• Journal of Advanced Marine Engineering and Technology
• /
• 제17권5호
• /
• pp.63-70
• /
• 1993

In 1980's to 1990's the marine propulsion diesel engines have been developed into lower speed and longer stroke for the energy saving(small S.F.O.C.). As these new trends the convetional mechnical-hydraulic governors were not adapted to the new requirements and the digital governors have been adopted in the marine use. The digital governors usually use the control algorithms such as the PID control, optimal control, adaptive control and etc. While the engine has delay time and parameter variations these control algorithms have difficulty in considering the stability and the robustness for the model uncertainty. In this study, the $H_{\infty}$ controller design method are applied to the speed control of the low speed marine diesel engine. By comparison the $H_{\infty}$ control results with the PID control results, the validity of the $H_{\infty}$ controller under the delay time and parameter variations is confirmed.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.906-912
• /
• 2000

In this study, for the use of LFG, the burning velocities of LFG and LFG mixed fuels have been numerically analyzed. C3 reaction mechanism which consists of 92 species and 621 reaction was adopted in the calculation. The results show that the burning velocities of LFG and LFG mixed fuels are obtained as a function of $CH_4$ and LFG percentage at stoichiometric conditions. In addition, the correlations of burning velocities LFG and LFG mixed fuels were obtained over a wide range of the equivalence ratio. The comparison of burning velocity correlated from numerically calculated results with experimental ones shows good agreements. From these results, the suggested burning velocity correlations far LFG and LFG mixed fuels in this study can be applied to the practical utilization of LFG.

• Macromolecular Research
• /
• 제11권4호
• /
• pp.224-230
• /
• 2003

The blends of polypropylene (PP) with glass filled thermotropic liquid crystalline polymer (LCP-g) have been prepared by melt mixing techniques at different blend ratios. The thermal, dynamic mechanical, crystalline and morphological characteristics of these blends were investigated. Higher percent crystallinity was observed for 10% level of LCP-g in the blend in comparison to that of other blend ratios. The thermal stability increased with LCP-g concentration in the blend with PP. The variation of storage modulus, stiffness and loss modulus as a function of blend ratios suggested the phase inversion at the 50% level of LCP-g in the blend. The scanning electron microscopy (SEM) photographs showed the creation of voids and destruction of the fiber structures during the dynamic mechanical measurements. Processing behavior of the blends depended on the fiber forming characteristics of LCP-g, which again varied with the molding temperatures.

• 대한조선학회지
• /
• 제19권4호
• /
• pp.53-59
• /
• 1982

Relative bow-motions of a ship in wave are investigated by using linear theory. The relative displacement is assumed to be composed of incident wave elevation, motion response, dynamic swell-up and ship wave elevation. Radiation problem is solved by distributing sources on the hull surface and wave elevation in a uniform stream is obtained by integrating Havelock's function with centerplane source distributions. Relative displacements for I.T.T.C. S7-175 model are calculated. Dynamic swell-ups make the relative displacement larger except small heading angles. Amplitudes of relative motion on weather-side are generally larger than those on lee-side. Ship wave elevations in a uniform stream also give considerable contributions and our calculations are verified to be reasonable in comparison with experimental results.

• 한국에너지공학회:학술대회논문집
• /
• 한국에너지공학회 1999년도 추계 학술발표회 논문집
• /
• pp.171-180
• /
• 1999

In this study, the burning velocity of LFG and LFG mixing fuels related with flame stabilization have been analyzed numerically using C3 reaction mechanism which consists of 92 species and 621 reaction for using LFG. The results show that the burning velocities of LFG and LFG mixing fuels are obtained as a function of CH$_4$ and LFG percent in stoichiometric conditions. Also, a correlation of the burning velocities LFG and LFG mixing fuels are obtained over a wide range of equivalence ratio. The comparison of burning velocity from correlation with that calculated numerically show good agreements. From these results, the proposed burning velocity correlations for LFG and LFG mixing fuels can be applied for the practice of LFG.

• 대한수학회논문집
• /
• 제37권2호
• /
• pp.503-520
• /
• 2022

We introduce a new type of fractional derivative, which we call as the right local general truncated M-fractional derivative for α-differentiable functions that generalizes the fractional derivative type introduced by Anastassiou. This newly defined operator generalizes the standard properties and results of the integer order calculus viz. the Rolle's theorem, the mean value theorem and its extension, inverse property, the fundamental theorem of calculus and the theorem of integration by parts. Then we represent a relation of the newly defined fractional derivative with known fractional derivative and in context with this derivative a physical problem, Kirchoff's voltage law, is generalized. Also, the importance of this newly defined operator with respect to the flexibility in the parametric values is described via the comparison of the solutions in the graphs using MATLAB software.

