• Structural Engineering and Mechanics
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• v.50 no.4
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• pp.487-500
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• 2014

An analytical solution for the nonlinear in-plane free oscillations of the suspended cable which contains the quadratic and cubic nonlinearities is investigated via the homotopy analysis method (HAM). Different from the existing analytical technique, the HAM is indeed independent of the small parameter assumption in the nonlinear vibration equation. The nonlinear equation is established by using the extended Hamilton's principle, which takes into account the effects of the geometric nonlinearity and quasi-static stretching. A non-zero equilibrium position term is introduced due to the quadratic nonlinearity in order to guarantee the rule of the solution expression. Therefore, the mth-order analytic solutions of the corresponding equation are explicitly obtained via the HAM. Numerical results show that the approximate solutions obtained by using the HAM are in good agreement with the numerical integrations (i.e., Runge-Kutta method). Moreover, the HAM provides a simple way to adjust and control the convergent regions of the series solutions by means of an auxiliary parameter. Finally, the effects of initial conditions on the linear and nonlinear frequency ratio are investigated.

• Structural Engineering and Mechanics
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• v.90 no.2
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• pp.209-218
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• 2024

The present paper is focused on the study of the propagation of plane waves in thermoelastic media under a modified Green-Lindsay (MG-L) model having the influence of non-local and two temperature. The problem is formulated for the considered model in dimensionless form and is explained by using the reflection phenomenon. The plane wave solution of these equations indicates the existence of three waves namely Longitudinal waves (LD-Wave), Thermal waves (T-wave), and Shear waves (SV-wave) from a stress-free surface. The variation of amplitude ratios is computed analytically and depicted graphically against the angle of incidence to elaborate the impact of non-local, two temperature, and different theories of thermoelasticity. Some particular cases of interest are also deduced from the present investigation. The present study finds applications in a wide range of problems in engineering and sciences, control theory, vibration mechanics, and continuum mechanics.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.6
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• pp.445-454
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• 2002

Torque ripple control of brushless DC motors has been the persisting issue of the servo drive systems in which the speed fluctuation, vibration and acoustic noise should be minimized. In this paper, a novel approach to achieve the ripple-free torque control with maximum efficiency based on the d-q reference frame is presented and analyzed. The proposed approach can provide the optimized phase current waveforms over wide speed range incorporating cogging torque compensation without an access to the neutral point of the motor windings. Moreover, the undesirable errors caused by the assumptions such as 3 phase balance or symmetry of the phase back EMF between electrical cycles, which are related with the manufacturing imperfections, can be also eliminated. As a result, the proposed approach provides a simple and clear way to obtain the optimal motor excitation currents. A hysteresis current control system is employed to produce high-frequency electromagnetic torque ripples for compensation. The validity and applicability of the proposed control scheme to real situations are verified through the simulations and experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.744-747
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• 2005

This research studied 6-Axes Articulated Robot Manipulator's gain Tuning in consideration of dynamic. First of all, search fur proportional gain of velocity control loop by dynamic signal analyzer. Proportional gain of velocity control loop is connected to dynamic signal analyzer. Next Select free Proportional Gain value. And Select amplitude X of sinusoidal properly so that enough Velocity Feedback Signal may be paid as there is no group to utensil department. Next step, We can get Bode Diagram of Closed loop transfer function response examination in interested frequency. Integral calculus for gain of velocity loop is depended on integral calculus correction's number. We can obtain open loop transfer function by integrator. And we can know bode diagram's special quality from calculated open loop transfer function. With this, Velocity Control Loop's Parameter as inner loop is controlled. Next In moving, when vibration occurs, it controls notch filter. And finally, we have to control fred-forward filter parameter for elevation of control performance.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.929-933
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• 2004

A robot manipulator is usually operated in two modes: free motion and constraint motion according to the fact whether the robot comes into contact with the environment or not. At the moment of contact, impact occurs, and sometimes, it can possibly degrade the robot's performance such as vibration and at worst, shortens its lifetime. In this article, a new proposed algorithm is described by introducing a command signal modification method on the basis of impedance control and a validity of the proposed algorithm is demonstrated by showing the simulation study.

• Explosives and Blasting
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• v.42 no.3
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• pp.49-57
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• 2024

Pre-fracturing is the blasting method to weaken the rock mass prior to the main excavation. This study aims to evaluate the effectiveness of pre-fracturing by using half the explosive charge typically employed in conventional blasting designs. Field tests conducted at a quarry in Gapyeong showed that noise levels were reduced by 2.7 dB due to the decreased amount of explosive per blast hole, and vibration levels were controlled to the precision vibration control blasting standard. Rock weakening was confirmed through induced cracks observed on the surface and core samples, and it was noted that the weakening effect of the blasting decreased as the burden increased. The vibrations from conventional blasting were found to be lower than those from pre-fracturing. This was attributed more to the geological conditions, such as joints, rather than the blasting design factors like explosive amount, burden, and the number of free face.

