Feasible Zone Research Articles

Combined heat and power economic dispatch problem using the invasive weed optimization algorithm

Cogeneration units which produce both heat and electric power are found in many process industries. These industries also consume heat directly in addition to electricity. The cogeneration units operate only within a feasible zone. Each point within the feasible zone consists of a specific value of heat and electric power. These units are used along with other units which produce either heat or power exclusively. Hence the economic dispatch problem for these plants optimizing the fuel cost is quite complex and several classical and meta-heuristic algorithms have been proposed earlier. This paper applies the invasive weed optimization algorithm which is inspired by the ecological process of weed colonization and distribution. The results obtained have been compared with those obtained by other methods earlier and showed a marked improvement over earlier ones.

Combined heat and power economic dispatch problem using firefly algorithm

Cogeneration units, which produce both heat and electric power, are found in many process industries. These industries also consume heat directly in addition to electricity. The cogeneration units operate only within a feasible zone. Each point within the feasible zone consists of a specific value of heat and electric power. These units are used along with other units, which produce either heat or power exclusively. Hence, the economic dispatch problem for these plants to optimize the fuel cost is quite complex and several classical and meta-heuristic algorithms have been proposed earlier. This paper applies the firefly algorithm, which is inspired by the behavior of fireflies which attract each other based on their luminosity. The results obtained have been compared with those obtained by other methods earlier and showed a marked improvement over the earlier methods.

Robust interval linear programming for environmental decision making under uncertainty

In this study, a robust interval linear programming (RILP) method is developed for dealing with uncertainties expressed as intervals with deterministic boundaries. An enhanced two-step method (ETSM) is also advanced to solve the RILP model. The developed RILP improves upon the conventional interval linear programming (ILP) method since it can generate solution intervals within a larger feasible zone. The decision space based on ETSM contains all feasible solutions, such that no useful information is neglected. Moreover, the RILP can guarantee the stability of the optimization model due to no violation for the best-case constraints. The results also suggest that the RILP is effective for practical environmental and engineering problems that involve uncertainties.

Brainstem cavernomas: a surgical challenge

The authors show their experience with brainstem cavernomas, comparing their data with the ones of a literature review. From 1998 to 2009, 13 patients harboring brainstem cavernomas underwent surgical resection. All plain films, medical records and images were reviewed in order to sample the most important data regarding epidemiology, clinical picture, radiological findings and surgical outcomes, as well as main complications. The mean age was 42.4 years (ranging from 19 to 70). No predominant gender: male-to-female ratio, 6:7. Pontine cases were more frequent. Magnetic resonance imaging was used as the imaging method to diagnose cavernomas in all cases. The mean follow-up was 71.3 months (range of 1 to 138 months). Clinical presentation was a single cranial nerve deficit, VIII paresis, tinnitus and hearing loss (69.2%). All 13 patients underwent resection of the symptomatic brainstem cavernoma. Complete removal was accomplished in 11 patients. Morbidity and mortality were 15.3 and 7.6%, respectively. Cavernomas can be resected safely with optimal surgical approach (feasible entry zone) and microsurgical techniques, and the goal is to remove all lesions with no cranial nerves impairment.

Short-term electricity dispatch optimization of Ertan hydropower plant based on data by field tests

A short-term electricity dispatch optimization program required by the Ertan hydropower plant is developed to maximize hydropower production. Three field tests in various operating heads were carried out in the period of May 2009 to March 2010. Based on data of five test conditions, three operating zones for units in various operating heads were proposed. A short-term electricity dispatch optimization model was developed with physical and operational constraints. Unit commitment strategy was put forward for model solution, in which unit statuses and output statuses were classified. The strategy aimed at formulating better unit commitment plan according to forecasted load demand, ancillary service requirements, and initial operating status. The model and the strategy were verified by real cases. The results show that the optimal load distribution among units at every interval can be easily solved by the genetic algorithm based on a fixed unit commitment plan. Schedules are developed with higher average generation efficiency. Units can also be scheduled to operate for a less time within the rough zone and the second feasible zone. The proposed method is already operational for dispatch engineers of the Ertan hydropower plant to determine half-hourly schedules in one day.

