• Coupled systems mechanics
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• 제9권5호
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• pp.455-471
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• 2020

This paper presents the results of the study of vertically natural frequency of tractor tires are effected by changing different ground contacts and inflation pressures using the Free Decay Method. The results show that the natural frequencies of the tire are not affected while the vertical acceleration increased strongly due to the increase of inflation pressure when the tire performs free decay vibration on rigid ground. In addition, the number of natural frequency peaks of the tire also increases with increasing tire inflation pressure. On the other hand, the natural frequencies of the tractor tire increases strongly while the vertical acceleration decreases slightly with the increase of tire inflation pressure as the tire performs free decay vibration on soft soil. Further, the natural frequencies of tire-soil system are always higher than that of tire only, and it changed with changing the soil depth. Results also show the natural frequency of tire and tire-soil system is in the range of 3.0 to 10.0 Hz that lie within the most critical natural frequency range of the human body. These findings have to be mentioned and used as design parameters of the tractor suspension system.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 임시총회 및 추계학술발표회
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• pp.450-452
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• 2004

Using factor analysis and bivariate comparisons of major components in ground water, three geochemical processes were identified as controlling factors of ground water chemistry; 1) natural mineralization by water rock interactions, 2) effect of seawater which includes salinization by seawater near seashores and deposition of sea salt, and 3) nitrate contamination by N fertilization. Contribution of rainfall was also estimated from the measured composition of wet deposition. The geochemical processes were separated using total alkalinity as an indicator for natural mineralization, Cl for effect of seawater, and nitrate for N fertilization. Relatively high correlation of major components with nitrate suggests that nitrification of nitrogenous fertilizers significantly affects ground water chemistry. Total cations derived from nitrate sources have good linearity for nitrate in equivalent basis with a slope of 1.8, which is a mean of proton production coefficients in nitrification of two major compounds in nitrogenous fertilizers, ammonium and urea. Contribution of nitrate sources to base cations, Cl, and SO$_4$ in ground water was determined considering maximum contribution of natural mineralization to estimate a threshold of the effect of N fertilization for ground water chemistry, which shows W fertilization has a greatest effect than any other processes in ground water with nitrate concentration greater than 50 mg/L for Ca, Mg, Na and with concentration greater than 30 mg/L for Cl and SO$_4$.

• 토지주택연구
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• 제6권1호
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• pp.31-39
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• 2015

공동주택 아파트의 조경공간이 변화하고 있다. 지하주차장 조성 면적이 증가하면서 자연지반 면적이 감소되었다. 그 결과 단지 대부분의 조경공간이 인공지반으로 전환되고 있다. 이에 본 연구는 공동주택 식재공간의 현재 토양품질 실태를 분석하여 단지 내 조경공간의 토양품질 관리를 위한 시사점 제시를 목적으로 한다. 이를 위해 토양반입형태가 상이한 3개 사업지구 대상으로 총 17개의 물리성 및 화학성 항목을 조사하여 현 토양품질수준을 진단하였다. 그리고 통계분석(T-test 검증)을 수행하여 지반특성별과 공정주체별 토양 품질의 유의성을 검토하였다. 그 결과, 대규모 지하통합주차장을 갖는 공동주택 단지의 토양수준은 인공토양 식재기준과 비교하여 낮은 것으로 분석되었다. 특히, 가시적 판단이 용이한 물리성은 양호하나 화학성 품질개선이 필요한 것으로 나타났다. 또한 공동주택 지반특성별 토양 품질과 담당공종별 토양 품질의 차이는 없는 것으로 분석되었다(유의수준 5%). 일반적으로 인공지반보다 자연지반의 식재환경이 양호하다는 인식이지만 실제 분석결과 토양품질에 있어서는 자연지반의 토양이 인공지반 토양 품질수준과 동일한 것으로 나타나, 자연지반 토양에 대한 관리기준 도입의 필요성을 제시하였다. 그리고 공종별 담당부서가 상이함에도 불구하고 동일한 수준의 토양이 반입되고 있는 점은 바람직하나 그 토양수준이 상대적으로 낮은 것으로 나타나 품질제고를 위한 관리강화가 필요한 것으로 나타났다.

• 충청수학회지
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• 제33권3호
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• pp.339-349
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• 2020

Let P ⋊ ℕ^x be a semidirect product of an additive semigroup P = {0, 2, 3, ⋯ } by a multiplicative positive natural numbers semigroup ℕ^x. We consider a covariant semigroup C^∗-algebra 𝓣(P ⋊ ℕ^x) of the semigroup P ⋊ ℕ^x. We obtain the condition that a state on 𝓣(P ⋊ ℕ^x) can be a ground state of the natural C^∗-dynamical system (𝓣(P ⋊ ℕ^x), ℝ, σ).

