• Structural Engineering and Mechanics
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• 제83권1호
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• pp.31-43
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• 2022

A nonlinear gas-spring tuned mass damper is proposed to mitigate the seismic responses of the multi-degree-of-freedom (MDOF) structure, in which the nine-story benchmark model is selected as the controlled object. The nonlinear mechanical properties of the gas-spring are investigated through theoretical analysis and experiments, and the damper's control parameters are designed. The control performance and damping mechanism of the proposed damper attached to the MDOF structure are systematically studied, and its reliability is also explored by parameter sensitivity analysis. The results illustrate that the nonlinear gas-spring TMD can transfer the primary structure's vibration energy from the lower to the higher modes, and consume energy through its own relative movement. The proposed damper has excellent "Reconciling Control Performance", which not only has a comparable control effect as the linear TMD, but also has certain advantages in working stroke. Furthermore, the control parameters of the gas-spring TMD can be determined according to the external excitation amplitude and the gas-spring's initial volume.

• 에너지공학
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• 제26권2호
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• pp.64-72
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• 2017

중동지역 환경에 적합한 70 W급 LED 조명등의 성능분석을 집중변수모델을 이용하여 수행하였다. LED 조명등은 발열기판, 히프파이프, 방열판으로 구성된다. LED 조명등을 4개의 물체로 구분하고, 각각에 대해 에너지평형을 적용하여, 4개의 연립 비선형미분방정식 형태의 집중변수모델을 수립하였다. 연립 방정식의 해는 Runge-Kutta법을 이용하여 구하였다. 집중변수모델의 대류열전달계수는 다차원해석을 통하여 구하였으며, 실험결과와 비교한 결과, 발열기판은 $1.5^{\circ}C$, 상부방열판에서 $1.8^{\circ}C$의 오차를 가지며, 상대오차는 약 0.6 %임을 확인하였다. 이 모델을 이용하여 대기온도가 $55^{\circ}C$인 정상 운전조건, 태양광만 주어질 때의 조건, 태양광이 주어진 상태에서의 비정상 운전조건, 상부방열판이 없는 경우 등에 대한 온도분포분석을 수행하였다.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.271-298
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• 2016

In this paper, we study a problem of passive suppression of helicopter Ground Resonance (GR) using a single degree freedom Nonlinear Energy Sink (NES), GR is a dynamic instability involving the coupling of the blades motion in the rotational plane (i.e. the lag motion) and the helicopter fuselage motion. A reduced linear system reproducing GR instability is used. It is obtained using successively Coleman transformation and binormal transformation. The analysis of the steadystate responses of this model is performed when a NES is attached on the helicopter fuselage. The NES involves an essential cubic restoring force and a linear damping force. The analysis is achieved applying complexification-averaging method. The resulting slow-flow model is finally analyzed using multiple scale approach. Four steady-state responses corresponding to complete suppression, partial suppression through strongly modulated response, partial suppression through periodic response and no suppression of the GR are highlighted. An algorithm based on simple criterions is developed to predict these steady-state response regimes. Numerical simulations of the complete system confirm this analysis of the slow-flow dynamics. A parametric analysis of the influence of the NES damping coefficient and the rotor speed on the response regime is finally proposed.