• Steel and Composite Structures
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• v.16 no.5
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• pp.455-480
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• 2014

Sixteen concrete filled square CFRP-steel tubular (S-CFRP-CFST) stub columns under axial compression were experimentally investigated. The experimental results showed that the failure mode of the specimens is strength loss of the materials, and the confined concrete has good plasticity due to confinement of the CFRP-steel composite tube. The steel tube and CFRP can work concurrently. The load versus longitudinal strain curves of the specimens can be divided into 3 stages, i.e., elastic stage, elasto-plastic stage and softening stage. Analysis based on finite element method showed that the longitudinal stress of the steel tube keeps almost constant along axial direction, and the transverse stress at the corner of the concrete is the maximum. The confinement effect of the outer tube to the concrete is mainly focused on the corner. The confinements along the side of the cross-section and the height of the specimen are both non-uniform. The adhesive strength has little effect both on the load versus longitudinal strain curves and on the confinement force versus longitudinal strain curves. With the increasing of the initial stress in the steel tube, the load carrying capacity, the stiffness and the peak value of the average confinement force are all reduced. Equation for calculating the load carrying capacity of the composite stub columns is presented, and the estimated results agree well with the experimental results.

• Journal of IKEEE
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• v.11 no.4
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• pp.219-226
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• 2007

An efficient block based two-layer JPEG encoding algorithm is proposed to compress high dynamic range (HDR) images in this work. The proposed algorithm separates an input HDR image into a tone-mapped low dynamic range (LDR) image and a ratio image, which represents the quotients of the original HDR pixels divided by the tone-mapped LDR pixels. Then, the tone-mapped LDR image is compressed using the standard JPEG scheme to preserve backward compatibility and the ratio image is encoded to minimize a cost function that models the perception of each block with different quantization parameters in the human visual system (HVS). Simulation results show that the proposed algorithm provides better performance than the conventional method, which encodes the ratio image without any prior information of blocks.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.48-54
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• 2014

In this paper, three refrigeration systems bypassing hot-gas to compressor outlet, compressor and condenser outlet and evaporator inlet are theoretically compared to offer basic design data for performance depending on cooling load using a HYSYS program. The main results are summarized as follows : First, the COP of third system is the highest. Next, the COP of second system is higher than first one. And, the temperature of compressor inlet of third system is constant for all cooling load. Compared to first and second system, the compressor inlet temperature of the first system is higher than second one for all cooling loads. From the above results, third system, which is bypassing hot-gas to evaporator inlet, is more advantageous when considering the precise temperature control and excellent performance of oil and water cooler of industrial machine.

• Tribology and Lubricants
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• v.15 no.1
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• pp.39-45
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• 1999

The wear behavior of $Al_2$O$_3$-40%TiO$_2$deposited on casted aluminum alloy (ASTM A356) by APS (Air Plasma Spray) against SiC ball has been investigated in this work. Wear tests were carried out at room temperature. The friction coefficient of $Al_2$O$_3$-40%TiO$_2$coating is lower than that of pure $Al_2$O$_3$coating(APS). $Al_2$O$_3$-40%TiO$_2$coating indicated the existence of the optimal coating thickness. It is found that voids and pores of coating surface resulted in the generation of cracks, and the cohesive of splats and the porosity of surface play a role in wear characteristics. It is suggested that the mismatch of thermal expansion of substrate and coating play an important role in wear performance. Tension and compression under thermo-mechanical stress may be occurred by the mismatch between thermal expansion of substrate and coating. The crack propagation above interface is observed in SEM.

• International Journal of Concrete Structures and Materials
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• v.9 no.1
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• pp.1-20
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• 2015

This work is devoted to the study of fresh and hardened properties of concrete containing recycled gravel. Four formulations were studied, the concrete of reference and three concretes containing recycled gravel with 30, 65 and 100 % replacement ratios. All materials were formulated on the basis of S4 class of flowability and a target C35 class of compressive strength according to the standard EN 206-1. The paper first presents the mix design method which was based on the optimization of cementitious paste and granular skeleton, then discusses experimental results. The results show that the elastic modulus and the tensile strength decrease while the peak strain in compression increases. Correlation with the water porosity is also established. The validity of analytical expressions proposed by Eurocode 2 is also discussed. The obtained results, together with results from the literature, show that these relationships do not predict adequately the mechanical properties as well as the stress-strain curve of tested materials. New expressions were established to predict the elastic modulus and the peak strain from the compressive strength of natural concrete. It was found that the proposed relationship E-$f_c$ is applicable for any type of concrete while the effect of substitution has to be introduced into the stress-strain (${\varepsilon}_{c1}-f_c$) relationship for recycled aggregate concrete. For the full stress-strain curve, the model of Carreira and Chu seems more adequate.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.5
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• pp.728-734
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• 2004

