• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.421-422
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• 2007

• Steel and Composite Structures
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• v.50 no.2
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• pp.159-181
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• 2024

In the present study, the effect of geometrical parameters of two different types of aluminum thin-walled structures on energy absorption under three-bending impact loading has been investigated experimentally and numerically. To evaluate the effect of parameters on the specific energy absorption (SEA), initial peak crushing force (IPCF), and the maximum crushing distance (δ), a design of experiment technique (DOE) with response surface method (RSM) was applied. Four different thin-walled structures have been tested under the low-velocity impact, and then they have simulated by ABAQUS software. An acceptable consistency between the numerical and experimental results was obtained. In this study, statistical analysis has been performed on various parameters of three different types of tubes. In the first and the second statistical analysis, the dimensional parameters of the cross-section, the number of holes, and the dimensional parameter of holes were considered as the design variables. The diameter reduction rate and the number of sections with different diameters are related to the third statistical analysis. All design points of the statistical method have been simulated by the finite element package, ABAQUS/Explicit. The final result shows that the height and thickness of tubes were more effective than other geometrical parameters, and despite the fact that the deformations of the cylindrical tubes were around forty percent greater than the rectangular tubes, the top desirability was relevant to the cylindrical tubes with reduced cross-sections.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.227-236
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• 1994

Steady flows of Newtonian and non-Newtonian fluids in the stenotic tubes with various stenotic shapes are numerically simulated. Validity of the modified power-law model as a constitutive equation for the purely viscous non-Newtonian fluid is discussed and the results of the power-law model are compared with those of the Carreau model, the Powell-Eyring model and experimental data for blood. Flow characteristics and reattachment lengths for non-Newtonian fluids in the stenotic tubes are presented extensively. Also, the analysis is extended to predict the influences of diameter ratio, stenosis spacing, number of stenosis and Reynolds number on the flow characteristics in the multiple stenotic tubes.

• Journal of Mechanical Science and Technology
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• v.15 no.11
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• pp.1555-1562
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• 2001

In a conventional shell-and-tube heat exchanger, fluid contacts with tubes flowing up and down in a shell, therefore there is a defect in the heat transfer with tubes due to the stagnation portions . Fins are attached to the tubes in order to increase heat transfer efficiency, but there exists a limit. Therefore, it is necessary to improve heat exchanger performance by changing the fluid flow in the shell. In this study, a highly efficient shell-and-tube heat exchanger with spiral baffle plates is simulated three-dimensionally using a commercial thermal-fluid analysis code, CFX4.2. In this type of heat exchanger, fluid contacts with tubes flowing rotationally in the shell. It could improve heat exchanger performance considerably because stagnation portions in the shell could be removed. It is proved that the shell-and-tube heat exchanger with spiral baffle plates is superior to the conventional heat exchanger in terms of heat transfer.

• Structural Engineering and Mechanics
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• v.91 no.3
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• pp.301-313
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• 2024

Plastic buckling of tubular columns has been attributed to rotational instability of plastic hinges. The present study aimed to characterize the plastic hinges for two different grades of strain-hardening, examined in mild-steel (MS) and stainless-teel (SS) tubes with un-strengthened and strengthened conditions. At the primary stage, the formerly tested experimental specimens were simulated using full-scale FE models considering nonlinear response of the materials, then to estimate the characteristics of the plastic hinges, a meso model was developed from the critical region of the tubes and the moment-rotation diagrams were depicted under pure bending conditions. By comparison of the relative rotation diagram obtained by the full-scale models with the critical rotation under pure bending, the length and critical rotation of the plastic hinges under eccentric axial load were estimated. The stress and displacement diagrams indicated the mechanism of higher energy absorption in the strengthened tubes, compared to unstrengthened specimens, due to establishment of stable wrinkles along the tubes. The meso model showed that by increasing the critical rotation in the strengthened MS tube equal to 1450%, the energy absorption of the tube has been enhanced to 2100%, prior to collapse.

