• Journal of Biosystems Engineering
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• 제14권4호
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• pp.229-241
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• 1989

The purposes of this study were to develop an electronic-hydraulic draft control system for tractor implements, to investigate the control performance of the system and the possibility of adaptation to the conventional tractor. Experiments were carried out to investigate the responses of the system to the step and sinusoidal inputs in draft control. The effects of control mode, hydraulic flow rate, reference deadband, and proportional constant on control performance of the system were investigated. Moreover, the effects of filtering signals from draft sensor were also investigated. The following conclusions were derived from the study; 1. In draft control, there were hunting problems in controlling the implement without filtering the draft signals. Filtering was performed by a control program of electronic controller and the control performance and stability of the system were improved significantly. 2. For the draft control system operated on on-off control mode, draft was controlled within ${\pm}27-{\pm}55kg_f$ to the reference draft when the hydraulic flow rates were 5-15 l/min. For the draft control system operated on PWM control, draft was controlled within ${\pm}27kg_f$ to the reference draft regardless of hydraulic flow rates. 3. In the frequency responses of the draft control system, control performance on PWM control mode was not better than on on-off control mode because of characteristics of hydraulic valve and drafe sensor. As the hydraulic flow rates increased for the system operated on on-off control mode, the corner frequency of amplitude attenuation increased, but the corner frequency of phase-angle change remained nearly the same. But, the system was unstable beyond the frequency of 3.1 rad/s. 4. The electronic-hydraulic hitch control system developed in this study showed superior control performance, stability and convenience compared to conventional mechanical-hydraulic hitch control system. It is considered to be a superior replacement for the conventional mechanical-hydraulic hitch control system.

• Journal of Biosystems Engineering
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• 제22권2호
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• pp.117-126
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• 1997

A series of soil bin experiment was carried out on sandy loam to investigate if it is possible to predict implement draft by some analog tool. Chisel configuration resembling a cone penetrometer section was used as an analog tool. The angle of cone was 30 degree. Three types of tillage implement, or oriental janggi, moldboard plow and chisel plow were chosen for this study. Experimental tillage speed was 0.22, 0.33, 0.49 m/s ad tillage depth was 8, 12, 16cm. For the experimental tillage speed range, the increase of tillage speed did not affect the tillage draft for the three types of implement and analog tool, but as the tillage depth increased, tillage draft of the three types of implement and analog tool increased linearly. The linear relationship was found between the tillage draft of analog tool and that of three types of tillage implement for the experimental tillage depth and speed range with high value of $R^2$ Thus it was concluded from the above results that an analog tool can be used to predict the tillage draft of oriental janggi, moldboard plow and chisel plow. But more experiment for various soil types and theoretical verification are needed for more generallization.

• 농업과학연구
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• 제5권2호
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• pp.149-157
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• 1978

