• Advances in aircraft and spacecraft science
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• 제5권2호
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• pp.205-223
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• 2018

During launch a spacecraft is subjected to a variety of dynamical loads transmitted through the launcher to spacecraft interface or air-born transmission excitations in the acoustic pressure field inside the fairing. As a result, spacecraft are tested on ground to ensure and demonstrate the global integrity of the structure against these loads, to screen the flight hardware for quality of workmanship and to validate mathematical models. This paper addresses the numerical modelling and simulation of the low frequency sine and random vibration tests performed on electrodynamic shaker facilities to comprise the mechanical-borne transmission loads through the launcher to spacecraft interface. Consequently, the paper reviews techniques and methodologies to derive a reliable and representative coupled virtual vibration testing simulation environment based on experimental data. These technologies are explored with the main objectives to ensure a stable, reliable and accurate control while testing. As a result, the use of the derived simulation models in combination with the added value of improved control and signal processing algorithms can lead to a safer and smoother vibration test control of the entire environmental test campaign.

• Smart Structures and Systems
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• 제22권1호
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• pp.71-79
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• 2018

The nonlinear vibration analysis of a magneto-rheological elastomer (MRE) sandwich plate is conducted experimentally. Experiments have been performed in order to construct the frequency-response curves in the vicinity of the fundamental natural frequency of an MRE sandwich plate (plate A) in either the absence or presence of a localised external magnetic field at 3 different geometrical locations, for both small and medium magnetic fields. Furthermore, experiments have also been conducted on a pure aluminium plate (plate B) with an equal thickness to the MRE sandwich plate (plate A) in order to examine the influence of the MRE layer on the nonlinear dynamics of the system. An electrodynamic shaker was used to directly force each system and the displacement at the centre of the plate was measured. Meanwhile, permanent magnets were used to apply a localised magnetic field for the experiments where the MRE sandwich plate was subject to an external magnetic field. It was observed all the MRE systems displayed strong hardening-type nonlinear behaviour, however, with increasing magnetic field this behaviour transitioned to a weak hardening-type nonlinearity.

• KEPCO Journal on Electric Power and Energy
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• 제7권2호
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• pp.241-248
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• 2021

High cycle fatigue life for the cables with two different types of clamps is estimated comparatively through acceleration testing. The high cycle fatigue fracture of overhead lines is caused mainly by the aeolian vibration which is induced by vortex shedding. It is necessary to manage the integrity of cables continuedly considering that the aeolian vibration is unavoidable since it occurs in steady and relatively low wind velocity. Two types of clamps which are largely used for overhead lines of the distribution grids are selected and failure data are obtained by step stress testing with a electrodynamic shaker with them. The inverse power law is assumed to describe the stress-life relationship and the fatigue limit at any specified life is supposed to follow Weibull distribution. The life of the cable is defined as the number of cycles to the time that one of strands is completely broken. Finally, the fatigue limits of the cables with two clamp types are estimated at the reference life of 500 Mcycles and compared each other based on a bending vibration amplitude.

• KEPCO Journal on Electric Power and Energy
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• 제3권2호
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• pp.107-111
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• 2017

$1100^{\circ}C$급 가스터빈 동익의 국산화 개발품에 대한 신뢰성을 무고장시험법에 의해 평가하였다. 터빈 동익은 기동, 정지 중에 발생하는 공진 또는 유체유발진동을 겪는 등 터빈 운전 중 상시 다양한 동하중에 노출되어 있으며, 이러한 변동하중은 터빈 동익에 고주기피로손상을 초래한다. 특히 동익의 파손에 의한 사고는 타 설비로의 파급이 크고, 막대한 경제적 피해를 야기하기 때문에, 발전소의 안정적인 운전을 위해 동익의 신뢰성이 우선 검증되어야 한다. 동익에 균열을 일으키기 위해서 전자식 가진기를 이용하여 공진에 의한 증폭된 동하중을 부과하였다. 가스터빈 동익의 수명분포를 와이블 분포로 가정하여 를 시험 시간을 계산하고, 시료 1개의 고장을 허용하는 조건으로 총 5개의 개발품을 대상으로 시험을 수행하여, 개발품 동익의 목표 수명을 90% 신뢰도로 보증할 수 있다는 것을 90% 신뢰수준에서 확인하였다.

• Smart Structures and Systems
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• 제25권1호
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• pp.57-64
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• 2020

The nonlinear dynamics of a directly forced clamped-clamped-free-free magneto-rheological elastomer (MRE) sandwich shell has been experimentally investigated. Experiments have been conducted on an aluminium shallow shell (shell A) and an MRE-aluminium sandwich shallow shell with single curvature (shell B). An electrodynamic shaker has been used to directly force shells A and B in the vicinity of their fundamental resonance frequency; a laser displacement sensor has been used to measure the vibration amplitude to construct the frequency-response curves. It was observed that for an aluminium shell (shell A), that at small forcing amplitudes, a weak softening-type nonlinear behaviour was observed, however, at higher forcing amplitudes the nonlinear dynamical behaviour shifted and a strong hardening-type response occurred. For the MRE shell (shell B), the effect of forcing amplitude showed softening at low magnetic fields and hardening for medium magnetic fields; it was also observed the mono-curved MRE sandwich shell changed dynamics to quasiperiodic displacement at some frequencies, from a periodic displacement. The presence of a magnetic field, initial curvature, and forcing amplitude has significant qualitative and quantitative effects on the nonlinear dynamical response of a mono curved MRE sandwich shell.