Actuated signals are able to adjust phase intervals in a real-time manner, in response to the traffic conditions obtained from vehicle detectors. These adjustments are implemented through a set of pre-determined contr...
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ISBN:
(纸本)9783037858585
Actuated signals are able to adjust phase intervals in a real-time manner, in response to the traffic conditions obtained from vehicle detectors. These adjustments are implemented through a set of pre-determined controller parameters, including the unit green extension. This paper develops a model based on cell transmission model (CTM) to optimize the unit green extension, explicitly considering the stochastic demand arrivals, which, from a disaggregated view, imposes significant impact on individual vehicle delay and thus influences the overall system performance. The vehicle actuation logic is mathematically formulated as a system of equalities and inequalities. Genetic algorithm is employed to solve the resulted mixed-integer problem and numerical examples are presented to generate optimal unit green extensions under various demand patterns.
A mixed-integer nonlinear programming model is proposed in this paper for reducing excessive standing phase angle difference (SPA) across open circuit breakers in transmission loop paralleling operation. The model ado...
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ISBN:
(纸本)9781479932542
A mixed-integer nonlinear programming model is proposed in this paper for reducing excessive standing phase angle difference (SPA) across open circuit breakers in transmission loop paralleling operation. The model adopts both the active power generation increment and the load switch as control variables and takes the relative importance of the loads to be restored into account, resulting in fewer rescheduled generators and less adjustment of active power generation. The condition for transmission loop paralleling operation can be reached from two ways of reducing generator adjustment time and optimally restoring load. The method can improve power restoration efficiency, speed up restoration progress, and hence reduce the loss of outage. Simulation results of New England 10-machine 39-bus test system demonstrate the effectiveness of the method.
Crude oil is primarily transported through sea using very large tankers. Efficient scheduling of these tankers is challenging as well as critical given long lead times, tight delivery time windows and high operational...
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Crude oil is primarily transported through sea using very large tankers. Efficient scheduling of these tankers is challenging as well as critical given long lead times, tight delivery time windows and high operational costs. We attempt to solve such a scheduling problem for an oil supplier facing supply quota and port capacity constraints. A mixed-integer programming formulation and two time-dependent solution techniques are proposed. Numerical results suggest that computing time was a function of the number, starting location, and time to availability of tankers at the supply sources. Finally, a time-based decomposition technique is presented to solve large problem instances, illustrating substantial reductions in computing time for marginally worse-off solutions.
The EU research project DISCUS defines a future proof end-to-end network architecture for next-generation communication networks. One central decision is at which and at how many Local Exchange (LE) locations the acti...
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ISBN:
(纸本)9781479956029
The EU research project DISCUS defines a future proof end-to-end network architecture for next-generation communication networks. One central decision is at which and at how many Local Exchange (LE) locations the active equipment has to be placed. The key drivers here are threefold: as hard constraint, technical requirements must be satisfied, while as softer constraints, reliability and cost-efficiency should be as high as possible. In this paper we present an optimization study on a set of parameters that influence the number of selected locations for active equipment. In particular we compute the number of active nodes that is actually necessary to connect all customers. Moreover, for this study we compute a realistic reference network that contains the Local Exchange (LE) locations of Italy provided by TELECOM ITALIA.
Recently, cooperative communication between users in wireless networks has attracted a considerable amount of attention. A significant amount of research has been conducted to optimize the performance of different coo...
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Recently, cooperative communication between users in wireless networks has attracted a considerable amount of attention. A significant amount of research has been conducted to optimize the performance of different cooperative communication schemes, subject to some resource constraints such as power, bandwidth, and time. However, in previous research, each optimization problem has been investigated separately, and the optimal solution for one problem is usually not optimal for the other problems. This dissertation focuses on joint optimization or cross-layer optimization in wireless cooperative networks. One important obstacle is the non-convexity of the joint optimization problem, which makes the problem difficult to solve efficiently. The first contribution of this dissertation is the proposal of a method to efficiently solve a joint optimization problem of power allocation, time scheduling and relay selection strategy in Decode-and-Forward cooperative networks. To overcome the non-convexity obstacle, the dual optimization method for non-convex problems [1], is applied by exploiting the time-sharing properties of wireless OFDM systems when the number of subcarriers approaches infinity. The second contribution of this dissertation is the design of practical algorithms to implement the aforementioned method for optimizing the cooperative network. The difficulty of this work is caused by the randomness of the data, specifically, the randomness of the channel condition, and the real-time requirements of computing. The proposed algorithms were analyzed rigorously and the convergence of the algorithms is shown. Furthermore, a joint optimization problem of power allocation and computational functions for the advanced cooperation scheme, Compute-and-Forward, is also analyzed, and an iterative algorithm to solve this problem is also introduced.
