Showing papers in "Turkish Journal of Engineering and Environmental Sciences in 2001"

Esterification of Acetic Acid with Ethanol Catalysed by an Acidic Ion-Exchange Resin

Abstract: The esterification of acetic acid with ethyl alcohol catalysed by an acidic ion-exchange resin (Amberlyst-15) was carried out in a batch reactor at temperatures between 323 and 353 K at various starting compositions ranging from stoichiometric regime to the dilute regions. The resultant kinetic model fitted the experimental data well. The activation energy was found to be 104129 kJ.kmol-1 for the formation of ethyl acetate. The ethyl acetate production was also carried out in a packed bed reactive distillation column operated in batch and continuous modes. The effects of the variables such as the reflux ratio, vapour rate and feed flow rate on ethyl acetate production were studied experimentally. A packed bed reactive distillation column operated in continuous mode gave the highest ethyl acetate composition, far surpassing the chemical equilibrium at operating conditions.

A Comparative Study of Multiobjective Optimization Methods in Structural Design

Abstract: The computational algorithms of different multiobjective optimization techniques and their applications to structural systems are presented. The weighting, e -constraint, goal programming and modified game theory methods are described along with a comparative study of the results. The conflicting nature of the objective functions is studied through two multiobjective optimization problems. Specifically, the design of a 25-bar space truss and that of a satellite with flexible appendages are considered in numerical studies. The results from the multiobjective optimization methods are evaluated in terms of a supercriterion. It is concluded that the results obtained using the goal programming and modified game theory/goal programming approaches are properly balanced yielding the best compromise in the presence of conflicting objectives.

Anthropogenic pollution in İzmit Bay: Heavy metal concentrations in surface sediments

Abstract: The extent of marine pollution in İzmit Bay is studied using geochemical data in surface sediments. The concentrations of 41 elements in 24 samples establish that surface sediments in inner and central İzmit Bay display significant enrichments in Ag, As, Cd, Cr, Co, Cu, Hg, Mo, P, Pb, Sb, Ti, V, and Zn associated with high concentrations of total organic carbon and sulphur. Geo-accumulation indices indicate that the inner and central İzmit Bay surface sediments are moderately to very strongly polluted with respect to Ag, Cd, Hg, Mo and Sb, and unpolluted to moderately polluted with respect to As, Co, Cu, Pb, and Zn. Despite total sedimentary concentrations above their pre-industrial background levels, geo-accumulation indices show that the surface sediments in İzmit Bay are unpolluted with respect to Cr, Ti and V. Except for a localized area offshore Tuzla, the outer İzmit Bay is generally unpolluted with respect to heavy metals.

Reduction of Iron Oxides in Solid Wastes Generated by Steelworks

Abstract: Solid wastes generated by integrated iron and steel works cause environmental pollution and therefore must be discarded accordingly. Extensive research is being conducted for the recovery and elimination of the iron oxide that these wastes contain. The production of sponge iron from these wastes could be considered a method of beneficiation. In this study, the reduction of cold-bonded pellets produced from the solid wastes of Eregli Integrated Iron and Steel Works (ERDEMIR), using different reducing agents, was investigated. A rotary furnace was utilized for this purpose and the effects of different reducing agents, the ratio of Cfix / Fetotal, temperature and time on the reduction were studied. The kinetics of the reduction process were also investigated and the data obtained were correlated with the Ginstling-Brounshtein model. The activation energy of the reduction was found to be 48.5 kJ/mol.

Electrical Spectroscopy of Kaolin and Bentonite Slurries

Abstract: The electrical conductivity and dielectric permittivity of clay-water systems were used to characterize the physicochemical state of kaolin and bentonite-water systems. The dielectric permittivity and electrical conductivity of kaolin and bentonite were determined at various water contents and NaCl concentrations as a function of frequency, ranging from 0.1 kHz to 13 MHz. The results indicate that kaolin and bentonite have similar dielectric behavior. An increase in the frequency produces a decrease in the dielectric permittivity of the soil-pore water mixture. As the ion concentration increases, the dielectric permittivity of the mixture increases at low frequency (kHz) whereas it decreases at high frequency (MHz). The electrical conductivity of kaolin and bentonite increases with an increase in the ion concentration in the soil-water mixture. The electrical conductivity of a kaolin-water mixture decreases with an increase in the solid concentration. In contrast, the electrical conductivity of a bentonite-water mixture increases with a decrease in the solid concentration. This indicates the importance of the surface conductivity of a bentonite-water mixture. Furthermore, the results of this study indicate that dielectric permittivity and electrical conductivity might be used to characterize the electrokinetic behavior of soil minerals to determine the physiochemical changes in clay soil-water systems, such as subsurface contaminations.

