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Many Constraints (many + constraint)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Transmission network expansion planning with security constraints based on bi-level linear programming

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2009
Hong Fan
Abstract In deregulated power market, multiple conflicting objectives with many constraints should be balanced in transmission planning. The primary objective is to ensure the reliable supply to the demand as economically as possible. In this paper, a new bi-level linear programming model for transmission network expansion planning (TNEP) with security constraints has been proposed. The modeling improves traditional building style by adding reliability planning into economy planning as constraints, letting optimal planning strategy be more economic and highly reliable. A hybrid algorithm which integrates improved niching genetic algorithm and prime-dual interior point method is newly proposed to solve the TNEP based on bi-level programming. The advantages of the new methodology include (1) the highest reliability planning scheme can be acquired as economically as possible; (2) new model avoids the contradictions of conflicting objectives in TNEP, and explores new ideas for TNEP modeling; (3) the proposed hybrid algorithm is able to solve bi-level programming and fully manifests the merits of two algorithms as well. Simulation results obtained from two well-known systems and comparison analysis reveal that the proposed methodology is valid. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Cost numerical optimization of the triple-pressure steam-reheat gas-reheat gas-recuperated combined power cycle that uses steam for cooling the first GT

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2008
A. M. Bassily
Abstract Optimization is an important method for improving the efficiency and power of the combined cycle. In this paper, the triple-pressure steam-reheat gas-reheat gas-recuperated combined cycle that uses steam for cooling the first gas turbine (the regular steam-cooled cycle) was optimized relative to its operating parameters. The optimized cycle generates more power and consumes more fuel than the regular steam-cooled cycle. An objective function of the net additional revenue (the saving of the optimization process) was defined in terms of the revenue of the additional generated power and the costs of replacing the heat recovery steam generator (HRSG) and the costs of the additional operation and maintenance, installation, and fuel. Constraints were set on many operating parameters such as air compression ratio, the minimum temperature difference for pinch points (,Tppm), the dryness fraction at steam turbine outlet, and stack temperature. The net additional revenue and cycle efficiency were optimized at 11 different maximum values of turbine inlet temperature (TIT) using two different methods: the direct search and the variable metric. The optima were found at the boundaries of many constraints such as the maximum values of air compression ratio, turbine outlet temperature (TOT), and the minimum value of stack temperature. The performance of the optimized cycles was compared with that for the regular steam-cooled cycle. The results indicate that the optimized cycles are 1.7,1.8 percentage points higher in efficiency and 4.4,7.1% higher in total specific work than the regular steam-cooled cycle when all cycles are compared at the same values of TIT and ,Tppm. Optimizing the net additional revenue could result in an annual saving of 21 million U.S. dollars for a 439,MW power plant. Increasing the maximum TOT to 1000°C and replacing the stainless steel recuperator heat exchanger of the optimized cycle with a super-alloys-recuperated heat exchanger could result in an additional efficiency increase of 1.1 percentage point and a specific work increase of 4.8,7.1%. The optimized cycles were about 3.3 percentage points higher in efficiency than the most efficient commercially available H-system combined cycle when compared at the same value of TIT. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A generalization of the mass-sheet degeneracy producing ring-like artefacts in the lens mass distribution

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
J. Liesenborgs
ABSTRACT The inversion of a gravitational lens system is, as is well known, plagued by the so-called mass-sheet degeneracy: one can always rescale the density distribution of the lens and add a constant-density mass sheet such that the, also properly rescaled, source plane is projected on to the same observed images. For strong lensing systems, it is often claimed that this degeneracy is broken as soon as two or more sources at different redshifts are available. This is definitely true in the strict sense that it is then impossible to add a constant-density mass sheet to the rescaled density of the lens without affecting the resulting images. However, often one can easily construct a more general mass distribution , instead of a constant-density sheet of mass , which gives rise to the same effect: a uniform scaling of the sources involved without affecting the observed images. We show that this can be achieved by adding one or more circularly symmetric mass distributions, each with its own centre of symmetry, to the rescaled mass distribution of the original lens. As it uses circularly symmetric distributions, this procedure can lead to the introduction of ring-shaped features in the mass distribution of the lens. In this paper, we show explicitly how degenerate inversions for a given strong lensing system can be constructed. It then becomes clear that many constraints are needed to effectively break this degeneracy. [source]

The link between sociotropy/autonomy and dimensions of relationship commitment: Evidence from gay and lesbian couples

PERSONAL RELATIONSHIPS, Issue 2 2000
LAWRENCE A. KURDEK
The tendency to be excessively concerned about either interpersonal relationships (sociotropy) or self-reliance (autonomy) has been regarded as increasing one's susceptibility to experience symptoms of depression. In this study, both one's own and one's partner's scores for each tendency were linked to two dimensions of one's own appraisal of relationship commitment (attractions to the relationship and constraints against leaving the relationship) in a sample of both partners from 29 gay and 35 lesbian cohabiting couples. One's own high autonomy was linked to perceiving few attractions to the relationship, whereas one's own high sociotropy was linked to perceiving many constraints to leaving the relationship under two conditions: when one's partner's sociotropy was low or when one regarded the partner as highly dependable. Findings support the view that individual differences variables may serve as either risk factors for or protective factors against difficulties in maintaining a close relationship and underscore the need to examine cross-partner effects and moderating effects in identifying the individual differences variables linked to relationship functioning. [source]