• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1851-1856
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• 2008

A numerical program based on computational fluid dynamics has been developed to simulate characteristics of an EHD induction micropump. The ambiguity of boundary conditions was removed by adopting an equation formulated for electric potential as the dependent variable. The calculations show that the dependency of frequency agrees well with the experiments and the previous analysis. The instability, caused by backflows, is getting stronger as the channel depth increases, which is consistent with experiments. The present study reveals that it is due to the limit in the penetration depth which the electric field can affect. Despite the disadvantage of large channel depth, there is a certain optimal depth for the maximum flow rate.

• 한국생산제조학회지
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• 제23권6호
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• pp.630-635
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• 2014

This study aims to develop a PZT-driven depth adjustment device with a flexure hinge and to investigate its static/dynamic characteristics. This device will be applied to rapidly and accurately trace a flat surface with slight waviness of up to several hundreds of micrometers in magnitude. One typical example is to cut a film coated on a steel plate. A depth control system composed of PMAC, PZT/PZT amplifier, flexure hinge/knife, and laser displacement sensor is implemented on a desktop three-axis machine and an actual cutting test is conducted on a steel workpiece with a sinusoidal-wavy surface. It is verified that the dynamic characteristics of the device limit the maximum cutting speed and depth precision.

• 한국해양공학회지
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• 제37권6호
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• pp.256-265
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• 2023

Many numerical methods have been developed since 1961, but unresolved issues remain. This study developed a numerical method to address these issues and determine the coefficients and properties of rotational waves with a shear current in a finite water depth. The number of unknown constants was reduced significantly by introducing a wavelength-independent coordinate system. The reference depth was calculated independently using the shooting method. Therefore, there was no need for partial derivatives with respect to the wavelength and the reference depth, which simplified the numerical formulation. This method had less than half of the unknown constants of the other method because Newton's method only determines the coefficients. The breaking limit was calculated for verification, and the result agreed with the Miche formula. The water particle velocities were calculated, and the results were consistent with the experimental data. Dispersion relations were calculated, and the results are consistent with other numerical findings. The convergence of this method was examined. Although the required series order was reduced significantly, the total error was smaller, with a faster convergence speed.

• International journal of advanced smart convergence
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• 제13권1호
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• pp.185-193
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• 2024

This study aimed to investigate the immediate physiological responses, including heart rate, blood pressure, and rate pressure product (RPP), following squat exercises performed at three water depths (ground, knee depth, waist depth) and two speed conditions (60bpm speed, Max speed). The participants consisted of 10 men in their 20s with over 6 months of resistance exercise experience. For the 60bpm speed squats, participants performed 30 repetitions in 1 minute at a rate of 2 seconds per repetition, while for Max speed squats, they performed at Max speed without a set limit on the number of repetitions for 1 minute. All experiments were conducted with a random assignment. The study results showed that immediately after the aquatic squat exercise, the average heart rate, blood pressure, and cardiac load were higher in the order of knee depth, ground level, and waist depth at both 60bpm speed and Max Speed. At 60bpm speed, the heart rate was higher in the order of ground level, knee depth, and waist depth. Overall, exercise in an aquatic environment was considered to impose relatively lower physical burden compared to land-based exercise. Therefore, it is suggested that depending on individual fitness levels and exercise goals, appropriately combining aquatic exercise, which imposes lower immediate physiological burden, and land-based exercise may lead to safer and more effective exercise methods.

• 대한수학회지
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• 제59권6호
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• pp.1185-1201
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• 2022

Feller introduced an unfair-fair-game in his famous book [3]. In this game, at each trial, player will win 2^k yuan with probability p_k = 1/2^kk(k + 1), k ∈ ℕ, and zero yuan with probability p₀ = 1 - Σ^∞_k=1 p_k. Because the expected gain is 1, player must pay one yuan as the entrance fee for each trial. Although this game seemed "fair", Feller [2] proved that when the total trial number n is large enough, player will loss n yuan with its probability approximate 1. So it's an "unfair" game. In this paper, we study in depth its convergence in probability, almost sure convergence and convergence in distribution. Furthermore, we try to take 2^k = m to reduce the values of random variables and their corresponding probabilities at the same time, thus a new probability model is introduced, which is called as the related model of Feller's unfair-fair-game. We find out that this new model follows a long-tailed distribution. We obtain its weak law of large numbers, strong law of large numbers and central limit theorem. These results show that their probability limit behaviours of these two models are quite different.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.351-356
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• 2001