Entropy-Based Assessment of Water Quality Monitoring Networks

Abstract: Assessment of water quality monitoring networks requires potential methods to delineate the efficiency and cost-effectiveness of current monitoring programs. To this end, the concept of entropy has been considered as a promising method in previous studies as it quantitatively measures the information produced by a network. This paper introduces a new approach for the assessment of combined spatial/temporal frequencies of monitoring networks. The results are demonstrated in the case of water quality data observed along the Gediz River Basin.

Generalized Reliability Model for Local Scour around Bridge Piers of Various Shapes

Abstract: Excessive local scour around piers and abutments is known as a major cause of bridge failure induced by hydraulic deciencies. Complexity of the scouring phenomenon and high degrees of uncertainties in governing parameters lead to an unavoidable risk in bridge pier design. In this paper, a generalized reliability model based on static resistance-loading interference is developed for the assessment of reliability of bridge scour for various pier shapes. In the model, the relative maximum scour depth and the linear combination of the relative approach flow depth and flow Froude number are dened as the system resistance and external loading, respectively. By examining sets of data, a two-parameter bivariate lognormal distribution is found to represent the joint probability density function of the resistance and loading. Reliability expressions are developed for various pier shapes. To obtain relevant information for decision-making, the model is applied to a case study in which a relationship is obtained between the reliability and safety factors for cylindrical and non-cylindrical piers under various return periods.

Experimental Investigation of Vegetable Oil Usage as Alternative Fuel in Diesel Engines

Abstract: In this experimental study, the effect of the usage of vegetable oils, as alternative fuels, on engine performance and exhaust emissions in a single cylinder diesel engine were investigated. No 2-D diesel fuel and nine different oils (raw sunflower oil, raw cottonseed oil, raw soybean oil, and sunflower methyl ester, cottonseed methyl ester, soybean methyl ester, obtained from the raw oils respectively and refined opium poppy oil, rapeseed and corn oil) were used. In order to determine emission and performance characteristics, the engine was tested with full load-varied speed and constant speed-varied load tests. Chemical and physical properties of the raw oils were improved by transesterification. Test results showed that, when using vegetable oils, the engine performance and NOX are lower, and smoke density is higher than the engine performance in which No 2-D diesel fuel is used. The engine performance with the methyl ester fuels is higher than that with the raw oils and are close to diesel fuel performance.

A Knowledge-Based Approach for Selection of Material Handling Equipment and Material Handling System Pre-design

Abstract: For material handling system design, material handling equipment selection is the first stage. Also the material handling system and facility layout design problems are coupled. Solving these problems needs consideration of these three different problems. Right material handling equipment selection and good design of the material handling system and facility layout can increase productivity and reduce investments and operations' costs. In this study, after describing the material handling equipment selection and pre-design of material handling systems problems and explaining their complexity and solution approaches, it is shown that material handling equipment selection and pre-design of a material handling system can be combined by using a knowledge-based approach.

Ageing Behaviour of Spray Cast Al-Zn-Mg-Cu Alloys

Abstract: Three 7xxx series aluminium SS70, N707 and 7075 alloys containing copper, zinc and magnesium were spray deposited using rapid solidification. Ageing of the 7075 alloy resulted in a peak hardnesses of 147, 186 and 191 MPa after 2, 24 and 48 h at temperatures of 175oC, 130oC and 120oC respectively. The other two alloys, SS70 and N707, were aged at 120oC, and both reached peak hardness after 24 h; SS70 had a peak hardness of 229 MPa and N707 of 228 MPa. A double ageing treatment at 105oC for 5 h then at 175oC for 1 h significantly increased the peak hardness to 185.6 MPa compared to a single stage of ageing at the higher temperatures in the 7075 alloy. TEM analysis of aged specimens revealed two types of precipitate that contributed to age hardening: h' and h (MgZn2).

