• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.1
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• pp.139-145
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• 2007

This paper presents the low cycle thermal fatigue of the engine exhaust manifold subject to thermomechanical cyclic loadings. The analysis includes the FE model of the exhaust system, temperature dependent material properties, and thermal loadings. The result shows that at an elevated temperature, large compressive plastic deformations are generated, and at a cold condition, tensile stresses are remained in several critical zones of the exhaust manifold. From the repetitions of thermal shock cycles, plastic strain ranges could be estimated by the stabilized stress-strain hysteresis loops. The method was applied to assess the low cycle thermal fatigue for the engine exhaust manifold. It shows a good agreement between numerical and experimental results.

• Proceedings of the KOR-KST Conference
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• 1998.09a
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• pp.141-151
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• 1998

Provision of Passing Sight Distance (PSD) is an important component in two-lane highway design and has a critical impact on capacity of highway and safety of drivers. Many models have been developed to estimate PSD reasonably. However, each of them has a number of shortcomings for reflecting the real traffic conditions. This paper introduces a revised model that reflects the characteristics of the passing maneuver. The changes in passing sight distances under different assumptions about acceleration and vehicle length, which are related to vehicle types, are presented. The results obtained by the revised model are compared with those obtained from the existing models. There is an important link between geometric design decisions which determine the available sight distance and the quality of service which the road provides. In this paper, we examine one aspect of this relationship. That is to determine whether the passing sight distance is provided by improving horizontal alignment for a specific roadway section or passing may be restricted to save the road construction cost. To do so, a simple method for estimating traffic delay in no-passing is introduced.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.2
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• pp.385-399
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• 2000

Groundwater contamination caused by landfill leachate leads to various changes in aquifer environment according to the characteristics of incoming contaminants and aquifer geochemistry. These changes in aquifer environment are known to contribute to the natural attenuation phenomena of contaminants. The knowledge on changes in aquifer environment is necessary to determine the extent of groundwater pollution, to assess risk of the pollution, and to develop an appropriate remediation technologies. In this paper, the changes in aquifer environment caused by landfill leachate development of various redox zones-and the natural attenuation phenomena occurred in each redox zone are reviewed. From this review, an appropriate research direction and control action is presented for the groundwater pollutions caused by unsanitary landfills scattered across the nation.

• Atmosphere
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• v.17 no.4
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• pp.315-326
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• 2007

The effects of windbreaks on the reduction of suspended particles are investigated using a computational fluid dynamics (CFD) model with the ${\kappa}-{\varepsilon}$ turbulence closure scheme based on the renormalization group (RNG) theory. In the control experiment, the recirculation zones behind the storage piles are generated and, as a whole, relatively monotonous flow patterns appear. When the windbreaks with the 0% porosity are constructed, the recirculation zones are generated by the windbreaks and very complicated flow patterns appear due to the interference between the windbreaks and storage piles. The porosity of the windbreaks suppresses the generation of the recirculation zone and decreases the wind velocity in the windbreaks as well as that outside the windbreaks. As the emission of suspended particles from the storage piles are closely related with the friction velocity at the surfaces of the storage piles, variation of the friction velocity and total amount of the emission of the suspended particles with the height and porosity of the windbreaks are investigated. The results show that higher and more porous windbreaks emit less suspended particles and that the reduction effect of the porosity is still more effective than that of the height. In the case of the windbreak with 30 m height and 50% porosity, friction velocities above the storage piles are smaller than the critical friction velocity above which particles would be suspended. As a result, total amount of suspended particles are much fewer than those in other cases.

• Journal of Korean Society on Water Environment
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• v.29 no.5
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• pp.630-640
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• 2013

It is one of the most critical steps identifying impaired waterbodies exactly in the selection of target water quality indicators for the management of Total Maximum Daily Loads (TMDLs). Excess ratio and excess level were applied and analyzed by the stream zone basis in order to evaluate water impairment for Nakdong, Geum, Youngsan and Seomjin rivers. Each river basin was divided into stream zones in the light of its watershed and waterbody characteristics. Selected water quality parameters discussed in this study were pH, DO, BOD, COD, SS, T-P, T-Coli and F-Coli. The excess ratios of the water quality parameters were used to discriminate water bodies that did not meet water quality standards. The excess levels were used to classify the degradation of water quality. The excess ratios and the excess levels to the water quality criteria of the medium influence areas were used for each stream zone. The results indicate that the excess ratios and the excess levels are varied on the stream zone in each river basin. Three parameters, pH, DO and SS, met water quality standards in all stream zones. The other five parameters indicated very high excess ratios in most waterbodies, and especially T-P and T-Coli revealed to be very high excess levels in some waterbodies. These parameters could be considered as major target indicators for the management of TMDLs.

