• Journal of Biosystems Engineering
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• 제42권2호
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• pp.117-125
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• 2017

Purpose: Damage to pulse crops by wild birds is a serious problem. The damage is to such an extent that the rate of damage during the period between seeding and cotyledon stages reaches 54.6% on an average. In this study, a crop-position detection method was developed wherein infrared (IR) sensors were used to determine the cotyledon position under a vinyl mulch. Methods: IR sensors that helped measure the temperature were used to locate the cotyledons below the vinyl mulch. A single IR sensor module was installed at three locations of the crops (peanut, red lettuce, and crown daisy) in the cotyledon stage. The representative thermal response of a $16{\times}4$ pixel area was detected using this sensor in the case where the distance from the target was 25 cm. A spatial image was applied to the two-dimensional temperature distribution using a non-integral moving-average method. The collected data were first processed by taking the moving average via interpolation to determine the frame where the variance was the lowest for a resolution unit of 1.02 cm. Results: The temperature distribution was plotted corresponding to a distance of 10 cm between the crops. A clear leaf pattern of the crop was visually confirmed. However, the temperature distribution after the normalization was unclear. The image conversion and frequency-conversion graphs were obtained based on the moving average by averaging the points corresponding to a frequency of 40 Hz for 8 pixels. The most optimized resolutions at locations 1, 2, and 3 were found on 3.4, 4.1, and 5.6 Pixels, respectively. Conclusions: In this study, to solve the problem of damage caused by birds to crops in the cotyledon stage after seeding, the vinyl mulch is punched after seeding. The crops in the cotyledon stage could be accurately located using the proposed method. By conducting the experiments using the single IR sensor and a sliding mechanical device with the help of a non-integral interpolation method, the crops in the cotyledon stage could be precisely located.

• 대한기계학회논문집A
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• 제20권8호
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• pp.2555-2560
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• 1996

Inspecting the dimensional accuracy of a car-body in assembly line is a very important process to assure high productivity. Now there exist two common inspecting methods in practice. One is to measure a sampled car-body with three dimensional measuring machine, and the other is to measure car-body with three dimensional measuring machine, and the other is to measure car-body in assembly line using many sensors fixed to a large jig frame. The formal method takes too long to inspect a sampled car-body of a same sort, and cannot therefore give an useful error trend for the whole production. On the other hand, the latter lacks flexibility and is very cost-intensive. By using industrial robots and sensors, an in-line Car-Body Measuring(CBM) system which ensured high flexiblity and sufficient accuracy was developed. This CBM cell operates in real production line and measures the check points by the non-contact type using camera and laser displacement sensor(LDS). This system can handle about 15 Measuring points within a cycle time of 40 seconds. A process computer controls whole process such as data acquisition file handling and data analysis. Robot arms changes in length due to ambient temperature fluctuation affecting the measuring accuracy. To compensate this error, a robot arm calibration process was developed.

• Steel and Composite Structures
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• 제18권1호
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• pp.187-212
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• 2015

In this paper, various four variable refined plate theories are presented to analyze vibration of temperature-dependent functionally graded (FG) plates. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations for the present model is reduced, significantly facilitating engineering analysis. These theories account for parabolic, sinusoidal, hyperbolic, and exponential distributions of the transverse shear strains and satisfy the zero traction boundary conditions on the surfaces of the plate without using shear correction factors. Power law material properties and linear steady-state thermal loads are assumed to be graded along the thickness. Uniform, linear, nonlinear and sinusoidal thermal conditions are imposed at the upper and lower surface for simply supported FG plates. Equations of motion are derived from Hamilton's principle. Analytical solutions for the free vibration analysis are obtained based on Fourier series that satisfy the boundary conditions (Navier's method). Non-dimensional results are compared for temperature-dependent and temperature-independent FG plates and validated with known results in the literature. Numerical investigation is conducted to show the effect of material composition, plate geometry, and temperature fields on the vibration characteristics. It can be concluded that the present theories are not only accurate but also simple in predicting the free vibration responses of temperature-dependent FG plates.

