• 대한기계학회논문집B
• /
• 제29권5호
• /
• pp.554-560
• /
• 2005

A new method to improve the efficiency of a hydrogen fuel cell system was introduced by using variable sonic/supersonic ejectors. To obtain the variable area ratio of the nozzle throat to ejector throat which controls the mass flow rate of the suction flow, the ejectors used a movable cylinder inserted into a conventional ejector-diffuser system. Experiments were carried out to understand the flow characteristics inside the variable ejector system. The secondary mass flow rates of subsonic and supersonic ejectors were examined by varying the operating pressure ratio and area ratio. The results showed that the variable sonic/supersonic ejectors could control the recirculation ratio by changing the throat area ratio, and also showed that the recirculation ratio increased fur the variable sonic ejector and decreased for the variable supersonic ejector, as the throat area ratio increases.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2000년도 추계학술대회 논문집
• /
• pp.120-123
• /
• 2000

It is well known, for many years, that deep drawability can be improved by applying variable blank holding force. To apply variable blank holding force during cup during, we set up pressure controlling system on experimental hydraulic press, and the pressure control system is often called NC(Numerically Controlled) cushion system Using the NC cushion system we compared the drawability of square steel cups with NC cushion and that with conventional cushion. The results show drawability is greatly improved when the pressure control curve is designed in a S-shaped curve. This paper includes design details of the NC cushion system and experimental analysis of drawability with experimental NC cushion system.

• 한국콘텐츠학회:학술대회논문집
• /
• 한국콘텐츠학회 2016년도 춘계 종합학술대회 논문집
• /
• pp.267-268
• /
• 2016

This study aimed to examine the therapeutic effects of backward walking. The subjects were randomly assigned to an experimental group of 16 subjects and a control group of 17 subjects. All subjects walked barefoot for twenty minutes on the treadmill (HM50EX, Daeho, Korea) for five times per week for total four weeks. The average gait velocities of subjects were 3 km/h on a slope of 10%. The experimental group walked back and the control group walked forward. The experimental group showed significant increments in variable of medial-lateral, anterior-posterior, step length, velocity compared to the pre-intervention results. In addition, the control group showed significant increments in the anterior-posterior, velocity compared to the pre-intervention results. Significant differences in the post-training gains in variable of anterior-posterior, step length, velocity were observed between the experimental group and the control group. There were positive effects of backward walking on their gait and balance ability after intervention.

• 한국과학교육학회지
• /
• 제31권4호
• /
• pp.587-599
• /
• 2011

이 연구에서는 '생각하는 과학' 활동을 경험한 중학생들이 이를 경험하지 못한 통제집단과 비교하여 변인 통제 전략의 적용과 변인의 효과를 추론하는 능력에 대해 분석하였다. 연구 결과 변인 통제 전략 유형은 조작변인의 인식과 변인 통제의 여부에 따라 변인 통제전략 성공형, 변인 통제전략 미완성형, 부분통제형, 통제 불가능형, 변인 통제전략 실패형으로 구분하였다. 실험집단이 통제집단에 비해 변인 통제 전략을 보다 정화하고 효과적으로 사용하였다. 직관적으로 알 수 있는 변인의 효과 추론 능력을 분석한 결과 가역적 사고가 가능한지의 여부와 변인의 효과를 추론할 수 있는지에 따라 변인효과 추론 가능형, 변인효과 추론 불가능형, 가역적 사고 불가능형으로 구분하여 유형화하였다. 실험집단 학생들이 변인효과 추론 가능형에서 통제집단보다 두 배 이상 많았다. 보상논리 조작을 포함하는 가역적 사고가 가능한 학생들은 형식적 조작기 이상의 학생들에게서 가능하였다. 직관적으로 얻기 힘든 변인의 효과를 추론하는 능력은 두 집단 모두 형식적 조작기 후기에 도달한 인지 수준의 비율과 비슷하였으며, 추론에 성공한 학생들의 비율은 실험집단이 통제집단 학생들 보다 1.5배 정도 더 많았다. 따라서 변인 통제능력과 변인을 추론하는 능력을 향상시키기 위해서는 '생각하는 과학' 활동 프로그램이 큰 영향을 미치고 있음을 알 수 있다.

