• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.451-456
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• 2011

To ensure structural integrity of membrane type LNG tank, the rational assessment of the sloshing impact responses of tank structures should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the resulting structural responses show very complex behaviors accompanied with fluid structure interaction. So it is not easy to estimate them accurately and immense time consuming calculation process would be necessary. In this research, a simplified method to analyse the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was studied. The proposed technique based on the concept of linear combination of the triangular response functions which are the transient responses of structures under the unit triangular impact pressure acting on structures. The validity of suggested method was verified through the example calculations and applied to the dynamic structural response analysis of a real Mark III membrane type insulation system using the sloshing impact pressure time histories obtained by model test.

• Smart Structures and Systems
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• v.18 no.3
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• pp.541-568
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• 2016

The goal of this study is to investigate the effect of non-synchronous sensing when using wireless sensors on structural identification and to attempt correcting such errors in order to obtain a better identification result. The sources causing non-synchronous sensing are discussed first and the magnitudes of such synchronization errors are estimated based on time stamps of data samples collected from Imote2 sensors; next the impact of synchronization errors on power spectral densities (PSDs) and correlation functions of output responses are derived analytically; finally a new method is proposed to correct such errors. In this correction method, the corrected PSDs of output responses are estimated using non-synchronous samples based on a modified FFT. The effect of synchronization errors in the measured output responses on structural identification and the application of this correction method are demonstrated using simulation examples. The simulation results show that even small synchronization errors in the output responses can distort the identified modal and stiffness parameters remarkably while the parameters identified using the proposed correction method can achieve high accuracy.

• Structural Engineering and Mechanics
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• v.77 no.3
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• pp.369-381
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• 2021

The seismic responses of elevated tanks considering liquid-structure interaction are presented under horizontal earthquake. The scaled model tank is fabricated to study the dynamic responses of anchored tank and newly designed uplift tank with replaced dampers. The natural frequencies for structural mode are obtained by modal analysis. The dynamic responses of tanks are completed by finite element method, which are compared with the results from experiment. The displacement parallel and perpendicular to the excitation direction are both gained as well as structural acceleration. The strain of tank walls and the axial strain of columns are also obtained afterwards. The seismic responses of liquid storage tank can be calculated by the finite element model effectively and the results match well with the one measured by experiment. The aim is to provide a new type of tank system with vertical constraint relaxed which leads to lower stress level. With the liquid volume increasing, the structural fundamental frequency has a great reduction and the one of uplift tank are even smaller. Compared with anchored tank, the displacement of uplift tank is magnified, the strain for tank walls and columns parallel to excitation direction reduces obviously, while the one perpendicular to earthquake direction increases a lot, but the values are still small. The stress level of new tank seems to be more even due to uplift effect. The new type of tank can realize recoverable function by replacing dampers after earthquake.

• Structural Engineering and Mechanics
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• v.82 no.3
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• pp.325-341
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• 2022

Previous major earthquakes indicated that the earthquake induced ground motions are typical non-stationary processes, which are non-stationary in both amplification and frequency. For the convenience of aseismic design and analysis, it usually assumes that the ground motions at structural supports are stationary processes. The development of time-frequency analysis technique makes it possible to evaluate the non-stationary responses of engineering structures subjected to non-stationary inputs, which is more general and realistic than the analysis method commonly used in engineering. In this paper, the wavelet-based stochastic vibration analysis methodology is adopted to calculate the non-stationary responses of multi-support structures. For comparison, the stationary response based on the standard random vibration method is also investigated. A frame structure and a two-span bridge are analyzed. The effects of non-stationary spatial ground motion and local site conditions are considered, and the influence of structural property on the structural responses are also considered. The analytical results demonstrate that the non-stationary spatial ground motions have significant influence on the response of multi-support structures.

