Round Operation Research Articles

A mixed-coding scheme of evolutionary algorithms to solve mixed-integer nonlinear programming problems

In this paper, mixed-integer hybrid differential evolution (MIHDE) is developed to deal with the mixed-integer optimization problems. This hybrid algorithm contains the migration operation to avoid candidate individuals clustering together. We introduce the population diversity measure to inspect when the migration operation should be performed so that the user can use a smaller population size to obtain a global solution. A mixed coding representation and a rounding operation are introduced in MIHDE so that the hybrid algorithm is not only used to solve the mixed-integer nonlinear optimization problems, but also used to solve the real and integer nonlinear optimization problems. Some numerical examples are tested to illustrate the performance of the proposed algorithm. Numerical examples show that the proposed algorithm converges to better solutions than the conventional genetic algorithms.

Simulation of the control of a salt gradient solar pond in the south of Tunisia

We are interested in the modeling and control of a salt gradient solar pond (SGSP) in the south of Tunisia. We developed a model of a closed cycle salt gradient solar pond (CCSGSP) that ensures successful year round operation. This model was used to study the response of the solar pond (SP) to various control techniques. It takes into account heat and salt diffusion within the pond and simulates the transient behavior of a SGSP. Furthermore, we investigated the dynamic process, which involves internal gradient stability, boundary behavior between the gradient zone and the convective zones. We thus incorporated the double diffusive processes into the SP model by using the one dimensional stability criterion produced by linear theory. The governing differential equations are solved numerically by using a control-volume scheme. The results show that successful operation of a SP requires three things: the maintenance of the storage zone temperature through heat extraction and brine injection, the use of surface washing to control the deepening of the upper mixed layer and a well designed initial salt stratification to prevent the formation of instability within the gradient. Using linear salinity profile as an initial condition, three round year simulations were run using average meteorological data with the result that adequate stability ( Rρ≻2 throughout the gradient and Rρ≅10 at the interfaces) was maintained. Numerical results show also that 10–30% efficiency could have been reached if heat extraction is performed routinely especially when one considers that the storage temperature is within 40–80 °C. The model is validated against data taken from the operation of the UTEP SP. Close correlation between computed and measured data was obtained.

An Evolutionary Lagrange Method For Mixed-Integer Constrained Optimization Problems

This study proposes a method for solving mixed-integer constrained optimization problems using an evolutionary Lagrange method. In this approach, an augmented Lagrange function is used to transform the mixed-integer constrained optimization problem into an unconstrained min—max problem with decision-variable minimization and Lagrange-multiplier maximization. The mixed-integer hybrid differential evolution (MIHDE) is introduced into the evolutionary min—max algorithm to accomplish the implementation of the evolutionary Lagrange method. MIHDE provides a mixed coding to denote genetic representations of teal and integer variables, and a rounding operation is used to guide the genetic evolution of integer variables. To fulfill global convergence, self-adaptation for penalty parameters is involved in the evolutionary min—max algorithm so that small penalty parameters can be used, not affecting the final search results. Some numerical experiments are tested to evacuate the performance of the proposed method. Numerical experiments demonstrate that the proposed method converges to better solutions than the conventional penalty function method

Small Activated Sludge Performance and Viability Characteristics under Intermittent and Reduced Flows

Small activated sludge systems operate in transient states under intermittent and variable flows. Simulations for such a treatment plant in a summer house site operating on a seasonal basis is investigated for system performance and viability using the five component inert soluble substrate generation model. The results have revealed that the viability drops to zero within the first month after the cessation of the feed for intermittently loaded systems that are fed during the summer months, while it never reaches that value for systems operating all year round with reduced flows off season. Restartup is compulsory for the intermittent loadings while the system adapts itself in a stepwise manner for the year round operation. Other factors being comparable, conventional operation with shorter sludge ages may be preferable since viability of the sludge is higher and the effluent COD is comparable.

