• Journal of the Korean Geotechnical Society
• /
• v.19 no.1
• /
• pp.93-102
• /
• 2003

Unconfined compression test (UC) has been widely used to determine the undrained shear strength ($c_u$) of clay, because it is convenient and economical. However, UC can not represent the behaviour of in-situ stress condition and the strength obtained by the test is generally underestimated compared to that of triaxial compression, due to no confining pressure. Therefore, a simple and practical method to correct the ($c_u$) for sample disturbance and to be used in geotechnical practice is needed. This study is aimed at proposing the method to estimate in-situ undrained shear strength from UC with suction measurement. The proposed method is based on theoretical shear strength equation of perfect sample (Noorany & Seed, 1965), and effective overburden stress and analysis results ($A_f,\phi'$) of effective stress behaviour by UC are needed for the equation. The shear resistance angle ($\phi'$) can be simply estimated through the result that $K_f$-line slope of the UC is 1.6 times higher than that of triaxial compression test. The result of this study shows that the measured strength by this method is very similar to that of the undrained shear strength by triaxial compression test (CK$_0$UC).

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.6
• /
• pp.521-527
• /
• 2016

This paper is concerned with the numerical analysis of dynamic response of floating offshore wind turbine subject to underwater explosion using an effective non-reflecting technique. An infinite sea water domain was truncated into a finite domain, and the non-reflecting technique called the perfectly matched layer(PML) was applied to the boundary of truncated finite domain to absorb the inherent reflection of out-going impact wave at the boundary. The generalized transport equations that govern the inviscid compressible water flow was split into three PML equations by introducing the direction-wise absorption coefficients and state variables. The fluid-structure interaction problem that is composed of the wind turbine and the sea water flow was solved by the iterative coupled Eulerian FVM and Largangian FEM. And, the explosion-induced hydrodynamic pressure was calculated by JWL(Jones-Wilkins-Lee) equation of state. Through the numerical experiment, the hydrodynamic pressure and the structural dynamic response were investigated. It has been confirmed that the case using PML technique provides more reliable numerical results than the case without using PML technique.

• Geotechnical Engineering
• /
• v.10 no.4
• /
• pp.103-118
• /
• 1994

The rapid motion of granular material is microscopically observed, and investigated by continuum theory. From the binary collision phenomenon two different times are introduced : flying time and contact time. The former says the non -stationary motion and at a same time the variation of bulk volume. The latter is operative by a delayed time during the contact and describes the elastic properties of granular material. With both times a dynamic constitutive equation is postulated for four state variables : dispersive pressure, viscosity, thermal diffusivity and energy annihilation rate. The balance laws of mass, momentum and energy which are represented through above four variabls, are applied to the model, in which due to the elastic property the relaxation and energy absorption are explained.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.6
• /
• pp.19-26
• /
• 2021

The lattice structure is attracting attention from industry because of its excellent strength and stiffness, ultra-lightweight, and energy absorption capability. Despite these advantages, widespread commercialization is limited by the difficult manufacturing processes for complex shapes. Additive manufacturing is attracting attention as an optimal technology for manufacturing lattice structures as a technology capable of fabricating complex geometric shapes. In this study, a unit cell was formed using a three-dimensional coordinate method. The relative density relational equation according to the boundary box size and strut radius of the unit cell was derived. Simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC) with a controlled relative density were designed using modeling software. The accuracy of the equations for calculating the relative density proposed in this study secured 98.3%, 98.6%, and 96.2% reliability in SC, BCC, and FCC, respectively. A simulation of the lattice structure revealed an increase in compressive yield load with increasing relative density under the same cell arrangement condition. The compressive yield load decreased in the order of SC, BCC, and FCC under the same arrangement conditions. Finally, structural optimization for the compressive load of a 20 mm × 20 mm × 20 mm structure was possible by configuring the SC unit cells in a 3 × 3 × 3 array.

