• Geomechanics and Engineering
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• v.24 no.3
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• pp.227-235
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• 2021

A criterion and a method for solving a problem on the prevention of mine working fracture under the action of tectonic and gravitational forces are offered. Based on minimal criterion, theoretical analysis of the definition of the optimal shape of working in the rock mass weakened by arbitrarily located rectilinear cracks was carried out. A closed system of algebraic equations allowing to minimize the stress state and stress intensity factors depending on mechanical and geometrical characteristics of the rock, is constructed. The relation between the shape of the working and the stress intensity factors and also location and sizes of the cracks is obtained. The found optimal shape of working increases load-bearing capacity of the rock.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.1
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• pp.1-8
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• 2003

An analytical and experimental study of the thermal performance of axial heat pipe with axial groove is conducted to determine the optimal mass of working fluid for the maximum heat transport capacity of heat pipe with axial grooves. Generally, the mass of working fluid has been fully charged by considering only a geometrical shape of axial grooves embedded in a heat pipe. When the heat pipe is operated in a steady state, the meniscus re-cession phenomena of working fluid is occurred in the evaporator region. In this work, the optimal mass of working fluid was obtained from the axial variation of capillary pressure, the radius of curvature and wetting angle of meniscus of liquid-vapor interface. Experimental results were also obtained by varying the mass of working fluid within a heat pipe, and presented for the maximum heat transport capacity corresponding to the operating temperature and the elevation of heat pipe. Finally, the analytical results of the optimal mass of working fluid were compared with those of the experimental mass of working fluid.

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.2
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• pp.79-86
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• 2004

An analytical and experimental study has been conducted to determine the optimal charging mass of working fluid for the maximum heat transport capacity of heat pipe with axially grooved wick. When the heat pipe is operated in a steady state, the liquid-vapor meniscus recession of working fluid to the bottom of groove is occurred in the evaporator region. In this work, the optimal charging mass of working fluid was obtained by considering the meniscus recession from the axial variation of capillary pressure, the radius of curvature and wetting angle of meniscus of liquid-vapor interface. Experimental results were also obtained by varying the charging mass of working fluid within a heat pipe, and presented for the trend of maximum heat transport capacity corresponding to the operating temperature and the elevation of heat pipe. Finally, the analytical results of the optimal charging mass of working fluid were compared with those from the experiment, both of which were in good agreement with each other.

• ETRI Journal
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• v.30 no.1
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• pp.81-88
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• 2008

The security threat posed by worms has steadily increased in recent years. This paper discusses the application of the optimal and sub-optimal Internet worm control via Pontryagin's maximum principle. To this end, a control variable representing the optimal treatment strategy for infectious hosts is introduced into the two-factor worm model. The numerical optimal control laws are implemented by the multiple shooting method and the sub-optimal solution is computed using genetic algorithms. Simulation results demonstrate the effectiveness of the proposed optimal and sub-optimal strategies. It also provides a theoretical interpretation of the practical experience that the maximum implementation of treatment in the early stage is critically important in controlling outbreaks of Internet worms. Furthermore, our results show that the proposed sub-optimal control can lead to performance close to the optimal control, but with much simpler strategies for long periods of time in practical use.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.12
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• pp.1063-1070
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• 2008

The performance of an acoustic transducer is determined by the effects of many design variables, and mostly the influences of these design variables are not linearly independent of each other. To achieve the optimal performance of an acoustic transducer, we must consider the cross-coupled effects of the design variables. In this study, the variation of the performances of underwater acoustic transducer in relation to its structural variables was analyzed. In addition, the new optimal design scheme of an acoustic transducer that could reflect not only individual but also all the cross-coupled effects of multiple structural variables, and could determine the detailed geometry of the transducer with great efficiency and rapidity was developed. The validation of the new optimal design scheme was verified by applying the optimal structure design of a flextensional transducer which are the most common use for high power underwater acoustic transducer. With the finite element analysis(FEA), we analyzed the variation of the resonance frequency, sound pressure, and working depth of a flextensional transducer in relation to its design variables. Through statistical multiple regression analysis of the results, we derived functional forms of the resonance frequency, sound pressure, and working depth in terms of the design variables. By applying the constrained optimization technique, Sequential Quadratic Programming Method of Phenichny and Danilin(SQP-PD), to the derived function, we designed and verified the optimal structure of the Class IV flextensional transducer that could provide the highest sound pressure level and highest working depth at a given operation frequency of 1 kHz.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.43 no.1
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• pp.61-69
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• 2020

