• Computers and Concrete
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• v.25 no.1
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• pp.67-73
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• 2020

Traditionally used analytical approach to predict the fatigue failure of reinforced concrete (RC) structure is generally conservative and has certain limitations. The nonlinear finite element method (FEM) offers less expensive solution for fatigue analysis with sufficient accuracy. However, the conventional implicit dynamic analysis is very expensive for high level computation. Whereas, an explicit dynamic analysis approach offers a computationally operative modelling to predict true responses of a structural element under periodic loading and might be perfectly matched to accomplish long life fatigue computations. Hence, this study simulates the fatigue behaviour of RC beams with finite element (FE) assemblage presenting a simplified explicit dynamic numerical solution to show computer aided fatigue behaviour of RC beam. A commercial FEM package, ABAQUS has been chosen for this complex modelling. The concrete has been modelled as a 8-node solid element providing competent compression hardening and tension stiffening. The steel reinforcements are simulated as two-node truss elements comprising elasto-plastic stress-strain behaviour. All the possible nonlinearities are duly incorporated. Time domain analysis has been adopted through an automatic Newmark-β time incremental technique. The program consists of twelve RC beams to visualize the real behaviour during fatigue process and to obtain the reliability of the study. Both the numerical and experimental results indicate a redistribution of stresses along the time and damage accumulation of beam which severely affect the serviceability and ultimate capacity of RC beam. The output of the FEM analysis demonstrates good match with the experimental consequences which affirm the efficacy of the computer aided model. The controlled fatigue damage evolution at service fatigue load limits makes the FE model an efficient tool in predicting high cycle fatigue behaviour of RC structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1599-1604
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• 2012

In general, internal defects, such as shrinkage in casting, cause stress concentration and can be a starting point for cracks. Therefore, it is important to understand the effects of internal defects on the mechanical properties including the impact behavior. This study aim is to evaluate the effects of internal casting defects on the impact performance of Al-alloy castings. Both an experimental method and computational analysis were used to achieve the research objective. The internal defects in the casting were scanned using an industrial CT scanner, and their shape was simplified using ellipsoidal primitives for impact analysis. The good agreement between the experimental and computer simulation results verified the reliability of the proposed computational method for the FEA of casting components with internal defects.

• Journal of Computational Design and Engineering
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• v.1 no.3
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• pp.173-186
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• 2014

The failure of a subsea production plant could induce fatal hazards and enormous loss to human lives, environments, and properties. Thus, for securing integrated design safety, core source technologies include subsea system integration that has high safety and reliability and a technique for the subsea flow assurance of subsea production plant and subsea pipeline network fluids. The evaluation of subsea flow assurance needs to be performed considering the performance of a subsea production plant, reservoir production characteristics, and the flow characteristics of multiphase fluids. A subsea production plant is installed in the deep sea, and thus is exposed to a high-pressure/ low-temperature environment. Accordingly, hydrates could be formed inside a subsea production plant or within a subsea pipeline network. These hydrates could induce serious damages by blocking the flow of subsea fluids. In this study, a simulation technology, which can visualize the system configuration of subsea production processes and can simulate stable flow of fluids, was introduced. Most existing subsea simulations have performed the analysis of dynamic behaviors for the installation of subsea facilities or the flow analysis of multiphase flow within pipes. The above studies occupy extensive research areas of the subsea field. In this study, with the goal of simulating the configuration of an entire deep sea production system compared to existing studies, a DES-based simulation technology, which can logically simulate oil production processes in the deep sea, was analyzed, and an implementation example of a simplified case was introduced.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.449-455
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• 2015

Owing to the trend of an increase in capacity and high-efficiency requirement, the life and reliability of power transformer depend significantly on the amount of heat generation per unit volume and the degradation of insulation oil. These problems can be solved by enhancing the cooling performance of the radiator. The purpose of this study was to find a suitable position of fans for a better cooling effect given by the forced-convection of air in an ONAF (Oil Natural Air Forced) type transformer. In the simulation, commercial software was used for flow analysis, and the cooling passage of the oil was simplified to shorten the time taken for computation. With the diameter of the fan fixed at a constant value, the analysis was performed only by changing the position of the fans. As a result, a vertical position change of the fans does not affect the cooling performance significantly. However, the temperature drop given by the fans positioned on the front region of the transformer is larger than that on the rear region.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.241-250
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• 2007

In case of retrofitting a concrete structure subjected to blast load by using retrofit materials such as FRP (fiber-reinforced polymer), appropriate ductility as well as raising stiffness must be obtained. But the previous approximate and simplified models, which have been generally used in the design and analysis of structures subjected to blast load, cannot accurately consider effects on retrofit materials. Problems on the accuracy and reliability of analysis results have also been pointed out. In addition, as the response of concrete and reinforcement on dynamic load is different from that on static load, it is not appropriate to use material properties defined in the previous static or quasi-static conditions to in calculating the response on the blast load. In this study, therefore, an accurate HFPB (high fidelity physics based) finite element analysis technique, which includes material models considering strength increase, and strain rate effect on blast load with very fast loading velocity, has been suggested using LS-DYNA, an explicit analysis program. Through the suggested analysis technique, the behavior on the blast load of retrofitted concrete walls using CFRP (carbon fiber-reinforced polymer) and GFRP (glass fiber-reinforced polymer) have been analyzed, and the retrofit capacity analysis has also been carried out by comparing with the analysis results of a wall without retrofit. As a result of the analysis, the retrofit capacity showing an approximate $26{\sim}28%$ reduction of maximum deflection, according to the retrofit, was confirmed, and it is judged ate suggested analysis technique can be effectively applicable in evaluating effectiveness of retrofit materials and techniques.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.49-54
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• 2009

