• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.1
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• pp.28-35
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• 2017

Recently, conventional hydraulic car lift systems face the technological limitations due to a lack of height control. The demand for height controllability is required in many tasks such as wheel alignment, and requires compensation for the structural deformation of the lift caused by irregular load distribution. In order to resolve this limitation of the conventional car lift, in this work, a new type of a hydraulic vehicle lift using a magneto-rheological (MR) valve system is proposed and analyzed. Firstly, the dynamic model of vehicle lift is formulated to evaluate control performance; subsequently, an MR valve is designed to obtain the desired pressure drop required in the car lift. Next, a proportional-integral-derivative (PID) controller is formulated to achieve accurate control of the lifting height and then computer simulations are undertaken to show accurate height control performances of the proposed new car lift system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.72-78
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• 2008

In this study, advanced (fluid-structure interaction (FSI)) analysis system has been developed in order to predict turbine cascade performance with blade deformation effect due to aerodynamic loads. Intereference effects due to the relative movement of the rotor cascade with respect to the stator cascade are also considered. Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation k-ω SST turbulence models are solved to accurately predict fluid dynamic loads considering flow separation effects. A fully implicit time marching scheme based on the (coupled Newmark time-integration method) with high artificial damping is efficiently used to compute the complex fluid-structure interaction problem. Predicted aerodynamic performance considering structural deformation effect of the blade shows somewhat different results compared to the case of rigid blade model. Cascade performance evaluations for different elastic axis positions are importantly presented and its aeroelastic effects are investigated.

• Earthquakes and Structures
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• v.14 no.4
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• pp.337-347
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• 2018

This paper presents some shaking table tests conducted on a 1/4-scaled model with 5-story steel reinforced concrete (SRC) spatial frame with irregular section columns under a series of base excitations with gradually increasing acceleration peaks. The test frame was subjected to a sequence of seismic simulation tests including 10 white noise vibrations and 51 seismic simulations. Each seismic simulation was associated with a different level of seismic disaster. Dynamic characteristic, strain response, acceleration response, displacement response, base shear and hysteretic behavior were analyzed. The test results demonstrate that at the end of the loading process, the failure mechanism of SRC frame with irregular section columns is the beam-hinged failure mechanism, which satisfies the seismic code of "strong column-weak beam". With the increase of acceleration peaks, accumulated damage of the frame increases gradually, which induces that the intrinsic frequency decreases whereas the damping ratio increases, and the peaks of acceleration and displacement occur later. During the loading process, torsion deformation appears and the base shear grows fast firstly and then slowly. The hysteretic curves are symmetric and plump, which shows a good capacity of energy dissipation. In summary, SRC frame with irregular section columns can satisfy the seismic requirements of "no collapse under seldom earthquake", which indicates that this structural system is suitable for the construction in the high seismic intensity zone.

• Computers and Concrete
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• v.12 no.2
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• pp.211-228
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• 2013

The structure analyzed in this paper has particular building style and special structural system. It is a rigid-connected twin-tower skyscraper with asymmetrical distribution of stiffness and masses in two towers. Because of the different stiffness between the north and the south towers, the torsion seismic vibration is significant. In this paper, in order to study the seismic response of the structure under both frequent low-intensity earthquakes as well as rare earthquakes at the levels of intensity 7, the analysis model is built and analyzed with NosaCAD. NosaCAD is an nonlinear structure analysis software based on second-development of AutoCAD with ObjectARX. It has convenient modeling function, high computational efficiency and diversity post-processing functions. The deformations, forces and damages of the structure are investigated based on the analysis. According to the analysis, there is no damage on the structure under frequent earthquakes, and the structure has sufficient capacity and ductility to resist rare earthquakes. Therefore the structure can reach the goal of no damage under frequent earthquakes and no collapse under rare earthquakes. The deformation of the structure is below the limit in Chinese code. The time sequence and distribution of damages on tubes are reasonable, which can dissipate some dynamic energy. At last, according to forces, load-carrying capacity and damage of elements, there are some suggestions on increasing the reinforcement in the core tube at base and in stiffened stories.

