• 한국지진공학회논문집
• /
• 제10권5호
• /
• pp.107-115
• /
• 2006

지진과 같은 재난이 발생하였을 때에도 전력설비는 그 본래의 기능을 상실하지 않고 구조적인 안정성을 유지해야 하는 핵심 산업시설물이다. 이 연구는 가장 대표적인 전력설비인 154kV 변압기에 부착된 애자형 부싱의 진동특성과 내진성능을 분석하였다. 연구의 목적에 따라 국내에서 운용하던 실제 154kV 변압기 부싱을 대상으로 30tonf 용량의 진동대를 이용하여 진동시험이 실시되었다. 진동시험은 동특성분석시험과 내진성능시험 그리고 파괴한도시험으로 구분하고, 각각의 시험에는 정현소인파, 인공지진파 그리고 연속공진정현파를 진동대운동으로 입력하였다. 이 논문에는 시험에 사용된 시편과 진동설비의 특성 그리고, 시험 방법 및 종류를 설명하고, 시험 결과 얻어진 계측자료의 특성에 대하여 논의한다. 이 연구를 통하여 국내에서 운용중인 154kV 변압기 부싱은 그 고유진동수가 20Hz 이상인 고진동수 설비이며, 감쇠비는 4%미만인 것으로 분석되었다. 또한, 특별한 경우를 제외하고, 변압기 부싱은 국내의 설계기준지진에 대하여 충분한 내진안전성을 보유하고 있으며, 강한 공진운동에 의해 예상되는 부싱의 최초 파괴모드는 하단 개스킷의 파손인 것으로 밝혀졌다.

• Journal of Biosystems Engineering
• /
• 제27권5호
• /
• pp.391-398
• /
• 2002

During handling unitized products, they are subjected to a variety of environmental hazards. Shock and vibration hazards are generally considered the most damaging of the environmental hazards on a product and it may encounter while passing through the distribution environment. A major cause of shock damage to products is drops during manual handling. The increasing use of unitization of pallets has been resulted in a reduction of the shock hazards. This has caused an increasing interest in research focused on vibration caused dam age. Damage to the product by the vibration most often occurs when a product or a product component has a natural frequency that falls within the range of the forcing frequencies of the particular mode of transportation being used. Transportation vibration is also a major cause of fruit and vegetable quality loss due to mechanical damage. This study was conducted to determine the vibration characteristics of the corrugated fiberboard bones for packages of pears, and to investigate the degree of vibration injury of the pears in the boxes during the simulated transportation environment. The vibration tests were performed on an electrohydraulic vibration exciter. The input acceleration to exciter was fixed at 0.25 G for a single container resonance test and 0.5 G for the vertical stacked container over the frequency range from 3 to 100 Hz. Function generator (HP-33120A) was connected by wire to the vibration exciter for controlling the input acceleration at a continuous logarithmic sweep rate of 1.0 octave per min. The peak frequency and acceleration on the single box test were 22.02 Hz, 1.5425 G respectively, and these values on the vertical stacked boxes were observed from the bottom box 19.02, 18.14, 16.62 and 15.40 Hz and 2.2987, 3.7654. 5.6087, and 7.9582 G, respectively. The pear in the bottom box had a slightly higher damage level than the fruit packed in the other stacked boxes. It is desirable that the package and transportation system has to be so designed that 15∼20 Hz frequency will not occur during the transportation environment.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2007년도 춘계학술대회논문집
• /
• pp.258-262
• /
• 2007

Satellite launch vehicle is exposed to some dynamic environment during its flight. Particularly, the safety of launch vehicle structure is surely verified under vibration environment in low frequency range. Sine sweep test is generally performed to describe this low frequency vibration environment. Dynamic property of vibration fixture is considered to get the correct property of target object. This vibration fixture should really be an extension of the armature in the form of a very rigid structure that can transfer the required force at the required frequency. An optimum fixture would have its lower natural frequency about 50% higher than the highest required forcing frequency in order to avoid fixture resonances during the test. In this study, the vibration mode analysis considering the mass of target object to design the vibration fixture. And the modal test of vibration fixture is performed to conform the design.

• Nuclear Engineering and Technology
• /
• 제42권3호
• /
• pp.319-328
• /
• 2010

Bonded tendons have been used in reactor buildings at some operating nuclear power plants in Korea. Assessing prestress force on these bonded tendons has become an important pending problem in efforts to assure continued operation beyond their design life. The System Identification (SI) technique was thus developed to improve upon the existing indirect assessment technique for bonded tendons. As a first step, this study analyzed the sensitivity of the key parameters to prestress force, and then determined the optimal parameters for the SI technique. A total of six scaled post-tensioned concrete beams with bonded tendons were manufactured. In order to investigate the correlation of the natural frequency and the displacement to prestress force, an impact test, a Single Input Multiple Output (SIMO) sine sweep test, and a bending test using an optical fiber sensor and compact displacement transducer were carried out. These tests found that both the natural frequency and the displacement show a good correlation with prestress force and that both parameters are available for the SI technique to predict prestress force. However, displacements by the optical fiber sensor and compact displacement transducer were shown to be more sensitive than the natural frequency to prestress force. Such displacements are more useful than the natural frequency as an input parameter for the SI technique.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
• /
• pp.19-22
• /
• 2001

This paper proposes a double cantilever sandwich-beam method for evaluating the frequency dependence of material dynamic characteristics. The flexural vibration of a double cantilever sandwich-beam specimen with a partially inserted rubber layer was studied using a finite element simulation in combination with the sine-sweep test. Quadratic relationships of dynamic elastic modulus and material loss factor of rubbers with frequency were quantitatively suggested employing the least square error method.