동력경운기용(動力耕耘機用) 두류(豆類)의 무경운(無耕耘) 파종기(播種機)에 부착(附着)하여 사용(使用)하는 구절기중(溝切器中)에서 소요색인력(所要索引力)이 작고 구절작업정도(溝切作業精度)가 양호(良好)한 구절기(溝切器)의 개발(開發)을 위(爲)한 기초자료(基礎資料)를 얻기 위(爲)하여 구동식(驅動式) 토조(土槽)에 인공토양(人工土壤)을 채우고 원판형(圓板型) 및 호우형(型) 구절기(溝切器)의 소요색인력(所要索引力)과 이에 영향(影響)을 미치는 인자(因子)들과의 관계(關係)를 구명(究明)코자 실내모형(室內模型) 실험(實驗)을 실시(實施)하여 다음과 같은 결과(結果)를 얻었다. 원판형(圓板型) 구절기(溝切器)에 대(對)하여 직경별(直徑別)로 조립각(組立角)을 $8^{\circ}$와 $16^{\circ}$, 경심(耕深)을 3cm와 6cm로 변화(變化)시키년서 2.75cm/sec의 속도(速度)로 색인력(索引力)을 측정(測定)한 결과(結果) 원판(圓板)의 직경(直徑)이 약(約) 28cm인 경우(境遇)에 색인력(索引力)이 최소(最少)로 나타났고, 직경(直徑)이 이보다 크거나 작은때는 색인력(索引力)은 증가(增加)하는 경향(傾向)을 나타냈으며 비저항(比抵抗)도 대체(大體)로 비슷한 경향(傾向)이었으나 원판(圓板)의 직경(直徑)이 약(約) 30cm일 때 최소(最少)로 나타났다. 종자파종(種子播種)의 심도조절(深度調節)을 목적(目的)으로 작구심(作溝深)(3cm 및 6cm)과 색인력(索引力)과의 관계(關係)를 조사(調査)하였던 바, 경심(徑深)과 색인력(索引力)과의 관계(關係)는 거의 직선적(直線的)인 변화(變化)를 나타냈으며 색인력(索引力)에 영향(影響)을 미치는 인자중(因子中)에서 경심(耕深)의 영향(影響)이 가장 컸음을 알 수 있었다. 일반적(一般的)으로 조립각(組立角) 및 주행속도(走行速度)에 별(別) 영향(影響)없이 경심(耕深) 3cm 및 6cm 공(共)히 색인력(索引力)은 직경(直徑) 약(約) 28cm에서, 비저항(比抵抗)은 약(約) 30cm에서 최소(最少)의 값을 나타내었다. 파종기(播種機)의 작업성능(作業性能)과 관계(關係)가 갚은 주행속도(走行速度) 및 파건(播巾)의 조절(調節)을 목적(目的)으로 원판(圓板)의 조립각(組立角)과 주행속도(走行速度)가 색인력(索引力)에 미치는 영향(影響)을 조사(調査)했던 바, 조립각(組立角)과 주행속도(走行速度)가 증가(增加)함에 따라 모두 색인력(索引力)이 증가(增加)하는 경향(傾向)을 나타내었으나 색인력(索引力)에 미치는 영향(影響)은 주행속도(走行速度)가 더욱 크게 나타났다. 원판형(圓板型) 구절기(溝切器)와 호우형(型) 구절기(溝切器)를 비교(比較)하기 위(爲)하여 쐐기각(角)이 $16^{\circ}$이고 리프트각(角)이 $20^{\circ}$인 호우형(型) 구절기(溝切器)와 조건(條件)이 비슷한 조립각(組立角) $16^{\circ}$의 원판형(圓板型) 구절기(溝切器)의 색인특성(索引特性)을 비교(比較)한 결과(結果) 직경(直徑) 30cm인 원판형(圓板型)의 경우(境遇)는 비저항(比抵抗)이 $0.35{\sim}0.5kg/cm^2$인데 비(比)해 호우형(型)의 경우(境遇)는 $0.71{\sim}1.02kg/cm^2$로 나타나 호우형(型)의 색인비저항(索引比抵抗)이 평균(平均) 2배정도(倍程度) 크게 나타났고 작구상태(作溝狀態)도 원판형(圓板型)의 경우(境遇)보다 불량(不良)하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제36권3호
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• pp.351-357
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• 2012

Small hydropower is a reliable energy technology to be considered for providing clean electricity generation. Producing electrical energy by small hydropower is the most efficient contribution to renewable energy. Cross-flow turbine is adopted primarily because of its simple structure and high possibility of applying to small hydropower. The purpose of this study is to investigate the effect of inlet nozzle shape on the performance and internal flow of a cross-flow turbine for small hydropower by CFD analysis. Moreover, the shape effect of draft tube has been investigated according to modified shapes of the length and the diffuse angle. The results show that relatively narrow and converging inlet nozzle shape gives better effect on the performance of the turbine.