Investigation of Geochemical and Leaching Characteristics of Solid Wastes from Yeniköy (Muğla-Turkey) Power Plant

Abstract: The use of lignite in power generation has led to increasing environmental problems associated not only with gaseous emissions but also with the disposal of ash residues. In particular, the use of low quality coals with high ash content results in huge quantities of both fly and bottom ash to be disposed of. An important problem related to coal ash disposal is the heavy metal content of the residue. In this regard, experimental results of numerous studies indicate that toxic trace metals may leach when fly ash and bottom ash come into contact with water. In this study, fly ash and bottom ash samples obtained from Yenikoy thermal power plant, located on the south-western coast of Turkey, were subjected to toxicity tests, namely, the extraction (EP) and toxicity characteristic leaching (TCLP) procedures of the U.S. Environmental Protection Agency (USEPA) and the Method A extraction procedure of the American Society of Testing and Material (ASTM).

Non-Linear Seismic Soil-Structure Interaction Analysis Based on the Substructure Method in the Time Domain

Abstract: This paper presents an idealized 2-dimensional plain strain finite element seismic soil-structure interaction (SSI) analysis based on a substructure method by using original software developed by the authors. To investigate the effects of SSI the following types of analysis were performed: linear SSI analysis and non-linear SSI analysis. For the same structure, analysis was carried out by the procedure without the consideration of soil-structure interaction. These computations were achieved for different peak accelerations: 0.15g, 0.30g and 0.45g. In another case for a different site soil with a shear wave velocity of 200, 300 and 500 m/s, a linear SSI analysis was performed. In the analysis, the radiation condition was fully accounted for, the soil plasticity was modeled with the Von Mises failure criterion, basemat uplift was not considered, and the action of gravity was not taken into consideration.

Suspended Sediment Loads Through Flood Events for Streams of Sakarya River Basin

Abstract: Most of the annual sediment yield from a watershed is transported by a stream during a small number of floods that occur in a relatively short period of time in a year. The aim of this article is to determine the possibilities of using only flood discharges for estimating transported suspended sediment loads to obtain easy and quick sediment load data for watershed conservation and reservoir planning studies. In this study, the transported suspended sediment load during flood events is examined, and relations between the annual sediment yield and the sediment load during the major floods in a given year are developed based on available stream suspended sediment data from the Sakarya River basin in Turkey. The importance of floods in the transport of a large percentage of annual sediment load can be illustrated very clearly by constructing cumulative sediment transport curves. In this study, for each station, cumulative sediment transport curves were determined. A total of 45 regression equations were found to estimate annual transported suspended sediment loads using the highest annual flood, two highest annual floods, three highest annual floods, and until ten highest annual floods for subbasins of the Sakarya River basin. From among these equations, seven equations with the highest R2were proposed to estimate annual transported suspended sediment loads.

Regression Analysis of Soil Compressibility

Abstract: A detailed study was carried out to determine the correlations between consolidation properties such as compression index, overconsolidation ratio and various index properties based on test results obtained from 300 soil samples. All of the tests were conducted in the I.T.U. Soil Mechanics Laboratory on samples taken from different construction sites distributed throughout Turkey during the last forty years. Different regression models were utilized and the most suitable relationships with the highest correlation coefficients were established. These developed relationships are compared with similar relationships suggested by various researchers. The proposed correlations appear to be very simple and practically applicable in assessing the consolidation of the soil layers most encountered in Turkey.

Sliding Mode Control of a Multi-Degree-of-Freedom Structural System With Active Tuned Mass Damper

Abstract: In this study, a sliding mode control system is designed for a multi-degree-of-freedom structure having an Active Tuned Mass Damper (ATMD) to suppress earthquake or wind induced vibration. Since the model might have uncertainties and/or parameter changes, sliding mode control is preferred because of its robust character and superior performance. In addition this control method can easily be applied to non-linear systems. The simulated system has five degrees of freedom. In this study, a linear motor is used as the control device. At the end of the study, the time history of the floor displacements, control voltage and frequency response of the both uncontrolled and sliding mode controlled structures are presented and the results are discussed.