• International Journal of Safety
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• v.10 no.2
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• pp.1-5
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• 2011

The structural integrity assessment of APR1400 (Advanced Power Reactor 1400) reactor vessel internals has been being performed referring the US Nuclear Regulatory Commission regulatory guide 1.20 comprehensive vibration assessment program prior to commercial operation. The program is composed of a hydraulic and structural analysis, a vibration measurement, and an inspection. This paper describes the hydraulic and structural analysis on the reactor vessel internals due to hydraulic loads caused by the turbulence of reactor coolant. Three-dimensional models were built for the hydraulic and structural analysis and then hydraulic loads and structural responses were predicted for five analysis cases with CFX and ANSYS respectively. The structural responses show that the APR1400 reactor vessel internals have sufficient structural integrity in comparison with the acceptance criteria.

• Smart Structures and Systems
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• v.15 no.2
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• pp.299-314
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• 2015

Submersed rock-berm structures are frequently used for protection of underwater lifelines such as pipelines and power cables. During the service life, the rock-berm structure can experience several accidental loads such as anchor collision. The consequences can be severe with a certain level of frequency; hence, the structural responses should be carefully understood for implementing a proper structural health monitoring method. However, no study has been made to quantify the structural responses because it is hard to deal with the individual behavior of each rock. Therefore, this study presents a collision analysis of the submersed rock-berm structure using a finite element software package by facilitating the smoothed-particle hydrodynamics (SPH) method. The analysis results were compared with those obtained from the Lagrange method. Moreover, two types of anchors (stock anchor and stockless anchor), three collision points and two different drop velocities (terminal velocity of each anchor and 5 m/s) were selected to investigate the changes in the responses. Finally, the effect of these parameters (analysis method, anchor type, collision point and drop velocity) on the analysis results was studied. Accordingly, the effectiveness of the SPH method is verified, a safe rock-berm height (over 1 m) is proposed, and a gauge point (0.5 m above the seabed) is suggested for a structural health monitoring implementation.

• Structural Engineering and Mechanics
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• v.21 no.3
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• pp.369-374
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• 2005

A big progress has been made for moving force identification from bridge dynamic responses in recent years. Current knowledge and the potentials on moving force identification methods are reviewed in this paper under main headings below: background of moving force identification, experimental verification in laboratory and its application in field.

• Journal of Korean Society of Steel Construction
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• v.8 no.4 s.29
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• pp.77-84
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• 1996

The structural members under seismic loading actually show inelastic behavior, so the inelastic responses should be calculated for the seismic design of structures or estimating the structural damage level. Although direct time history analysis may calculate the exact dynamic nonlinear responses for given ground motions, this approach involves a high computational cost and long period. Therefore, it should be developed the approach to estimate nonlinear responses for the practical purpose. The artificial earthquake accelerograms were generated to obtain the smoothed responses spectra, and the samples of generated accelerogram for each seismic event was used to examine average nonlinear response spectra. The stabilized response spectra for each earthquake event was used to evaluate the effects of various yield strength ratios, damping values and nonlinear hysteretic models. The approach, which can simply predict the nonlinear seismic responses of structures, was shown in this study.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.224-231
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• 1997

A study on the seismic responses for a base isolated structure subjected to earthquakes with different frequency characteristics is peformed with time history analyses. Two types of seismic inputs are considered in these analyses, one is short period earthquakes such as El Centro(1940, NS), the other is long period ones such as Mexico(1985). The seismic responses of the base isolated structure depend on seismic input types and isolation frequencies. In this study the 0.5 Hz of isolation frequency for short period earthquakes remarkably reduces the acceleration responses, increases the relative displacements of isolator that are still within the proposed limits of isolator. However higher isolation frequency for long period earthquakes is more adequate to reduce the seismic responses of the base isolated structures; in the study 0.75 Hz is effective to Mexico 1985 earthquake.

• Structural Engineering and Mechanics
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• v.8 no.5
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• pp.477-490
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• 1999

The uncertainties associated with structural parameters and dynamic loading are identified and discussed. Structural parametric uncertainties are treated as random variables and dynamic wind load is simulated as a random process. Dynamic wind-induced responses of structures with parametric uncertainties are investigated by using stochastic finite element method. The formulas for structural dynamic reliability analysis considering the randomness of structural resistance and loading are proposed. Two numerical examples of high-rise structures are presented to illustrate the proposed methodology. The calculated results demonstrate that the variation in structural parameters indeed influences the dynamic response and the first passage probability evaluation of structures.