Production of charcoal briquettes from cotton stalk in malawi: Methodology for feasibility studies using experiences in Sudan

The feasibility of charcoal production from cotton stalks in Malawi was studied based on experience from Sudan. The country relies considerably on biomass fuels. Of the total energy consumption in Malawi of 2.376 MTOE in 1989, 92% was met by biomass (fuelwood: 83.6% and charcoal: 8.3% Petroleum fuels and ethanol contributed 5.4%; electricity, 1.6%; and coal, 1.0%. Most of the energy (84.8%) was consumed in the household sector. The “Malawi Charcoal Project”, which is the main charcoal project carried out in the country, attempted to produce alternative softwood charcoal from the large resource of pine plantations but was not successful because of unacceptability of the product for household use, long transport distances and costs, and the equipment required for industrial uses. Briquetting of uncarbonized sawdust was also carried out by the Wood Industries Corporation (WICO), but failed due to unacceptability of the products and technical problems. The estimated total national demand for cotton stalk charcoal (CSC) briquettes is 15,000 t yr −1 made up of 7000 and 8000 t yr −1 for household and industrial sectors, respectively. The household demand is most substantial in Blantyre (3500 t yr −1) and Lilongwe (2700). t yr −1 Ngabu town was found to be the most appropriate location for a plant to supply the Blantyre market. Of the many plant options that were found financially and economically viable, four, using drum kilns for carbonization, were the most attractive. These were the 800 t yr −1 agglomeration process with seasonal sun drying operation, 2- and 3-shifts, and the 3000 t yr −1 roll process, year round operation, 2- and 3-shifts with financial internal rates of return of 28.1%, 38.3%, 26.6% and 40.0% respectively and a pay-back period of three years. The agglomeration process was overall the most attractive, though not significantly so financially.

IEEE floating-point format

The IEEE Proposed Standard for Binary Floating-Point Arithmetic (P754, draft 10.0) is a standard for the representation of 32-, 64- and 128-bit floating-point numbers. This paper provides a tutorial overview of the standard, covering operations, the sign bit, rounding and flag operation. An implementation of the standard in the Advanced Micro Devices Am29325 floating-point processor is discussed.

An Extended Rounding Operation for Modeling Solids with Free-Form Surfaces

An extended rounding operation can be an excellent tool for modeling solids with free-form surfaces. Using the rounding operation, the edges and vertices of a solid can be locally rounded, and those parts of the solid are changed to free-form surfaces. As a user, you put in information about edges that should be rounded and the radii of curves generated by the operation. This facility has been implemented in our solid modeling system, Desiqnbase.

Reversed Chebyshev implementation of McClellan transform and its roundoff error

A new structure, called the reversed Chebyshev structure, for the fixed point implementation of the FIR filters designed with the McClellan transformation is presented. It shows the best roundoff noise performance among the existing ones for both rounding and truncation operations. The incremental rate of the upper bound on the variance of the roundoff noise, as the size of the 2-D filters increases, is very small. The reversed Chebyshev structure is rooted from our calculation of the upper bound on the variance of the output roundoff noise of 2-D FIR filters designed with the McClellan transformation. This upper bound is independent of the transformation filters and can be easily calculated to estimate the number of bits needed for the desired accuracy in the fixed point implementation.

Large-scale microalgae production for nursery rearing of marine bivalves

The feasibility of large-scale bloom induction of nutritionally suited natural phytoplankton species, to feed a semi-industrial nursery of edible shellfish, built on the Belgian coast, was tested. The outdoor microalgal production unit consisted of four tanks of 100 m 2 surface each (two of 1 m depth and two of 0·5 m depth), equipped with different mixing devices. The cultures were run as chemostats in which seawater was enriched with commercial inorganic N, P, and Si fertilizers. Depending on the season, between 5–10 and 80% of the culture volume could be harvested daily, with algal densities ranging from 50 000 to 500 000 cells per ml. By manipulation of operational parameters such as detention time, nutrient levels and nutrient ratios (N:Si:P), unsuited or less suited species of algae (e.g. Chlorella and Phaeodactylum) could be replaced by more desirable species (e.g. Skeletonema, Nitzschia, Chaetoceros). Various biological and technological problems encountered during year round operation, including collapsing of the culture, seawater enrichment, water quality, fouling and water treatment, are commented.