English

In semi-arid regions, particularly in hard rock areas (Southern India), shallow aquifers are a major source of potable groundwater. These aquifers are indiscriminately exploited to meet the growing demand of water for domestic, irrigation as well as industrial uses. In order to achieve sustainable development, it is essential not only to delineate the groundwater potential zones but also suitable augmentation schemes which, in turn, require delineation of feasible recharge zones. Such zones are conventionally delineated through the application of various indirect methods, such as geological, hydro-geomorphological, geophysical, 14C-age dating, tracer, entropy method, and groundwater modeling. These methods are, in general, time consuming and may not be economical in the developing countries. A simple, efficient and cost-effective based on cross-correlation method, which takes into consideration the shallow aquifer response to rainfall, is presented to delineate groundwater recharge zones in hard rock areas. The zones so delineated were compared with the results obtained from remote sensing (RS) and GIS techniques and were further validated with the aid of estimated recharge values calculated using the modified water-table fluctuation (WTF) method. Key words: Shallow aquifers, rainfall, cross-correlation coefficient, recharge zone, water-table fluctuation, hard rock, Southern India.

Exurban development

Exurbia, the rural area beyond the built-up urban and contiguous suburban area, is being developed rapidly with attendant losses in habitat and ecosystem services. This paper analyzes a spatial dynamic model with two production technologies for residential development—municipal sewer service for suburban development and septic systems for exurban development. In outlying agricultural areas, the additional sewer extension costs can significantly reduce the value of agricultural land in suburban use. Exurban development, while at lower density, can occur immediately and requires only the onsite conversion costs of septic systems. Hence, the willingness to pay for exurban use from households with higher preferences for lot size may exceed the agricultural landowner's reservation price on future suburban use for a range of distances from the city boundary. This results in a “feasible zone” for exurban leapfrog development and another fundamental reason for scattered development in the urban–rural fringe.

The Limit Load Interactions of the Brazed Aluminum Plate-Fin Heat Exchanger Header Under Combined Piping Loads

In order to investigate the strength design problem of the brazed aluminum plate-fin heat exchanger header under complex external piping loads, the limit load interactions of the header under combined piping loads are studied in this paper. To establish the limit piping load interaction curves, nonlinear finite element analysis assuming the elastic perfectly plastic material model is performed by using the commercial finite element analysis software ANSYS and multiple piping load combinations, which are the combination of orthogonal bending moment components, torque component-shear force component, bending moment component-axial force component, compound bending moment-axial force component, and torque component-compound shear force, of the header with six opening ratios ranging from 0.5 to 1 are explored. The results of the interaction diagrams show that the feasible combined piping load zone of the header derived from the interaction curves can be simplified as a triangular zone determined by the individual limit piping load components safely and the simplified feasible zone is suggested to be used for establishing a simplified safety assessment method for the header under combined piping loads.

A Short Method To Calculate Residue Curve Maps in Multireactive and Multicomponent Systems

Reactive residue curve maps (RRCMs) are useful for the design of reactive distillation columns as a tool to establish feasible zones of reaction−separation. However, the calculation of an RRCM usually involves great computational effort due to the nonlinearity of the model equations and its iterative nature for the determination of reactive phase equilibrium. In this study, a simplified method for the generation of RRCMs is presented. This method is based on the application of reaction-invariant composition variables and assumes that the phase equilibrium constants (i.e., the relative volatilities) are independent of the temperature. Specifically, the phase equilibrium constants are calculated using a suitable estimation of the bubble temperature obtained from pure-component boiling temperatures and the reaction-invariant composition of liquid phase. These assumptions avoid iterative phase equilibrium calculations for obtaining a good approximation of RRCMs. Several reactive systems are used to identify t...

Robust model predictive control with zone control

Model predictive control (MPC) is usually implemented as a control strategy where the system outputs are controlled within specified zones, instead of fixed set points. One strategy to implement the zone control is by means of the selection of different weights for the output error in the control cost function. A disadvantage of this approach is that closed-loop stability cannot be guaranteed, as a different linear controller may be activated at each time step. A way to implement a stable zone control is by means of the use of an infinite horizon cost in which the set point is an additional variable of the control problem. In this case, the set point is restricted to remain inside the output zone and an appropriate output slack variable is included in the optimisation problem to assure the recursive feasibility of the control optimisation problem. Following this approach, a robust MPC is developed for the case of multi-model uncertainty of open-loop stable systems. The controller is devoted to maintain the outputs within their corresponding feasible zone, while reaching the desired optimal input target. Simulation of a process of the oil refining industry illustrates the performance of the proposed strategy.

