A new method is introduced for packing items in convex regions of the Euclidian n-dimensional space. By means of this approach the packing problem becomes a global finite-dimensional continuous optimization problem. T...
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A new method is introduced for packing items in convex regions of the Euclidian n-dimensional space. By means of this approach the packing problem becomes a global finite-dimensional continuous optimization problem. The strategy is based on the new concept of sentinels. Sentinels sets are finite subsets of the items to be packed such that, when two items are superposed, at least one sentinel of one item is in the interior of the other. Minimal sets of sentinels are found in simple two-dimensional cases. Numerical experiments and pictures showing the potentiality of the new technique are presented.
Interplanetary trajectories for a propulsion system providing a continuous outward radial thrust that varies according to the inverse square of heliocentric distance are investigated. This type of radial acceleration ...
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Interplanetary trajectories for a propulsion system providing a continuous outward radial thrust that varies according to the inverse square of heliocentric distance are investigated. This type of radial acceleration regime is realized by sun-facing solar sails and minimagnetospheric plasma propulsion, which allow the acceleration magnitude to be modulated in flight. Formulating the interplanetary trajectories as an optimal control problem, the escape from the solar system is studied, considering the maximization of the terminal orbital energy, while conserving the orbital angular momentum. The achievable hyperbolic excess velocity is studied in terms of the available maximum radial acceleration and the transfer angle. The inclusion of the Earth gravity assist for the escape from the solar system is shown to provide a more efficient means of achieving escape at the expense of flight time. Transfer between circular orbits is similarly realized by a combination of radial acceleration propulsion and planetary gravity assist, in which the radial acceleration acts as a control of the orbital energy and the planetary gravity assist acts as a control of the angular momentum.
A numerical approach for directly computing periodic orbits and theircorresponding stability via pseudospectral methods has been presented. The method is able togenerate periodic orbits without continuation, and is ap...
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A numerical approach for directly computing periodic orbits and theircorresponding stability via pseudospectral methods has been presented. The method is able togenerate periodic orbits without continuation, and is applicable to natural and forced periodicorbits. The approach relates the Jacobian of the discretized equations used in the determination ofthe periodic orbits to the monodromy matrix, which yields the stability information. This makesstability computations very efficient and effective for complex systems for which analyticderivatives may be difficult to construct. Furthermore, no propagation of equations of motion isnecessary, thus alleviating difficulties associated with sensitivity issues.
During construction, progress payments (cash inflow) are made periodically to contractors based oil work performed. Contractors are required to pay the direct costs (cash outflow) during construction. The net differen...
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During construction, progress payments (cash inflow) are made periodically to contractors based oil work performed. Contractors are required to pay the direct costs (cash outflow) during construction. The net difference between the cash inflow and outflow is the overdraft, which contractors must finance either from the bank or from their own resources. To increase profit margin, contractors consider methods to improve their cash flow, which will increase profit. These methods include front end loading (Stark 1974) and shifting of activities (Easa 1992). These two linear procedures could be done sequentially. However, this sequential linear formulation may not produce an optimized solution because of the nonlinear characteristics of the model. This note examines the combination of the two linear procedures into a single nonlinear formulation Such that better profit margin call be achieved.
This paper addresses the congestion management problem avoiding offline transmission capacity limits related to stability. These limits on line power flows are replaced by optimal power flow-related constraints that e...
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This paper addresses the congestion management problem avoiding offline transmission capacity limits related to stability. These limits on line power flows are replaced by optimal power flow-related constraints that ensure an appropriate level of security, mainly targeting voltage instabilities, which are the most common source of stability problems. Results from an illustrative case study based on the IEEE 24-bus Reliability Test System are analyzed. Conclusions are duly drawn.
A strategy for the control of the librations of a tethered satellite systemin elliptic orbits using tether length control, which drives the system to controlled periodiclibration trajectories, is suggested. There is a...
