• Journal of Energy Engineering
• /
• v.26 no.3
• /
• pp.105-112
• /
• 2017

A lot of piping systems have been used from nuclear power systems to water supply systems. The maintenance of the piping systems is needed to ensure proper operation of the piping systems. Failure of the large pipe systems especially such as KDHC(Korea District Heating Corporation) can be a matter directly related to the enterprise productivity and profitability. It can also lead to very important issues in promoting public safety and convenience. Therefore a method of quick and safety repairs have been emerged as the most important problem. In this study, freezing seal isolation method using liquid nitrogen cryogenic refrigerant was developed for the maintenance of a pre insulated heat transport pipe of KDHC with a diameter of 300 mm. In this study, by employing computational analysis techniques we performed the flow and heat transfer analysis for the targeted pre insulated heat transfer pipe and freezing seal jacket(ice-Plug) and have selected for optimal system. The detailed design model based on the results of the computational analysis finally was produced. A laboratory-scale test apparatus were designed and the freezing seal isolation self-test carried out. Also the performance assessment tests in the test bed of KDHC were carried out for on-site application.

• Polymer(Korea)
• /
• v.31 no.5
• /
• pp.399-403
• /
• 2007

Trans-esterification behavior of polycarbonate/poly(butylene terephthalate) (PC/PBT) blends was investigated during the melt mixing process. Rheological and fracture behaviors, and fracture morphology were also investigated as a function of PC/PBT blend ratio. Based on FT-IR and $^1H-NMR$ results, a trans-esterification reaction was confirmed to occur between PC and PBT during the melt mixing process. The melt index(MI) decreased with increased PC content, indicating the higher flow resistance of PC. The storage and loss moduli were increased by increasing the PC loading, and the PC/PBT blends were rheologically incompatible based on the Cole-Cole plot. The tensile property increased linearly with the increased PC content. However, the impact strength increased until 50 wt% of PC loading, notably around $30{\sim}40wt%$, and then was levelled off at 50 wt%. Rough ridges were formed on the impact fracture surfaces above the 40 wt% of PC content, supporting the observed higher impact strength in this range.

• Proceedings of the Korean Institute Of Construction Engineering and Management
• /
• 2008.11a
• /
• pp.733-737
• /
• 2008

Construction supply chain management focused on materials in construction industry plays a critical role which controls the success and failure of a project. For the efficiency of construction supply chain management, the framework which provides project participants with the information originated from whole construction logistics steps without the omission and discontinuation of information flow is required. The new management framework that can support this environment is necessary because of setting up the complicated and distributed environment including logistics information management by intelligent equipment, co-working management with pre-framework legacy system and various devices(UMPC and PDA etc.) as the information confirmation and electrical transmission tool between the project participants different from former construction supply chain management environment while recently developing ubiquitous technologies such as RFID/USN and intelligent equipment to support logistics process. Therefore, the objective of this study is to introduce the concept of SOA (Service Oriented Architecture) as an alternative of effective information integration under the complex and distributed environment and to propose the SOA-based application model for building intelligent construction supply chain management framework.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.2 no.3
• /
• pp.1-11
• /
• 2011

The typical truss-lattice material successively packed by repeated cubic symmetric unit cells consists of sub-elements (SE) proposed in this study. The representative continuum model for this truss-lattice material such as the effective strain and stress relationship can be formulated by the homogenization procedure based on the notation of averaged mechanical properties. The volume fractions of micro-scale struts have a significant influence on the effective strength as well as the relative density in the lattice plate with replicable unit cell structures. Most of the strength contribution in the lattice material is induced by axial stiffness under uniform stretching or compression responses. Therefore, continuum based constitutive models composed of homogenized member stiffness include these mechanical characteristics with respect to strength, internal stress state, material density based on the volume fraction and even failure modes. It can be also recognized that the stress state of micro-scale struts is directly associated with the continuum constitutive model. The plastic flow at the micro-scale stress can extend the envelope of the analytical stress function on the surface of macro-scale stress derived from homogenized constitutive equations. The main focus of this study is to investigate the basic topology of unit cell structures with the cubic symmetric system and to formulate the plastic models to predict pressure dependent macro-scale stress surface functions.