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.65-72
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• 2001

Since Pyoungtaek thermal power plant began using natural gas in 1986, the annual using volume has rapidly increased and reached 12.7 million tons in 1999. When the natural gas is cooled to a temperature of approximately -162$^{\circ}$C at atmospheric pressure, it condenses to a liquid called liquefied natural gas(LNG). LNG has a special characters such as odorless, colorless, non-corrosive, and non-toxic. So, LNG storage tank, tanker ship, transfer pipelines are required the special storage and transportation systems and technology. The presently operating LNG terminals are Pyongtaek and Inchon terminals. A total of 19 above-ground LNG storage tanks(100 thousand ㎘ grade) are currently in operation with a sendout capacity of 4,360tons/hour. To meet the growing domestic demand of LNG supply, the Inchon receiving terminal is expanding(six in-ground tank) and constructing a third LNG terminal at Tongyong. In this paper, case study on seepage analysis and countermeasure against increasing the seepage volume of in-ground LNG storage tank excavation work is reported. The results of an additional seepage analysis are presented to verify the design seepage volume of assumption section and seepage volume after curtain-grouting in the slurry wall.

• 한국안전학회지
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• 제13권2호
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• pp.54-64
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• 1998

This study was initiated to examine the stress and deformation characteristics of the pipelines which were subjected to various environmental conditions in order to confirm their integrity. As the part of them, this paper presents the analysis results for the effect of ground subsidence combined with main loads on buried natural gas pipelines. The ground subsidence which can occur for buried gas pipeline has been classified to the three cases. Finite element method was used to analyze the effect of ground subsidences on pipeline of 26 inch(0.660 m) and 30 inch(0.762 m) diameter used as high pressure ($70 kg_f/cm^2(6.86 MPa)$) main pipelines of KOGAS. This paper shows the result of stress analysis for the pipelines subjected to those three case ground subsidence. Comparing these results with safety criterion of KOGAS(0.9 $\sigma_y$), maximum allowable settlement and loads have been calculated.

• 한국군사과학기술학회지
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• 제10권4호
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• pp.176-184
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• 2007

The missile for this study has shown different natural frequency characteristics depending on the test conditions; natural frequencies obtained from its flight test are higher than those in its ground test. It was found that the hinged joints connecting front airframe to rear one had the nonlinear stiffness and caused the missile to show very complex dynamic characteristics. The angular stiffness at hinged joints was calculated using 3D finite element analysis, and it was verified that there was a highly nonlinear relationship between angular stiffness and external load. Natural frequencies calculated considering the nonlinearity of angular stiffness were nearly the same as test results. Through this study, the dynamic characteristics of a missile having split airframes with hinged joints could be clearly identified and a way of maintaining its natural frequencies consistent was generated.

• 대한기계학회논문집A
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• 제28권4호
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• pp.325-332
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• 2004

Tire vibration modes are known to play a key role in vehicle ride and comfort characteristics. Inputs to the tire such as impacts, rough road surface, tire nonuniformities, and tread patterns can potentially excite tire vibration. In this study, experimental modal analysis on the tire with ground contact are performed by impacting the tire in the radial direction at the center of contact patch. To investigate which modes of tire influence the vibration of wheel and axle when the tire is in contact with ground, the vibration characteristics such as frequency response functions, natural frequencies and their mode shapes from tire to wheel/axle are examined.

• 한국군사과학기술학회지
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• 제23권3호
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• pp.257-266
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• 2020

It is very important to share tactical information such as video, images, and text messages among soldiers for situational awareness. Under the wireless environment of the battlefield, the available bandwidth varies dynamically and is insufficient to transmit high quality images, so it is necessary to minimize the distortion of the area of interests such as targets. A natural operating method for soldiers is also required considering the difficulty in handling while moving. In this paper, we propose a natural ROI(region of interest) setting and image compression method for effective image sharing among soldiers. We verify the proposed method through prototype system design and implementation of eye gaze detection and ROI-based image compression.

• 한국기계기술학회지
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• 제20권6호
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• pp.894-900
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• 2018

Among the soft ground improvement methods, PBD is the most common construction method because it is cheap and construction is fast. However, if the ground is rigid, additional work is required. In this study, the structural safety, natural vibration, and safety angle of the steel vertical tower structure were evaluated in the development of the PBD composite perforator which can be combined with drilling work and PBD construction. Structural safety was assessed when the wind load of 20 m/s was simultaneously applied to the PBD construction load of 20 tons, the perforating operation of 25 tons, and the wind speed of 50 m/s was applied only to the wind load. The natural frequencies were evaluated up to the sixth mode, and the safety angle was evaluated for static and dynamic safety angles.