A potential loss of structural integrity due to aging of nuclear piping may have a significant effect on the safety of nuclear power plants. In particular, failures due to the erosion and corrosion defects are a major concern. As a result, there is a need to assess the remaining strength of pipe with erosion/corrosion defects. In this paper, a limit load solution for the eroded and corroded SA106 Grade B pipes subjected by internal pressure is developed. based in 3-D finite element analyses, considering a wide range of the shape of pipeline, flaw depth and axial flaw length parametrically.

• 한국철도학회논문집
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• 제8권1호
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• pp.93-100
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• 2005

The turnout system is typical railway facility to be in the way of conventional railway line's speed-up. The KNR(Korean National Railroad) has a speed limit regulation (130km/h) for the passing the turnout to guarantee a safety. This research had been performed to confirm the propriety of this regulation by using experimental and analytical way before it was carried out. The reasonableness of the speed-limit regulation was judged base on the several experiments. It was proved that the regulation was not useless as it had been regarded and very important guide at least up to now.

• 대한기계학회논문집A
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• 제28권5호
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• pp.524-531
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• 2004

To investigate relevance of the definition of the reference stress to estimate J and $C^{*}$ for surface crack problems, this paper compares FE J and $C^{*}$ results for surface cracked pipes with those estimated according to the reference stress approach using various definitions of the reference stress. Pipes with part circumferential inner surface crack and finite internal axial crack are considered, subject to internal pressure and global bending. The crack depth and aspect ratio are systematically varied. The reference stress is defined in four different ways using (i) the local limit load, (ii) the global limit load, (iii) the global limit load determined from the FE limit analysis, and (iv) the optimized reference load. It is found that the reference stress based on the local limit load gives overall excessively conservative estimates of J and $^{*}$. Use of the global limit load clearly reduces the conservatism, compared to that of the local limit load, although it can provide sometimes non-conservative estimates of J and $^{*}$. The use of the FE global limit load gives overall non-conservative estimates of J and $^{*}$. The reference stress based on the optimised reference load gives overall accurate estimates of J and $^{*}$, compared to other definitions of the reference stress. Based on the present finding, general guidance on the choice of the reference stress for surface crack problems is given.

• 마케팅과학연구
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• 제18권4호
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• pp.195-215
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• 2008

본 연구는 기업에 대한 소비자의 의도추론이 희소성 효과에 미치는 영향에 있어서 희소성 메시지의 수량한정 유형 및 폭의 조절효과를 파악하고자 진행되었다. 연구결과는 크게 두 가지로 요약할 수 있다. 첫째, 특별한정으로 제시되는 경우에는 소비자의 기업에 대한 의도추론은 희소성 효과에 영향을 미치지 않았다. 그러나 일반한정으로 제시되는 경우에는 소비자가 기업의 의도를 추론하는 경우가 그렇지 않은 경우에 비해 구매의도가 더욱 낮았다. 둘째, 수량한정의 폭이 작은 경우에는 소비자의 기업에 대한 의도추론은 희소성 효과에 영향을 미치지 않았다. 그러나 수량한정의 폭이 큰 경우에는 소비자가 기업의 의도를 추론하는 경우가 그렇지 않은 경우에 비해 구매의도가 더욱 낮았다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.136-143
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• 2002

Warm draw die technique which is one of the new forming technologies to improve formability of sheet metal is applied to the cylindrical and square cup drawing of stainless-aluminum clad sheets. In experiments the temperature of die and blank holder is varied from room temperature to $180^{\circ}C$, while the punch is cooled by circulation of coolant to increase the fracture strength of workpiece on the punch comer area. Test materials chosen for experiments are STS304-A1050-STS304 clad sheets. Teflon film as a lubricant is used on both sides of a workpiece. The limit drawing ratio and relative drawing depth as well as quality of drawn cups(distribution of thickness)are investigated and validity of warm drawing process is also discussed. No separation between each laminated material after drawing occurred through inspection by microscope as well as application of penetrant remover and bond strength test. Therefore, warm forming technique was confirmed to give better results in deep drawing of stainless clad sheet metal.