• Structural Engineering and Mechanics
• /
• 제56권1호
• /
• pp.49-56
• /
• 2015

Dynamic compaction (DC) is a useful method for improvement of granular soils. The method is based on falling a tamper (weighting 5 to 40 ton) from the height of 15 to 30 meters on loose soil that results in stress distribution, vibration of soil particles and desirable compaction of the soil. Propagation of the waves during tamping affects adjacent structures and causes structural damage or loss of performance. Therefore, determination of the safe or critical distance from tamping point to prevent structural hazards is necessary. According to FHWA, the critical distance is defined as the limit of a particle velocity of 76 mm/s. In present study, the ABAQUS software was used for numerical modeling of DC process and determination of the safe distance based on particle velocity criterion. Different variables like alluvium depth, relative density, and impact energy were considered in finite element modeling. It was concluded that for alluvium depths less than 10 m, reflection of the body waves from lower boundaries back to the soil and resonance phenomenon increases the critical distance. However, the critical distance decreases for alluvium depths more than 10 m. Moreover, it was observed that relative density of the alluvium does not significantly influence the critical distance value.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2009년도 춘계 학술발표회
• /
• pp.888-895
• /
• 2009

Compaction is a process of increasing soil density using physical energy. It is intended to improve the strength and stiffness of soil. In embankment, degree of compaction affects the construction time, money, also method of soil improvement. In large scale embankment project, difficulties of embankment should change due to uncertainty of settlement. So it is very important to predict the final settlement and factor of safety induced by embankment. In many construction site, there are primarily design of high embankment using in-situ soil. Therefore numerical analyses are necessary for valid evaluation of the settlement prediction. But due to the construction cost and schedule, there were lacking in properties of soil and also limited number of in-situ test were performed. So we proposed the method that can easily estimate the proper soil parameters and suggest the proper method of numerical analysis. From this, two-dimensional finite-difference numerical analysis was conducted to investigate the settlement and factor of safety induced by embankment with various case of compaction rate and embankment height.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1993년도 학술발표집 지반진동 영향평가
• /
• pp.55-72
• /
• 1993

동다짐은 무거운 다짐추를 고공에서 낙하시켜 낙하시 지반에 가하는 충격을 이용하여 지반을 개량하는 공법으로서, 시공시 발생하는 진동에 의하여 주변 구조물매 피해가 유발될 수도 있다. 본 연구는 쓰레기 매립지반에서 동다짐을 시공할시 수행된 진동 측정자료들을 분석하였으며 그 결과 다음과 같은 사실들을 확인할 수 있었다. \circled1 동다짐시 발생하는 진동의 입자속도는 Longitudinal, vertical, Transversal 방향순으로 그 크기가 크며, 체감을 또한 Lcugitudinal, Vertical, Transversal 방향순으로 큰 것으로 나타났다. \circled2동다짐시 발생하는 진동의 탁훨 진동수는 7-9 Hz내외이다. \circled3구조물에 인접한 동다짐은 다짐추의 낙하고를 저하시켜 충격에너지를 감소시켰으며, 이를 이용하여 구조물께 대한 피해를 애방할 수 있었다. \circled4사무기기는 켜놓은 상태가 꺼놓은 상태보다 진동에 대하여 약하므로 사무기기에 대한 진동피해를 줄이기 위하여는 비 업무시간을 이용하여 사무실에 10m까지 인접하여 동다짐을 실시할 수 있었다.

• 임산에너지
• /
• 제22권2호
• /
• pp.54-59
• /
• 2003

최근 들어 북미와 유럽에서는 고밀화한 목질펠릿연료가 재생가능하며 카본뉴트럴한 바이오매스 에너지로서 널리 사용되고 있다. 본 연구에서는 현사시 톱밥의 고밀화를 통한 고형연료화에 관하여 연구하였다. 현사시 품종의 연료적 가치를 평가하기 위하여 열량 및 원소 분석을 수행하였다. 고밀화를 위하여 열압공정을 채택하였으며, 압밀화는 100∼180℃, 250∼1000 kgf/㎠, 2.5∼10분의 조건으로 행하였다. 고밀화연료의 특성은 밀도와 미세분 발생량으로 평가하였다. 목표치로서 고밀화연료의 전건밀도는 1.2 g/㎠ 이상, 5분간 진탕 후의 미세분 발생량은 0.5% 이하로 설정하였다. 목표 밀도와 목표미세분을 만족하기 위해서는 160℃ 이상의 압체온도가 요구되었다. 이 때의 압체압력은 750 kgf/㎠ 이상이 효과적이었다 180℃에서 1000 kgf/㎠으로 5분 이상의 압체가 고밀화연료 제조에 가장 적절한 조건으로 밝혀졌다.

• 대한기계학회논문집A
• /
• 제27권7호
• /
• pp.1076-1086
• /
• 2003

The effect of a rubber mould on densification behavior of aluminum alloy powder was investigated under cold isostatic compaction. A thickness of rubber mould and friction effect between die wall and rubber mould were also studied. The hyperelastic constitutive equation based on the Ogden strain energy potential was employed to analyze deformation of rubber. The elastoplastic constitutive equation of Shima and Oyane and that of Lee on densification were implemented into a finite element program (ABAQUS) to simulate densification of metal powder for cold isostatic pressing and rubber isostatic pressing. Finite element results were compared with experimental data for densification and deformation of aluminum alloy powder under isostatic compaction.

