• Advances in aircraft and spacecraft science
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• 제5권3호
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• pp.349-362
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• 2018

A non-linear numerical simulation technique for predicting the unsteady performances of an airbreathing engine is developed. The study focuses on the simulation of integrated propulsion systems, where a closer coupling is needed between the airframe and the engine dynamics. In fact, the solution of the fully unsteady flow governing equations, rather than a lumped volume gas dynamics discretization, is essential for modeling the coupling between aero-servoelastic modes and engine dynamics in highly integrated propulsion systems. This consideration holds for any propulsion system when a full separation between the fluid dynamic time-scale and engine transient cannot be appreciated, as in the case of flow instabilities (e.g., rotating stall, surge, inlet unstart), or in case of sudden external perturbations (e.g., gas ingestion). Simulations of the coupling between external and internal flow are performed. The flow around the nacelle and inside the engine ducts (i.e., air intakes, nozzles) is solved by CFD computations, whereas the flow evolution through compressor and turbine bladings is simulated by actuator disks. Shaft work balance and rotor dynamics are deduced from the estimated torque on each turbine/compressor blade row.

• Advances in Computational Design
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• 제7권3호
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• pp.189-210
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• 2022

Deployable structures have the ability to shift from a compact state to an expanded functional configuration. By extension, reconfigurability is another function that relies on embedded computation and actuators. Linkage-based mechanisms constitute promising systems in the development of deployable and reconfigurable structures with high flexibility and controllability. The present paper investigates the deployment and reconfigurability of modular linkage structures with a pin and a sliding support, the latter connected to a linear motion actuator. An appropriate control sequence consists of stepwise reconfigurations that involve the selective releasing of one intermediate joint in each closed-loop linkage, effectively reducing it to a 1-DOF "effective crank-slider" mechanism. This approach enables low self-weight and reduced energy consumption. A kinematics and finite-element analysis of different linkage systems, in all intermediate reconfiguration steps of a sequence, have been conducted for different lengths and geometrical characteristics of the members, as well as different actuation methods, i.e., direct and cable-driven actuation. The study provides insight into the impact of various structural typological and geometrical factors on the systems' behavior.

• 로봇학회논문지
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• 제17권2호
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• pp.172-177
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• 2022

In general, detection robots using ultrasonic sensors are equipped with sensors to protrude outward or to contact objects. However, in the case of a screw-propelled robot that detects the inside of a reactor tendon duct, if the ultrasonic sensor protrudes to the outside, resistance due to grease is generated, and thus the propulsion efficiency is reduced. In order to increase the propulsion efficiency, the screw must be sharp, and the sharper the screw, the more difficult it is to apply a high-performance ultrasonic sensor, and the detection efficiency decreases. This paper proposes a screw shape-changing mechanism that can improve both propulsion efficiency and detection efficiency. This mechanism includes an overlapped helical ring (OHR) structure and a magnetic clutch system (MCS), and thus the shape of a screw may be changed to a compact size. As a result, the Screw-propelled robot with this mechanism can reduce the overall length by about 150 mm and change the shape of the screw faster and more accurately than a robot with a linear actuator.

• 한국해양공학회지
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• 제36권4호
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• pp.243-250
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• 2022

Subsea power cables are subjected to various external loads induced by environmental and mechanical factors during manufacturing, shipping, and installation. Therefore, the prediction of the structural strength is essential. In this study, experimental and theoretical analyses were performed to investigate the axial stiffness of subsea power cables. A uniaxial tensile test of a 6.5 m three-core AC inter-array subsea power cable was carried out using a 10 MN hydraulic actuator. In addition, the resultant force was measured as a function of displacement. The theoretical model proposed by Witz and Tan (1992) was used to numerically predict the axial stiffness of the specimen. The Newton-Raphson method was employed to solve the governing equation in the theoretical analysis. A comparison of the experimental and theoretical results for axial stiffness revealed satisfactory agreement. In addition, the predicted axial stiffness was linear notwithstanding the nonlinear geometry of the subsea power cable or the nonlinearity of the governing equation. The feasibility of both experimental and theoretical framework for predicting the axial stiffness of subsea power cables was validated. Nevertheless, the need for further numerical study using the finite element method to validate the framework is acknowledged.

• 한국기계가공학회지
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• 제20권11호
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• pp.43-51
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• 2021

A robust tracking controller design was developed for a rotary motion control system. The friction force versus the angular velocity was measured and modeled as a combination of linear and nonlinear components. By adding a model-based friction compensator to a nominal proportional-integral-derivative controller, it was possible to build a simulated control system model that agreed well with the experimental results. A zero-phase error tracking controller was selected as the feedforward tracking controller and implemented based on the estimated closed-loop transfer function. To provide robustness against external disturbances and modeling uncertainties, a disturbance observer was added in the position feedback loop. The performance improvement of the overall tracking controller structure was verified through simulations and experiments.