• 한국소음진동공학회논문집
• /
• 제11권8호
• /
• pp.374-383
• /
• 2001

A reciprocating compressor unit with variable rotating speed driven by BLDC motor is mounted Inside hermetic chamber on an internal suspension composed of 4 roil springs and a discharge pipe. A method for predicting the dynamic behavior of compressor body is required for a reduction of transmitted vibrations. The mechanical characteristics of spring and discharge pipe stiffness properties have been obtained from experimental tests and mass moment of inertia of the compressor body iron CAD. To confirm the vibration model for the compressor body, free vibration analyses are performed with theoretical and experimental methods. results for analytical investigations on the dynamic behavior of the compressor body and the transmitted forces to the hermetic chamber through the suspension elements are Presented.

• 한국자동차공학회논문집
• /
• 제10권3호
• /
• pp.85-92
• /
• 2002

This paper presents the effects of design and operating parameters to meet the static and dynamic performances of the electro-mechanical valve(EMV) actuator which can provide more flexible controllability of valve events compared to conventional variable valve actuation devices. The model of the EMV system was also set up and applied to identify the dynamic behavior of the system. And the effects of external disturbances were also investigated such as cylinder pressure, armature neutral position and current supplying time effects and so on. Experiments were carried out to verify the model using the prototype actuator on test bench, it was found that there is a relatively good agreement between experimental data and modeling results. Also, the actuators meet the general engine speed range (over 6000rpm) and the variable valve event control for various VVT effects.

• 대한기계학회논문집A
• /
• 제27권1호
• /
• pp.1-7
• /
• 2003

The optimal design for the shape of MIL-S-46119 ring obturator under the high pressure using parameter stud:』 on the stress analysis considering effects of design variable is presented, and it is compared to experimental results. The trends of parametric study are in good agreement with the experimental results. The more thickness the higher stress. The more taper the higher stress. And maximum stress of circumferential surface is larger than maximum stress of forward surface. The design variable!; are such as thickness, taper, radius of shape of the obturator. In order to optimize the shape of obturation ring, the weight is maximized subject to maximum stress of the obturator within allowable stress. The design constraints are geometric elements of design variables.

• 설비공학논문집
• /
• 제13권4호
• /
• pp.233-241
• /
• 2001

In the present study, various experiments were performed to investigate the capacity modulation and transient response control using a variable speed compressor and electronic expansion valve(EEV). Based on the experimental results, the operation control algorithm and real time digital control system were constructed to adjust the superheat at the inlet of the compressor. Superheat control was fulfilled using both the PI feedback controller and PI controller combined with a feedforward concept. As a result, the tracking performance of the latter was better than that of former.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 춘계학술대회논문집
• /
• pp.362-367
• /
• 2001

A reciprocating compressor unit with variable rotating speed driven by BLDC motor is mounted inside hermetic chamber on an internal suspension composed of 4 coil springs and a discharge pipe. A method for predicting the dynamic behavior of compressor frame is required to reduce the transmitted vibration level. Mechanical characteristics such as mass, spring and discharge pipe stiffness properties are obtained with experimentation. To confirm the vibration model for compressor frame, free vibration analyses are performed with theoretical and experimental methods. Results for analytical and experimental investigations on dynamic behavior of the compressor frame are presented, and the agreement between measured and predicted results are satisfactory.

• Structural Engineering and Mechanics
• /
• 제60권1호
• /
• pp.71-90
• /
• 2016

In this paper, the normalized variable V=(log N-B)(log ${\Delta}{\sigma}-C$-C), as derived from the probabilistic S-N field of Castillo and Canteli, is taken as a reference for calculation of damage accumulation and probability of failure using the Miner number in scenarios of variable amplitude loading. Alternative damage measures, such as the classical Miner and logarithmic Miner, are also considered for comparison between theoretical lifetime prediction and experimental data. The suitability of this approach is confirmed for it provides safe lifetime prediction when applied to fatigue data obtained for riveted joints made of a puddle iron original from the Fao bridge, as well as for data from experimental programs published elsewhere carried out for different materials (aluminium and concrete specimens) under distinct variable loading histories.