• Journal of the Korean Mathematical Society
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• v.48 no.6
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• pp.1225-1248
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• 2011

The present paper is concerned with a two-competitor/oneprey population system with Holling type-II functional response and two discrete delays. By linearizing the system at the positive equilibrium and analyzing the associated characteristic equation, the asymptotic stability of the positive equilibrium and existence of local Hopf bifurcations are investigated. Particularly, by applying the normal form theory and the center manifold reduction for functional differential equations (FDEs) explicit formulae determining the direction of bifurcations and the stability of bifurcating periodic solutions are derived. Finally, to verify our theoretical predictions, some numerical simulations are also included at the end of this paper.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.717-720
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• 2000

Event-driven communication protocols such as CAN(Controller Area Network) have inherent packet delays due to the contention process for the use of network medium. These delays are stochastic in nature because most packets arrive at random time instants. The stochastic property of the delay adversely influences the control system's performance in terms of stability, responsiveness and steady-state error. Another problem for safety-critical application such as brake-by-wire systems is the reliability of the communication modules that can fail abruptly. This paper deals with two methods to overcome the above problems : (i) scheduling method that can maintain packet delays under some acceptable level, and (ii) redundancy management of communication modules that prescribes dual-redundancy modules' behavior when one of them fails.

• Journal of the Korean Mathematical Society
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• v.51 no.4
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• pp.703-719
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• 2014

This paper is concerned with the traveling wave solutions of nonlocal dispersal models with nonlocal delays. The existence of traveling wave solutions is investigated by the upper and lower solutions, and the asymptotic behavior of traveling wave solutions is studied by the idea of contracting rectangles. To illustrate these results, a delayed competition model is considered by presenting the existence and nonexistence of traveling wave solutions, which completes and improves some known results. In particular, our conclusions can deal with the traveling wave solutions of evolutionary systems which admit large time delays reflecting intraspecific competition in population dynamics and leading to the failure of comparison principle in literature.

• Ocean Systems Engineering
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• v.12 no.2
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• pp.159-172
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• 2022

To ensure stable performance, adaptive regulators with new theories are designed for steel-covered offshore platforms to withstand anomalous wave loads. This model shows how to control the vibration of the ocean panel as a solution using new results from Lyapunov's stability criteria, an evolutionary bat algorithm that simplifies computational complexity and utilities. Used to reduce the storage space required for the method. The results show that the proposed operator can effectively compensate for random delays. The results show that the proposed controller can effectively compensate for delays and random anomalies. The improved prediction method means that the vibration of the offshore structure can be significantly reduced. While maintaining the required controllability within the ideal narrow range.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.6
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• pp.550-556
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• 2009

In an application of a time reversal(TR) focusing of array transducer on a defect inside the test material, we employ a new time delay focusing technique based the TR process. In order to realize this idea, a multi-channel ultrasonic system is constructed capable of applying necessary time delays to each channel. The TR-based focusing procedure first measures the backscattered signals after firing one of the array elements. A phase slope method is then used to determine the time-of-flights of the backscattered signals received by all elements of the array. These time delays are used to adjust the time of excitation of the elements for transmission focusing on the defect. In addition to the TR focusing, the classical phased array focusing is also considered for comparison. Experimental results show that the TR-based time delay focusing produces much stronger backscattered signals than the phased array focusing, demonstrating the enhanced capability of the TR focusing.

• Industrial Engineering and Management Systems
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• v.15 no.4
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• pp.335-344
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• 2016

Construction project is a competitive business with high risk especially in developing countries like Iran which faces with many problems such as delay and time and costs increases. Thus, the first priority here is to determine the causes of prolongation of construction projects and to evaluate their importance. Khuzestan Steel Company (KSC) has made important contribution to the projects in Iran and in turn is required to finish them on time. In this study, an attempt was made to investigate the causes of delay in implementation of construction projects held by this company. Data was collected through questionnaire distributed among the sample including 10 owners, 10 consultants and 15 con-tractors. Accordingly, participants rated the causes in the questionnaire so the most important priorities of each area were specified using TOPSIS method. The results showed that according to the employers, consultants and contractors' viewpoints, the most important reason for delays in construction projects of KSC is related to the financial matters. Hence, according to the results obtained, causes for delays in the company's projects are largely related to the drilling permits and long administrative cycle to renew them. Besides, continuous production of steel in this company is another reason to delays of construction projects.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.30B no.1
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• pp.18-28
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• 1993

Processes in the real-time distributed control systems share a network medium to exchange their data. Performance of feedback control loops in the real-time distributed control systems is subject to the network-induced delays from sensor to controller, and from controller to actuator. The network-induced delays are directly dependent upon the data sampling times of control components which share a network medium. In this study, an algorithm of determining data sampling times is developed using the "window concept". where the sampling datafrom the control components dynamically share a limited number of windows. The scheduling algorithm is validated through the aimulation experiments.

• Journal of Institute of Control, Robotics and Systems
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• v.10 no.7
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• pp.583-589
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• 2004

Modem control systems often use a communication network to send measurement and control signals between nodes. Communication delays can be time varying. The length of the time delays is often hard to predict and modeled as being random. This paper proposes a combined controller used to compensate network time delay by estimating the delay with the interacting multiple model (IMM). The network delay is modeled as a Markov chain and 3 modes representing heavy, medium, and low network loads are used in the IMM. The proposed method is applied to an optimal control system with double integrators and the results are compared with the existing control methods.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.915-920
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• 2003

Modern control systems often use a communication network to send measurement and control signals between nodes. Communication delays can be time varying. The length of the time delays is often hard to predict and are modeled as being random. This paper proposes a combined controller used to compensate network time delay by estimating the delay with the interacting multiple model (IMM). The network delay is modeled as a Markov chain and 3 modes representing heavy, medium, and low network loads are used in the IMM. The proposed method is applied to an optimal control system with double integrators and the results are compared with the existing control methods.

• Journal of Institute of Control, Robotics and Systems
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• v.2 no.1
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• pp.1-4
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• 1996

This paper presents a state feedback $H^{\infty}$ controller design method for linear systems with delayed states and inputs. We derive a sufficient condition that the closed-loop system is asymptotically stable for all time-delays and that the $H^{\infty}$-norm of the closed-loop transfer function is less than or equal to some prescribed level $\gamma$. And we propose a sufficient condition for the existence of a state feedback $H^{\infty}$ controller using a form of linear matrix inequality(LMI). Furthermore, we show that the state feedback $H^{\infty}$ controllers can be obtained from solutions satisfying LMI.