• 드라이브 ㆍ 컨트롤
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• 제20권4호
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• pp.71-79
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• 2023

In the field of agricultural machinery, various on-field tests are conducted to measure design load for optimal design of agricultural equipment. However, field test procedures are costly and time-consuming, and there are many constraints on field soil conditions due to weather, so research on utilizing simulation to overcome these shortcomings is needed. Therefore, this study aimed to model agricultural soils using discrete element method (DEM) software. To simulate draft force, predictions are made according to travel speed and compared to field test results to validate the prediction accuracy. The measured soil properties are used for DEM modeling. In this study, the soil property measurement procedure was designed to measure the physical and mechanical properties. DEM soil model calibration was performed using a virtual vane shear test instead of the repose angle test. The DEM simulation results showed that the prediction accuracy of the draft force was within 4.8% (2.16~6.71%) when compared to the draft force measured by the field test. In addition, it was confirmed that the result was up to 72.51% more accurate than those obtained through theoretical methods for predicting draft force. This study provides useful information for the DEM soil modeling process that considers the working speed from the perspective of agricultural machinery research and it is expected to be utilized in agricultural machinery design research.

• Journal of Biosystems Engineering
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• 제5권2호
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• pp.26-39
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• 1980

A study was investigated to find out the mechanical optimum conditions of power tiller-plow system on both paddy field and upland. Mathematical model was developed for the theoretical analysis of this system and the experimentation on the field was carried out with two different sizes of 5PS and 8PS power tiller equipped with rubber tire. 1) The relationship between the plowing depth and draft resistance of the power tiller-plow system was a quadratic function. 2) The minimum point of the specific draft resistance of the 5 PS plow was found at the smaller plowing depth than that of 8 PS plow, therefore we can find that the curved surface of 5PS plow bottom should be improved for the effective plowing operation. 3) As the improvement of the mechanical balance by the desirable change of the curved surface of plow bottom, the relative position of hitch point and dimension of plow beam would be realized, the 5 PS power tiller could be used to plow deeply (about 16-17cm). 4) The virtual acting point of the total draft resistance on the plow bottom approached to the land side as the plowing depth increased. 5) The resultant of vertical reaction force $R_2$ on the landside was increased with the plowing depth, while the vertical reaction force $R_1$ on the wheel was decreased as the slope angle of the body of power tiller increased. 6) For the effective plowing operations ; a) The slope angle of the body should be as small as possible. b) The diameter of the wheel should be as small possible. c) The horizontal and vertical distances $l_2, h_1$ between the wheel axis and plow bottom should be as large as possible. 7) To use the 5PS power tiller as the major unit of agricultural machinery, the curved surface of the 5 PS plower bottom and the mechanism of attachment between the power tiller and the plow should be changed as the indications of this study, and in addition to these, the new operation method of the field work should be developed.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2017년도 학술발표회
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• pp.514-514
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• 2017

Floating breakwaters were treated as solid bodies without any perforation in previous studies. In this study, however, a floating breakwater is perforated to allow the partial absorption of the energy produced by incident waves and an air chamber is placed in the upper part to control the breakwater draft. A series of laboratory experiments for a floating breakwater installed with a mooring system are carried out. In general, a mooring system can be classified by the number of mooring points, the shape of the mooring lines, and the degree of line tension. In this study, a four-point mooring is employed since it is relatively easier to analyze the measured results. Furthermore, both the tension-leg and the catenary mooring systems have been adopted to compare the performance of the system. In laboratory experiments, the hydraulic characteristics of a floating breakwater were obtained and analyzed in detail. Also, a hydraulic model test was carried out on variable changes by changing the mooring angle and thickness of perforated wall. A hydraulic model was designed to produce wave energy by generating a vortex with the existing reflection method. Analysis on wave changes was conducted and the flow field around the floating breakwater and draft area, which have elastic behavior, was collected using the PIV system. From the test results the strong vortex was identified in the draft area of the perforated both-sides-type floating breakwater. Also, the wave control performance of the floating breakwater was improved due to the vortex produced as the tension in the mooring line decreased.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권6호
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• pp.794-802
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• 2018