• KSTLE International Journal
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• v.3 no.2
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• pp.101-109
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• 2002

This paper presents the fabrication and performance inspection of a peristaltic micropump by flow simulation. The valve-less micropump using the diffuser/nozzle is consists of base plate, mid plate, top plate and connection tubes fur inlet and outlet. In detail, the base plate is composed of two diffuser nozzles and three chambers, the mid plate consists of a glass diaphragm for the volumetric change of the pumping chamber. The inlet and outlet tubes are connected at the top plate and the actuator fur pressing the diaphragm is located beneath the top plate. The micropump is fabricated on the silicon wafer by DRIE (Deep Reactive ion Etching) process. The pumping performances are tested by the pneumatic test rig and compared with the simulated results fur various dimensions of diffuser nozzles. The pumping characteristics of the micropump by the volumetric change at the pumping chamber is modeled and simulated by the commercial software of FLOW-3D. The simulated results shows that reverse flow is the inherent phenomena in the diffuser nozzle type micropump, but it can be reduced at the dual pumping chamber model.

• Smart Structures and Systems
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• v.19 no.4
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• pp.371-382
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• 2017

Concrete filled steel tubes are extensively applied in engineering structures due to their resistance to high tensile and compressive load and convenience in construction. But one major flaw, their vulnerability to environmental attack, can severely reduce the strength and life of these structures. Degradation due to corrosion of steel confining the concrete is one of the major durability problems faced by civil engineers to maintain these structures. The problem accelerates as inner surface of steel tube is in contact with concrete which serves as electrolyte. If it remains unnoticed, it further accelerates and can be catastrophic. This paper discusses a non-destructive degradation monitoring technique for early detection corrosion in steel tubes in CFST members. Due to corrosion, damage in the form of debonding and pitting occurs in steel sections. Guided ultrasonic waves have been used as a feasible and attractive solution for the detection and monitoring of corrosion damages in CFST sections. Guided waves have been utilized to monitor the effect of notch and debond defects in concrete filled steel tubes simulating pitting and delamination of steel tubes from surrounding concrete caused by corrosion. Pulse transmission has been used to monitor the healthy and simulated damaged specimens. A methodology is developed and successfully applied for the monitoring of concrete filled steel tubular sections undergoing accelerated chloride corrosion. The ultrasonic signals efficiently narrate the state of steel tube undergoing corrosion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.811-819
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• 2012

An air-cooled condenser is a device that is used for converting steam into condensate by using ambient air. The air-cooled condenser is prone to suffer from a serious explosion when the condensate inside the tubes of a heat exchanger is frozen; in particular, tubes can break during winter. This is primarily due to the structural problem of the tube outlet of an existing conventional air-cooled condenser system, which causes the backflow of residual steam and noncondensable gases. To solve the backflow problem in such condensers, such a system was simulated and a new system was designed and evaluated in this study. The experimental results using the simulated condenser showed the occurrence of freezing because of the backflow inside the tube. On the other hand, no backflow and freezing occurred in the advanced new condenser, and efficient heat exchange occurred.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.151-154
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• 2004

The HANARO, a multi-purpose research reactor of 30 MWth open-tank-in-pool type, has been under normal operation since its initial criticality in February, 1995. Many experiments should be safely performed to activate the utilization of the HANARO. A flow simulated test facility has been developed for the verification of structural integrity of those experimental facilities prior to loading In the HANARO. This test facility is composed of three major parts; a half-core structure assembly, flow circulation system and support system. The half-core structure assembly is composed of plenum, grid plate, core channel with flow tubes, chimney and dummy pool. The flow channels are to be filled with flow orifices to simulate similar flow characteristics to the HANARO. This paper describes an analysis of the flow distribution of the cote channel and compares with the test results. As results, the analysis showed similar flow characteristics compared with those in the test results.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.49-55
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• 2004

This paper addresses a numerical simulation of the flow and heat transfer in a simplified model of helically coiled tube steam generator using a general purpose computational fluid dynamic analysis computer code. The steam generator model is comprised of a cylindrical shell and helically coiled tubes. A cold feed water entered the tubes is heated up, evaporates. and finally become a superheated steam with a large amount of heat transferred continuously from the hot compressed water at higher pressure flowing counter-currently through the shell side. For the calculation of tube side two-phase flow field formed by boiling, inhomogeneous two-fluid model is used. Both the internal and external turbulent flows are simulated using the standard k-e model. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. The numerical calculations are peformed for helically coiled tubes of steam generator at an integral type pressurized water reactor under normal operation. The effects of tube-side inlet flow velocity are discussed in details. The results of present numerical simulation are considered to be physically plausible based on the data and knowledge from previous experimental and numerical studies where available.