Serious environmental and economic problems of using fossil fuels in transportation sections force managers to think of alternative fuels such as hydrogen, ethanol, biodiesel, natural gas, or electricity. Meanwhile, l...
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Serious environmental and economic problems of using fossil fuels in transportation sections force managers to think of alternative fuels such as hydrogen, ethanol, biodiesel, natural gas, or electricity. Meanwhile, lack of fuel network infrastructures is a major problem, which needs to be investigated considering the number and optimal location of alternative fuel stations. In the literature, two different flow-based demand modeling concepts (the maximum cover and set cover) have been proposed for solving this problem. Because of the huge number of combinations of fuel stations for covering the flow of each path, the models are impractical for the real size problems. In this paper, the flow refueling location model was reformulated and a flexible mixed-integer linear programming model was presented, which was able to obtain an optimal solution much faster than the previous set cover version. The model also could be solved in the maximum cover form in a reasonable time on the large-sized networks.
This paper considers a minimum-cost network flow problem in a bipartite graph with a single sink. The transportation costs exhibit a staircase cost structure because such types of transportation cost functions are oft...
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This paper considers a minimum-cost network flow problem in a bipartite graph with a single sink. The transportation costs exhibit a staircase cost structure because such types of transportation cost functions are often found in practice. We present a dynamic programming algorithm for solving this so-called single-sink, fixed-charge, multiple-choice transportation problem exactly. The method exploits heuristics and lower bounds to peg binary variables, improve bounds on flow variables, and reduce the state-space variable. In this way, the dynamic programming method is able to solve large instances with up to 10,000 nodes and 10 different transportation modes in a few seconds, much less time than required by a widely used mixed-integer programming solver and other methods proposed in the literature for this problem.
Numerous planning models within the chemical, petroleum, and process industries involve coordinating the movement of raw materials in distribution networks so they can be blended into final products. The uncapacitated...
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Numerous planning models within the chemical, petroleum, and process industries involve coordinating the movement of raw materials in distribution networks so they can be blended into final products. The uncapacitated fixed-charge transportation problem with blending (FCTPwB) studied in this paper captures a core structure encountered in many of these environments. We model the FCTPwB as a mixed-integer linear program, and we derive two classes of facets, both exponential in size, for the convex hull of solutions for the problem with a single consumer and show that they can be separated in polynomial time. Furthermore, we prove that, in certain situations, these classes of facets along with the continuous relaxation of the original constraints yield a description of the convex hull. Finally, we present a computational study that demonstrates that these classes of facets are effective in reducing the integrality gap and solution time for more general instances of the FCTPwB with arc capacities and multiple consumers.
We consider mixed-integer linear programs where free integer variables are expressed in terms of nonnegative continuous variables. When this model only has two integer variables, Dey and Louveaux characterized the int...
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We consider mixed-integer linear programs where free integer variables are expressed in terms of nonnegative continuous variables. When this model only has two integer variables, Dey and Louveaux characterized the intersection cuts that have infinite split rank. We show that, for any number of integer variables, the split rank of an intersection cut generated from a rational lattice-free polytope L is finite if and only if the integer points on the boundary of L satisfy a certain "2-hyperplane property." The Dey-Louveaux characterization is a consequence of this more general result.
A parallel Simulated Annealing algorithm with multi-threaded architecture is proposed to solve a real bi-objective maintenance scheduling problem with conflicting objectives: the minimisation of the total equipment do...
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A parallel Simulated Annealing algorithm with multi-threaded architecture is proposed to solve a real bi-objective maintenance scheduling problem with conflicting objectives: the minimisation of the total equipment downtime caused by maintenance jobs and the minimisation of the multi-skilled workforce requirements over the given horizon. The maintenance jobs have different priorities with some precedence relations between different skills. The total weighted flow time is used as a scheduling criterion to measure the equipment availability. The multi-threaded architecture is used to speed up a multi-objective Simulated Annealing algorithm to solve the considered problem. Multi-threading is a form of parallelism based on shared memory architecture where multiple logical processing units, so-called threads, run concurrently and communicate via shared memory. The performance of the parallel method compared to the exact method is verified using a number of test problems. The obtained results imply the high efficiency and robustness of the proposed heuristic for both solution quality and computational effort.
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