• Earthquakes and Structures
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• 제12권6호
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• pp.629-641
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• 2017

Foundation plays a significant role in safe and efficient turbo machinery operation. Turbo machineries generate harmonic load on the foundation due to their high speed rotating motion which causes vibration in the machinery, foundation and soil beneath the foundation. The problems caused by vibration get multiplied if the soil is poor. An improperly designed machine foundation increases the vibration and reduces machinery health leading to frequent maintenance. Hence it is very important to study the soil structure interaction and effect of machine vibration on the foundation during turbo machinery operation in the design stage itself. The present work studies the effect of harmonic load due to machine operation along with earthquake loading on the frame foundation for poor soil conditions. Various alternative foundations like rafts, barrette, batter pile and combinations of barrettes with batter pile are analyzed to study the improvements in the vibration patterns. Detailed computational analysis was carried out in SAP 2000 software; the numerical model was analyzed and compared with the shaking table experiment results. The numerical results are found to be closely matching with the experimental data which confirms the accuracy of the numerical model predictions. Both shake table and SAP 2000 results reveal that combination of barrette and batter piles with raft are best suitable for poor soil conditions because it reduces the displacement at top deck, bending moment and horizontal displacement of pile and thereby making the foundation more stable under seismic loading.

• Smart Structures and Systems
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• 제9권1호
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• pp.71-104
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• 2012

In this research, a typical tension-leg type of floating platform incorporated with an innovative concept of underwater tuned liquid column damper system (UWTLCD) is studied. The purpose of this study is to improve the structural safety by means of mitigating the wave induced vibrations and stresses on the offshore floating Tension Leg Platform (TLP) system. Based on some encouraging results from a previous study, where a Tuned Liquid Column Damper (TLCD) system was employed in a floating platform system to reduce the vibration of the main structure, in this study, the traditional TLCD system was modified and tested. Firstly, the orifice-tube was replaced with a smaller horizontal tube and secondly, the TLCD system was combined into the pontoon system under the platform. The modification creates a multipurpose pontoon system associated with vibration mitigation function. On the other hand, the UWTLCD that is installed underwater instead would not occupy any additional space on the platform and yet provide buoyancy to the system. Experimental tests were performed for the mitigation effect and parameters besides the wave conditions, such as pontoon draught and liquid-length in the TLCD were taken into account in the test. It is found that the accurately tuned UWTLCD system could effectively reduce the dynamic response of the offshore platform system in terms of both the vibration amplitude and tensile forces measured in the mooring tethers.

• 한국소음진동공학회논문집
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• 제16권9호
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• pp.949-957
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• 2006

In this Paper, reduction of noise and vibration in ship cabins by using floating floor is studied. Two theoretical models are presented and predicted insertion losses of floating floor are compared to experimental results, where measurements have been done in mock-up built for simulating typical ship cabin structures. In ships, mineral wool is usually used as the impact absorbing materials. The first model (M-S-Plate Model) is that upper plate and mineral wool are assumed as a one-dimensional mass-spring system, which is in turn attached to the simply supported elastic floor. The second model (Wave-Plate Model) is that mineral wool is assumed as an elastic medium for wave propagation. The comparisons show that M-S-Plate model is in good agreement with experimental results when density of mineral wool is 140K, and fiber direction is horizontal. For higher density and vertical fiber direction, Wave-Plate model shows good agreements with measurements. It is found that including the elastic behavior of the floor is essential in improving accuracy of the prediction for low frequency ranges below $100{sim}200Hz$.

• Structural Engineering and Mechanics
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• 제64권2호
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• pp.259-270
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• 2017

The stochastic vibration response of the sandwich beam with the nonlinear adjustable visco-elastomer core and supported mass under stochastic support motion excitations is studied. The nonlinear dynamic properties of the visco-elastomer core are considered. The nonlinear partial differential equations for the horizontal and vertical coupling motions of the sandwich beam are derived. An analytical solution method for the stochastic vibration response of the nonlinear sandwich beam is developed. The nonlinear partial differential equations are converted into the nonlinear ordinary differential equations representing the nonlinear stochastic multi-degree-of-freedom system by using the Galerkin method. The nonlinear stochastic system is converted further into the equivalent quasi-linear system by using the statistic linearization method. The frequency-response function, response spectral density and mean square response expressions of the nonlinear sandwich beam are obtained. Numerical results are given to illustrate new stochastic vibration response characteristics and response reduction capability of the sandwich beam with the nonlinear visco-elastomer core and supported mass under stochastic support motion excitations. The influences of geometric and physical parameters on the stochastic response of the nonlinear sandwich beam are discussed, and the numerical results of the nonlinear sandwich beam are compared with those of the sandwich beam with linear visco-elastomer core.

• 한국항공우주학회지
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• 제35권11호
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• pp.1028-1035
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• 2007

논문에서는 시험선인 소형 위그선의 주날개 구조를 엔진 및 프로펠러에 의해 유발되는 진동을 가진력으로 하여 강제진동 해석을 수행하였다. 대상 위그선은 2행정의 왕복엔진을 날개에 장착하여 프로펠러에 의한 추력으로 비행하며, 미는 형식(Pusher Type)의 엔진 배열을 취하고 있다. 유한요소해석을 위해서 구조해석 상용프로그램인 MSC/NASTRAN을 사용하였으며, 엔진의 주요 진동 특성인 H-mode 와 V-mode 그리고 X-mode를 특정 가진 주파수로 하여 주파수 응답 해석을 수행하였고, 엔진의 횡방향 진동 모드인 L-mode를 프로펠러의 회전에 의해 진동을 수반하는 가진 추력으로 가정하여 과도응답 해석을 수행한 후 날개의 진동 특성을 살펴보았다.