• Geotechnical Engineering
• /
• v.12 no.2
• /
• pp.59-70
• /
• 1996

The EPS has the unit weight of only 20~30kg/m3 and is used as one of the methods of reducing road embankment loads. Parts of it's applications are for backfill materials of structures like abutment, retaining wall, etc., to reduce horizontal earth pressure and for banking materials to secure the safety of settlement and bearing capacity by minimizing the stress Increment. However, the Korean Standards (KS) has not yet proposed any testing method for use of EPS as a engineering banking material. Only its testing and quality ordinance as a heat insulation material has been standardized. Therefore, in Korea, EPS is used as banking material without any systematic testing data as a civil engineering material. In this point of view, this paper deals with the engineering characteristics of EPS through many laboratory tests on strength, strain, absorption, and creep. from the results achived through tests, this paper proposes the enactment of a suitable quality testing ordinance and the criteria of unconfined design strength of EPS for use as engineering material.

• Journal of Korean Society of Steel Construction
• /
• v.15 no.5 s.66
• /
• pp.561-570
• /
• 2003

This study evaluate the characteristics of stainless steel for the use of stainless steel tubes as structural members. The strength of stainless steel tube was compared with that of steel tube stub-columns through tensile experiment and compressed experiment. The selected experimental parameters were diameter (width)-thickness and section shape. The results of tests showed that stainless steel tubes could be predicted as superior to steel tubes in terms of tensile strength, yield ratio, elongation percentage, and absorption ability of energy. The yield strength of stainless steel tubes were found to be higher than the Korean Standards ($Fy=2.1tf/cm^2$) and the design strength of SIJ-ASD($Fy=2.4tf/cm^2$). It was also higher then the yield strength of steel tubes. The plastic deformation of stainless steel tubes was found to beto that of steel tubes.

• Composites Research
• /
• v.33 no.3
• /
• pp.108-114
• /
• 2020

Piecewise Integrated Composite (PIC) beam is composed of different stacking against loading type depending upon location. The aim of current study is to assign robust stacking sequences against external loading to every corresponding part of the PIC beam based on the value of stress triaxiality at generated reference points using the k-NN (k-Nearest Neighbor) classification, which is one of representative machine learning techniques, in order to excellent superior bending characteristics. The stress triaxiality at reference points is obtained by three-point bending analysis of the Al beam with training data categorizing the type of external loading, i.e., tension, compression or shear. Loading types of each plane of the beam were classified by independent plane scheme as well as total beam scheme. Also, loading fidelities were calibrated for each case with the variation of hyper-parameters. Most effective stacking sequences were mapped into the PIC beam based on the k-NN classification model with the highest loading fidelity. FE analysis result shows the PIC beam has superior external loading resistance and energy absorption compared to conventional beam.

• Composites Research
• /
• v.32 no.5
• /
• pp.216-221
• /
• 2019

Piecewise integrated composite (PIC) beam has different stacking sequences for several regions with respect to their superior load-resisting capabilities. On the interest of current research is to improve bending characteristics of PIC beam, with assigning specific stacking sequence to a specific region with the help of machine learning techniques. 240 elements of from the FE model were chosen to be reference points. Preliminary FE analysis revealed triaxialities at those regularly distributed reference points to obtain learning data creation of machine learning. Triaxiality values catagorise the type of loading i.e. tension, compression or shear. Machine learning model was formulated by learning data as well as hyperparameters and proper load fidelity was suggested by tuned values of hyperparameters, however, comparatively higher nonlinearity intensive region, such as side face of the beam showed poor load fidelity. Therefore, irregular distribution of reference points, i.e., dense reference points were distributed in the severe changes of loading, on the contrary, coarse distribution for rare changes of loading, was prepared for machine learning model. FE model with irregularly distributed reference points showed better load fidelity compared to the results from the model with regular distribution of reference points.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.12
• /
• pp.1102-1139
• /
• 2002