Environmentally friendly refrigerants with zero ozone layer depletion potential are required to be used in refrigerators and air conditioners due to the difficulties related to ozone layer depletion and global warming. A rigorous study for the system performance with new refrigerants having zero ozone layer depletion potential is inevitable before adopting that as a new fluid. The HFC(Hydrofluorocarbon) potential has been recommended as alternatives. In this paper. system performance in the heat pump facilities were studied using R-290, R-600a. R-1270 as an environment friendly refrigerant. R-22 as a HCFC's refrigerant. The experimental apparatus has been set-up as a conventional vapor compression type heat Pump system. The test section is a horizontal double pipe heat exchanger. A tube diameter of 12.70mm with 1.315mm wall thickness is used for this investigation. The test results showed that the COP of hydrocarbon refrigerants were superior to that of R-22 and the maximum increasing rate of COP was found in R-1270. The refrigeration capacity of hydrocarbon refrigerants were higher than that of R-22. The compressor work was obtained with the maximum value in R-1270 and the minimum one in R-22.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.21-27
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• 2001

Springs are widely utilized in machine element. To find out stiffness of frustum-shaped coil spring, the space beam theory using the finite element method is adopted in this paper In three dimensional space, a space frame element is a straight bar of uniform cross section which is capable of resisting axial forces, bending moments about two principal axes in the plane of its cross section and twisting moment about its centroidal axis. The corresponding displacement degrees of freedom are twelve. To find out load vector of coil spring subjected to distributed compression, principle of virtual work is adapted The displacements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displacements are added to coordinates of nodal points. The new stiffness matrix of the system using the new coordinates of nodal points is adopted to calculate the another increments of nodal displacements, that is, the step by step method is used in this paper. The results of the finite element method are fairly well agreed with those of various experiments. Using MATLAB program developed in this paper, spring constants and stresses can be predicted by input of few factors.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.4
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• pp.1-10
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• 2014

A progressive failure analysis procedure for composite laminates is developed in here and in the companion paper. An anisotropic plastic constitutive model for fiber-reinforced composite material, is developed, which is simple and efficient to be implemented into computer program for a predictive analysis procedure of composites. In current development of the constitutive model, an incremental elastic-plastic constitutive model is adopted to represent progressively the nonlinear material behavior of composite materials until a material failure is predicted. An anisotropic initial yield criterion is established that includes the effects of different yield strengths in each material direction, and between tension and compression. Anisotropic work-hardening model and subsequent yield surface are developed to describe material behavior beyond the initial yield under the general loading condition. The current model is implemented into a computer code, which is Predictive Analysis for Composite Structures (PACS), and is presented in the companion paper. The accuracy and efficiency of the anisotropic plastic constitutive model are verified by solving a number of various fiber-reinforced composite laminates with and without geometric discontinuity. The comparisons of the numerical results to the experimental and other numerical results available in the literature indicate the validity and efficiency of the developed model.

• Bulletin of the Korean Mathematical Society
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• v.52 no.6
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• pp.1973-2000
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• 2015

In this study, we present a multidimensional open system for valveless pumping (VP). This system consists of an elastic tube connected to two open tanks filled with a fluid under gravity. The two-dimensional elastic tube model is constructed based on the immersed boundary method, and the tank model is governed by a system of ordinary differential equations based on the work-energy principle. The flows into and out of the elastic tube are modeled in terms of the source/sink patches inside the tube. The fluid dynamics of this system is generated by the periodic compress-and-release action applied to an asymmetric region of the elastic tube. We have developed an algorithm to couple these partial differential equations and ordinary differential equations using the pressure-flow relationship and the linearity of the discretized Navier-Stokes equations. We have observed the most important feature of VP, namely, the existence of a unidirectional net flow in the system. Our computations are focused on the factors that strongly influence the occurrence of unidirectional flows, for example, the frequency, compression duration, and location of pumping. Based on these investigations, some case studies are performed to observe the details of the ow features.

• Archives of Plastic Surgery
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• v.39 no.4
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• pp.284-290
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• 2012

Open reduction and anatomic reduction can create better function for the temporomandibular joint, compared with closed treatment in mandible fracture surgery. Therefore, the double miniplate fixation technique via mini-retromandibular incision was used in order to make the most stable fixation when performing subcondylar fracture surgery. Those approaches provide good visualization of the subcondyle from the posterior edge of the ramus, allow the surgeon to work perpendicularly to the fracture, and enable direct fracture management. Understanding the biomechanical load in the fixation of subcondylar fractures is also necessary in order to optimize fixation methods. Therefore, we measured the biomechanical loads of four different plate fixation techniques in the experimental model regarding mandibular subcondylar fractures. It was found that the loads measured in the two-plate fixation group with one dynamic compression plate (DCP) and one adaption plate showed the highest deformation and failure loads among the four fixation groups. The loads measured in the one DCP plate fixation group showed higher deformation and failure loads than the loads measured in the two adaption plate fixation group. Therefore, we conclude that the selection of the high profile plate (DCP) is also important in order to create a stable load in the subcondylar fracture.