• 한국안전학회지
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• 제16권4호
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• pp.200-207
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• 2001

회전하는 기계에서 전달되는 조화적인 진동력이 수동 및 능동 진동 격리기를 통하여 중간 지지구조물에 어떻게 전달되는 것인가를 연구하였다. 이를 위하여 이론적인 모델은 모든 축에 대하여 수평과 수직방향의 힘과 모멘트를 고려하여 작성되었으며, 실험은 중간 구조물에 전달되는 회전방향 및 직선방향의 진동을 최소화하기 위하여 2단으로 구성된 중간 지지구조물에 부착된 진동 액츄에이터를 사용하였다. 진동원에 의하여 발생된 진동이 에러 센서에서 측정되었으며 제어원과 에러센서사이의 전달함수가 측정되었다. 1-100Hz사이의 주파수 범위에 있어서 기존의 수동격리기와 직렬로 설치된 능동격리기를 통하여 전달된 힘이 실제로 감소되었음을 실험결과를 통하여 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.810-812
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• 2008

Previously study on structural design of the main wing of the twenty-seat class WIG(Wing in Ground Effect) craft. In the final design, three spars construction was selected for safety in the critical flight load, and the Carbon-Epoxy material was selected for lightness and structural stability. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the H-mode(horizontal mode), the V-mode(vertical mode) and the X-mode(twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the L-mode(longitudinal mode) with the oscillating propeller thrust which occurs in operation. According to the result of forced vibration analysis, structural design was modified to reduce the vibrations.

• Ocean Systems Engineering
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• 제11권1호
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• pp.59-81
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• 2021

The nonlinear formulation using the principle of virtual work-energy for free vibration of a large-sag extensible catenary riser in two dimensions is presented in this paper. A support at one end is hinged and the other is a free-sliding roller in the horizontal direction. The catenary riser has a large-sag configuration in the static equilibrium state and is assumed to displace with large amplitude to the motion state. The total virtual work of the catenary riser system involves the virtual strain energy due to bending, the virtual strain energy due to axial deformation, the virtual work done by the effective weight, and the inertia forces. The nonlinear equations of motion for two-dimensional free vibration in the Cartesian coordinate system is developed based on the difference between the Euler's equations in the static state and the displaced state. The linear and nonlinear stiffness matrices of the catenary riser are obtained and the eigenvalue problem is solved using the Galerkin finite element procedure. The natural frequencies and mode shapes are obtained. The results are validated with regard to the reference research addressing the accuracy and efficiency of the proposed nonlinear formulation. The numerical results for free vibration and the effect of the nonlinear behavior for catenary riser are presented.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4561-4569
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• 2023

A correct understanding of vibration-based degradation is crucial from the standpoint of maintenance for Steam Generators (SG) as crucial mechanical equipment in nuclear power plants. This study has established a novel approach to developing a model for investigating tube bundle degradation according to crack growth caused by two-phase Flow-Induced Vibration (FIV). An important step in the approach is to calculate the two-phase flow field parameters between the SG tube bundles in various zones using the porous media model to determine the velocity and vapor volume fraction. Afterward, to determine the vibration properties of the tube bundles, the Fluid-Solid Interaction (FSI) analysis is performed in eighteen thermal-hydraulic zones. Tube bundle degradation based on crack growth using the sixteen most probable initial cracks and within each SG thermal-hydraulic zone is performed to calculate useful lifetime. Large Eddy Simulation (LES) model, Paris law, and Wiener process model are considered to model the turbulent crossflow around the tube bundles, simulation of elliptical crack growth due to the vibration characteristics, and estimation of SG tube bundles degradation, respectively. The analysis shows that the tube deforms most noticeably in the zone with the highest velocity. As a result, cracks propagate more quickly in the tube with a higher height. In all simulations based on different initial crack sizes, it was observed that zone 16 experiences the greatest deformation and, subsequently, the fastest degradation, with a velocity and vapor volume fraction of 0.5 m/s and 0.4, respectively.

• 한국공간구조학회논문집
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• 제8권2호
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• pp.73-84
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• 2008

지진에 의한 구조물의 응답을 저감시키기 위하여 내진, 면진, 제진 등 다양한 장치가 사용되고 있으며 그 중에서 면진장치는 구조물로 전달되는 지진에너지를 최소화하기 위한 시스템으로 그 주된 목적은 구조물의 주기를 길게 만들어 지진파의 탁월주기를 벗어나게 하는 것이다. 본 연구에서는 대공간구조물의 기본적인 동적특성을 가지고 있으며 동시에 가장 간단한 구조이기도 한 아치에 납-고무면진장치와 마찰진자면진장치를 적용하여 지진거동을 분석하였다. 대공간구조물의 지진거동은 일반적인 골조구조물의 지진거동과 달리 수평지진에 의하여 수직방향으로 큰 지진응답이 나타나고 있다. 면진장치를 대공간 구조물에 적용할 경우에 수평지진하중에 의하여 수평방향 지진응답이 저감되는 것은 물론 면진장치의 수직강성으로 인하여 수직응답도 현저하게 저감되는 것을 알 수 있었다.