• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.233-243
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• 1998

The demand of high speed machining is increasing due to the high speed cutting and grinding provides high efficiency of process, short process time, improved metal removal capacity and better surface finish. Active magnetic bearings allow much high surface speed than conventional ball bearings and therefore greatly suitable for high speed cutting or grinding. This paper describes a design process of an active magnetic bearing system for a high speed grinding spindle with power 5.5kW and maximum speed 60,000rpm. Magnetic actuators are designed by the magnetic circuit theory considering static load condition, and examined with FEM analysis. Dynamic characteristics are also considered, such as bandwidth, stiffness, natural frequency and static deflection. System characteristics are simulated with a rigid rotor model.

• Proceedings of the KIEE Conference
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• summer
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• pp.30-32
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• 2004

This paper describes control system design for the DH(dynamic voltage restorer) consisted of a diode rectifier and series inverter applied to 22.9kV distribution system. The DVR control system is consisted of the main two parts. One is a voltage event detector using a neural network and the other is deadbeat controller for the output voltage and current control of the DVR. A simulation model was developed for analyzing performance of the controller and the whole system. The results confirm that the DVR can restore load voltage under the fault of the distribution system.

• International Journal of Railway
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• v.2 no.4
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• pp.180-186
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• 2009

High speed railway challenge the design, construction and maintaining of traditional railway, many traditional design concepts have been changed. Transition of railway and bridge has two main problems. one is that different lines have different ability of resisting distortion in area of trial load, which was known that problem of smooth transition of stiffness, the other is that differential settlement between artificial structure and earth structure cause bending of railway. The two problems have effect on train moving. The principle of processing transition of railway and bridge is same in world, but it is difficult to find relationship between design standard of transition, vehicle performance, line standard, design speed and so on form documentation and data reports. Based on mechanics, the paper analyzed dynamic performance of transition of high speed railway, studied various rough elements which is effective to train moving, built mathematical model of interaction of train and transition of high speed railway and developed numerical simulation software. In various different work conditions, we did great quantity of numerical simulation, comprehensive analysis and performance analysis.

• Computers and Concrete
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• v.33 no.6
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• pp.725-738
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• 2024

This study presents a macro-modeling procedure for nonlinear finite element analysis of reinforced and prestressed concrete panels under blast loading. The analysis procedure treats cracked concrete as an orthotropic material based on a smeared rotating crack model within the context of total-load secant stiffness-based formulation. A direct time integration method compatible with the analysis formulation is adapted to solve the dynamic equation of motion. Considerations are made to account for strain rate effects. The analysis procedure is verified by modeling 14 blast tests from various sources reported in the literature including a blast simulation contest. The analysis results are compared against those obtained from experiments, simplified single-degree-of-freedom (SDOF) methods, and sophisticated hydrocodes. It is demonstrated that the smeared crack macro-modeling approach is a viable alternative analysis procedure that gives more information about the structural behavior than SDOF methods, but does not require detailed micro-modeling and extensive material characterization typically needed with hydrocodes.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.389-403
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• 2004

This study presents the structural model modification based on the modal data such as natural frequencies and mode shapes. Preliminary structural model can be obtained using design drawings and field measurement, and therefore the deteriorated stiffness of a structure and the effect of the boundary conditions are difficult to be evaluated in preliminary analysis model, and the preliminary model can be modified using structural response data including static and/or dynamic characteristics. In this study, the structural model is modified based on the structural modal data using genetic algorithm. Modal testing were carried out for Imjin River Bridge and Hangjoo Bridge, the modal properties were estimated using modal identification techniques, and finally the structural models were updated using genetic algorithm. The modified structural model could give us more reliable structural analysis results and therefore those can be used for structural performance evaluation such as load carrying capacity and seismic capacity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1D
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• pp.45-55
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• 2008