Systems such as database and socal network systems have been broadly used, and their unexpected failure, with great losses and sometimes a social confusion, has received attention in recent years. Therefore, it is an important issue to find optimal maintenance plans for such kind of systems from the points of system reliability and maintaining cost. However, it is difficult to maintain a system during its working cycle, since stopping works might incur users some troubles. From the above viewpoint, this paper discusses minimal repair maintenance policy with periodic replacement, while considering the random working cycles. The random working cycle and periodic replacement policies with minimal repair has been discussed in traditional literatures by usually analyzing cases for the nonstopping works. However, maintenance can be more conveniently done at discrete time and even during the working cycle in real applications. So, we propose that periodic replacement is planned at discrete times while considering the random working cycle, and moreover provide a model in which system, with a minimal repair at failures between replacements, is replaced at the minimum of discrete times KT and random cycles Y. The average cost rate model is used to determine the optimal number of periodic replacement.

• The Journal of Asian Finance, Economics and Business
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• v.3 no.2
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• pp.13-20
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• 2016

Firms can use working capital management which is one of the essential determinants to influence their profitability. The main theme of present study is to investigate the relationship between working capital management and profitability of Tobacco Industry of Pakistan. This study is based on secondary data collected from financial statements of selected companies of Tobacco Industry of Pakistan for the period of 2005-2014. For data analysis, both descriptive and inferential statistics were used. Correlation analysis is used to check the relationship between the variables, while multiple regression analysis is used to examine the effects of working capital management on profitability of firms. The result reveals that there is a strong negative relationship between variables of working capital management and profitability of Tobacco Industry of Pakistan. This means that as the cash conversion cycle increases, it will lead to declining of firm profitability and managers can create a positive value for shareholders by reducing the cash conversion cycle at optimal level. The study concludes that managers can create value for shareholders by managing the working capital well designed and implemented, and by keeping each components of it at optimal level.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.2
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• pp.94-105
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• 2015

In this study, a thruster allocation method of a deep-sea working vessel was proposed with the aims of producing the demanded generalized forces and moment for dynamic positioning while at the same time minimizing total power. For this, an optimization problem for thrust allocation was mathematically formulated with design variables, objective function, and constraints. The genetic algorithms (GA) was used to solve the formulated problem. The proposed method was applied to an example of finding optimal thrust allocation of the deep-sea working vessel having 5 thrusters. The result showed that the method could be used to determine better strategy for thruster allocation of the vessel as compared to existing study.

• Korean Journal of Social Welfare
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• v.60 no.4
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• pp.55-77
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• 2008

After the economic crisis of Korea, the character of Korean Poverty has changed. Most notably, many people are working but poor. Therefore it is important to understand the characteristics of the working poor, especially the unstable work experiences of the working poor since one of the causes of poverty is that. Prior research about the working poor has not fully proven this issue. This study is to examine the job sequences of the working poor. Thus I utilized the KLIPS(Korea Labor and Income Study), and analyzed it by event sequence analysis and optimal matching methods. The job sequences are divided as follows: total years of working in the labor market, the number of gaps and the length of gaps in their careers, and the characteristics of experienced jobs since they have entered the labor market from age 15. As a result, there are no statistically significant in the total years of working in the labor market. And the number of gaps and the length of gaps in their careers, and the characteristics of experienced jobs show that working poor have been experiencing more unstable than non-poor. Thus, almost all of the male working poor has unstable jobs their whole lives, and the female working poor's job sequences show distinct features according to women's life course. These results can give political implications to the anti-poverty policy in Korea.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.11-20
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• 2014

This study analyzed the optimal routes of auxiliary vehicles in an open-pit mine that need to traverse the entire mine through many working points. Unlike previous studies which usually used the Dijkstra's algorithm, this study utilized a heuristic algorithm for the Traveling Salesman Problem(TSP). Thus, the optimal routes of auxiliary vehicles could be determined by considering the visiting order of multiple working points. A case study at the Pasir open-pit coal mine, Indonesia was conducted to analyze the travel route of an auxiliary vehicle that monitors the working condition by traversing the entire mine without stopping. As a result, we could know that the heuristic TSP algorithm is more efficient than intuitive judgment in determining the optimal travel route; 20 minutes can be shortened when the auxiliary vehicle traverses the entire mine through 25 working points according to the route determined by the heuristic TSP algorithm. It is expected that the results of this study can be utilized as a basis to set the direction of future research for the system optimization of auxiliary vehicles in open-pit mines.