• 한국환경과학회지
• /
• 제20권1호
• /
• pp.71-79
• /
• 2011

In this study, a series of soil concrete mixtures were tested for the compressive strength according to ratio of aggregate to binder, compaction energy, maximum aggregate size, ratio of silica fume to cement, and ratio of water to binder. The optimum mixing ratio of soil concrete mixtures composed of volcaniclastic, cement, silica fume, concrete polymer and water were analysed. The test results for optimum proportion were as follows ; (1)ratio of aggregate to binder was 4 : 1, (2)compaction energy level was level 2, (3)maximum aggregate size was 13 mm, (4)ratio of silica fume to cement was 10%, (5)ratio of water to binder was 25%. Also, dry type construction techniques were applied using the optimum soil concrete mixture. From the results of this study, the compressive strength of soil concrete and construction techniques were suitable for making eco-friendly soil pavement.

• 한국통신학회논문지
• /
• 제21권5호
• /
• pp.1141-1154
• /
• 1996

The para-unitary (PU) M band filter bank, which can beused for M band decomposition, has many useful properties. In this ppaer, attempts have been made to design and and analyze the linear phase para-unitary (LPPU) M band filter bank, which is appropriate to the image coding application. First, we derive a unified coding gain in terms of the correlation in the band, as well as the energy compaction. And M band filter bank has been designed, maximizing the new coding gain. Then, we analyze the image coding performance of the LPPU M band filter bank, such as the energy compaction, the correlation in the band and the entropy. From the analysis, it is shown that the coding gain for LPPU M band filter bank improves, and the coding gain for the LPPU 4 band filter bank approaches very closely to that for LPPU 8 band filter bank, as the length of the filter increases. This fact is also verified by the coding results on the real images.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 춘계학술강연 및 발표대회강연 및 발표논문 초록집
• /
• pp.54-54
• /
• 2006

• 농업과학연구
• /
• 제14권2호
• /
• pp.329-344
• /
• 1987

과압밀비(過壓密比)와 전단속도(剪斷速度) 및 다짐율(率)이 점성토(粘性土)의 응력변형특성(應力變形特性)에 미치는 영향(影響)을 검토(檢討)하기 위해서 반부극하(反復戟荷)에 의(依)한 삼축압축시험(三軸壓縮試驗)을 한 결과(結果)를 요약(要約)하면 다음과 같다. 1. 반부재하(反復載荷)를 했을 때 같은 변형(變形)에서 축차응력의 차(差)는 큰 변형(變形)에서 반부재하(反復載荷)했을 때 더욱 크게 나타났고 공극수압(空隙水壓)은 제하시(除荷時)에는 감소(減少)하다가 다시 증가(增加)하며 재재하(再載荷)되면서 급격히 증가하는 현상(現象)을 나타냈다. 2. 과압밀비(過壓密比)가 클수록 변형(變形)의 증가(增加)에 따라 회복되는 탄성변형률은 감소(減少)하였으며 제일재하계수(除一載荷係數)는 과압밀비가 증가(增加)할수록 감소(減少)하였다. 3. 전단속도(剪斷速度)가 증가(增加)함에 따라 탄성변형율(彈性變形率)은 증가(增加)하였고 변형(變形)의 증가(增加)에 따라 탄성변형율(彈性變形率)은 감소(減少)하였다. 제일재하계수(除一載荷係數)는 변형(變形)이 증가(增加)함에 따라 감소(減少)하였고 전단속도(剪斷速度)가 빠른 경우에 큰 값을 나타냈다. 4. 회복되는 탄성변형율(彈性變形率)은 다짐율이 증가(增加)함에 따라 크게 나타났고 또 변형(變形)이 증가(增加)함에 따라 탄성변형율(彈性變形率)은 약간 감소(減少)하는 경향(傾向)을 나타냈다. 제일재하계수(除一載荷係數)는 다짐율(率)의 증가(增加)에 따라 뚜렷한 경향(傾向)은 보이지 않았으나 일반적(一般的)으로 변형(變形)이 증가(增加)함에 따라 감소(減少)하는 경향(傾向)을 나타냈다.

• 한국재료학회지
• /
• 제28권3호
• /
• pp.166-173
• /
• 2018

Molybdenum (Mo) is one of the representative refractory metals for its high melting point, superior thermal conductivity, low density and low thermal expansion coefficient. However, due to its high melting point, it is necessary for Mo products to be fabricated at a high sintering temperature of over $1800-2000^{\circ}C$. Because this process is expensive and inefficient, studies to improve sintering property of Mo have been researched actively. In this study, we fabricated Mo nanopowders to lower the sintering temperature of Mo and tried to consolidate the Mo nanopowders through ultra high pressure compaction. We first fabricated Mo nanopowders by a mechano-chemical process to increase the specific surface area of the Mo powders. This process includes a high-energy ball milling step and a reduction step in a hydrogen atmosphere. We compacted the Mo nanopowders with ultra high pressure by magnetic pulsed compaction (MPC) before pressureless sintering. Through this process, we were able to improve the green density of the Mo compacts by more than 20 % and fabricate a high density Mo sintered body with more than a 95 % sintered density at relatively low temperature.