• 대한기계학회논문집B
• /
• 제26권9호
• /
• pp.1325-1331
• /
• 2002

This study presents a numerical model to predict the behavior of frost layer growth. The characteristics of the heat and mass transfer inside the frost layer are analyzed by coupling the air flow with the frost layer. The present model is validated by comparing with the several other analytical models. It has been known that most of the previous models cause considerable errors depending on the working conditions or correlations used in predicting the frost thickness growth, whereas the model in this work estimates the thickness of the frost layer more accurately within an error of 10% in comparison with the experimental data. Simulation results are presented for variations of heat and mass transfer during the frost formation and for the behavior of frost layer growth along the direction of air flow.

• 한국안전학회지
• /
• 제14권3호
• /
• pp.174-180
• /
• 1999

The objective of this study was to investigate the effects of carrying postures and weight of load carried one time on a worker when carrying heavy loads. Six male students participated in this study to perform a manual materials carrying task as subjects. To make comparison of work loads with physical work capacity, maximal oxygen uptake measurement tests were performed with submaximal test. The average oxygen consumption for the tasks of this study was 27.59~31.93% $VO_2$max. The results showed that the weight of load carried one time affects on working heart rate and oxygen consumption($VO_2$). It was found that the workload was significantly lower when handling a 20kg load at a frequency rate of 3times/min than when handling a 40kg load at a frequency rate of 1.5 times/min. There was no difference between carrying postures. It is concluded from the results of this study that the workload can be reduced by controlling conditions of a manual materials handling task.

• The Journal of Korean Physical Therapy
• /
• 제13권3호
• /
• pp.829-837
• /
• 2001

Using Video Display Terminals(VDT) in the working environment often causes health complaints in the neck and shoulder region. This study was conducted on ten subjects, in order to investigate the change of electromyographic activities in the neck region(sternocleidomastoid muscle, upper trapezius muscle and erector muscle of cervical spine)with regards to the screen height and document holder position. A total of six different conditions of screen height and document holder position were measured during subjects performed a text-entry task for a duration of 10min. The raw EMG signal was transmuted into the root mean square(RMS). Two-way ANOVA for repeated measures was used to analyse the effects of the two factors. As a result, changing the screen height and document holder position has no effect on electromyographic activities in the neck region.

• 대한안전경영과학회지
• /
• 제12권3호
• /
• pp.21-26
• /
• 2010

This study compared the effects of praise and punishment for improving safety behaviors. Participants were 30 volunteer undergraduate students and they were randomly assigned to one of two experimental conditions: (1) praise under which positive feedback was delivered for safe behaviors, (2) punishment under which negative feedback was delivered for unsafe behaviors. A simulated computerized work task was developed specifically for this study. Participants had to work on the work task and follow seven safety rules while working. When they follow all the seven safety rules, their behaviors were considered safe. If they did not follow any one of the rules, their behaviors were considered unsafe. Results showed that the percentage of safe behavior under group of praise feedback was significantly higher than under group of punish feedback.

• 산업경영시스템학회지
• /
• 제27권4호
• /
• pp.133-140
• /
• 2004

This study deals with human reaction speed according to human physical conditions (body size) such as head width, thickness, breast width, arm extent, and age. Especially, the results of this study are compared between young and old generation. According to this study, the thickness and extent factor do not have any correlation with human reaction speed, but width factors(head width, breast width, etc) have some correlation with human reaction speed. The result of this study can be used to find fitter person for a special job such as emergency condition job, sports man (because you can find a person having a good talent for it without test). Also, the purpose of this study is to find CNT (Channel Noise Time). The word of CNT is to explain the relation between Channel Noise and working speed. (Channel Noise is a kind of noise happening between the human information transmission channel.)

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
• /
• pp.402-406
• /
• 1995

The purpose of this paper is to decrease shotcrete rebound losses and to produce economic effectiveness at the same time in construction. The mechanical properties and quick acceleration of various shoterete mixes were analyzed, which were intuenced by several accelerators and their amouts used. And the application and construction in the felds were evaluated. The shotcrete rebounds relied on the condition of construction rather than on the quality of materials, but it is found that the decreasing of the cost and time in shotcreting under the same condition was based on the rebounds which were affected by the accelerating capability of the accelerators. The application of the accelerator was limited by the condition of tunnel construction ; such as ground water, anti-corrosive, or anti-chemistry. It is important to choose a proper accelerator. Therefore, it is necessary that better accelerators which satisfly mechanical characteristics and economy are developed. Optimal working conditions should be announced to the workers and workers' skill be improved in the shotcrete construction feld as well.

• 한국정밀공학회지
• /
• 제1권1호
• /
• pp.34-49
• /
• 1984

The stability of machine tool systems is analyzed by considering the machining process as a stochastic process without decomposing into machine tool structural dynamics and cutting processes. In doing so the time series analysis technique developed by Wu and Pandit is applied systematically to the relative vibration between cutting tool and work- piece measured under actual working conditions. Various characteristic properties derived from the fitted ARMA(Autoregressive Moving Average) Models and those from raw data directly are investigated in relation with the system stability. Both damping ratio and absolute value of the characteristic roots of the AR part of the most significant dynamic mode are preferred as stability indicating factors to the other pro-perties such as theoretical variance .gamma. (o) or absolute power of the most dominant dynamic mode. Maximum aplitude during a certain interval and variance estimated from raw data are shown to be very sensi- tive to the type of the signal and the location of measurement point although they can be obtained rather easily. The relative vibration signal is also analyzed by FFT(Fast Fourier Transform) Analyzer for the purpose of comparison with the spectrums derived from the fitted ARMA models.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
• /
• pp.769-774
• /
• 2001

The purpose of this study is to analyze the curing effect of heating cable for concreting in cold weather. An experiment was conducted to evaluate the temperature history of concrete structures cured with embedded heating cables. Results are as follows : In comparison with the non-heating case, applying of heating cable resulted in the rise of temperature in the range of $10^{\circ}C$. In order to get successful results, the optimal pitch length for the embedded heating cables ranged from 20cm to 25cm. When working with the existing curing methods, applying this heating cable would be more effective in concrete curing. Finally, a formula and process was suggested to predict the Internal temperature history of concrete structures under the various curing conditions.

• 동력기계공학회지
• /
• 제8권1호
• /
• pp.24-29
• /
• 2004

In this study, a computer analysis has been developed for predicting the pipe pressure of the intake and exhaust manifold. To obtain the boundary conditions for a numerical analysis, one dimensional and non-steady gas dynamic calculation is performed by using the MOC(Method Of Characteristic). The main numerical parameters are the variation of the engine revolution to calculate the pulsating flow which the intake and exhaust valves arc working. The comparison of exhaust pressure in case of numerical results is quite matched with in case of experimental results. When engine revaluation is increased, the pressure amplitude showed a high value, but the pressure frequency was decreased.

• 드라이브 ㆍ 컨트롤
• /
• 제14권4호
• /
• pp.17-22
• /
• 2017

In this study, the back-drivability of the single-rod and double-rod type EHAs (Electro-Hydrostatic Actuators) was compared by computer simulation and experiments. The back-drivability of EHAs exhibit non-linear behavior like their force tracking performance. In case of the double-rod type EHA, the back-drivability was mostly influenced by the bulk modulus of oil that changes with the working pressure due to entrapped air. The back-drivability of the single-rod type EHA was directly affected by the operation states of its pilot-operated check valves, while the asymmetrical piston geometry and the non-linear bulk modulus of oil also made the dynamic response in building up the cylinder pressure dependent on the operating conditions.