Constant flow solar pond collector/storage system

This paper presents a periodic analysis of the process of heat extraction by the brine layer circulating at constant flow rate through the bottom convective zone of a solar pond. Explicit expressions for the transient rate of heat extraction and the temperature at which heat can be extracted, as a function of time, depths of convective as well as non-convective zones and the flow rate, are derived. Extensive analytical results for the optimum performance of a pond during its year round operation are presented. In a pond with an upper convective zone depth of 0.2 m optimum heat extraction efficiencies of 24 per cent, 29 per cent and 32 per cent corresponding to heat extraction temperatures of 89, 55 and 42°C are predicted for water flow rates of 2 × 10−4, 5 × 10−4 and 10−3 kg/s m2, respectively. The load levelling in the extracted heat flux as well as in its temperature improves as the flow rate is lowered and the non-convective zone is over sized. An increase in the total depth of the solar pond improves the load levelling in extraction temperature, but influences the extracted heat flux differently; shifts its maximum to winter months and deteriorates the load levelling. The variability in flow rate required for the maintenance of constant temperature of the heat extraction zone is also investigated. It is found that the required variability is less for higher temperatures of the heat extraction zone and larger depths of the non-convective zone.

Performance of flat plate solar collectors in off-south orientation in India

This paper presents the effect of off-south orientation on the performance of flat plate solar collectors. This study is done, taking into consideration the building's off-south orientation. The present work investigates collector performance and optimum tilt as functions of the off-south angle, collection temperature, latitude and wind velocity. The three latitudes considered are of New Delhi(L = 28.38°N), Bangalore (L = 12.97°N) and Madras (13.0°N). It has been found that, for the best average winter performance, the tilt is latitude angle +15°, whereas, for the best average summer performance, it is latitude angle −15°. It has also been confirmed that, for year round operation, the maximum solar energy is collected when the tilt is 0.9 times the latitude angle. Further, it has been noticed that there is an optimum value of collector tilt for a given azimuthal angle at which yearly effectiveness is a maximum. The effect of increase in off-south angle is to decrease the yearly effectiveness.

Thermal analysis of three zone solar pond

This paper presents a periodic analysis of a three zone solar pond as a solar energy collector and long term storage system. We explicitly take into account the convective heat and mass flux through the pond surface and evaluate the temperature and heat fluxes at various levels in the pond during its year round operation by solving the time dependent Fourier heat conduction equation with internal heat generation resulting from the absorption of solar radiation in the pond water. Eventually, an expression, for the transient rate at which heat can be retrieved from the solar pond to keep the temperature of the zone of heat extraction as constant, is derived. Heat retrieval efficiencies of 40.0 per cent, 32.1 per cent, 28.3 per cent and 25.5 per cent are predicted at collection temperatures of 40, 60, 80 and 100°C, respectively. the retrieved heat flux exhibits a phase difference of about 30 to 45 days with the incident solar flux; the load levelling in the retrieved heat flux improves as the thickness of the non-convective zone increases. the efficiency of the solar pond system for conversion of solar energy into mechanical work is also studied. This efficiency is found to increase with collection temperature and it tends to level around 5 per cent at collection temperatures about 90°C.

