• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.12
• /
• pp.38-44
• /
• 2002

A walking training robot is proposed to provide stable and comfortable walking supports by reducing body weight load partially and a force control of an arm of walking training robot using sliding mode controller is also proposed. The current gait training apparatus in hospital are ineffective for the difficulty in keeping constant unloading level and for the constraint of patients' free walking. The proposed walking training robot effectively unloads body weight during walking. The walking training robot consists of an unloading manipulator and a mobile platform. The manipulator driven by an electro-mechanical linear mechanism unloads body weight in various levels. The mobile platform is wheel type, which allows patients to walt freely. The developed unloading system has advantages such as low noise level, lightweight, low manufacturing cost and low power consumption. A system model fur the manipulator is established using Lagrange's equation. To unload the weight of the patients, sliding mode control with p-control is adopted. Both control responses with a weight and human walking control responses are analyzed through experimental implementation to demonstrate performance characteristics of the proposed force controller.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.597-600
• /
• 2004

A two-degree-of-freedom out-of-plane model with contact stiffness is presented to describe dynamical interaction between the pad and disc of a disc brake system. It is assumed that the out-of-plane motion of the system depends on the friction force acting along the in-plane direction. Dynamic friction coefficient is modelled as a function of both in-plane relative velocity and out-of-plane normal force. When the friction coefficient depends only on the relative velocity, the contact stiffness has the role of negative stiffness. The results of stability analysis show that the stiffness of both pad and disc are equally important. Complex eigenvalue analysis is conducted for the case that the friction coefficient is also dependent on the normal force. The results further verify the importance of the stiffness. It has also been found that increasing the gradient of friction coefficient with respect to the normal force makes the system more unstable. Nonlinear analysis is also performed to demonstrate various responses. Comparing the responses with experimental data has shown that the proposed model may qualitatively well represent a certain type of brake noise.

• Journal of The Korean Association For Science Education
• /
• v.16 no.1
• /
• pp.87-96
• /
• 1996

In this study, students' performances on the reasoning tasks dealing with physical situations were analyzed. Through these analysis, the influences of students' preconceptions and logical abilities in reasoning process were described. For this study, 97 high school students were randomly selected. Among them, the number of the students who changed their misconceptions is 62% for the first task(force acting on the upward moving body), and 25% for the second task(force acting on the body when it is on the top of its motion). The students who show the premise-based response changed their conceptions in both of the tasks are more than those who responded in the idea based responses. The index of the influence of prior knowledge, ${\alpha}$ is 33% for the first task, and 67% for the second task, and ${\beta}$ is 41% for the first task, and 17% for the second task. When students performed the reasoning tasks about force and motion, the misconcepts frequently influenced their performances. But for the first task, the precentage of students who changed their concepts is about 62%. It shows the possibility that if the task is simple and appropriate, students can change their concepts.

• Structural Engineering and Mechanics
• /
• v.14 no.2
• /
• pp.151-170
• /
• 2002

Moving force identification is a very important inverse problem in structural dynamics. Most of the identification methods are eventually converted to a linear algebraic equation set. Different ways to solve the equation set may lead to solutions with completely different levels of accuracy. Based on the measured bending moment responses of the bridge made in laboratory, this paper presented the time domain method (TDM) and frequency-time domain method (FTDM) for identifying the two moving wheel loads of a vehicle moving across a bridge. Directly calculating pseudo-inverse (PI) matrix and using the singular value decomposition (SVD) technique are adopted as means for solving the over-determined system equation in the TDM and FTDM. The effects of bridge and vehicle parameters on the TDM and FTDM are also investigated. Assessment results show that the SVD technique can effectively improve identification accuracy when using the TDM and FTDM, particularly in the case of the FTDM. This improved accuracy makes the TDM and FTDM more feasible and acceptable as methods for moving force identification.

• Coupled systems mechanics
• /
• v.1 no.1
• /
• pp.39-57
• /
• 2012

This study intends to explore dynamic interaction behaviors between actively controlled maglev vehicle and guideway girders by considering the nonlinear forms of electromagnetic force and current exactly. For this, governing equations for the maglev vehicle with ten degrees of freedom are derived by considering the nonlinear equation of electromagnetic force, surface irregularity, and the deflection of the guideway girder. Next, equations of motion of the guideway girder, based on the mode superposition method, are obtained by applying the UTM-01 control algorithm for electromagnetic suspension to make the maglev vehicle system stable. Finally, the numerical studies under various conditions are carried out to investigate the dynamic characteristics of the maglev system based on consideration of the linear and nonlinear electromagnetic forces. From numerical simulation, it is observed that the dynamic responses between nonlinear and linear analysis make little difference in the stable region. But unstable responses in nonlinear analysis under poor conditions can sometimes be obtained because the nominal air-gap is too small to control the maglev vehicle stably. However, it is demonstrated that this unstable phenomenon can be removed by making the nominal air-gap related to electromagnetic force larger. Consequently it is judged that the nonlinear analysis method considering the nonlinear equations of electromagnetic force and current can provide more realistic solutions than the linear analysis.