• Smart Structures and Systems
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• 제31권5호
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• pp.437-454
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• 2023

Real-time hybrid simulation (RTHS), which has the advantages of a substructure pseudo-dynamic test, is widely used to investigate the rate-dependent mechanical response of structures under earthquake excitation. However, time delay in RTHS can cause inaccurate results and experimental instabilities. Thus, this study proposes a model-based adaptive control strategy using a Kalman filter (KF) to minimize the time delay and improve RTHS stability and accuracy. In this method, the adaptive control strategy consists of three parts-a feedforward controller based on the discrete inverse model of a servohydraulic actuator and physical specimen, a parameter estimator using the KF, and a feedback controller. The KF with the feedforward controller can significantly reduce the variable time delay due to its fast convergence and high sensitivity to the error between the desired displacement and the measured one. The feedback control can remedy the residual time delay and minimize the method's dependence on the inverse model, thereby improving the robustness of the proposed control method. The tracking performance and parametric studies are conducted using the benchmark problem in RTHS. The results reveal that better tracking performance can be obtained, and the KF's initial settings have limited influence on the proposed strategy. Virtual RTHSs are conducted with linear and nonlinear physical substructures, respectively, and the results indicate brilliant tracking performance and superb robustness of the proposed method.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2022년도 추계학술발표대회
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• pp.767-769
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• 2022

본 논문에서는 현대인들의 일상생활 속 누적된 스트레스를 완화하고 사용자의 편의를 고려한 "아로마테라피를 지원하는 지능형 샤워부스" 시스템을 제안한다. 제안하는 시스템의 주요 기능은 다음과 같다. 첫째, 적외선 온도 센서와 초음파 센서, 카메라를 통해 사용자의 신체 정보와 기분을 측정한다. 둘째, 측정된 사용자의 신체 정보를 반영하여 Linear actuator를 이용해 샤워기의 높낮이 및 수온을 자동으로 조절한다. 셋째, OpenCV와 앱 내에 만족도 평가를 통해 사용자의 기분에 따라 알맞은 아로마오일을 추천하고 이를 샤워기 필터에 주입한다. IoT기술과 연동된 샤워부스 시스템을 통해 사용자 컨디션에 맞춘 아로마테라피를 지원하여 현대인의 지친 심신 회복과 사용자 편의성이 증대될 것으로 기대된다.

• 센서학회지
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• 제1권2호
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• pp.183-194
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• 1992

실리콘 기판을 HF용액 내에서 양극반응을 시켜 electropolishing법 또는 PSL 형성법으로 센서와 actuator에 유용한 다양한 모양의 실리콘 미세 기계구조를 제조하였다. 미세구조는 시편의 결정면에 관계없이 형성되었으며, 저농도 도핑된 단결정 실리콘이다. $n^{+}/n$ 실리콘 시편을 HF용액(20-48%)내에서 양극반응시켜 $n^{+}$ 영역에 선택적으로 PSL을 형성하였으며, HF농도, 반응전압 및 반응시간에 따른 PSL 형성의 특성을 조사였다. $n^{+}$ 영역에만 PSL이 형성되었으며 PSL의 다공도는 HF 농도 증가에 따라 감소하였으며, 반응전압에는 무관하였다. $n/n^{+}/n$형 구조를 이용하여 미세구조를 제조한 경우, 식각된 실리콘 표면이 균일하고 cusp가 제거되었으며, 미세구조의 두께는 전 영역을 통하여 n-epi.층의 두께로 일정하였다. HF용액(5 wt%)에서의 양극반응과 planar기술을 이용하여 가속도센서를 제조하여 기존의 IC 공정기술과 함께 사용이 가능함을 확인하였다. 또 모터의 회전자, 기어 등의 미세 기계구조를 PSL 형성법으로 제조하고 SEM 사진으로 조사하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 춘계학술대회
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• pp.84-87
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• 1996

We have been developed electrohydraulic left ventricular assist device and done various in vivo evaluation on the device. Through the in vivo experiment conducted from Jan. 23, 1996 to Feb. 8, we could have experience of long-term evaluation fur the first time. The sheep used in this experiment had survived for 16 days. We used new actuator with reduced size and linear motion guide replacing oil box and ball bearings. Also, we used improved blood chamber with reduced size, reduced weight facilitating fixing the chamber to animal's body, and polymer sac having improved folding pattern. Against suction problem, we used absolute pressure limiter only. Motor current for driving this new actuator was not much higher than older one. Effective stroke volume was about 48 cc. Thrombosis was found around top area and peripheral boundary of the sac and valves. There was no sign of damage from suction problem in the atrium observed at autopsy. Main cause of death was presumed to be progressive formation of thrombosis in the cannulae. In this paper, the results of this experiment are documented.

• Ocean Systems Engineering
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• 제9권4호
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• pp.409-422
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• 2019

Sloshing is a phenomenon which may lead to dynamic stability and damages on the local structure of the tank. Hence, several anti-sloshing devices are introduced in order to reduce the impact pressure and free surface elevation of liquid. A fixed baffle is the most prevailing anti-sloshing mechanism compared to the other methods. However, the additional of the baffle as the internal structure of the LNG tank can lead to frequent damages in long-term usage as this structure absorbs the sloshing loads and thus increases the maintenance cost and downtime. In this paper, a novel type of floating baffle is proposed to suppress the sloshing effect in LNG tank without the need for reconstructing the tank. The sloshing phenomenon in a membrane type LNG tank model was excited under sway motion with 30% and 50% filling condition in the model test. A regular motion by a linear actuator was applied to the tank model at different amplitudes and constant period at 1.1 seconds. Three pressure sensors were installed on the tank wall to measure the impact pressure, and a high-speed camera was utilized to record the sloshing motion. The floater baffle was modeled on the basis of uniform-discretization of domain and tested based on parametric variations. Data of pressure sensors were collected for cases without- and with-floating baffle. The results indicated successful reduction of surface run-up and impulsive pressure by using a floating baffle. The findings are expected to bring significant impacts towards safer sea transportation of LNG.