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A strategy for the control of the librations of a tethered satellite systemin elliptic orbits using tether length control, which drives the system to controlled periodiclibration trajectories, is suggested. There is a range of eccentricities up to about 0.4453 forwhich no length variations are needed for the system to follow the periodic trajectory. Above thiseccentricity, it is necessary to vary the length of tether to maintain a periodic trajectory. Themethod for finding these trajectories to minimize the control input utilizes a collocation ***-loop stability is provided by a linear feedback control law, whose feedback gains are alsoperiodic. Consequently, Floquet theory demonstrates the stability of the closed-loop system.
作者：
Barles, GuyUniv Tours
CNRS UMR 6083 Lab Math & Phys TheorFederat Denis Poisson F-37200 Tours France
We present a new stability result for viscosity solutions of fully nonlinear parabolic equations which allows to pass to the limit when one has only weak convergence in time of the nonlinearities.
We present a new stability result for viscosity solutions of fully nonlinear parabolic equations which allows to pass to the limit when one has only weak convergence in time of the nonlinearities.
In order to solve the optimization problem of designing the trajectory of three-dimensional horizontal well, we establish a multi-phase, nonlinear, stochastic dynamic system of the trajectory of horizontal well. We ta...
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In order to solve the optimization problem of designing the trajectory of three-dimensional horizontal well, we establish a multi-phase, nonlinear, stochastic dynamic system of the trajectory of horizontal well. We take the precision of hitting target and the total length of the trajectory as the performance index. By the integration of the state equation, this model can be transformed into a nonlinear stochastic programming. We discuss here the necessary conditions under which a local solution exists and depends in a continuous way on the parameter (perturbation). According to the properties we propose a revised Hooke-Jeeves algorithm and work out corresponding software to calculate the local solution of the nonlinear stochastic programming and the expectancy of the performance index. The numerical results illustrate the validity of the proposed model and algorithm.
In this paper, a nonlinear numerical technique is developed to calculate the limit load and failure mode of structures obeying an ellipsoid yield criterion by means of the kinematic limit theorem, nonlinear programmin...
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In this paper, a nonlinear numerical technique is developed to calculate the limit load and failure mode of structures obeying an ellipsoid yield criterion by means of the kinematic limit theorem, nonlinear programming theory and displacement-based finite element method. Using an associated flow rule, a general yield criterion expressed by an ellipsoid equation can be directly introduced into the kinematic theorem of limit analysis. The yield surface is not linearized and instead a nonlinear purely kinematic formulation is obtained. The nonlinear formulation has a smaller number of constraints and requires less computational effort than a linear formulation. By applying the finite element method, the kinematic limit analysis with an ellipsoid yield criterion is formulated as a nonlinear mathematical programming problem subject to only a small number of equality constraints. The objective function corresponds to the dissipation power which is to be minimized and an upper bound to the plastic limit load of a structure can then be calculated by solving the minimum optimization problem. An effective, direct iterative algorithm has been developed to solve the resulting nonlinear programming formulation. The calculation is based purely on kinematically admissible velocities. The stress field does not need to be calculated and the failure mode of structures can be obtained. The proposed method can be used to calculate the bearing capacity of clay soils in a direct way. Some examples are given to illustrate the validity and effectiveness of the proposed method.
in this paper, Celis-Dennis-Tapia (C-D-T or CDT) subproblem approach, is given a new use and is employed to tackle the system of nonlinear equations. In the new method, the system of nonlinear equations is transferred...
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in this paper, Celis-Dennis-Tapia (C-D-T or CDT) subproblem approach, is given a new use and is employed to tackle the system of nonlinear equations. In the new method, the system of nonlinear equations is transferred into a constrained nonlinear programming problem, which is then solved by C-D-T subproblem algorithms. We handle a C-D-T subproblem to obtain a trial step. Some criterion, similar to that in the trust region technique, is then employed to determine whether to accept this trial point or not. In the new algorithm, an c approximate solution or an locally infeasible point is obtained. In essence, constrained optimization methods are utilized to cope with the system of nonlinear equations. (c) 2005 Elsevier Inc. All rights reserved.
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