Design and test of non-evacuated solar collectors with compound parabolic concentrators

The intermediate range of concentration ratios (1.5X–10X) which can be achieved with CPCs without diurnal tracking provides both economic and thermal advantages for solar collector design even when used with non-evacuated absorbers. The present paper summarizes more than 3 yr of research on non-evacuated CPCs and reviews measured performance data and critical design considerations. Concentrations in the upper portions of the practical range (e.g. 6X) can provide good efficiency (40–50 per cent) in the 100–160°C temperature range with relatively frequent tilt adjustments (12–20 times per year). At lower concentrations (e.g. 3X) performance will still be substantially better than that for a double glazed flat plate collector above about 70°C and competitive below, while requiring only semi-annual adjustments for year round operation. In both cases the cost savings associated with inexpensive reflectors, and the optimal coupling to smaller, simple inexpensive absorbers (e.g. tubes, fins, etc.) can be as important an advantage as the improved thermal performance. The design problems for non-evacuated CPC collectors are entirely different from those for CPC collectors with evacuated receivers. For example, heat loss through the reflector can become critical, since ideal CPC optics demands that the reflector extend all the way to the absorber. Recent improvements in reflector surfaces and low cost antireflection coatings have made practical a double-glazed non-evacuated CPC design. It is calculated that a 1.5X version of such a collector would have an optical efficiency η o = 0.71, a heat loss coefficient U = 2.2 W/m 2°C and a heat extraction effciency factor F′ ≥ 0.98, while requiring no tilt adjustments.

Fast Numerically Stable Computations for Generalized Linear Least Squares Problems

The generalized linear least squares problem is treated here as a linear least squares problem with linear equality constraints. Advantage is taken of this formulation to produce a numerically stable algorithm based on plane rotations which is designed for fast computation, especially for large structured problems. The algorithm can be made to handle any rank deficiency in the matrices. A rounding error analysis and operation counts are given. The use of nonunitary transformations is considered.

Solar ponds for space heating

Solar ponds are shallow bodies of water in which an artificially maintained salt concentration gradient prevents convection. They combine heat collection with long-term storage and can provide sufficient heat for the entire year. We consider the absorption of radiation as it passes through the water, and we derive equations for the resulting temperature range of the pond during year round operation, taking into account the heat that can be stored in the ground underneath the pond. Assuming a heating demand of 25000 Btu/degree day (Fahrenheit), characteristic of a 2000 ft 2 house with fair insulation, and using records of the U.S. Weather Bureau, we carry out detailed calculations for several different locations and climates. We find that solar ponds can supply adequate heating, even in regions near the arctic circle. In midlatitudes the pond should be, roughly speaking, comparable in surface area and volume to the space it is to heat. Under some circumstances, the most economical system will employ a heat pump in conjunction with the solar pond. Cost estimates based on present technology and construction methods indicate that solar ponds may be competitive with conventional heating.

Note on a Revised Sugar Coating Procedure for Tablets

A method is presented which describes a revised sugar coating procedure. The procedure eliminates the rounding and smoothing operations usually employed in pan-coated tablets. The resulting coating is approximately one-half as thick as the standard method and coating time is greatly reduced.

Round ligament sling operation for stress incontinence: Barns, H. H. Fouracre: J. Obst. & Gynaec. Brit. Emp. 57: 404, 1950

Round ligament sling operation for stress incontinence: Barns, H. H. Fouracre: J. Obst. & Gynaec. Brit. Emp. 57: 404, 1950

XXV A Summary of round Window Graft Operations Performed for Deafness

XXV A Summary of round Window Graft Operations Performed for Deafness

SHORTENING OF THE SUSPENSORY LIGAMENT OF THE LIVER FOR PTOSIS BY THE "ROUND LIGAMENT" METHOD

In doing Rovsing's operation for visceral ptosis, it is often necessary to elevate the liver also. It occurred to me, while operating in a case in which the liver was very low, that the suspensory might be treated as the is done in shortening the uterine supports. A long curved forceps is pushed through the posterior layer of fascia just below the tip of the ensiform cartilage; the suspensory is caught and pulled back through this small opening, and drawn down tight enough to bring the liver up snugly against the diaphragm, and is sutured to the fascia and muscles. In a series of sixteen cases in which I have done Rovsing's operation, modified, I have done the round ligament operation four times, with most excellent results. In one case in which the left lobe was very long, I passed sutures through the liver and attached