• 한국소음진동공학회논문집
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• 제18권12호
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• pp.1278-1285
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• 2008

This paper presents an inertia type of piezostack based active mount fur unmanned aero vehicle (UAV) camera system. After identifying the stiffness and damping properties of the rubber element and piezostack a mechanical model of the active mount system is established. The governing equation of mount is then derived and expressed in a state space form. Subsequently, a sliding mode controller which is robust to uncertain parameters is designed in order to reduce the vibration imposed according to the military specification associated with UAV camera mount system operation. Control performances such as acceleration and transmitted force are evaluated through both computer simulation and experimental implementation.

• 한국건설관리학회논문집
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• 제9권2호
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• pp.108-116
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• 2008

현재 건설현장에서는 인력수급의 어려움과 숙련공의 노령화의 해법으로 건설 자동화가 추진되고 있다. 특히, 건축물의 대형화 및 고층화에 따라 양중작업의 중요성이 높아지면서 작업의 효율성을 향상시킬 수 있도록 타워크레인을 대상으로 한 많은 자동화연구가 진행 중이다. 타워크레인을 이용한 양중작업의 자동화를 위해서는 부재의 관성과 풍하중에 의한 진동을 제어해야 하는데, 제어하기에 앞서 진동을 예측하는 것은 매우 어렵다. 따라서 본 연구에서는 타워크레인과 부재를 대상으로 동적 모델링을 실시하고 시뮬레이션을 통해 부재의 동적 진동을 분석하였다. 그 결과, 작업조건에 따른 발생하는 부재의 최대진동폭과 특징을 분석하였다. 그리고 분석자료를 바탕으로 부재의 특성에 따라 양중작업 자동화가 가능한 풍속기준을 판단할 수 있는 방안을 제시하였다.

• Smart Structures and Systems
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• 제26권2호
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• pp.195-211
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• 2020

Among anti-seismic technologies, base isolation is a very effective means of mitigating damage to structural and nonstructural components, such as equipment. However, most seismic isolation systems are designed for mitigating only horizontal seismic responses because the realization of a vertical isolation system (VIS) is difficult. The difficulty is primarily due to conflicting isolation stiffness demands in the static and dynamic states for a VIS, which requires sufficient rigidity to support the self-weight of the isolated object in the static state, but sufficient flexibility to lengthen the isolation period and uncouple the ground motion in the dynamic state. To overcome this problem, a semi-active VIS, called the piezoelectric inertia-type vertical isolation system (PIVIS), is proposed in this study. PIVIS is composed of a piezoelectric friction damper (PFD) and a leverage mechanism with a counterweight. The counterweight provides an uplifting force in the static state and an extra inertial force in the dynamic state; therefore, the effective vertical stiffness of PIVIS is higher in the static state and lower in the dynamic state. The PFD provides a controllable friction force for PIVIS to further prevent its excessive displacement. For experimental verification, a shaking table test was conducted on a prototype PIVIS controlled by a simple controller. The experimental results well agree with the theoretical results. To further investigate the isolation performance of PIVIS, the seismic responses of PIVIS were simulated numerically by considering 14 vertical ground motions with different characteristics. The responses of PIVIS were compared with those of a traditional VIS and a passive system (PIVIS without control). The numerical results demonstrate that compared with the traditional and passive systems, PIVIS can effectively suppress isolation displacement in all kinds of earthquake with various peak ground accelerations and frequency content while maintaining its isolation efficiency. The proposed system is particularly effective for near-fault earthquakes with long-period components, for which it prevents resonant-like motion.

• 국제초고층학회논문집
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• 제12권1호
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• pp.93-105
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• 2023

Seismic isolation and vibration control techniques have been developed and put into practical use by challenging researchers and engineers worldwide since the latter half of the 20th century, and after more than 40 years, they are now used in thousands of buildings, private residences, highways in many seismic areas in the world. Seismic isolation and vibration control structures can keep the structures undamaged even in a major earthquake and realize continuous occupancy. This performance has come to be recognized not only by engineers but also by ordinary people, becoming indispensable for the formation of a resilient society. However, the dynamic characteristics of seismically isolated bearings, the key elements, are highly dependent on the size effect and rate-of-loading, especially under extreme loading conditions. Therefore, confirming the actual properties and performance of these bearings with full-scale specimens under prescribed dynamic loading protocols is essential. The number of testing facilities with such capacity is still limited and even though the existing labs in the US, China, Taiwan, Italy, etc. are conducting these tests, their dynamic loading test setups are subjected to friction generated by the large vertical loads and inertial force of the heavy table which affect the accuracy of measured forces. To solve this problem, the authors have proposed a direct reaction force measuring system that can eliminate the effects of friction and inertia forces, and a seismic isolation testing facility with the proposed system (E-isolation) will be completed on March 2023 in Japan. This test facility is designed to conduct not only dynamic loading tests of seismic isolation bearings and dampers but also to perform hybrid simulations of seismically isolated structures. In this paper, design details and the realization of this system into an actual dynamic testing facility are presented and the outcomes are discussed.