• 한국대기환경학회지
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• 제25권4호
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• pp.304-315
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• 2009

Numerical simulations were carried out to understand the effect of Sea Surface Temperature (SST) spatial distribution on regional circulation. A three-dimensional non-hydrostatic atmospheric model RAMS, version 6.0, was applied to examine the impact of SST forcing on regional circulation. New Generation Sea Surface Temperature (NGSST) data were implemented to RAMS to compare the results of modeling with default SST data. Several numerical experiments have been undertaken to evaluate the effect of SST for initialization. First was the case with NGSST data (Case NG), second was the case with RAMS monthly data (Case RM) and third was the case with seasonally averaged RAMS monthly data (Case RS). Case NG showed accurate spatial distributions of SST but, the results of RM and RS were $3{\sim}4^{\circ}C$ lower than buoy observation data. By analyzing practical sea surface conditions, large difference in horizontal temperature and wind field for each run were revealed. Case RM and Case RS showed similar horizontal and vertical distributions of temperature and wind field but, Case NG estimated the intensity of sea breeze weakly and land breeze strongly. These differences were due to the difference of the temperature gradient caused by different spatial distributions of SST. Diurnal variations of temperature and wind speed for Case NG indicated great agreement with the observation data and statistics such as root mean squared error, index of agreement, regression were also better than Case RM and Case RS.

• 대한기계학회논문집B
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• 제26권6호
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• pp.859-867
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• 2002

Radiative transfer in energy systems such as furnaces, combustors, boilers and high temperature machineries is a significant mode of heat transfer. Although there are many solution schemes suggested for analysis of radiative transfer in multi-dimensional systems, the applicabilities and accuracies of these schemes have not fully tested for nongray gases. Especially reference data for enclosures of non-orthogonal shapes are not yet enough. In this paper we present some precise radiative transfer solutions for a black walled 3-dimensional cylindrical system filled with nongray gases. The SNB(statistical narrow band) model and the ray-tracing method with the T$_{N}$ quadrature set are used for finding nongray solutions. Although the solution method used in this study is not suitable for engineering purposes, the resulting solutions are proved to be quite accurate and can be regarded as the exact solutions and the results presented in this paper can be used in developing various solution schemes fur radiative transfer by real gas mixtures.s.

• 소성∙가공
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• 제19권3호
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• pp.152-159
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• 2010

Rapid mold heating has been recent issue to enable the injection molding of thin-walled parts or micro/nano structures. High-frequency induction is an efficient way to heat mold surface by electromagnetic induction in a non-contact manner, and has been recently applied to the injection molding due to its capability of rapid heating and cooling of mold surface. The present study covers a three-dimensional finite element analysis to investigate heating efficiency and structural safety of the induction heating process of an injection mold. To simulate the induction heating process, an integrated simulation method is proposed by effectively connecting an electromagnetic field analysis, a transient heat transfer analysis and a thermal stress analysis. The estimated temperature changes are compared with experimental measurements for various types of induction coil, from which heating efficiency according to the coil shape is discussed. The resulting thermal stress distributions of the mold plate for various types of induction coils are also evaluated and discussed in terms of the structural safety.

• 대한기계학회논문집A
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• 제35권11호
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• pp.1437-1443
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• 2011

선박 건조를 위한 기본 자재인 후판은 압연공정을 통해 생산된다. 본 논문에서는 후판압연 중에 발생하는 폭방향 휨을 일으키는 비대칭 요인들을 제어할 수 있는 설정모델을 제시한다. 일련의 삼차원 유한요소해석을 통해서 휨과 비대칭 요인 사이의 관계를 예측한다. 그 관계를 무차원 변수로 이루어진 선형 방정식으로 수식화 시킴으로써 설정모델을 도출한다. 소재 폭방향으로 두께 편차와 온도차이가 있는 경우에 대해서 파이롯트 압연 시험으로 통해서 설정모델의 정도를 검증한다. 본 모델에 의해 예측된 휨 곡률이 각각의 비대칭 요인들에 의해 측정된 휨 곡률과 상당히 일치하는 결과를 보여 주었다.