Use of Non-Uniform Rational B-Splines for Three-Dimensional Computer Simulation of Warp Knitted Structures

Abstract: Some specific curves and surfaces have been used by engineers in the aerospace and automotive industries to design parts, such as car-body panels, for the last three decades. In this study, a method is developed for 3D solid computer representation of warp knitted structures using a similar technique. For this purpose, a three-dimensional cylindrical uniform solid yarn model was developed, such that the central axis is a space curve, by using the Non-Uniform Rational B-Spline (NURBS) surfaces. Then this model was applied to warp knitted fabrics using a CAD program written in C++ on a Silicon Graphics (SGI) workstation, which has an Open Inventor graphical library. The computer generated images of some structures are also given as examples in the study. This paper describes the methodology and mathematics used to create the three-dimensional solid yarn model and apply this model to textile structures.

Investigation of Turbulators for Fire Tube Boilers Using Exergy Analysis

Abstract: In this paper, an experimental study of five different types of ``turbulator" inserts for fire tube boilers is presented. The experimental setup was constructed in the Department of Mechanical Engineering Laboratory of Karadeniz Technical University. It was tested to evaluate the boiler efficiency according to TS 4040 standard, and to evaluate the second law efficiency of thermodynamics for the cases with and without inserts under the same operating conditions. Four new types of turbulator consisted of truncated hollow cones. They were placed in tandem parallel to the gas flow direction to allow no contact with the fire tube wall. The half-apex angles of the conical turbulators used in the experiments were 14o and 20o. The number of the turbulators inserted in the of the boiler was 200, their installation arrangements in the fire tubes were periodic, and their enlarging positions were in accordance with the gas flow direction. It was found that turbulators increased the boiler efficiency from 8% to 12% and the second law efficiency of the boiler from 24% to 27%. It is also shown that the one with the half-apex angle of 20o gives better results, about 4% enhancement compared with the other ones. A fifth new turbulator, consisting of a truncated half-cylindrical surface and placed in tandem with flow direction, also periodically interrupted and transposed in the fire tube boilers, provided a 4% increase in the boiler efficiency. The second law efficiency of the boiler was improved from 24% to 25.2%. It was also shown that there was no need to use an excess fan for the flue gas in the chimney because of the very low pressure drops in the new types of turbulator.

Equilibrium Data on Water-Ethanol-1-Dodecanol Ternary System

Abstract: The experimental liquid-liquid equilibria of a water-ethanol-1-dodecanol system were investigated at temperatures of 298.16\pm0.20, 303.16\pm0.20 and 308.16\pm0.20 K. The reliability of experimental tie-line data was ascertained by using Othmer-Tobias and Hand plots. Distribution coefficients (Di) and separation factors (S) were evaluated for the immiscibility region. It was concluded that the high boiling solvent 1-dodecanol, is a possible separating agent for dilute aqueous ethyl alcohol solutions.

Optimum Design of Space Trusses with Buckling Constraints by Means of Spreadsheets

Abstract: In this paper, an algorithm is developed for the optimum design of space trusses with the help of spreadsheets. The algorithm depends on the interactive computing capability of spreadsheets. A general purpose optimization tool in spreadsheets is used for the optimization procedures. The analyses of space trusses are performed by the matrix displacement method. Specific macros have been developed for matrix calculations related to the truss systems. The displacement, tensile stress, buckling stress and minimum size constraints are considered in the formulation of the design problem. A number of design examples are presented to demonstrate the application of the algorithm. The optimum designs obtained using the spreadsheets are compared with those where a classical optimization method is employed.

Uncertainty of Local Scouring Parameters Around Bridge Piers

Abstract: Reliability-based assessment of local scouring mechanism around bridge piers provides information for decision-making regarding the pier footing design. Parameter uncertainties that may arise from various sources due to the inability to precisely quantify a parameter need to be estimated in order to quantify the level of risk of pier failure during the physical life of a bridge. By examining extensive experimental data from the literature on local scour depth around various shapes of bridge pier the functional dependence of relevant parameters is examined. The degree of uncertainty and the statistical randomness of these parameters are assessed in terms of coefficients of variation and probability distribution functions, respectively.