• Industrial Engineering and Management Systems
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• v.15 no.4
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• pp.396-402
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• 2016

In this study, hydraulic analysis of water-supply networks in Marivan was performed by modeling. WATERGEMS was used for modeling and it was calibrated using existing rules and regulations. The purpose of this research is modeling urban water network and its analysis based on hydraulic criteria and meeting pressure conditions at the nodes and complying the economic speed. To achieve this goal, first the pipelines of city streets was designed in AutoCAD on a map of the city. It should be mentioned that it was tried to prevent from creating additional loops in the network and the optimal network was designed by a combination of annular and branch loops. In the next step, the pipes were called in WATERGEMS and then we continue the operation by the allocation of elevation digits to the pipes. Since the topography of this city is very specific and unique, the number of pressure zones was increased. Three zones created only covers about 20% of the population in the city. In this dissertation, the design was performed on the city's main zone with the largest density in the Figures 1,320-1,340. In the next step, the network triangulation was conducted. Finally, the Debiw as allocated based on the triangulation conducted and considering the density of the city for year of horizon. Ultimately, the network of Marivan was designed and calibrated according to hydraulic criteria and pressure zoning. The output of this model can be used in water-supply projects, improvement and reform of the existing net-work in the city, and various other studies. Numerous and various graphs obtained in different parts of a network modelled can be used in the analysis of critical situation, leakage.

• Structural Engineering and Mechanics
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• v.25 no.4
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• pp.481-500
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• 2007

The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading $P(t)=P_s+P_d\;{\cos}{\Omega}t$ is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at ${\Omega}={\omega}_m+{\omega}_n$, (${\Omega}$ is the excitation frequency and ${\omega}_m$ and ${\omega}_n$ are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at ${\Omega}=2{\omega}_1$, where ${\omega}_1$ is the fundamental frequency, other cases of ${\Omega}={\omega}_m+{\omega}_n$, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.109-120
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• 2007

Auxiliary support systems such as the reinforced protective umbrella method have been applied before tunnel excavation to increase ground stiffness and to prevent the large deformation. However, determination procedure of geotechnical parameters along the construction sequence contains various errors. This study suggests a method to characterize the time-dependent behavior of pre-reinforced zones around the tunnel using elastic waves. Experimental results show that shear strength as well as elastic wave velocities increase with the curing time. Shear strength and strength parameters can be uniquely correlated to elastic wave velocities. Obtained results from the laboratory tests are applied to numerical simulation of tunnel considering its construction sequences. Based on numerical analysis, initial installation part of pre-reinforcement and portal of tunnel are critical for tunnel stability. Result of the time-dependent condition is similar to the results of for $1{\sim}2$ days of the constant time conditions. Finally, suggested simple analysis method combining experimental and numerical procedure which considering time-dependent behavior of pre-reinforced zone on tunnel would provide reliable and reasonable design and analysis for tunnel.

• Plant Biotechnology Reports
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• v.4 no.2
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• pp.139-148
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• 2010

Jatropha curcas L. (Physic nut) is a commercially important non-edible oil seed crop known for its use as an alternate source of biodiesel. In order to investigate the morphogenic potential of immature embryo, explants from four developmental stages were cultured on medium supplemented with combinations of auxins and cytokinins. It was found that the size of embryo is critical for the establishment of callus. Immature embryos (1.1-1.5 cm) obtained from the fruits 6 weeks after pollination showed a good response of morphogenic callus induction (85.7%) and subsequent plant regeneration (70%) with the maximum number of plantlets (4.7/explant) on Murashige and Skoog's (MS) medium supplemented with IBA (0.5 $mg\;l^{-1}$) and BA (1.0 $mg\;l^{-1}$). The above medium when supplemented with growth adjuvants such as 100 $mg\;l^{-1}$ casein hydrolysate + 200 $mg\;l^{-1}$ L-glutamine + 8.0 $mg\;l^{-1}$ $CuSO_4$ resulted in an even higher frequency of callus induction (100%). Plant regeneration (90%) with the maximum number of plantlets (10/explant) was achieved on MS medium supplemented with 500 $mg\;l^{-1}$ polyvinyl pyrrolidone + 30 $mg\;l^{-1}$ citric acid + 1 $mg\;l^{-1}$ BA + 0.5 $mg\;l^{-1}$ Kn + 0.25 $mg\;l^{-1}$ IBA. It was observed that plantlet regeneration could occur either through organogenesis of morphogenic callus or via multiplication of pre-existing meristem in immature embryos. The age of immature embryos and addition of a combination of growth adjuvants to the culture medium appear to be critical for obtaining high regeneration rates. Well-developed shoots rooted on half-halfstrength MS medium supplemented with 0.5 $mg\;l^{-1}$ IBA and 342 $mg\;l^{-1}$ trehalose. The rooted plants after acclimatization were successfully transferred to the field in different agro-climatic zones in India. This protocol has been successfully evaluated on five elite lines of J. curcas.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.199-210
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• 2003

The development of strain localization within shear zones is frequently observed during soil deformation. In fact, the phenomenon appears to be more often the norm rather than the exception. Conceptually, any soil condition that renders negative work increment is prone to localization. In this study, a broad range of soil and loading conditions are investigated to test this criterion, including: dilative soil subjected to drained shear (standard case), contractive soil sheared under undrained conditions, cavitation in dilative soil in undrained shear, inhomogeneous soils, particle alignment in contractive soils made of platy particles, soils that experience particle crushing, and the shear of low-moisture and/or lightly cemented loose soils. Unique specimens and test procedures are designed to separately test each of these soil conditions in the laboratory According to experimental test results, soil specimens with post-peak strain softening behavior are prone to progressive failure, localization of deformations, and shear banding. The state of stress, the soil density, inherent mechanical and geometrical properties of soil particles, low water content, and heterogeneity can contribute to triggering strain localization. Considering all possible cases of localization, the best method to obtain the critical state line in the laboratory is to use contractive homogeneous specimens subjected to drained shear.