• Korean Chemical Engineering Research
• /
• 제62권1호
• /
• pp.112-117
• /
• 2024

Numerical simulations on the onset and the growth of viscous fingering during the miscible displacement due to the radial source flow were conducted. With introduction of a new stability criterion, the critical log-viscosity ratio, R_c, was found as a function of the Peclet number, Pe. Similar to the previous linear stability analyses, Pe made the system unstable, i.e., accelerated the onset of instability. For a large Pe system, the present numerical simulation yielded much stable results than the previous theoretical predictions This discrepancy was commonly encountered in the comparison between the theoretical prediction and the experimental finding. Additionally, the difference between the rectilinear system and the present one was also discussed. The present system was found more insensitive to the Peclet number than the rectilinear one.

• 대한물리치료과학회지
• /
• 제14권1_4호
• /
• pp.11-23
• /
• 2007

This study was performed to evaluate the effects of low-intensity ultrasound application to the peripheral nerve injury animal model on enhancement of nerve regeneration and functional recovery. Using aseptic microsurgical techniques, the sciatic nerve of adult male Sprague-Dawley rats was crushed at the outside of right mid-thigh for 30 seconds with fine forceps. Beginning just after surgery, various continuous-wave ultrasound treatments with intensities of 0.2 W/$cm^2$, 0.5 W /$cm^2$ and 1.0 W /$cm^2$ operated at 1 MHz or sham treatment were applied to the opposite inside of the crush site for 1 minute every other day with a transducer moving speed of 2cm/sec. For evaluation of the progress of sciatic nerve regeneration, c-Fos expression in the lumbar spinal cord (L4-5) dorsal horn was investigated. c-fos expression was markedly increased at 1hour after sciatic nerve crush injury, then gradually decreased thereafter. The c-fos expressions were significantly decreased (p<0.05) in all the experimental groups in comparison with the control group until 3days post-crush, and the degrees of decrease were higher in 0.5 W/$cm^2$ and 1 W/$cm^2$ intensity ultrasound application groups. It is suggested that low-intensity ultrasound application to an animal model of sciatic crush injury may suppress pain transmission and promote nerve regeneration, and which may result in delayed progress of muscle atrophy and accelerated progress of muscle recovery and eventually may result in accelerated and improved foot function recovery.

• Investigative Magnetic Resonance Imaging
• /
• 제19권4호
• /
• pp.212-217
• /
• 2015

Purpose: For a single time-point hyperpolarized $^{13}C$ magnetic resonance spectroscopy imaging (MRSI) of animal models, scan-time window after injecting substrates is critical in terms of signal-to-noise ratio (SNR) of downstream metabolites. Pre-scans of time-resolved magnetic resonance spectroscopy (MRS) can be performed to determine the scan-time window. In this study, based on two-site exchange model, protocol-specific simulation approaches were developed for $^{13}C$ MRSI and the optimal scan-time window was determined to maximize the SNR of downstream metabolites. Materials and Methods: The arterial input function and conversion rate constant from injected substrates (pyruvate) to downstream metabolite (lactate) were precalibrated, based on pre-scans of time-resolved MRS. MRSI was simulated using two-site exchange model with considerations of scan parameters of MRSI. Optimal scan-time window for mapping lactate was chosen from simulated lactate intensity maps. The performance was validated by multiple in vivo experiments of BALB/C nude mice with MDA-MB-231 breast tumor cells. As a comparison, MRSI were performed with other scan-time windows simply chosen from the lactate signal intensities of pre-scan time-resolved MRS. Results: The optimal scan timing for our animal models was determined by simulation, and was found to be 15 s after injection of the pyruvate. Compared to the simple approach, we observed that the lactate peak signal to noise ratio (PSNR) was increased by 230%. Conclusion: Optimal scan timing to measure downstream metabolites using hyperpolarized $^{13}C$ MRSI can be determined by the proposed protocol-specific simulation approaches.

• 한국건설관리학회:학술대회논문집
• /
• 한국건설관리학회 2006년도 정기학술발표대회 논문집
• /
• pp.271-273
• /
• 2006

건설 VE는 실시시기가 빠를수록 가치향상의 효과가 크므로 시공단계보다는 설계단계의 VE가 더욱 더 중요하다. 그러나 설계단계에서 발생하는 여러 가지 문제점으로 인하여 시공단계에 악영향을 미치고 있으며, 사업주체간에도 갈등을 야기하고 있다. 그러므로 설계단계에서의 품질확보가 무엇보다도 중요하다. 이에 본 연구는 설계단계의 연약지반처리공법 선정과정에서 VE/LCC 분석 사례를 통하여 비교공법별 설계기능점수(F)와 LCC비용(C)의 대비를 통해 가치지수(V)를 산정하여 최적의 공법을 선정함으로써 정성적인 판단을 정량적인 값으로 도출하는 과정을 수행하였으므로 앞으로 더욱 더 설계 VE의 확대방안이 필요함을 강조하였다.