• 대한조선학회논문집
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• 제54권4호
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• pp.329-334
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• 2017

As the motion response of heave for floating bodies on the water surface is relatively large near the natural frequency, it is necessary to predict its value accurately from the stage of initial design. Bodies accelerating in fluid experience force acted upon by the fluid, and this force is quantified by using the concept of added mass. For predicting the natural frequency of heave we need to know the added mass, which is given as a function of frequency, and hence the natural frequency can be obtained through only by iteration process, as was pointed out by Lee (2008). His method was applied to circular cylinders, and two dimensional cylinders of Lewis form by making use of the Ursell-Tasai method in the previous works, Lee and Lee (2013), Kim and Lee (2013), and Song and Lee (2015). In this work, a similar algorithm employing the concept of strip method is adopted for predicting the heave natural frequency of KCS(KRISO Container Ship), and the obtained computational result was compared with other existing experimental data, and the agreement seems reasonable. Furthermore, through the error analysis, it is shown that why the frequency corresponding to the local minimum of the added mass and the natural frequency are very close. And it seems probable that we can predict the heave natural frequency if we know only the local minimum of added mass and the corresponding frequency under a condition, which holds for ship-like bodies in general.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.409-422
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• 2016

A parametric study based on an unsteady mathematical model of a pyrotechnically actuated device was performed for design optimization. The model simulates time histories for the chamber pressure, temperature, mass transfer and pin motion. It is validated through a comparison with experimentally measured pressure and pin displacement. Parametric analyses were conducted to observe the detailed effects of the design parameters using a validated performance analysis code. The detailed effects of the design variables on the performance were evaluated using the one-at-a-time (OAT) method, while the scatter plot method was used to evaluate relative sensitivity. Finally, the design optimization was conducted by employing a genetic algorithm (GA). Six major design parameters for the GA were chosen based on the results of the sensitivity analysis. A fitness function was suggested, which included the following targets: minimum explosive mass for the uniform ignition (small deviation), light casing weight, short operational time, allowable pyrotechnic shock force and finally the designated pin kinetic energy. The propellant mass and cross-sectional area were the first and the second most sensitive parameters, which significantly affected the pin's kinetic energy. Even though the peak chamber pressure decreased, the pin kinetic energy maintained its designated value because the widened pin cross-sectional area induced enough force at low pressure.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.6-8
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• 1996

The multiobjective optimization is presented for the optimal design of induction motors. The aim of design is to find an optimized induction motor in terms of both the efficiency and the mass. The efficiency and the mass are linearly combined using the weighting factors. Optimization process is performed by using the improved (1+1) evolution strategy (ES). ES is the algorithm that can find the global minimum. To verify the validity of the proposed method. the method is applied to a sample design.

• 대한기계학회논문집B
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• 제37권3호
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• pp.267-273
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• 2013

막충진재(film fill)를 갖는 냉각탑용 팬의 효율적인 운전조건을 제시하기 위하여, Merkel의 이론을 바탕으로 한 종전의 최적 총연간비용 모델을 사용하여 입구 물온도와 열부하에 따른 최소팬동력을 구하는 프로그램이 새로이 개발되었으며, 냉각탑의 설계 맵이 본 연구로부터 제시되었다. 전형적인 예들을 통하여 본 프로그램의 타당성이 입증되었다. 주어진 열부하에서 이들 팬동력(z 축)-공기질량플럭스(x 축, 최소팬동력 존재)-입구물온도(y 축, 최소팬동력의 최대값 존재)의 3차원 그래프는 말안장 형상으로 나타났다. 최소팬동력들은 열부하에 따라 증가하였다. 따라서, '고온수 유입과 저유량의 공기로 작동' 될 때가 항상 최소팬동력 조건이 아니며, '주어진 입구물온도에 대하여 최소팬동력에 대응하는 최적의 공기질량플럭스가 (열부하와 무관하게) 존재한다'는 사실이 본 연구결과로부터 밝혀졌다.

• Journal of Biosystems Engineering
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• 제9권1호
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• pp.11-21
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• 1984

This study was intended to analyze the dynamic force system which induced the shattering of paddy grains. A model to predict the shattering of paddy grains was developed, and physical quantities, such as mass distribution and rigidity of rice plant, needed for evaluating the minimum shattering forces were also measured. Under the assumption that rice plant right before harvesting is a vibratory system, the mathematical model of the vibratory system was developed and solved with the varied conditions of forcing functions. The results of the study were summarized as follows: 1. The shattering of grain occurred at the abscission layer of grain by the bending moments resulted from the impact force due to the collision of panicles of rice plant. 2. The vibratory model developed for milyang 23 rice variety was analyzed to give the natural frequencies of 7-9 Hz, which were closely related with the excitation frequencies of 4-10 Hz caused by various machine parts besides engine. Thus, avoiding the resonance should be taken into consideration in the design of the harvesting machinery. 3. It was analyzed to predict the lowest frequency that could develop the shattering when the excitation force was applied to the lower end of stem. The lowest frequency for the Milyang 23 rice variety ranged from 8.33 Hz to 11.66 Hz as the amplitude varied from 1 cm to 2.5 cm. 4. The degree of shattering depended upon the magnitude of the impact force and its application point. For Milyang 23 rice variety, the minimum impact force developing the shattering was $5g_f$ when it was applied at 1 cm above the lower end of stern and $1g_f$ when applied at 5 cm above the lower end of stem. 5. The minimum colliding velocity of the panicle, when it was on the ground that would just develop the shattering, was given as follows, $$V=\sqrt{\frac{K_t}{m_g}{\cdot}{{\phi}^2}}$$ where V : The colliding velocity of the panicle against ground to cause the shatteering of rice grain. (cm/sec) $K_t$ : The minimum spring constant for bending at the abscission layer of grain. (dyne-cm/rad) ${\phi}$ : The minimum shattering angle of grain (rad) $m_g$ : The maximum mass of grain. (g).