• The Journal of Korean Academy of Prosthodontics
• /
• v.41 no.6
• /
• pp.732-746
• /
• 2003

Statement of problem. Soft lining materials, also referred to as tissue conditioning materials, tissue heating materials, relining materials, soft liners or tissue conditioners, were first introduced to dentistry by a plastic manufacturer in 1959. Since the introduction of the materials to the dental field, their material properties have been continually improved through the effort of many researchers. Soft lining materials have become widely accepted, particularly by prosthodontists, because of their numerous clinical advantages and ease of manipulation. Unfortunately, few reports have been issued upon the topic of increasing the bond strength between the base metal alloy used in cast denture bases and PMMA soft liner modified with 4-META, nor upon the pattern of debonding and material change in wet environment like a intra oral situation. Purpose. The purposes of this study were comparing the bond strength between base metal alloy used for the cast denture bases and PMMA soft liner modified with 4-META, and describing the pattern of debonding and material property change in wet environment like the intraoral situation. Material and Methods. This study consisted of four experiments: 1. The in vitro measurement of shear bond strength of the adhesive soft liner. 2. The in vitro measurement of shear bond strength of the adhesive soft liner after 2 weeks of aging. 3. A comparison of debonding patterns. 4. An evaluation the Relation time of modified soft liner. The soft liner used in this study was commercially available as Coe-soft (GC America.IL.,USA), which is provided in forms of powder and liquid. This is a PMMA soft liner commonly used in dental clinics. The metal primer used in this study was 4-META containing primer packed in Meta fast denture base resin (Sun Medical Co., Osaka, Japan). The specimens were formed in a single lap joint desist which is useful for evaluating the apparent shear bond strength of adhesively bonded metal plate by tensile loading. Using the $20{\times}20mm$ transparent grid, percent area of adhesive soft liner remaining on the shear area was calculated to classify the debonding patterns. To evaluate the change of the initial flow of the modified adhesive soft liner, the gelation time was measured with an oscillating rheometer (Haake RS150W/ TC50, Haake Co., Germany). It was a stress control and parallel plate type with the diameter of 35mm. Conclusion. Within the conditions and limitations of this study, the following conclusions were drawn as follows. 1. There was significant increase of bond strength in the 5% 4-META, 10% 4-META containing groups and in the primer coated groups versus the control group(P<0.05). 2. After 2 weeks of aging, no significant increase in bond strength was found except for the group containing 10% 4-META (P<0.05). 3. The gelation times of the modified soft liner were 9.3 minutes for the 5% 4-META containing liner and 11.5 minutes for the 10% 4-META liner. 4. The debonding patterns of the 4-META containing group after 2 weeks of aging were similar to those of immediaely after preparation, but the debonding pattern of the primer group showed more adhesive failure after 2 weeks of aging.

• Journal of Korea Water Resources Association
• /
• v.44 no.5
• /
• pp.363-376
• /
• 2011

1-D hydrodynamic numerical models have been most widely used in the field of flood analysis. The model's input data are upstream/downstream boundaries, roughness coefficients, cross-sections, and so on, and computational distance step and time step are the most important factors in order to guarantee the computational accuracy, stability, and efficiency. In this study, a theoretical explanation is presented for the basis of the previous empirical selection criteria of cross-section's location; also, the estimation technique of computationally variable distance step is proposed to reflect the properties of flow at every computational time step. Combining this technique with 1-D unsteady numerical model, it was applied to two events of Teton dam failure flood and the Han River flood. The numerical experimental results demonstrate that the accuracy and stability is increased when used more interpolated cross-sections and show that the proposed technique of computationally variable distance step has the same order of accuracy with smaller numbers of cross-section than previous empirical selection criteria. The practical use of this technique will be possible to analyze the river floods with high efficiency as well as accuracy and stability.