A Comparison of the Performances between a Genetic Algorithm and the Taguchi Method over Artificial Problems

Abstract: In the manufacturing industry, to produce the best quality product, it is important to define several levels of inputs. The Taguchi method is proposed for the solution of this problem and is widely used. In this study, a steady-state genetic algorithm (GA), called Genmak, is developed for the solution of the experimental design problems. In order to compare the performance of the suggested algorithm with that of the Taguchi method, 3 sets with different characteristics are carefully designed. Each set has 1000 test problems. Each of these test problems is an experimental design problem having 4 factors with 3 levels. Significant effects and optimum solution are determinated by statistical methods for every problem generated. Two methods are applied to the problems and the number of problems in which the optimum solution is reached is recorded. Then, the methods are compared with respect to these records. The results show that the performance of the GA is as high as that of the Taguchi method. Another important result is that the performance of the methods decreases as the amount of interaction in a problem increases. Overall, it is concluded that GAs are suitable for finding the optimum solution to this kind of problem and can be used as an alternative to the Taguchi method.

Factor Analysis of Water Quality Observations in the Sakarya River

Abstract: In this study, 42 water quality parameters obtained monthly from 1992 to 1996 at the last monitoring station on Sakarya River, namely Adatepe, have been evaluated. The results of factor analysis obtained from Adatepe indicate that 42 parameters can be reduced to 12 factors. Therefore, instead of measuring a large number of parameters in water quality research studies, a smaller number of carefully chosen parameters which are more critical have been determined.

Numerical Computation of Pressure in a Rigid Rectangular Tank due to Large Amplitude Liquid Sloshing

Abstract: In this study, sloshing inside partially filled enclosed baffled and unbaffled tanks was investigated. The fluid is assumed to be homogeneous, isotropic, viscous, and Newtonian and exhibiting only limited compressibility. Tank and fluid motions are assumed to be two-dimensional. A moving coordinate system is employed so that the tank movement is set to rest. The volume of fluid technique will, then, be used to track the free surface. The model solves the complete Navier-Stokes equations in primitive variables by the use of finite difference approximations. At each time step, a donor-acceptor method is used to transport the volume of fluid function and hence the locations of the free surface. Ten different cases including baffled and unbaffled tanks with different fill depths are studied near and on the resonant frequency. In order to assess the accuracy of the method used, computations are compared with theoretical and experimental results.

A Synoptic Study on the Phosphate and Phytoplankton Relationship in the Hypereutrophicated İzmir bay (Aegean Sea)

Abstract: Eutrophication has become an important environmental problem in coastal waters and its effects have increased due to the inflow of organic compounds and nutrients as well as the alterations in nutrient ratios. Besides the impact of streams, Izmir Bay, particularly the inner part of the bay, receives mainly continuous domestic and industrial inputs of phosphate. Occasionally, these inputs can reach extreme levels. Consequently, continuous phosphorus enrichment has been occurring. Nevertheless, the fate of phosphate, its effect on the phytoplankton biomass and the species dominancy in this biomass are poorly known. The seasonal patterns of phosphate, chlorophyll-a and abundance distributions of phytoplankton were determined in Izmir Bay between 1993 and 1994 in order to document the relationship between phosphate and phytoplankton. In spring, the increase in phytoplankton abundance associated with the phosphate decline suggested that the phosphorus uptake by phytoplankton was a major process responsible for the phosphate removal. It seemed that the bulk of inorganic phosphate in summer, i.e., June 94, results from the resuspended anthropogenic sediment load in the water column in the inner part of the bay, which is a semi-enclosed coastal basin. Owing to inadequate light conditions caused by high turbidity in this basin, it was assumed that the high amount of phosphate could not be recycled, but rather transported to the middle part of the bay where it enhanced the formation of phytoplankton bloom.

Preparation of Homogeneous Feedstocks for Injection Moulding of Zirconia-Based Ceramics

Abstract: In this study, a new method for preparing homogeneous feedstocks for injection moulding of ZrO2 ceramics was developed and explained in detail. Mixture homogeneity on a large scale was assessed by measuring green density after moulding and weight loss after partial debinding for several tube samples from different batches. The grain structure of a sintered specimen was examined using SEM for the packing of ceramic particles.

