• International Journal of Air-Conditioning and Refrigeration
• /
• v.14 no.2
• /
• pp.41-48
• /
• 2006

Absorption performance at the vertical interface between refrigerant vapor and liquid solution of $LiBr-H_{2}O$ solution was enhanced by the waves formed due to the interfacial shear stress. The present study investigated experimentally and analytically the improvements of absorption performance in a falling film by wavy film flow. The dynamic parameter was the film Reynolds numbers ranged from 50 to 150. The energy and diffusion equations were solved simultaneously to find the temperature and concentration profiles at the interface of liquid solution and refrigerant vapor. Absorption characteristics due to heat and mass transfer were analyzed for the falling film of the LiBr aqueous solution contacted by refrigerant vapor in the absorber. Absorption performance showed a peak value at the solution flow rate of $Re_{f}>100$. Absorption performance for the wavy film flow was found to be greater by approximately 10% than that for uniform film flow. Based on numerical and experimental results, the maximum absorption rate was obtained for the wavy flow caused by spring insert. The difference between the measured and the predicted results were ranged from 5.8 to 12%.

• Steel and Composite Structures
• /
• v.43 no.1
• /
• pp.91-106
• /
• 2022

This paper has focused on presenting a three dimensional theory of elasticity for free vibration of 3D-graphene foam reinforced polymer matrix composites (GrF-PMC) cylindrical panels resting on two-parameter elastic foundations. The elastic foundation is considered as a Pasternak model with adding a Shear layer to the Winkler model. The porous graphene foams possessing 3D scaffold structures have been introduced into polymers for enhancing the overall stiffness of the composite structure. Also, 3D graphene foams can distribute uniformly or non-uniformly in the shell thickness direction. The effective Young's modulus, mass density and Poisson's ratio are predicted by the rule of mixture. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary at the curved edges. It is explicated that 3D-GrF skeleton type and weight fraction can significantly affect the vibrational characteristics of GrF-PMC panel resting on two-parameter elastic foundations.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.10
• /
• pp.13-23
• /
• 2011

Bearing capacity of pile foundations in cold region is dominated by adfreeze bond strength between surrounding soil and pile perimeter. It denotes that adfreeze bond strength is the most important design parameter for foundations in cold region. Adfreeze bond strength is affected by various factors like 'soil type', 'frozen temperature', 'normal stress acting on soil/pile interface', 'loading rate', 'roughness of pile surface', etc. Several methods have already been proposed to estimate adfreeze bond strength during past 50 years. However, most methods have not considered the effect of normal stress for adfreeze bond strength. In this study, both freezing temperature and normal stress have been controlled as primary factors affecting adfreeze bond strength. A direct shear box was used to measure adfreeze bond strength between sand and aluminum under different temperature conditions. Based on the test results, the relation between shear strength of frozen sand and adfreeze bond strength have been investigated. The test results showed that both of shear strength and adfreeze bond strength tend to increase with decreasing frozen temperature or increasing confining pressure. The ratio of shear strength and adfreeze bond strength, expressed as $r_s$, decreased initially frozen section but increased at much lower frozen temperature and there were uniform intervals under the different normal stress conditions. A method for predicting adfreeze bond strength using $r_s$ has finally been proposed in this study.

• Korean Journal of Food Science and Technology
• /
• v.33 no.6
• /
• pp.645-650
• /
• 2001

A study was carried out to establish the detection method for irradiated cereals. Cereals were ground and irradiated at 2.5, 5.0, 7.5, 10, 15 kGy using a $Co^{60}$ irradiator. The viscosities decreased in all samples by increasing irradiation dose. The viscosity of the Panicum millaceum (Korean) and Andropogon sorghum (Korean) paste dropped from $143.38{\pm}0.44$ and $35.92{\pm}1.90$ in the control to $6.60{\pm}1.16$ and $3.86{\pm}0.32$, respectively, in the samples irradiated at 15 kGy. These trends were similar to samples from china. Regression equation and coefficients of viscosity of Panicum millaceum (Korean and China) and Andropogon sorghum (Korean and China) were 0.80 (y=-27.789x＋150.17), 0.98 (y=-3.367x＋88.93), 0.84 (y=-6.0466x＋35.49) and 0.84 (y=-13.346x＋101.67) at 50 rpm. All samples resulted in a decrease in specific parameter by increasing rpm after irradiation. Parameter values showed dose-dependent relationship between unirradiated and irradiated samples and indicated that all values of unirradiated samples were higher than the irradiated ones. These results suggest that the detection of irradiated cereals at various doses using viscometric methods is possible.

• Magazine of the Korea Concrete Institute
• /
• v.11 no.2
• /
• pp.177-186
• /
• 1999

The purpose of this study is to analyze the interface debonding of RC beams strengthened by carbon fiber sheet(CFS). The behavior of damaged RC beams strengthened with CFS is analytically investigated next using linear elastic fracture mechanics(LEFM) approach and the finite element method. The study includes an investigation of the separation mode by interface fracture of the strengthening materials due to the interfacial shear and normal stresses. The numerical method is presented to obtain the value of interfacial fracture parameter such as the strain energy release rate. Based on the results of this study, it is found that the critical case occurs when the interfacial cracks occur within a short region of the flexural crack. The CFS strengthening has not an adequate factor of safety against interfacial debonding of CFS. Furthermore, for the thicknesses of the adhesive studied[1mm~3mm], it is no noticeable effect on the strain energy release rate.