• Structural Engineering and Mechanics
• /
• v.77 no.6
• /
• pp.721-734
• /
• 2021

The seismic analysis of structures without applying the effects of soil can undermine functional objectives of structure so that it can affect all the desired purposes at the design and control stages of the structure. In this research, employing OpenSees and MATLAB software simultaneously and developing a definite three-dimensional finite element model of a high-rise concrete structure, designed using performance-based plastic design approach, the performance of Tuned Mass Damper (TMD) and Active Mass Damper (AMD) is both examined and compared. Moreover some less noted aspects such as nonlinear interaction of soil and structure, uplift, nonlinear behavior of structure and structural torsion have received more attention. For this purpose, the analysis of time history on the structural model has been performed under 22 far-field accelerogram records. Examining a full range of all structural seismic responses, including lateral displacement, acceleration, inter-story drift, lost plastic energy, number of plastic hinges, story shear force and uplift. The results indicate that TMD performs better than AMD except for lateral displacement and inter-story drift to control other structural responses. Because on the one hand, nonlinear structural parameters and soil-structure interaction have been added and on the other hand, the restriction on the control force applied that leads up to saturation phenomenon in the active control system affect the performance of AMD. Moreover, the control force applied by structural control system has created undesirable acceleration and shear force in the structure.

• Tribology and Lubricants
• /
• v.28 no.2
• /
• pp.62-69
• /
• 2012

Atomic force microscopy (AFM) has been widely utilized as a versatile tool not only for imaging surfaces but also for understanding nano-scale interfacial phenomena. By measuring the responses of the photo detector due to bending and torsion of the cantilever, which are caused by the interactions between the probe and the sample surface, various interfacial phenomena and properties can be explored. One of the challenges faced by AFM researchers originates in the physics of measuring the small forces that act between the probe of a force sensing cantilever and the sample. To understand the interactions between the probe and the sample quantitatively, the force calibration is essential. In this work, the procedures used to calibrate AFM instrumentation for nano-scale force measurement in normal and lateral directions are reviewed.

• Journal of Korean Association for Spatial Structures
• /
• v.7 no.6
• /
• pp.103-110
• /
• 2007

Only horizontal seismic waves are often applied as designed load to a rectangular rigid frame because the influence of vertical seismic waves is considered small so as to be able to ignore it. But, as for the seismic responses of shell and spatial structures, the responses in the vortical direction is significantly amplified and the vertical responses are amplified even if they are subjected to the horizontal seismic wave only. And also, the horizontal and vertical seismic responses of shell and spatial structures are amplified by vortical seismic waves. An arch has been often used as the main structure component of the large spatial structures and is the mostly simple structure with the seismic response characteristics of the spatial structures. In this paper, for arches as a simple example of the shell and spatial structures, the dynamic characteristics, when the structures are subjected to the horizontal and vertical seismic wave at the same time, are studied, and the horizontal and vertical static seismic force, which have simple forms but hold the response characteristics of arches, are proposed.

• Ocean Systems Engineering
• /
• v.10 no.4
• /
• pp.399-414
• /
• 2020

A floating bridge is an innovative solution for deep-water and long-distance crossing. This paper presents a curved floating bridge's dynamic behaviors under the wind, wave, and current loads. Since the present curved bridge need not have mooring lines, its deep-water application can be more straightforward than conventional straight floating bridges with mooring lines. We solve the coupled interaction among the bridge girders, pontoons, and columns in the time-domain and to consider various load combinations to evaluate each force's contribution to overall dynamic responses. Discrete pontoons are uniformly spaced, and the pontoon's hydrodynamic coefficients and excitation forces are computed in the frequency domain by using the potential-theory-based 3D diffraction/radiation program. In the successive time-domain simulation, the Cummins equation is used for solving the pontoon's dynamics, and the bridge girders and columns are modeled by the beam theory and finite element formulation. Then, all the components are fully coupled to solve the fully-coupled equation of motion. Subsequently, the wet natural frequencies for various bending modes are identified. Then, the time histories and spectra of the girder's dynamic responses are presented and systematically analyzed. The second-order difference-frequency wave force and slowly-varying wind force may significantly affect the girder's lateral responses through resonance if the bridge's lateral bending stiffness is not sufficient. On the other hand, the first-order wave-frequency forces play a crucial role in the vertical responses.

• Earthquakes and Structures
• /
• v.20 no.1
• /
• pp.39-53
• /
• 2021

By means of installing sloped rolling-type seismic isolators (SRI), the horizontal acceleration transmitted to the to-be-protected object above can be effectively and significantly reduced under external disturbance. To prevent the maximum horizontal displacement response of SRI from reaching a threshold, designing large and conservative damping force for SRI might be required, which will also enlarge the transmitted acceleration response. In a word, when adopting seismic isolation, minimizing acceleration or displacement responses is always a trade-off. Therefore, this paper proposes that by exploiting the possible information provided by an earthquake early warning system, the damping force applied to SRI which can better control both acceleration and displacement responses might be determined in advance and accordingly adjusted in a semi-active control manner. By using a large number of ground motion records with peak ground acceleration not less than 80 gal, the numerical results present that the maximum horizontal displacement response of SRI is highly correlated with and proportional to some important parameters of input excitations, the velocity pulse energy rate and peak velocity in particular. A control law employing the basic form of hyperbolic tangent function and two objective functions are considered in this study for conceptually developing suitable control algorithms. Compared with the numerical results of simply designing a constant, large damping factor to prevent SRI from pounding, adopting the recommended control algorithms can have more than 60% reduction of acceleration responses in average under the excitations. More importantly, it is effective in reducing acceleration responses under approximately 98% of the excitations.