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 2000 and 2001 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. (1) Most of fundamental studies on fluid flow were related with heat transportation of facilities. Drop formation and rivulet flow on solid surfaces were interesting topics related with condensation augmentation. Research on micro environment considering flow, heat, humidity was also interesting for comfortable living environment. It can be extended considering biological aspects. Development of fans and blowers of high performance and low noise were continuing topics. Well developed CFD technologies were widely applied for developing facilities and their systems. (2) Most of papers related with heat transfer analysis and heat exchanger shows dealt with convection, evaporation, and channel flow for the design application of heat exchanger. The numerical heat transfer simulation studies have been peformed and reported to show heat transfer characteristics. Experimental as well as numerical studies on heat exchanger were reported, while not many papers are available for the system analysis including heat exchanger. (3) A review of the recent studies on heat pump system shows that performance analysis and control of heat pump have been peformed by various simulations and experiments. The research papers on multi-type heat pump system increased significantly. The studies on heat pipe have been examined experimently for change of working characteristics and strut lure. Research on the phase change has been carried out steadily and operation strategies of encapsulated ice storage tank are reported experimentally in several papers. (4) A review of recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. Evaporation and condensation heat transfer characteristics are investigated for tube shapes and new alternative refrigerants. Studies on components of refrigeration/air conditioning system are carried to examine efficiency for various compressors and performance of new expansion devices. In addition to thermophysical properties of refrigerant mixtures, studies on new refrigerants are also carried out, however research works on two-phase flow seemed to be insufficient. (5) A review of the recent studies on absorption cooling system indicates that heat and mass transfer phenomena have been investigated to improve absorber performance. Various experimental data have been presented and several simulation models have been proposed. A review of the recent studies on duct and ventilation shows that ventilation indices have been proposed to quantify the ventilation performance in buildings and tunnels. Main efforts have been focused on the applications of ventilation effectiveness in practice, either numerically using computational fluid dynamics or experimentally using tracer gas techniques. (6) Based on a review of recent studies on indoor thermal environment and building service systems, research issues have mainly focused on many innovative ideas such as underfloor air-conditioning system, personal environmental modules, radiant floor cooling and etc. Also, the new approaches for minimizing energy consumption as well as improving indoor environmental conditions through predictive control of HVAC systems, various activities of building energy management and cost-benefit analysis for economic evaluation were highlighted.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.12
• /
• pp.1098-1125
• /
• 2000

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 1998 and 1999 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. 1) A review of the recent studies on fluid flow, turbomachinery and pipe-network shows that many experimental investigations are conducted in applications of impingement jets. Researches on turbulent flows, pipe flows, pipe-networks are focused on analyses of practical systems and prediction of system performance. The results of noise reduction in the turbomachinery are also reported. 2) A review of the recent studies on heat transfer analysis and heat exchanger shows that there were many papers on the channel flow with the application to the design of heat exchanger in the heat transfer analysis. Various experimental and numerical papers on heat exchanger were also published, however, there were few papers available for the analysis of whole system including heat exchanger. 3) A review of the recent studies on heat pump system have focused on the multi-type system and the heat pump cycle to utilize treated sewage as the heat source. The defrosting and the frosting behaviors in the fin-tube heat exchanger is experimentally examined by several authors. Several papers on the ice storage cooling system are presented to show the dynamic simulation program and optimal operation conditions. The study on the micro heat pipes for the cooling of high power electronic components is carried out to examine the characteristics of heat and mass transfer processed. In addition to these, new type of separate thermosyphon is studied experimentally. 4) The recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. New systems operating with natural refrigerants are drawing lots of attention. In addition to these, evaporation and condensation heat transfer characteristics of traditional and new refrigerants are investigated for plain tubes and also for microfin tubes. Capillary tubes and orifice are main topics of research as expansion devices and studies on thermophysical properties of new refrigerants and refrigerant/oil mixtures are widely carried out. 5) A review of the recent studies on absorption cooling system shows that numerous experimental and analytical studies on the improvement of absorber performance have been presented. Dynamic analysis of compressor have been performed to understand its vibration characteristics. However research works on tow-phase flow and heat transfer, which could be encountered in the refrigeration system and various phase-change heat exchanger, were seemed to be insufficient. 6) A review of recent studies on duct system shows that the methods for circuit analysis, and flow balancing have been presented. Researches on ventilation are focused on the measurement of ventilation efficiency, and variation of ventilation efficiency with ventilation methods by numerous experimental and numerical studies. Furthermore, many studies have been conducted in real building in order to estimate indoor thermal environments. Many research works to get some information for cooling tower design have been performed but are insufficient. 7) A review on the recent studies on architectural thermal environment and building mechanical systems design shows that thermal comfort analysis is sitting environment, thermal performance analysis of Korean traditional building structures., and evaluation of building environmental load have been performed. However research works to improve the performance of mechanical system design and construction technology were seemed to be insufficient.