Search results for "Operation"
showing 10 items of 2969 documents
Optimal Trajectories for Spacecraft Rendezvous
2007
The efficient execution of a rendezvous maneuver is an essential component of various types of space missions. This work describes the formulation and numerical investigation of the thrust function required to minimize the time or fuel required for the terminal phase of the rendezvous of two spacecraft. The particular rendezvous studied concerns a target spacecraft in a circular orbit and a chaser spacecraft with an initial separation distance and separation velocity in all three dimensions. First, the time-optimal rendezvous is investigated followed by the fuel-optimal rendezvous for three values of the max-thrust acceleration via the sequential gradient-restoration algorithm. Then, the ti…
Optimistic NAUTILUS navigator for multiobjective optimization with costly function evaluations
2022
AbstractWe introduce novel concepts to solve multiobjective optimization problems involving (computationally) expensive function evaluations and propose a new interactive method called O-NAUTILUS. It combines ideas of trade-off free search and navigation (where a decision maker sees changes in objective function values in real time) and extends the NAUTILUS Navigator method to surrogate-assisted optimization. Importantly, it utilizes uncertainty quantification from surrogate models like Kriging or properties like Lipschitz continuity to approximate a so-called optimistic Pareto optimal set. This enables the decision maker to search in unexplored parts of the Pareto optimal set and requires …
An Adaptive Alternating Direction Method of Multipliers
2021
AbstractThe alternating direction method of multipliers (ADMM) is a powerful splitting algorithm for linearly constrained convex optimization problems. In view of its popularity and applicability, a growing attention is drawn toward the ADMM in nonconvex settings. Recent studies of minimization problems for nonconvex functions include various combinations of assumptions on the objective function including, in particular, a Lipschitz gradient assumption. We consider the case where the objective is the sum of a strongly convex function and a weakly convex function. To this end, we present and study an adaptive version of the ADMM which incorporates generalized notions of convexity and penalty…
Coordination and profit rate maximization
1995
We study the effects over the coordination between firms of the choice of another objectivefunction for the firm: the profit rate maximization which seems to be closer to business practice than the classical pure profit maximization. After recalling the effect of the new objective function over the optimum (the optimal production is lower), two cases are considered : perfect competition (the price signal disappear), and duopoly-oligopoly (the functions of reactions may vanish). (FR) Nous étudions les effets sur la coordination inter-firmes du choix d'une autre fonction objectif pour la firme: la maximisation du taux de profit qui semble être plus proche de la pratique des affaires que la cl…
Modelisation of the labor demand on a sample of Tunisian industrial firms
1993
The purpose of this paper is a modelisation of the demand labor in Tunisian industrial firms. The determination of labor input is deduced from a classical decisional problem of profit maximisation under technical constraints and constraints reported from the markets in relation with the labor market. Different specifications of the labor demand model were formulated and estimated on a sample of Tunisian industrial firms (on panel data)
The HOTELLING model : contributions and limits (application to the case where strategic variables are localizations and prices)
1991
Ix modèle de H O T E L L I N G a fait l'objet de nombreuses discussions. O n sait en particulier que lorsque le domaine des paramètres de localisation s'élargit et pour des coûts de transport linéaires, le prix d'équilibre en stratégie pure n'existe plus. I æ coût de transport linéaire et les discontinuités desfonctions sont responsables de l'absence d'équilibre. L'objet, de cette étude est de démontrer l'existence d'un équilibre à partir d'un jeu séquentiel. Toutd'abord les firmes choisisent leur localisation en anticipant des prix d'équilibre. Après avoir vérifié que, dans la pratique des affaires, les coûts de transport peuvent être soit de forme concave, soit de forme convexe, on introd…
Configuration optimale des aires de marché et coûts de transport
1991
La théorie des Places Centrales étudiée par LÖSCH (4) et CHRISTALLER (5) a pour objet l'examen et la construction d'un paysage hiérarchisé. Celui-ci est basé sur un système d'aires de marché qui possèdent des configurations précises (hexagonales et carrées principalement). En fait raire de marché correspond à la zone d'influence d'un offreur. LÖSCH (4, p 130) a supposé que la libre entrée de firmes indépendantes localisées sur une plaine où sont situés des demandeurs équidistants entraine une transformation des aires circulaires en aires hexagonales et ainsi une maximisation du nombre de firmes par unité d'aire. HARTWICK (2) examine analytiquement le théorème de LÖSCH concernant les aires d…
Three-mode pneumatic management of marine U-tank systems
2012
Abstract This paper deals with a new pneumatic control strategy for the roll damping enhancement of marine U-tank stabilizers. The proposed technique consists in a three-mode operation, where the control is active only within a limited resonant range around the ship natural frequency, whereas the control valves are kept closed in the remaining frequency range. Moreover the connection valve between the two air chambers is either closed or partially opened for the low or high frequencies, respectively. The pressurized air for the active control is fed by a turbo-blower set aboard and operates accelerating the motion of the water mass in the U-duct. The theoretical analysis is conducted in the…
Sea breeze thunderstorms in the eastern Iberian Peninsula. Neighborhood verification of HIRLAM and HARMONIE precipitation forecasts
2014
In this study we investigated sea breeze thunderstorms with intense convective activity (i.e., heavy rainfall, hail and gusty winds) that occurred over the eastern Iberian Peninsula (Spain) and were missed by the operational HIRLAM model. We used two grid-spacing setups (5.0. km and 2.5. km) of the hydrostatic HIRLAM model, and the non-hydrostatic spectral HARMONIE suite (2.5. km), to simulate isolated convection associated with sea breezes. The overall aim is to estimate the ability of these three experimental setups, in particular the HARMONIE model as the forthcoming operational numerical weather prediction in most European Weather Services, to correctly simulate convective precipitation…
Natural Convection Cooling of a Hot Vertical Wall Wet by a Falling Liquid Film
2008
Abstract The system studied is a plane channel in which one of the two vertical walls is kept at an arbitrary temperature profile and may be partially or completely wet by a falling liquid film, while the opposite wall is adiabatic. Air from the environment flows along the channel with a mass flow rate which depends on the balance between hydraulic resistances and buoyancy forces. These latter, in their turn, depend on the distribution of temperature and humidity (hence, density) along the channel and eventually on the heat and mass transferred from wall and film to the humid air. A simplified computational model of the above system was developed and applied to the prediction of relevant qu…