The objective of this research was to develop a VEPCD (ViscoElastoPlastic Continuum Damage) Model which is used to predict the behavior of asphalt concrete under various loading and temperature conditions. This paper presents the VEPCD model formulated in a tension mode and its validation using four hot mix asphalt (HMA) mixtures: dense-graded HMA, SBS, CR-TB, and Terpolymer. Modelling approaches consist of two components: the ViscoElastic Continuum Damage (VECD) mechanics and the ViscoPlastic (VP) theory. The VECD model was to describe the time-dependent behavior of HMA with growing damage. The irrecoverable (whether time-dependent or independent) strain has been described by the VP model. Based on the strain decomposition principle, these two models are integrated to form the VEPCD model. For validating the VEPCD model, two types of laboratory tests were performed: 1) a constant crosshead strain rate tension test, 2) a fatigue test with randomly selected load levels and frequencies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.64-70
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• 2018

Rollover is a major concern for vehicles with a higher center of gravity and for improving driving performance. This study investigates a tilting system to prevent rollover, which was successfully implemented for high-speed trains. It may be useful to apply the concept of the tilting system to a large truck such as a trailer. Even a small adjustment in the tilting angle can improve the driving stability during a steep turn. The equation of motion was derived from a dynamic model of the trailer with the tilting system. The balance of the centrifugal force and normal force determines the rollover critical speed for a given radius of the turn and load. To obtain a more conservative criterion, the rollover critical state was defined as the instant when any side wheel loses contact with the road. To actuate the tilting system, the optimal tilting angle must be calculated from the steering angle and the vehicle speed. Using a simplified model of a large truck, the effects of the tilting angle and load on the rollover critical speed were investigated.

• Journal of the Korean Institute of Gas
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• v.12 no.1
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• pp.7-12
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• 2008

In order to estimate the integrity and identify the dynamic characteristics of buried gas pipelines subjected to vehicle loads, FE analysis is performed based on the 'Highway and Local Road Design Criteria' and the 'KOGAS Guideline for Pipeline Management'. The FE model describes the current burial condition of Korea properly, and the DB-24 load model is adopted for this research. This study considers a varying velocity in the range of $40{\sim}160\;km/h$ and $P_i=8$ MPa(internal pressure) with depth cover, Z=1.5 m. Maximum stress occurs at v=80 km/h and decreases after v=80 km/h. The maximum induced stress by DB-24 loads is about 10 MPa. Under the design pressure, however, the analysis results show that API 5L Gr. X65 pipelines have sufficient integrity to withstand the vibration of vehicle loads.

• Tribology and Lubricants
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• v.32 no.4
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• pp.132-139
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• 2016

The piston of a marine diesel engine works under severe conditions, including a combustion pressure of over 180 bar, high thermal load, and high speed. Therefore, the analyses of the fatigue strength, thermal load, clamping (bolting) system and lubrication performance are important in achieving a robust piston design. Designing the surface profile and the skirt ovality carefully is important to prevent severe wear and reduce frictional loss for engine efficiency. This study performs flexible multi-body dynamic and elasto-hydrodynamic (EHD) analyses using AVL/EXCITE/PU are performed to evaluate tribological characteristics. The numerical techniques employed to perform the EHD analysis are as follows: (1) averaged Reynolds equation considering the surface roughness; (2) Greenwood_Tripp model considering the solid_to_solid contact using the statistical values of the summit roughness; and (3) flow factor considering the surface topology. This study also compares two cases of skirt shapes with minimum oil film thickness, peak oil film pressure, asperity contact pressure, wear rate using the Archard model and friction power loss (i.e., frictional loss mean effective pressure (FMEP)). Accordingly, the study compares the calculated wear pattern with the field test result of the piston operating for 12,000h to verify the quantitative integrity of the numerical analysis. The results show that the selected profile and the piston skirt ovality reduce friction power loss and peak oil film pressure by 7% and 57%, respectively. They also increase the minimum oil film thickness by 34%.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.2
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• pp.85-91
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• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.