• Steel and Composite Structures
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• 제26권5호
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• pp.533-547
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• 2018

In this paper the time-dependent creep analysis of a thick-walled FG cylinder with finite length subjected to axisymmetric mechanical and thermal loads are presented. First order shear deformation theory (FSDT) is used for description of displacement components. Inner and outer temperatures and outer pressure are considered as thermo-mechanical loadings. Both thermal and mechanical loadings are assumed variable along the axial direction using the sinusoidal distribution. To find temperature distribution, two dimensional heat transfer equation is solved using the required boundary conditions. The energy method and Euler equations are employed to reach final governing equations of the cylinder. After determination of elastic stresses and strains, the creep analysis can be performed based on the Yang method. The results of this research indicate that the boundaries have important effects on the responses of the cylinder. The effect of important parameters of this analysis such as variable loading, non-homogeneous index of functionally graded materials and time of creep is studied on the behaviors of the cylinder.

• 대한토목학회논문집
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• 제28권1A호
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• pp.105-113
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• 2008

곡선 강박스거더교는 부분적인 일사에 의해 교량단면에 불균등한 온도분포와 함께 기타 불리한 하중조건이 복합되어 작용되므로 교량의 수명이 단축되거나 사용성을 저하시킬 수 있는 문제점을 가지고 있다. 따라서 곡선교 설계 시 방위각, 받침배치방식, 형상 등에 따라 온도에 의한 영향을 고려해야 하지만 온도거동의 특성이 명확히 규명되어 있지 않을 뿐만 아니라 현행 설계기준의 규정도 명확하지 못하여 보다 많은 연구가 필요한 실정이다. 본 연구에서는 기존의 연구에서 제안된 일사량 계산식과 열전달 유한요소해석기법을 병용하여 곡선 강박스거더교의 기하학적 형상 및 방위각에 따라 변화하는 온도분포를 보다 쉬운 방법으로 예측하는 기법을 개발하였고 실측된 곡선교의 온도자료를 통해 검증하였다. 또한, 개발된 온도분포예측기법과 3차원 구조해석을 이용하여 일사에 의한 곡선교의 거동을 분석한 결과, 곡선 외측면이 남측을 향하는 경우에서 고정단측 받침의 교축방향과 교축직각방향 반력이 크게 나타났으며 곡선반경이 감소할수록 모든 방향의 반력이 증가하는 경향을 보였다. 본 연구에서 제안한 온도분포예측기법을 바탕으로 향후 관련 연구를 통해 현재의 설계기준을 보완할 수 있는 합리적인 온도하중의 제시가 가능할 것으로 판단된다.

• 한국안전학회지
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• 제30권6호
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• pp.18-25
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• 2015

Computational study of a gravity current prior to the backdraft was conducted using fire dynamic simulator (FDS). Various initial conditions of mixture compositions and compartment temperature as well as four opening geometries (Horizontal, Door, Vertical, and Full opening) were considered to figure out their effects on the gravity current. The density difference ratio (${\beta}$) between inside and outside of compartment, the gravity current time ($t_{grav}$) and velocity ($v_{grav}$), and non-dimensional velocity ($v^*$) were introduced to quantify the flow characteristics of the gravity current. Overall fluid structure of the gravity current at the fixed opening geometry showed similar development process for different ${\beta}$ conditions. However, $t_{grav}$ for entering air to reach the opposed wall to the opening geometry increased with ${\beta}$. Door, Vertical, and Horizontal openings where openings are attached on the ground showed similar development process of the gravity current except for Horizontal opening, which located on the middle of the opening wall. The magnitude of $v_{grav}$ at fixed ${\beta}$ was, from largest to smallest, Full > Vertical > Door > Horizontal, but it depended on both the size and location of the opening. On the other hand, $v^*$ was found to be independent to ${\beta}$, and only depended on the geometry of the opening.