Experience of microsurgical treatment of brainstem cavernomas: Report of 37 cases

Cavernomas are rare in the brainstem and account for 18-35% of central nervous cavernomas and can cause recurrent hemorrhages, devastating neurological deficits and mortality. To summarize the experience of microsurgical treatment of brainstem cavernomas and to investigate curative effect of microsurgical treatment of brainstem cavernomas. A retrospective analysis clinical data of 37 patients with brainstem cavernomas seen between 2003 and 2007. The analysis included age distribution, hemorrhage rates, clinical presentation, location of the lesions, and preoperative and postoperative Karnofsky Performance Scale (KPS) scores. The surgical indications, the timing of surgery and the surgical techniques were also assessed. All the 37 patients received microsurgical resections, there was no surgery-related mortality. Histopathological examination confirmed the diagnosis of cavernoma. Postoperatively, 20 patients had functional improvement, 15 patients had no change in the neurological status, and two patients deteriorated. Early surgery was associated with better outcomes. Mean followed up period was 21.5 months (range 6-36 months). During the follow-up 20 patients had resumed activities of daily living (KPS scores of 90-100), 10 patients were able to self-care with some efforts (KPS scores of 70-80), five patients needed considerable assistance (KPS score of 50-60) and two patients suffered hemiparesis (KPS scores of 40). None of the patient had recurrent hemorrhage. Brainstem cavernomas can safely be resected. Successful resection of brainstem cavernomas can be achieved by optimal surgical approaches, feasible entry zone and meticulous microsurgical techniques. The goal of surgical intervention should be the total resection of the lesion without any deteriorative in the neurological deficits.

Optimization of β/near-β forging process parameters of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si by using processing maps

The isothermal and constant strain rate compression tests of titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si are conducted by Thermecmaster-Z simulator and the deformation behaviors at the temperature of 990 ∼ 1080 °C and strain rate of 0.001 ∼ 70 s − 1 are extensively investigated. The processing maps (P-maps) under these deformation conditions are constructed and the forging process parameters are then optimized based on the generated P-maps. The experimental results show that most of the deformation is located at the flow instability zone when the strain rate is high ( ε̇ ≥ 0.6 s − 1 ). At the near-β forging temperature range, the feasible deformation conditions are (990 ∼ 1008 °C, 0.001 ∼ 0.01 s − 1 ) and its deformation mechanism is superplasticity. The optimum process parameters are (990 °C, 0.001 s − 1 ). At the β forging temperature range, when the deformation strain is smaller ( ε̄ ≤ 0.7), the suitable deformation conditions are (1035 ∼ 1070 °C, 0.001 ∼ 0.08 s − 1 ). The optimum deformation parameters, however, are 1055 °C and 0.001 s − 1 . If the strain is increased ( ε̄ = 0.8 ∼ 1.2), there are two feasible deformation zones, viz., (1008 ∼ 1025 °C, 0.001 ∼ 0.02 s − 1 ) and (1025 ∼ 1050 °C, 0.008 ∼ 0.16 s − 1 ), respectively. At the β forging temperature range, the main deformation mechanism is dynamic recrystallization.

Design for a tandem AGV system with two-load AGVs

Abstract The tandem AGV system is obtained by partitioning all workstations into multiple zones. Then, a single vehicle is assigned to each zone. In this paper, we present an analytical model to design a tandem AGV system with two-load AGVs. The analytical model is obtained by performing a design procedure which consists of two steps, ‘selection of feasible zones’ and ‘selection of final guide path.’ A numerical example is presented to show the design procedure.

Computer modeling of displacement ventilation systems based on plume rise in stratified environment

A model for displacement ventilation system based on plume rise of single point heat source was developed. The errors for temperature gradient ratio were less than 6% in most cases. Errors for temperature gradient and displacement zone height were relatively higher (up to 28.1%) which might be due to the derivation of the parameters from experimental data. Still, the errors were lower than those from design model/method of some other workers (68.5% for the temperature gradient ratio and 15.7% for the temperature difference between the supply air and at 0.1 m above floor level). With a room height of 2.4 m (common for office in Hong Kong) and design room temperature 25.5 °C defined at 1.1 m above floor level under the normal load to air flow ratio of 12,000 W/m 3/s (typical values for sub-tropical region) and minimum supply temperature of 18 °C, there existed a zone capacity range from 1000 to 5000 W that stand alone operation displacement ventilation system was feasible and that the displacement zone height (minimum 2.2 m) was above normal breathing level. The feasible zone capacity range diminished with decrease in design room temperature and/or room height. In this case, the load to air flow ratio had to be reduced, resulting in a higher flow rate when compared to a mixing ventilation system, or an auxiliary cooling facility such as a chilled ceiling had to be used.

Capillary electrophoresis analysis of fosfomycin in biological fluids for clinical pharmacokinetic studies.