The seismic slope stability is most often evaluated by the pseudo-static limit analysis, in which the earthquake loading is simplified as static inertial loads acting in horizontal and/or vertical directions. The transient loading is represented by constant acceleration via the pseudostatic coefficients. The result of a pseudostatic analysis is governed by the selection of the value of the pseudostatic coefficient. However, selection of the value is very difficult and often done in an ad hoc manner without a sound physical reasoning. In addition, the maximum acceleration is commonly estimated from the design guideline, which cannot accurately estimate the dynamic response of a slope. There is a need to perform a 2D dynamic analysis to properly define the dynamic response characteristics. This paper develops a new hybrid pseudostatic method that links the modified one-dimensional seismic site response analysis and the pseudostatic algorithm. The modified site response analysis adjusts the density of the layers to simulate the change in mass and weight of the layers of the slope with depth. Multiple analyses were performed at various locations within the slope to estimate the change in seismic response of the slope. The calculated peak acceleration profiles with depth from the developed procedure were compared to those by the two-dimensional analyses. Comparisons show that the two methods result in remarkable match. The calculated profiles are used to perform pseudostatic analysis. The results show that use of peak or a fraction of acceleration at the surface can seriously underestimate or overestimate the factor of safety, and that the proposed procedure significantly enhances the reliability of a standard procedure.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.2
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• pp.198-204
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• 2016

In this study, a wind tunnel test was conducted to measure the aerodynamic characteristics of a streamline-designed high-speed bus with the change of wind direction and speed and the result is compared with the aerodynamic performance of a commercialized high-speed bus model (Model-0) manufactured by Zyle Daewoo Bus Corp. Aerodynamic performance of the existing rear-spoiler was tested to prove its aerodynamic effect on the test model bus. From the study, it was found that 24.6 % of the total drag of the original bus model (Model-0) was reduced on the streamline-designed model bus(model-1) without the rear-spoiler but only 14.3 % of the total drag was reduced with the spoiler on the streamlined model bus. It means that the rear spoiler does not work properly with the streamlined model bus (model-1) and should be noted that an optimum design of a rear-spoiler of a vehicle is important to reduce the induced pressure drag and increase the driving stability of a vehicle against yaw motion. The experimental outcome was also compared to the previous numerical research result to evaluate the reliability of the numerical algorithm of the aerodynamic performance analysis of a vehicle. The error rate (%) of the numerical result to the experimental output is about 5.4 % and it is due to the simplified body configuration of the numerical model bus. The drag increases at the higher yaw angle because the transparent frontal area of the model vehicle increases and the downward force increases with the yaw angle as well. It has a positive effect to the driving stability of the vehicle but the moderated downward force should be kept for the fuel economy of a vehicle.

• Steel and Composite Structures
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• v.34 no.4
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• pp.487-497
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• 2020

During the last few decades, fluid viscous dampers have been significantly improved in terms of performance and reliability. Viscous dampers dissipate the input energy into heat and the increased temperature may damage internal seals of the damper. As a result, thermal compensation is crucial for almost all fluid viscous dampers. In this study, while referring to the main working principles of the recently developed bypass viscous damper in Iran, a comprehensive case study is conducted on a RC building having diagonal braces equipped with such viscous dampers. Experimental results of a small-scale bypass viscous damper is presented and it is shown that the currently available simplified Maxwell models can simulate behavior of the bypass viscous damper with good accuracy. Using a case study, contribution of bypass viscous dampers to seismic behavior of structural and non-structural elements are investigated. A designed procedure is adopted to increase damping ratio of the building from 3% to 15%. In this way, reductions of 25% and 13% in the required concrete and steel rebar materials have been achieved. From nonlinear time history analyses, it is observed that bypass viscous dampers can greatly improve seismic behavior of structural elements and non-structural elements.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1061-1069
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• 2010

In this study, a simplified axisymmetric model is proposed for the problem of compressible internal flow past a microgap. Using numerical and experimental methods, the phenomena of choked flows are observed; these flows are induced by the acceleration of subsonic flows past the narrow cross-section of an annular shape made by a microgap. The relation between mass flow rate and differential pressure is obtained, and by comparing the result with experimental results, the reliability of the numerical results is discussed. The generation of a supersonic jet flow and its diffraction are visualized by performing the numerical analysis of axisymmetric compressible Navier-Stokes equations. This investigation greatly extends the physical understanding of the axisymmetric compressible flow, which has a wide range of engineering applications, e.g., in the case of valves in automotive power systems.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.509-517
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• 2016

In terms of bridge construction, the concrete deck slab is weak members compared to beam members of the bridge supports. Deck slabs must be sound to support and distribute vehicle loads. If slabs are not enough to support the loads, it should be replaced. Bridge deck replacement has been an important industry over the world since the construction is simplified to shorten construction time and to save construction costs. Slab module provides a quickly, easily and reliably construction method in order to avoid high cost and minimum traffic disruption. in addition, slab module shows high reliability since they are factory products. However, slab module should be considered in the performance under various loads. In this study, structural analysis is performed to evaluate the performance of slab module under vehicle loads and temperature loads. Spiral rebar is also utilized around the vertical joints to improve the structural integrity under the lifting loads. In order to confirm the weak area of slab module for the lift condition, numerical analysis has been performed.