• ETRI Journal
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• v.34 no.2
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• pp.272-275
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• 2012

This letter studies the problem of exploiting multichannel diversity in a spectrum sharing system, where the secondary user (SU) sequentially explores channel state information on the licensed channels with time consumption. To maximize the expected achievable throughput for the SU, we formulate this problem as an optimal stopping problem, whose objective is to choose the right channel to stop exploration based on the observed signal-to-noise ratio sequence. Moreover, we propose a myopic but optimal rule, called one-stage look-ahead rule, to solve the stopping problem.

• International Journal of Control, Automation, and Systems
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• v.6 no.2
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• pp.160-170
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• 2008

Temperature control of an enclosed thermal system which has many applications including Rapid Thermal Processing (RTP) of semiconductor wafers showed an input-constraint violation for nonlinear controllers due to inherent strong coupling between the elements [1]. In this paper, a constrained nonlinear optimal control design is developed, which accommodates input constraints using the linear algebraic equivalence of the nonlinear controllers, for the temperature control of an enclosed thermal process. First, it will be shown that design of nonlinear controllers is equivalent to solving a set of linear algebraic equations-the linear algebraic equivalence of nonlinear controllers (LAENC). Then an input-constrained nonlinear optimal controller is designed based on that LAENC using the constrained linear least squares method. Through numerical simulations, it is demonstrated that the proposed controller achieves the equivalent performances to the classical nonlinear controllers with less total energy consumption. Moreover, it generates the practical control solution, in other words, control solutions do not violate the input-constraints.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.365-367
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• 1998

This paper shows the form of the optimal solution and how to minimize energy of train driving control. In this paper we consider the case where a train is to be driven by manual operation mode along a straight level track, and with speed limits. Using the constrained optimal technique(Lagrange Function & Kuhn-Tucker equations), we constructed optimal train driving strategy.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2122-2125
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• 2008

Because the reheating furnace consumes a large amount of energy to heat up the slabs, it is very important to find an optimal temperature patterns in the furnace for energy saving as well as uniform target temperature at the exit of the furnace. In this study, the temperature profiles in the slab are determined by solving the transient one-dimensional heat conduction equation in conjunction with boundary conditions with total heat exchange factors. The optimal temperature patterns are obtained to minimize the fuel consumption with satisfying the predetermined constraint conditions. The design optimization is performed by using a genetic algorithm and the optimal results are validated with results obtained from the PIDO tool, called as P.I.A.n.O.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.16 no.4
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• pp.1-8
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• 2020

For a central cooling system of a medical facility composed of absorption chiller and screw chiller, the study was conducted on how to minimize the energy cost. In consideration of the energy cost, the optimal operation method in which the operation method of the heat source is changed according to the size of the cooling load was derived through simulation analysis. When applying the optimal operation method, the indoor environment, energy consumption, and energy cost were analyzed and compared with the reference operation method.

• East Asian mathematical journal
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• v.38 no.3
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• pp.277-292
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• 2022

This study investigates the convergence of the optimal consumption and investment policies in a binomial-tree model to those in the continuous-time model of Merton (1969). We provide the convergence in explicit form and show that the convergence rate is of order ∆t, which is the length of time between consecutive time points. We also show by numerical solutions with realistic parameter values that the optimal policies in the binomial-tree model do not differ significantly from those in the continuous-time model for long-term portfolio management with a horizon over 30 years if rebalancing is done every 6 months.

• Journal of Biosystems Engineering
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• v.16 no.3
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• pp.248-262
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• 1991