• Smart Structures and Systems
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• v.34 no.2
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• pp.73-85
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• 2024

Smart base-isolated buildings rest on flexible pads known as base isolators that minimize the effect of external disturbances along with active/semi-active actuators. The strategies used to control these active components are typically based on system models that are known a priori. Although these models describe some of the most important dynamics of the elements involved in the system, the high degree of uncertainty in the behavior of a structure under external disturbances is very difficult to characterize using a fixed model. In this work, we propose a strategy that deals with this issue: the input that controls the actuator in the base isolation system results from the compound action of a controller that relies on a model of the system that is known a priori, and a control policy that is designed based on online data-driven inferences on the behavior of the system. In this way, the control design process incorporates both the prior information about the system and the unknowns of the system, such as non-modeled parameters and nonlinear behaviors in the building. We show through simulations the performance of the proposed method in an eight-story building subjected to seismic loading.

• Wind and Structures
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• v.30 no.5
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• pp.465-474
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• 2020

Vortex-induced vibrations of a yawed flexible cylinder near a plane boundary are numerically investigated at a Reynolds number Re_n= 500 based on normal component of freestream velocity. Free to oscillate in the in-line and cross-flow directions, the cylinder with an aspect ratio of 25 is pinned-pinned at both ends at a fixed wall-cylinder gap ratio G/D = 0.8, where D is the cylinder diameter. The cylinder yaw angle (α) is varied from 0° to 60° with an increment of 15°. The main focus is given on the influence of α on structural vibrations, flow patterns, hydrodynamic forces, and IP (Independence Principle) validity. The vortex shedding pattern, contingent on α, is parallel at α=0°, negatively-yawed at α ≤ 15° and positively-yawed at α ≥ 30°. In the negatively- and positively-yawed vortex shedding patterns, the inclination direction of the spanwise vortex rows is in the opposite and same directions of α, respectively. Both in-line and cross-flow vibration amplitudes are symmetric to the midspan, regardless of α. The RMS lift coefficient C_L,rms exhibits asymmetry along the span when α ≠ 0°, maximum C_L,rms occurring on the lower and upper halves of the cylinder for negatively- and positively-yawed vortex shedding patterns, respectively. The IP is well followed in predicting the vibration amplitudes and drag forces for α ≤ 45° while invalid in predicting lift forces for α ≥ 30°. The vortex-shedding frequency and the vibration frequency are well predicted for α = 0° - 60° examined.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.50-57
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• 2004

For the application of structural health monitoring such as AE detection, a stabilized FBG sensor system with wide dynamic range was proposed. A tunable Fabry-Perot filter with narrow free spectral range(FSR) was used to simplify the multiplexing demodulator for FBG vibration sensors. Stabilization controlling system was also developed for the maintenance of maximum sensitivity of the sensors. In order to verify the performance of the proposed FBG vibration sensor system, we measured sensitivity, and the system showed the average sensitivity of 256 $n{\in}_{mas}/{\sqrt{Hz}}$. Finally, multi-points vibration tests using in-line FBG sensors were conducted to validate the multiplexing performance of the FBG system.

• Smart Structures and Systems
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• v.24 no.1
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• pp.83-94
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• 2019

Passive negative stiffness dampers (NSDs) that possess superior energy dissipation abilities, have been proved to be more efficient than commonly adopted passive viscous dampers in controlling stay cable vibrations. Recently, inertial mass dampers (IMDs) have attracted extensive attentions since their properties are similar to NSDs. It has been theoretically predicted that superior supplemental damping can be generated for a taut cable with an IMD. This paper aims to theoretically investigate the impact of the cable sag on the efficiency of an IMD in controlling stay cable vibrations, and experimentally validate superior vibration mitigation performance of the IMD. Both the numerical and asymptotic solutions were obtained for an inclined sag cable with an IMD installed close to the cable end. Based on the asymptotic solution, the cable attainable maximum modal damping ratio and the corresponding optimal damping coefficient of the IMD were derived for a given inertial mass. An electromagnetic IMD (EIMD) with adjustable inertial mass was developed to investigate the effects of inertial mass and cable sag on the vibration mitigation performance of two model cables with different sags through series of first modal free vibration tests. The results show that the sag generally reduces the attainable first modal damping ratio of the cable with a passive viscous damper, while tends to increase the cable maximum attainable modal damping ratio provided by the IMD. The cable sag also decreases the optimum damping coefficient of the IMD when the inertial mass is less than its optimal value. The theoretically predicted first modal damping ratio of the cable with an IMD, taking into account the sag generally, agrees well with that identified from experimental results, while it will be significantly overestimated with a taut-cable model, especially for the cable with large sag.