• Geotechnical Engineering
• /
• v.9 no.4
• /
• pp.103-118
• /
• 1993

This paper presents the results of investigation of the rainstorm induced landslides occurred in the districts of Yongin, Ansung and Osan on July 21st 1991. More than two thousand and sirs hundred landsilides took place during or after a 3-t hours heavy rainfall and about 466 ha mountain slopes were affected by slope failures. The result of study on the effect of-iainfall on landslides shows that landslides began to occur where daily and maximum hourly rainfall exceeded 114mm and 40mm respectively, and all districts (myun) where maximum hourly rainfall exceeded 62mm were affected by landslides. The morphological study on landslides on Talbongsan area reveals that, by Walker's classi fication using D IL(failure depth ratio), 50% of the landslides were classified as flows, 20% of them as translational slides, and 30% were between flow and slide and there were few rotational slides. Over 90% of landslides tookplace at slopes of 20$^{\circ}$-40$^{\circ}$ in slope and 50m or shorter in length And more than 50% of the crown of slides locates at higher than 0.7 times of slope hight. Any differences between the kinds of tree in landslide resisting effects are shown in this case.

• Journal of the Korea Concrete Institute
• /
• v.20 no.2
• /
• pp.147-156
• /
• 2008

In an uniaxial compressive test of a concrete standard specimen (150$\times$300 mm) the crack initiation and extension with the stress increase are the major reason of the failure, which is similar to the breakage of the particle bonding in the simulation by using particle bonded model, especially particle flow code in 3 dimensions (PFC3D) developed by Itasca Consulting Group Inc. That is the main motive to study the possibility of an uniaxial compressive strength test simulation. It is important to investigate the relationship between the micro-parameters and the macro-properties because the 3-dimensional particle bonded model uses the spherical particles to analyze the physical phenomena. Contact bonded model used herein has eight micro-parameters and there are five macro-properties; Young's modulus, Poisson's ratio, uniaxial compressive strength and the crack initiation stress and the ratio concerning the crack propagation with the stress. To simulate the compressive test we made quantitative relationships between the micro-parameters and the macro-properties by using the fractional factorial design and various sensitivity analyses including regression analysis, which result in the good agreement with the previous studies. Also, the stress-stain curve and the crack distribution over the specimen given by PFC3D showed the mechanical behavior of the concrete standard specimen under the uniaxial compression. It is concluded that the particle bonded model can be a good tool for the analyzing the mechanical behavior of concrete under the uniaxial compressive load.

• The Journal of Engineering Geology
• /
• v.27 no.2
• /
• pp.125-132
• /
• 2017

Approximately 64 percent of Korean territory is covered with mountains, and there is occurred a continuous mountain disaster such as landslide, debris flow and slope failure around mountain slopes due to heavy rainfall and typhoon in the summer season. Even in such a reality, the development of mountain areas is being carried out through the development and expansion of social infrastructures centered on mountain areas, but systematic management is insufficient. Constructions of a forest road facility for mountain slopes can be a cause of mountain disasters intensively in the summer season due to artificially changing the mountain area. In this unstable mountain environment, efforts to build a disaster-resistant environment are urgently needed. This research is to analyze the stability of mountain slopes according to soil depth (1~5 m) and mountain slope ($20{\sim}60^{\circ}$) considering the characteristics of rainfall infiltration under extreme rainfall conditions. As a result, the stability of the mountain slope was found to be different according to the depth of soils and the saturation area of the soil layer. As well as the stability of the mountain area was found to be lower than that of the natural mountain area. Specially, rainfall infiltration occurs at the upper slope of the forest road. For this reason, the runoff phenomenon of rainfall infiltration water occurs clearly when the depth of soil layer is low.

• Journal of the Korean Institute of Gas
• /
• v.14 no.6
• /
• pp.15-20
• /
• 2010

Compressed Natural Gas (CNG) buses have been supplied since the year 2000 in order to resolve severe atmospheric pollution in metropolitan area and contributed on the improvement of urban atmospheric environment. However, it is indispensible to take an adequate measure to guarantee the safety of CNG vehicles because of the possibility of huge fire accident. A receptacle, connecting device between high pressure fuel supply tank and fuel line, plays an important role in CNG supply system. In recent, leakage of CNG from receptacles has been reported. So, the concern about the security and reliability of receptacles has been arisen. Therefore, a lot of efforts to prevent leakage are invested among researchers and the durability of this component should be guaranteed despite repeated operation. This research has performed durability tests of a CNG receptacle regarding the repeated usage, extreme chattering, and continuous full flow test. Although a receptacle used for CNG vehicle satisfies validation requirements in the test results, it has been found that failure in the function of leakage prevention in a receptacle could take place in the case of prolonged exposure to high supply pressure in common quick charging environment on site.