• Earthquakes and Structures
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• 제27권1호
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• pp.1-15
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• 2024

In order to enhance the seismic performance of base-isolated structures on soft foundations, the hybrid system of base-isolated system (BIS) and shape memory alloy inerter (SMAI), referred to as BIS+SMAI, is for the first time here proposed. Considering the nonlinear hysteretic relationships of both the isolation layer and SMA, and soil-structure interaction (SSI), the equivalent linearized state space equation is established of the structure-BIS+SMAI system. The displacement variance based on the H₂ norm is then formulated for the structure with BIS+SMAI. Employing the particle swarm optimization, the optimization design methodology of BIS+SMAI is presented in the frequency domain. The evolvement rules of BIS+SMAI in the effectiveness, robustness, SMA driving force, inertia force, stroke, and damping enhancement effect are revealed in the frequency domain through changing the inerter-mass ratio, structural height, aspect ratio, and relative stiffness ratio between the soil and structure. Meanwhile, the validation of BIS+SMAI is conducted using real earthquake records. Results demonstrate that BIS+SMAI can effectively reduce the isolation layer displacement. The inerter can significantly increase the hysteretic displacement of SMA and thus enhance its energy dissipation capacity, implying that BIS+SMAI has better effectiveness than BIS+SMA. Although BIS+SMAI and BIS+ tuned inerter damper (TID) have practically the same effectiveness, BIS+SMAI has the lower optimum damping, significantly smaller inertia force, and higher robustness to perturbations of the optimum parameters. Therefore, BIS+SMAI can be used as a more engineering realizable hybrid system for enhancing the performance of base-isolated structures in soft soil areas.

• Structural Engineering and Mechanics
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• 제47권2호
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• pp.149-166
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• 2013

Flexible behaviors in new aerospace structures can lead to a degradation of their control and guidance system and undesired performance. The objectives of the current work are to analyze the vibration resulting from the propulsion force on a Single Stage to Orbit (SSTO) launch vehicle (LV). This is modeled as a follower force on a free-free Euler-Bernoulli beam consisting of two concentrated masses at the two free ends. Once the effects on the oscillation of the actuators are studied, a solution to reduce these oscillations will also be developed. To pursue this goal, the stability of the beam model is studied using Ritz method. It is determined that the transverse and rotary inertia of the concentrated masses cause a change in the critical follower force. A new dynamic model and an adaptive control system for an SSTO LV have been developed that allow the aerospace structure to run on its maximum bearable propulsion force with the optimum effects on the oscillation of its actuators. Simulation results show that such a control model provides an effective way to reduce the undesirable oscillations of the actuators.

• 대한조선학회논문집
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• 제61권4호
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• pp.236-246
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• 2024

The present study aims to identify the effects of the oblique inflow and vertical acceleration on a marine propeller's hydrodynamic force and moment. Computational Fluid Dynamics analysis is performed for a rotating propeller in open water conditions with heave motion after performing validation against experiment in straightforward conditions. The oblique inflow results in a linear increase of the off-axial component of the hydrodynamic force and moment rather than the axial one. Pitch and yaw moments due to the hull motion are dominated by the heave force and the moment arm of the propeller location. Additionally, the vertical acceleration leads to a linear augmentation of off-axial hydrodynamic force and moment, implying the added mass and moment of inertia. Notably, it is found that the off-axial hydrodynamic force and moment are dominated by the oblique inflow velocity rather than the acceleration.

• 한국운동역학회지
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• 제14권2호
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• pp.57-68
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• 2004

This study was to evaluate the consistency of the vertical force($F_z$) of the force platform and the impact force. Two experiments were performed. First, the force platform was vertically placed to hang to the wall. While the rotating iron body hit the force platform, $F_z$ was measured. Then $F_z$ was compared with the impact force of the rotating iron body that was precalculated by using the inertia moments and the rotating force. Second, six Taekwondo masters punched the force platform to show what a certain pattern the impart force has. They were asked to punch the target depending on target distances. The target distances were differed from the relative arm segment of subjects as 90%, 80%, 70%, 60%, and 50% (100% target distance equals the aim length of each subject). Pearson's correlations were used between $F_z$ and the impact force. Also the linear regression was also performed to show the linearity. At the first experiment, $F_z$ and the impact force had much correlations and showed linear characteristics. Therefore, $F_z$ could be regarded as the impact force. At the second experiment, the strongest impact force was measured at the target distance of 80% and the time taken to the maximum impact force was within 0.02 seconds. The result of this study recommends that it can help the comparative study between the impact forces and other hitting sports.

• 대한기계학회논문집A
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• 제24권1호
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• pp.232-239
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• 2000

The paper describes the parametric instability of free-free beams subjected to a controlled pulsating follower force. The beam has a tip rigid body not a mass point, and the direction of pulsating follower force is controlled by the direction control sensor. Equations of motion are derived by Hamilton's principle and the instability regions are obtained by finite element formulation. The effects of magnitude, rotary inertia, the distance between free end of the beam and the center of gravity of the rigid body on the instability types and regions are investigated by the change of the constant and periodic part of the follower force.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.84-87
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• 1999

This paper proposes an interfaces control system to drive a ultrasonic motors(USMs). To touch surfaces and objects created within a virtua environment, the 3 DOF force-reflecting interfaces provides force feedback to users, so to feel touching real things. To effectively display the mechanical impedance of the human hand we need a device with specific characteristics, such as low inertia almost zero friction and very high stiffness. As an actuator for direct drive method, the USMs have many good advantages satisfied these conditions over conventional servo motors. To estimate capability of this interface, we did an experiment. The device works very well, as user are able to detect the edge of the wall and the stiffness of the button.