• 대한기계학회논문집A
• /
• 제26권2호
• /
• pp.225-233
• /
• 2002

The flexural vibration characteristics of a sandwich beam system with a partially inserted viscoelastic layer have been quantitatively studied using a finite element analysis in combination with a sine-sweep test. Antisymmetric mode shapes of the flexural vibration were visualized by the holographic interferometry and agreed with those calculated by the finite element simulation. Effects of the beam thickness as well as the length and thickness of partial viscoelastic layers on the system loss factor(η$\_$s/) and resonant frequency($\omega$$\_$r/) were significantly large fur the symmetric and antisymmetric modes of the beam system.

• Composites Research
• /
• 제14권3호
• /
• pp.69-76
• /
• 2001

본 연구에서는 고무의 동탄성계수와 손실계수에 대한 주파수 의존성을 평가하기 위한 새로운 양팔 샌드위치보 시험법을 제안하였다. 고무층이 삽입되어 접착된 양팔샌드위치보 시험편의 횡진동 거동에 대해 유한요소 모달변형률 에너지법을 조합한 사인스위프 시험을 이용하여 분석하고 동적 점 탄성해석시험 및 단순공진시험 결과와 비교 검토하였다. 양팔 샌드위치보의 횡진동 모드에 따라 고무층의 주파수별 동탄성계수와 재료감쇠계수를 측정하고, 이들을 최소자승오차법에 의거하여 주파수의 이차함수로 회귀시켜 평가할 수 있었다.

• Advances in aircraft and spacecraft science
• /
• 제1권4호
• /
• pp.379-398
• /
• 2014

This article discusses the microvibration analysis of a cantilever configured reaction wheel assembly. Disturbances induced by the reaction wheel assembly were measured using a previously designed platform. Modelling strategies for the effect of damping are presented. Sine-sweep tests are performed and a method is developed to model harmonic excitations based on the corresponding test results. The often ignored broadband noise is modelled by removing spikes identified in the raw signal including a method of identifying spikes from energy variation and band-stop filter design. The validation of the reaction wheel disturbance model with full excitations (harmonics and broadband noise) is presented and flaws due to missing broadband noise in conventional reaction wheel assembly microvibration analysis are discussed.

• 한국음향학회지
• /
• 제26권1호
• /
• pp.1-7
• /
• 2007

본 논문에서는 여름철마다 소음으로 사회적인 문제가 되고 있는 말매미 노랫소리의 음향특성과 발음 메커니즘을 연구하였다. 자연 상태에서의 노랫소리를 대상으로 파형과 FFT를 분석하였으며, 고속사진촬영으로 진동막 운동 형태를 분석하였다. 수컷 말매미의 복부 공동 (Cavity)의 공진주파수를 알기 위해 강제 공진 실험을 실시하였다. 실험 결과, 말매미의 두 진동막은 시간적으로나 형태적으로 비대칭 운동을 하며 매 진동시마다 다양한 주파수가 발생하는 것으로 관찰되었다. 또한 말매미는 약 $7{\sim}7.5 kHz$ 영역의 소리를 공명시킬 수 있는 구조를 갖는 것으로 확인되었다.

• Earthquakes and Structures
• /
• 제7권6호
• /
• pp.955-967
• /
• 2014

Storage racks are used worldwide in industries and commercial outlets due to the advantage of lighter, faster erection and easy alteration of pallet level as required. The studies to understand the behaviour of cold formed steel pallet racks, under seismic action is one of the emerging area of research. The rack consists of perforated uprights and beams with hook-in end connector, which enables the floor height adjustments. The dynamic characteristics of these racks are not well established. This paper presents the dynamic characteristics of 3-D single bay two storey pallet rack system with hook-in end connectors, which is tested on shake table. The sweep sine test and El Centro earthquake acceleration is used to evaluate the seismic performance of the cold formed steel pallet racks. Also an attempt is made to evaluate the realistic dynamic characteristics by using STAAD Pro software. Modal analysis is performed by incorporating the effective moment of inertia of the upright, which considers the effect of presence of perforations and rotational stiffness of the beam-to-upright connection to determine the realistic fundamental frequency of pallet racks, which is required for carrying out the seismic design. Finite element model of the perforated upright section has been developed as a cantilever beam through which effective moment of inertia is evaluated. The stiffness of the hook-in connector is taken from the previous study by Prabha et al. (2010). The results from modal analysis are in good agreement with the respective experimental results.