• The Korean Journal of Rheology
• /
• v.8 no.3_4
• /
• pp.199-206
• /
• 1996

산마와 재배마에서 점질다당류를 추출하여 리올러지 및 열특성을 연구하였다. D.I.W 에서 산마와 재배마 점질다당류의 고유점도(η)는 각각 16.1 이/g. 25.1 이/g 이고 pH7일 때 최대값을 나타내었고 염을 가했을 때 (η)가 급격히 감소하다가 일정한 값을 나타내었으며 urea 용액에서 NaCl, MaCl2 용액에서보다 (η)가 높았다. 마 점질다당류의 chain stiffness는 0,0050이고 Overlap parameter는 산마와 재배마 점질다당류가 각각 0.06 g/이. 0.04 g/이였 다. 마 점질 다당류는 shear rate가 증가함에 따라 겉보기 점도가 감소하여꼬 농도가 증가함 에따라 yield stress 와 점조성 지수는 증가하고 shear index가 감소하는 가소성유동체였다. 산마 점질다당류는 35$^{\circ}C$까지 온도에 대하여 비교적 안정하였지만 그이상의 온도에서는 겉보 기 점도가 급격히 감소하였고 재배마 점질다당류는 온도가 증가할수록 겉보기 점도가 점차 적으로 감소하였다. 겉보기 점도는 1가 염가 2가 염 사이에 큰 차이가 없었고 염농도가 증 가함에 따라 겉보기 점도가 감소하였으나 urea를 첨가했을 때 겉보기 점도가 약간 감소하다 가 다시 증가하는 것을 알수 있었다. DSC로 산마와 재배마 점질다당류의 "true melting"을 측정했을 때 각각 92$^{\circ}C$, 93$^{\circ}C$였고, enthalpy는 67.06 cal/g, 75.83 cal/g였다. 겔화에 소요된 enthalpy는 pH가 증가할수록 큰 값을 나타냈고 NaCl을 첨가했을 때 감소하다가 염농도 증 가에는 영향을 받지 않았으며 Urea와 glycerol을 각각 첨가했을 때 D. I. W.오세보다 감소 하였다. TGA로 열분해 현상을 측정했을 때 분해 온도는 산마와 재배와 점질다당류가 각각 219~332$^{\circ}C$, 229~341$^{\circ}C$ 범위였다.TEX> 범위였다.

• Transactions of Materials Processing
• /
• v.25 no.1
• /
• pp.36-42
• /
• 2016

Fiber metal laminates (FMLs) are well known for improved fatigue strength, better impact resistance, superior damage tolerance and slow crack growth rate compared to traditional metallic materials. However, defects and loss of strength of a composite material can occur due to the vertical load from the punch during the joining with a dissimilar material using a conventional clinching method. In the current study, tapered-hole clinching was an alternative process used to join Al 5052 and FMLs. The tapered hole was formed in the FML before the joining. For the better understanding of static and dynamic characteristics, a clinched joining followed by a tensile-shear test was numerically simulated using the finite element analysis. The design parameters were also evaluated for the geometry of the tapered hole by the Taguchi method in order to improve and compare the lateral joining strength of the clinched joint. The influence of the neck thickness and the undercut were evaluated and the contribution of each design parameter was determined. Then, actual experiments for the joining and tensile-shear test were conducted to verify the results of the numerical simulations. In conclusion, the appropriate combination of the design parameters can improve the joining strength and the cross-sections of the tapered-hole clinched joint formed in the actual experiments were in good agreement with the results of the numerical simulations.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.13 no.2
• /
• pp.191-199
• /
• 1993

Diffusion of a steady horizontal line source in a turbulent shear flow is simulated by numerically solving a steady two-dimensional advective diffusion equation. The computational result is compared with the analytic solution for uniform velocity and diffusivity distributions over the depth. The analytic solution for constant velocity and diffusivity overestimates the degree of vertical mixing. The normalized equation indicates that friction factor is the only physical parameter that governs the vertical diffusion process. Sensitivities of the diffusion process to the friction factor and initial source position are analyzed. The rate of vertical mixing varies approximately as the square root of the friction factor. The optimal source position, which gives the most rapid mixing, lies above the mid-depth and moves toward the water surface as the friction factor increases.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.19 no.4
• /
• pp.405-414
• /
• 2001

Plate tectonics is a dominant paradigm in modern geophysics. Because of its geological mechanism, Korea has a possibility of earthquake according to plate motion. Besides the disaster of earthquake grows rapidly, the importance of recognition for earthquake has been emphasized. This study attempts to decide crustal movement parameters with GPS data, analysed baseline after processing data with GIPSY-OASIS II S/W, observed from 6 stations in and around the Korean peninsula, and obtained from selected 11 stations in Korea. As a results, maximum shear strain was $0.04{\mu}/yr$ and the mean azimuth of the maximum compression axes$(A_{z2})$ is estimated as $97.75^{\circ}$ in and around the Korean peninsula. The average rate of the maximum shear strain($({\gamma}_max)$) is $0.17{\mu}/yr$. The mean azimuth of the maximum compression axes$(A_{z2})$ is estimated as $70.25^{\circ}$ in Korea. Such a pattern of strain distribution is harmonious with that of seismic activity in Korea both historically as well as today.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.4
• /
• pp.354-361
• /
• 2008

Cold rolled steel sheet for automotive was treated by Ar/$O_2$ atmospheric pressure plasma to improve the adhesive bonding strength. Through the contact angle test and calculation of surface free energy for cold rolled steel sheet, the changes of surface properties were investigated before and after plasma treatment. The contact angle was decreased and surface free energy was increased after plasma treatment. And the change of surface roughness and morphology were observed by AFM(Atomic Force Microscope). The surface roughness of steel sheet was slightly changed. Based on Taguchi method, single lap shear test was performed to investigate the effect of experimental parameter such as plasma power, treatment time and flow rate of $O_2$ gas. Results shows that the bonding strength of steel sheet treated in Ar/$O_2$ atmospheric pressure plasma was improved about 20% compared with untreated sheet.