atomic simulations. The displacements of molecular dynamic simulations in a region far away from the crack tip are transferred to finite element nodes by using moving least square approximation. Inverse analyses for extracting unknown cohesive tractions and separation behind the crack tip can be carried out by using conservation nature of the interaction J- and M-integrals with numerical auxiliary fields which are generated by systematically imposing uniform surface tractions element-by-element along the crack surfaces in finite element models. The preset method can be a very successful approach to extract crack-tip cohesive laws from molecular dynamic simulations as a scale bridging method.

• Structural Engineering and Mechanics
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• v.54 no.6
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• pp.1153-1174
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• 2015

Deployable structures have gained more and more applications in space and civil structures, while it takes a large amount of computational resources to analyze this kind of multibody systems using common analysis methods. This paper presents a new approach for dynamic analysis of multibody systems consisting of both rigid bars and arbitrarily shaped rigid bodies. The bars and rigid bodies are connected through their nodes by ideal pin joints, which are usually fundamental components of deployable structures. Utilizing the Moore-Penrose generalized inverse matrix, equations of motion and constraint equations of the bars and rigid bodies are formulated with nodal Cartesian coordinates as unknowns. Based on the constraint equations, the nodal displacements are expressed as linear combination of the independent modes of the rigid body displacements, i.e., the null space orthogonal basis of the constraint matrix. The proposed method has less unknowns and a simple formulation compared with common multibody dynamic methods. An analysis program for the proposed method is developed, and its validity and efficiency are investigated by analyses of several representative numerical examples, where good accuracy and efficiency are demonstrated through comparison with commercial software package ADAMS.

• Structural Engineering and Mechanics
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• v.56 no.4
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• pp.625-648
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• 2015

Modern super-tall buildings are more sensitive to strong winds. The evaluation of wind loads for the design of these buildings is of primary importance. A direct monitoring of wind forces acting on super-tall structures is quite difficult to be realized. Indirect measurements interpreted by inverse techniques are therefore favourable since dynamic response measurements are easier to be carried out. To this end, a Kalman filtering based inverse approach is developed in this study so as to estimate the wind loads on super-tall buildings based on limited structural responses. The optimum solution of Kalman filter gain by solving the Riccati equation is used to update the identification accuracy of external loads. The feasibility of the developed estimation method is investigated through the wind tunnel test of a typical super-tall building by using a Synchronous Multi-Pressure Scanning System. The effects of crucial factors such as the type of wind-induced response, the covariance matrix of noise, errors of structural modal parameters and levels of noise involved in the measurements on the wind load estimations are examined through detailed parametric study. The effects of the number of vibration modes on the identification quality are studied and discussed in detail. The made observations indicate that the proposed inverse approach is an effective tool for predicting the wind loads on super-tall buildings.

• Structural Engineering and Mechanics
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• v.88 no.4
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• pp.301-309
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• 2023

In this paper, a new modified conjugate gradient (MCG) method is presented which is based on a new gradient regularizer, and this method is used to identify the dynamic load on airfoil structure without and with considering random structure parameters. First of all, the newly proposed algorithm is proved to be efficient and convergent through the rigorous mathematics theory and the numerical results of determinate dynamic load identification. Secondly, using the perturbation method, we transform uncertain inverse problem about force reconstruction into determinate load identification problem. Lastly, the statistical characteristics of identified load are evaluated by statistical methods. Especially, this newly proposed approach has successfully solved determinate and uncertain inverse problems about dynamic load identification. Numerical simulations validate that the newly developed method in this paper is feasible and stable in solving load identification problems without and with considering random structure parameters. Additionally, it also shows that most of the observation error of the proposed algorithm in solving dynamic load identification of deterministic and random structure is respectively within 11.13%, 20%.

• Structural Engineering and Mechanics
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• v.35 no.6
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• pp.773-789
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• 2010

It is well known that the analytical vibration characteristic of a cracked beam depends largely on the crack model. In the forward analysis, an improved and simplified approach in modeling discrete open cracks in beams is presented. The effective length of the crack zone on both sides of a crack with stiffness reduction is formulated in terms of the crack depth. Both free and forced vibrations of cracked beams are studied in this paper and the results from the proposed modified crack model and other existing models are compared. The modified crack model gives very accurate predictions in the modal frequencies and time responses of the beams particularly with overlaps in the effective lengths with reduced stiffness. In the inverse analysis, the response sensitivity with respect to damage parameters (the location and depth of crack, etc.) is derived. And the dynamic response sensitivity is used to update the damage parameters. The identified results from both numerical simulations and experiment work illustrate the effectiveness of the proposed method.

• Advances in aircraft and spacecraft science
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• v.9 no.4
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• pp.301-318
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• 2022

This paper presents the free vibration analysis of 3D printed sandwich beams by using high-order theories based on the Carrera Unified Formulation (CUF). In particular, the component-wise (CW) approach is adopted to achieve a high fidelity model of the printed part. The present model has been used to build an accurate database for collecting first natural frequency of the beams, then predicting Young's modulus based on an inverse problem formulation. The database is built from a set of randomly generated material properties of various values of modulus of elasticity. The inverse problem then allows finding the elastic modulus of the input parameters starting from the information on the required set of the output achieved experimentally. The natural frequencies evaluated during the experimental test acquired using a Digital Image Correlation method have been compared with the results obtained by the means of CUF-CW model. The results obtained from the free-vibration analysis of the FDM beams, performed by higher-order one-dimensional models contained in CUF, are compared with ABAQUS results both first five natural frequency and degree of freedoms. The results have shown that the proposed 1D approach can provide 3D accuracy, in terms of free vibration analysis of FDM printed sandwich beams with a significant reduction in the computational costs.