Removal of Natural Organic Matter and Trihalomethanes from the Drinking Water of Ankara City

Abstract: The effectiveness of granular activated carbon (GAC) adsorption for the removal of natural organic matter (NOM) and trihalomethanes (THM) from the drinking water treated at Ivedik Water Treatment Plant in Ankara City is investigated. Freundlich Isotherm constants K and n were determined as 17.61 (mg/g)(L/mg)1 / n and 1.66 respectively to determine the carbon capacity. Bench-scale GAC columns were run with empty bed contact times (EBCT) varying from 0.40 to 2.67 min to evaluate adsorption performance and to investigate the effect of EBCT on service life. The treated volumes of water increased with EBCT, showing a linear increase in GAC service life. A five-fold increase in EBCT resulted in an almost 16-fold increase in service life. Correspondingly, the carbon usage rate (CUR) decreased and the optimum bed depth was observed to be 10 cm. The capacities calculated by the isotherm equation and achieved in columns were also compared. The column capacities were within 43-65% of the isotherm capacities at complete breakthrough. However, they were only within 8-17% of the isotherm capacities at 50% breakthrough.

Stable Isotope Mass Balance Method to Find the Water Budget of a Lake

Abstract: Determination of a lake water budget is essential for water resources engineers. Some of these elements, such as surface inflow, precipitation, evaporation, surface outflow, and variation of lake level, can be measured easily at the site. However, it is difficult to determine the groundwater inflow and outflow. Although these quantities could be calculated as a residual term of the water budget equation, they yield information only on absolute contributions of groundwater flow. At least one additional equation is needed to solve the unknowns separately. Stable isotopes (oxygen-18 and deuterium), exist in water naturally, provide additional equations, and simultaneous solutions of these equations make it possible to quantify the groundwater inflow into and the outflow from the lake. In this paper, the stable isotope mass balance method, which is an expensive technique, together with the conventional water budget method are applied to Mogan Lake, located south of Ankara, Turkey, to determine the groundwater contribution to the lake. It was found that the average groundwater inflow to Mogan Lake is 20.42 million m3 \pm 17.22% while the average groundwater outflow is 16.44 million m3 \pm 24.95% for the 1994 water year.

Elastic-Plastic Deformation of a Tube with Free Ends Subjected to Internal Energy Generation

Abstract: The elastic-plastic deformation of a tube with free ends subjected to uniform internal energy generation is evaluated using Tresca's yield condition and the associated flow rule Yielding starts at the outer boundary and later another plastic region develops at the center, both of them corresponding to an `edge regime' of Tresca's prism The expansion of the plastic regions with increasing thermal load and the distribution of stresses and plastic strains are displayed graphically and discussed

Properties of Roller Compacted Concretes with Fly Ash

Abstract: In this study, brief information on zero slump concrete, which is not in common use in Turkey, is given. Zero slump concrete, also known as roller compacted concrete (RCC), is produced at a very low water-binder ratio. The vibrating slump method for determining the water-binder ratio of RCC is discussed. A laboratory investigation is carried out to assess the properties of RCC, which is a cost-effective and an attractive material for pavements. The strength characteristics of the concrete studied are presented. In the investigation, two fly ashes are employed to provide savings on cement. The influences of loss on ignition and the replacement ratio of fly ash as well as curing condition on the properties of RCC containing fly ash are assessed. The results show that a fly ash concrete having a similar strength value to that of conventional concrete can be produced at a 50% (by mass) replacement of cement by fly ash, provided that the fly ash used complies with the relevant standards. Fly ash concrete can also be produced with satisfactory strength development at a 70% replacement ratio (by mass). Loss in ignition content of fly ash was found to increase the mixing water, thus resulting in a reduction in strength development. The relation between the strength characteristics of RCC containing fly ash was found to be similar to that of conventional concrete. Considering strength and other properties, it was concluded that the concrete studied can be used for road paving material.

Determination of Flood Inundated Areas Using RS Techniques in the Western Black Sea Region of Turkey

Abstract: The remote sensing and geographic information systems are supplying new tools for flood inundation studies. RS/GIS techniques are used for the determination of the flood extent in the 20-21 May 1998 flood in the Western Black Sea region of Turkey. Two Advanced Very High Resolution Radiometer (NOAA/AVHRR) satellite images are processed in this study. The images are geocoded, and radiometrically and geometrically corrected. Unsupervised and supervised classification techniques are applied to the pre-processed images respectively in order to determine the flooded areas. The classified images are then compared for change detection. Detailed statistical analyses are performed with the results of the classifications. Ground truth observations for accuracy assessment of the classification are prepared as GIS layers after digitizing the land use maps, river networks, city locations and gaging stations. Various overlay analyses and spatial queries are performed for the interpretation of the classified image.