A feasible capillary zone electrophoresis (CZE) method with indirect UV and contactless conductivity detection was developed for the determination of fosfomycin, an antibiotic, in human plasma and microdialysis samples. Samples were collected from test persons during a clinical trial. The background electrolytes used consisted of 25 mM benzoic acid and 0.5 mM hexadecyltrimethylammonium bromide, adjusted with tris(hydroxymethyl)aminomethane solution to pH 6.95 for plasma, and to pH 8.05 for microdialysis samples. CZE separations of the anionic analyte were carried out with reversed electroosmotic flow directed towards the anode. The limit of detection was between 0.6 and 2 microg/mL, depending on the matrix and the detection method. No sample preparation was needed for microdialysis samples; for plasma samples, proteins were precipitated with methanol (1+2, v+v), and the supernatant was analyzed. The yield determined with spiked samples was about 100%, the reproducibility of the entire method, expressed by the RSD% of three independent determinations of fosfomycin in triplicate after spiking Ringer's solutions and plasma samples, respectively, was better than 8%. The method is thus well-suited for clinical studies for the determination of the antibiotic in biological fluids.

Design of a variable path tandem layout for automated guided vehicle systems

The tandem AGV system is obtained by partitioning all workstations into multiple zones. Then, a single vehicle is assigned to each zone. In this paper, we present an analytical model to design a tandem AGV system with two-load AGVs. The analytical model is obtained by performing a design procedure which consists of two steps, ‘selection of feasible zones’ and ‘selection of final guide path.’ A numerical example is presented to show the design procedure.

The impact of flexible process capability on the product–process matrix: an empirical examination

Hayes and Wheelwright (Har. Bus. Rev. 57 (1) (1979) 127). provided the product–process matrix to emphasize the importance of the cooperation of manufacturing (processes) and marketing (products) to achieve the unified goals based on Skinner's tradeoff theory. But the environments have dramatically changed, and recently, some authors (Ferdows and De Meyer, J. Oper. Manage. 9 (1990) 168; Noble, Dec. Sci. J. 26(5) (1995) 693) have empirically verified that firms can achieve multiple competitive performances simultaneously. Their research especially illustrates how the high flexible process capability that a firm possesses greatly enlarges the feasible zones and reduces the constrained zone in the product–process matrix. Therefore, the product–process matrix needs some modifications to guide researchers and practitioners. This paper discusses and empirically tests the impact of flexible process capability on the product–process matrix and provides further evidence of the compatibility of multiple competitive performances rather than tradeoffs.

On the frequency and location of set point adjustments in sequential tolerance control

Sequential tolerance control (STC) is an approach that uses real-time measurement information at the completion of a stage to exploit the available space inside a dynamic feasible zone and reposition the set points for the remaining operations. STC has been shown to produce significantly higher yields than conventional tolerance control given constant equipment precision. STC was developed under the premise that a measurement and set point adjustment would follow each operation. However, measuring after each operation may not be practical under certain conditions. This study develops techniques for determining when measurements and set point adjustments should take place so that the benefits of STC are realized without interrupting the process after every operation.

A comparative evaluation of sequential set point adjustment procedures for tolerance control

The machining of complex parts typically involves a logical and chronological sequence of n operations on m machine tools. Because manufacturing datums cannot always match design datums, some of the design specifications imposed on the part are usually satisfied by distinct subsets of the n operations prescribed in the process plan. Conventional tolerance control specifies a fixed set point for each operation and permissible variation about this set point to insure compliance with the specifications. Sequential tolerance control (STC) uses real-time measurement information at the completion of one stage to exploit the available space inside a dynamic feasible zone and reposition the set point for subsequent operations. This paper introduces an extension of STC that utilizes the variability of the operations to scale the problem data and further enhance the ability of STC to optimize the production of an acceptable part.

Sequential tolerance control in discrete parts manufacturing

The machining of complex parts typically involves a logical and chronological sequence of n operations on m machine tools. Because manufacturing datums cannot always match design datums, some of the design specifications imposed on the part are usually satisfied by distinct subsets of the n operations prescribed in the process plan. Conventional tolerance control specifies a fixed set point for each operation and permissible variation about this set point to insure compliance with the specifications. This approach is inadequate for complex, low volume, highvalue added parts such as those found in the aircraft, nuclear, or precision instrument manufacturing industry. This paper introduces the concept of Sequential Tolerance Control, an approach that uses real-time measurement information at the completion of stage j to exploit available space inside a dynamic feasible zone and reposition the set point for operations j + 1 to n. The procedure is repeated at appropriate locations along the n operations so as to optimize the production of an acceptable part.