• Wind and Structures
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• v.25 no.1
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• pp.79-100
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• 2017

The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65 m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.4
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• pp.39-45
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• 2008

Breakaway support for small signs of size $0.293\;m^2{\sim}0.360\;m^2$ using indented tube type bolt of D12 mm with 6 mm inner diameter has been developed and the structural strength of the support system for the wind load was verified through static shear and tension tests. One important value in understanding the dynamic behavior of sign post and impact vehicle is the fracture energy of the sign support. In this study, fracture energy needed to break the sign support was estimated by pendulum test and computer simulation using LS-DYNA program. Support system composed of 3 indented bolts was found to sustain the 43.1 kg$\sim$51.2 kg wind load safely. Fracture energy for one indented bolt was measured as 163.3J from the pendulum test, and was calculated as 153J from the LS-DYNA simulation. The closeness between these two values verified the validity of the simulation model.

• Journal of the Economic Geographical Society of Korea
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• v.15 no.4
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• pp.628-641
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• 2012

This research investigates a dynamic mechanism underlying the co-evolution between network and space by applying hype-curve model, typical phenomenon which shows how new technologies and ideas initially adapted in the society. This study analysis the knowledge intensive industry of digital contents using social network analysis (SNA) in terms of structural, spatial, and temporal aspects, year of 2000, 2005, and 2010 focused on Seoul area. First of all, network and space establish 'inter-feedback' as a result of evolution and differentiation process. Second, it happen temporal 'delay' through the learning process stage of 'peak of inflated expectation' and 'trough of disillusionment.' As a result, Seoul develops with the technology commercialized-orient strategy affect government policy. This trend changes to technology-oriented development in Seoul area in the late of 2000 established 'self-organization' with geographical proximity organizations through learning process.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2004.10a
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• pp.433-436
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• 2004

In this paper, we introduce a new Fuzzy Polynomial Neural Networks (FPNNS)-like structure whose neuron is based on the Fuzzy Set-based Fuzzy Inference System (FS-FIS) and is different from that of FPNNS based on the Fuzzy relation-based Fuzzy Inference System (FR-FIS) and discuss the ability of the new FPNNS-like structure named Fuzzy Set-based Polynomial Neural Networks (FSPNN). The premise parts of their fuzzy rules are not identical, while the consequent parts of the both Networks (such as FPNN and FSPNN) are identical. This difference results from the angle of a viewpoint of partition of input space of system. In other word, from a point of view of FS-FIS, the input variables are mutually independent under input space of system, while from a viewpoint of FR-FIS they are related each other. The proposed design procedure for networks architecture involves the selection of appropriate nodes with specific local characteristics such as the number of input variables, the order of the polynomial that is constant, linear, quadratic, or modified quadratic functions being viewed as the consequent part of fuzzy rules, and a collection of the specific subset of input variables. On the parameter optimization phase, we adopt Information Granulation (IC) based on HCM clustering algorithm and a standard least square method-based learning. Through the consecutive process of such structural and parametric optimization, an optimized and flexible fuzzy neural network is generated in a dynamic fashion. To evaluate the performance of the genetically optimized FSPNN (gFSPNN), the model is experimented with using the time series dataset of gas furnace process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2C
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• pp.61-68
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• 2012

In general, verticality error necessarily occurs in marine pile foundation due to construction error or marine environmental effects. In marine structure, design by vertical load rather than horizontal load is dominant, but in the offshore wind turbine foundation, horizontal load is dominant. As the structure type that has dynamic movement by blade rotation, verticality error may have structurally significant effects. In this study, structural response feature of foundation and ground were analyzed according to verticality error of monopile foundation of 5MW offshore wind turbine. Marine environmental load was calculated per ISO standard and the margin of verticality error was calculated to be $L/{\infty}$(=0), L/300, L/200 and L/100. As a result of analysis, it was found that the maximum value of member force of the foundation with L/100 error increased about 7.2% compared to the monopile without verticality error.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.1
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• pp.20-27
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• 2016

The prediction of combustion instability is important to avoid an obvious threat to the structural safety and the motor performance because it affects the apparent response function of the propellant, the burning rate, and a mean flow Mach number at the local surface. The combustion instability occurs in case acoustic waves were coupled with the combustion/flow dynamic frequency. In this paper, an acoustic instability model is derived from the nonlinear wave equation for analysing acoustic dynamics in solid rocket motors. The chamber pressure and burning rate effects on combustion instability have been investigated.