The ice resistance series charts for icebreaking ships were developed through a series of systematic model tests in the ice tank of the Korean Research Institute of Ship and Ocean Engineering (KRISO). Spencer's (1992) component-based scaling system for ship-ice model tests was applied to extend the model ship correlations. Beam to draft ratio (B/T), length to beam ratio (L/B), block coefficient ($C_B$) and stem angle (${\alpha}$) were selected as geometric parameters for hull form development. The basic hull form (S1) of twin pod type with B/T of 3.0, L/B of 6.0, $C_B$ of 0.75 and stem angle of $25^{\circ}$ was generated with a modern hull design concept. A total of 13 hulls were designed varying the geometric parameters; B/T of 2.5 and 3.5, L/B of 5.0 and 7.0, $C_B$ from 0.65 to 0.85 in intervals of 0.05, and 5 stem angles from $15^{\circ}$ to $35^{\circ}$. Ice resistance tests were first carried out with the basic hull form in level ice with suitable speed. Four more tests for $C_B$ variations from 0.65 to 0.85 were conducted and two more for beam to draft and length to beam ratios were also performed to study the effect of the geometric parameters on ice resistance. Ice resistance tests were summarized using the volumetric coefficient, $C_V$ ($={\nabla}/L^3$), instead of L/B and $C_B$ variations. Additional model tests were also carried out to account for the effect of the stem angle, ice thickness and ice strength on ice resistance. In order to develop the ice resistance series charts with a minimum number of experiments, the trends of the ice resistance obtained from the experiments were assumed to be similar for other model ship with different geometric parameters. A total of 18 sheets composed of combinations of three different beam to draft ratios and six block coefficients were developed as a parameter of $C_V$ in the low speed regions. Three correction charts were also developed for stem angles, ice thickness and ice strength respectively. The charts were applied to estimate ice resistance for existing icebreaking ships including ARAON, and the results were satisfactory with reasonable accuracy.

• 대한조선학회논문집
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• 제43권5호
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• pp.529-537
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• 2006

International Maritime Organization (IMO) is planning to include the Alternative Assessment of the Weather Criterion in the new Intact Stability (IS) Code to be revised. In this study, the procedure of the model test in the Interim Guidelines was reviewed by carrying out the model test and analyzing the test results. For this purpose, RO/RO passenger ship whose ratios of breadth to draft and the height of weight to draft were above 3.5 and above 0.6 respectively was selected as a test ship. Drifting test and motion test in regular waves were performed to estimate the hydrodynamic heeling lever and roll-back angle. Motion tests in waves were carried out in the three wave steepness conditions to measure roll-back angle and examine the feasibility of so called, the Three-step method. Using the test data, satisfaction of the Weather Criterion was assessed for the test ship by using the alternative method and compared with the current method.

• 한국항해학회지
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• 제15권3호
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• pp.73-97
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• 1991

The analysis and investigation are described for White's[2] equations compared to the equations of Runeburg[3] and Milano[5] for continuous icebreaking mode, Tunik[8-1] and Ghoneim[8-2] for ramming icebreaking mode. Calculation results compare reasonably well with published model-scale and full-scale icebreaker data by Baker[1] and Dick[11]. During continuous and ramming mode operation, using characteristics of an incebreaker, down ward force on ice and standard ice thickness broken are predicted. Additionally draft, trim and extraction difficulty are also predicted. The bow part line of an icebreakin $g^{ply}$ vessel is designed aiming to maximize the ice breaking capabiltiy as following conditions-low bow angle[20 degrees] at designed waterline, small spread angle complement [6 degrees] at designed waterline, small spread angle complement [6 degrees] and high propeller thrust [220tons]. with plow, two reamers and wave type bumper.