• 한국농공학회지
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• 제33권3호
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• pp.91-100
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• 1991

Since ventilation in livestock buildings is critical for indoor air quality, the first step in designing environmental control is to determine required ventilation rate. The purpose of the study was to suggest a conceptually new ventilation graph for determining minimum/maximum ventilation rate based on the conservation law of the thermal energy and mass in livestock buildings. PC-based programs coded with PASCAL language, [RVALUE] for overall thermal resistance of composite structural walls/ceilings, [POLYNOM] for coefficients values of animal's sensible heat equation were involved in developing a computer program, [VENTGRPH] for the determination of ventilation rate. It would be useful for design, for such a program would permit the designer to explore various design options and immediately, see the result in terms of its effect on minimum ventilation rates.

• Composites Research
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• 제27권6호
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• pp.207-212
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• 2014

The shape optimization of composite flexbeam sections of a bearingless helicopter rotor is studied using a finite element (FE) sectional analysis integrated with an efficient evolutionary optimization algorithm called particle swarm assisted genetic algorithm (PSGA). The sectional optimization framework is developed by automating the processes for geometry and mesh generation, and the sectional analysis to compute the elastic and inertial properties. Several section shapes are explored, modeled using quadratic B-splines with control points as design variables, through a multiobjective design optimization aiming minimum torsional stiffness, lag bending stiffness, and sectional mass while maximizing the critical strength ratio. The constraints are imposed on the mass, stiffnesses, and critical strength ratio corresponding to multiple design load cases. The optimal results reveal a simpler and better feasible section with double-H shape compared to the triple-H shape of the baseline where reductions of 9.46%, 67.44% and 30% each are reported in torsional stiffness, lag bending stiffness, and sectional mass, respectively, with critical strength ratio greater than 1.5.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권2호
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• pp.180-187
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• 2018

Corrugated bulkhead has been adopted for cargo tank bulkheads of commercial vessels such as bulk carriers, product oil carriers and chemical tankers. It is considered that corrugated bulkhead is a preferred structural solution, compared to the flat stiffened bulkhead, due to several advantages such as lower mass, easier maintenance and smaller corrosion problems. Many researches to find the optimum shape of corrugated bulkhead have been mostly carried out for bulk carriers. Compared to corrugated bulkheads of bulk carriers, ones of chemical tankers are more complicated since they are composed of transverse and longitudinal bulkheads, and they are made of higher priced materials. The purpose of this study is the development of minimum weight design method for corrugated bulkhead of chemical tankers. Evolution strategy is applied as an optimization technique. It has been verified from many researches that evolution strategy searches global optimum point prominently by using multi-individual searching technique. Multi-individual searching methods need excessive time if they connect to 3-D finite element model for repetitive structural analyses. In order to resolve this issue, 2-D beam element connected to deck and lower stool is substituted for a corrugated structure in this study. To verify the reliability of the structural responses by idealized 2-D beam model, they have been compared with ones by 3-D finite element model. In this study, optimum design for corrugated bulkhead of 30 K chemical tanker has been carried out, and the results by developed optimum design program have been compared with design data of existing ship. It is found out that optimum design is about 9% lighter than one of existing ship.

• 설비공학논문집
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• 제6권4호
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• pp.406-416
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• 1994

In this study the reactor design procedure and method of solid-solid-gas chemical heat pump system using STELF technology were investigated. For manufacturing IMPEX block which is the kernel of reactor, proper salt pair should be selected, and equilibrium temperature drop and COP should be examined for selected salt pair. Moreover, apparent density, residual porosity, and graphite ratio should be calculated to give minimum block volume and mass, and maximum energy density without causing heat and mass transfer problems. Since heat exchange area can be changed with operating condition, reactor diameter, length, and stainless steel thickness should be decided for desired specifications. These procedure and method were applied to the case study of 6kW cold production and 8 hours storage capacity reactor.

• 콘크리트학회논문집
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• 제11권3호
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• pp.59-67
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• 1999

The mass concrete structures are generally constructed in an incremental manner by deviding the whole structures by a series of many blocks. The temperature and stress distributions of any specific block are continuously affected by the blocks placed before and after the specific block. For an accurate analysis of mass concrete structures, the sequence of all the blocks must be accordingly considered including the change of material properties with time for those blocks considered. The purpose of this study is to propose a realistic analysis method which can take into account not only the influence of the sequence, time interval and size of concrete block placement on the temperatures and stresses, but also the change of material properties with time. It is seen from this study that the conventional simplified analysis, which neglects material property changes of some blocks with time and does not consider the effect of adjacent blocks in the analysis, may yield large discrepancies in the temperature and stress distributions of mass concrete structures. This study gives a method to choose the minimum number of blocks required to obtain reasonably accurate results in analysis. The study provides a realistic method which can determine the appropriate size and time interval of block placement, and can be efficiently used in the design and construction of mass concrete structures.