Simulation model was developed to analyze drying process for tray type red pepper dryer and validated by experiments. This model could predict satisfactorily temperatures and moisture contents of red pepper and temperatures of drying air during drying. Optimize algorithm was developed to search control valiables (drying air temperature, air recycle ratio and air flow rate) of red pepper dryer based on a criterion of minimizing energy consumption under the constraint conditions that statisfied carotenoid retension of at least 210mg per 100g dry matter, the moisture content of bottom layer of 15% (d.b) and drying time of less than 35 hours. Step changes in drying air temperature and air recycle ratio were considered in the optimization. In single step in control variables, the difference of the moisture content between top layer and bottom layer was great and more fan power was required. As the drying trays were exchanged when the moisture content of bottom layer reached to 100% (d.b), fifty percent of energy was saved and the difference of moisture content was little. In double step changes in control variables, optimal conditions were found by changing the step when the moisture content of bottom layer reached to 100% (d.b) (about 19.8 hours from starting drying). Optimum air flow rate was $18.1cmm/m^2$. Optimum drying air temperature and air recycle ratio in the first step was $55.8^{\circ}C$ and 0.80, and in the second step $65.6^{\circ}C$ and 0.88, respectively. In triple step changes in control variables, the optimal conditions were found by changing the steps when the moisture content of bottom layer reached to 250% (d.b) and 150% (d.b). Optimal air temperatures were $66.2^{\circ}C$, $58.4^{\circ}C$ and $66.9^{\circ}C$, and optimal air recycle ratios were 0.778, 0.785, 0.862 at each step, respectively. Optimal air flow rate was $18.9cmm/m^2$. The best operating mode was triple step mode considering energy consumption, drying time, fan power, and quality of dried red pepper. When the triple step mode was used to dry the red pepper, the energy consumption was about 16.5%~57.2% less than that of the single step mode and the drying time was 6.6 hours shorter than that of the double step mode.

• Korean Journal of Food Science and Technology
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• v.21 no.5
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• pp.676-685
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• 1989

Optimal operating conditions of on-farm red pepper dryer were searched by using the simulation-optimization algorithm combining the drying and quality deterioration models of red pepper with Box's complex method. Determination of control variables such as air temperature, air recycle ratio and air flow rate was based on a criterion of minimizing energy consumption under the constrainst conditions that satisfied the specified color retention of carotenoids. As quality constraint was stricter, energy consumption increased and total drying time decreased with lower recycle ratio and higher air flow rate Product mixing during drying was found to be able to improve the energy efficiency and product quality. Currently used air flow rate was assessed to be increased for the optimal operation. Two stage drying at the fixed optimal air flow rate was proven to be useful means for further saying of energy consumption. In the optimal bistaged drying, the second stage began at about one third of the total drying time and low air temperature in the first stage Increased to a high value and air recycle ratio increased slightly in the second stage. Optimal control variable scheme could be explained by the dryer performance and the carotenoids destruction kinetics in red pepper drying.

• The KIPS Transactions:PartC
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• v.14C no.7
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• pp.583-588
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• 2007

It is easy to implement a temporary network with a mobile ad-hoc network in which mobile nodes have without using a infrastructure network. They depend on their limited power. Recently, it is a hot issue to save the energy in a mobile ad-hoc network because a mobile nodes have a limited energy. Research of IEEE 802.11 PSM was proposed in a single hop ad-hoc assumption. If IEEE 802.11 PSM is applied to multi hop ad-hoc network, non-optimal paths will be generated by the mobile nodes which didn't receive a message of routing request. Non-optimal paths increase not only a network latency but also energy consumption of mobile nodes. Reconfiguring algorithm of non-optimal paths caused by the mobile nodes which didn't receive a message of routing request is proposed in this paper. A mobile node can overhear the data in his range. A wireless medium is shared by all mobile nodes using the same bandwidth. All mobile nodes lookout the non-optimal paths with these properties of a medium, if non-optimal path is generated, optimal reconfiguring will be accomplished by modifying routing table of itself or sending a request message of routing update to nearby nodes. By reconfiguring the non-optimal paths to optimized ones, network latency and energy consumption was decreased. It is confirmed to ignore the overhead caused by a algorithm presented in this paper through the result of the simulation.

• Journal of Korea Multimedia Society
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• v.15 no.12
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• pp.1456-1463
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• 2012

In this paper, we study the ON/OFF control policy of base stations in two-tier heterogeneous cellular networks to minimize the total power consumption of the system. Using heterogeneous cellular networks is a potential approach of providing higher throughput and coverage compared to conventional networks with only macrocell deployment, but in fact heterogeneous cellular networks often operates regardless of total power consumption, which is a very important issue of modern cellular networks. We propose a policy that controls the activation/deactivation of base stations in heterogeneous cellular networks to minimize total power consumption. Under this policy, the total power consumed can be significantly reduced when the traffic is low while the QoS requirement is satisfied.