Dams are large hydraulic structures constructed to meet various project demands. Their roles in both environment and the economy of a country are so important that their design and construction should be carried out for negligibly small risk. Conventional design approaches are deterministic, which ignore variations of the governing variables. To offset this limitation, high safety factors are considered that increase the cost of the structure. Reliability&ndash / based design approaches are probabilistic in nature since possible sources of uncertainties associated with the variables are identified using statistical information, which are incorporated into the reliability models. Risk analysis with the integration of risk management and risk assessment is a growing trend in dam safety. A computer program, named CADAM, which is based on probabilistic treatment of random loading and resistance terms using Monte&ndash / Carlo simulation technique, can be used for the safety analysis of gravity dams. A case study is conducted to illustrate the use of this program.

A model study on laterally braced sheet pile walls retaining cohesionless soil was conducted using 1-g shaking table. Lateral dynamic earth pressures, backfill accelerations and dynamic displacement of walls were measured. Input accelerations were kept between 0.03g to 0.27g. A data acquisition system consisting of dynamic pressure transducers, accelerometers, displacement transducer, signal conditioning board and a data acquisition card compatible with a personal computer was used during the study. Three different walls with thicknesses of 6.6, 3.2 and 2.0 mm were used in order to investigate the effects of changing wall stiffness value on lateral seismic pressures developed on the wall. In addition to that, steel blocks were placed on top of the backfill in order to simulate a surcharge effect of 1.57 kPa to 3.14 kPa during shaking. Amplification of input acceleration, incremental seismic lateral thrusts and corresponding maximum dynamic pressures, application point of the resultant, effect of stiffness and surcharge on maximum seismic lateral thrust and dynamic wall deflections were calculated by processing raw data stored. The results were compared to previous model studies and some analytical methods available.

The productivity of most gas condensate wells is reduced significantly due to condensate banking when the bottom hole pressure falls below the dew point. The liquid drop-out in these very high rate gas wells may lead to low recovery problems. The most important parameter for determining condensate well productivity is the effective gas permeability in the near wellbore region, where very high velocities can occur. An understanding of the characteristics of the high-velocity gas-condensate flow and relative permeability data is necessary for accurate forecast of well productivity. In order to tackle this goal, a series of two-phase drainage relative permeability measurements on a moderate permeability North Marmara &ndash / 1 gas well carbonate core plug sample, using a simple synthetic binary retrograde condensate fluid sample were conducted under reservoir conditions which corresponded to near miscible conditions. As a fluid system, the model of methanol/n-hexane system was used as a binary model that exhibits a critical point at ambient conditions. The interfacial tension by means of temperature and the flow rate were varied in the laboratory measurements. The laboratory experiments were repeated for the same conditions of interfacial tension and flow rate at immobile water saturation to observe the influence of brine saturation in gas condensate systems. The laboratory experiment results show a clear trend from the immiscible relative permeability to miscible relative permeability lines with decreasing interfacial tension and increasing velocity. So that, if the interfacial tension is high and the flow velocity is low, the relative permeability functions clearly curved, whereas the relative permeability curves straighten as a linear at lower values of the interfacial tension and higher values of the flow velocity. The presence of the immobile brine saturation in the porous medium shows the same shape of behavior for relative permeability curves with a small difference that is the initial wetting phase saturations in the relative permeability curve shifts to the left in the presence of immobile water saturation. A simple new mathematical model is developed to compute the gas and condensate relative permeabilities as a function of the three-parameter. It is called as condensate number / NK so that the new model is more sensitivity to temperature that represents implicitly the effect of interfacial tension. The new model generated the results were in good agreement with the literature data and the laboratory test results. Additionally, the end point relative permeability data and residual saturations satisfactorily correlate with literature data. The proposed model has fairly good fitness results for the condensate relative permeability curves compared to that of gas case. This model, with typical parameters for gas condensates, can be used to describe the relative permeability behavior and to run a compositional simulation study of a single well to better understand the productivity of the field.

Difficult gradient calculations, converging to a local optimum without exploring the design space adequately, too much dependency on the starting solution, lacking capabilities to treat discrete and mixed design variables are the main drawbacks of conventional optimization techniques. So evolutionary optimization methods received significant interest amongst researchers in the optimization area. Genetic algorithms (GAs) and simulated annealing (SA) are the main representatives of evolutionary optimization methods. These techniques emerged as powerful and modern strategies to efficiently deal with the difficulties encountered in conventional techniques, and therefore rightly attracted a substantial interest and popularity. The underlying concepts of these techniques and thus their algorithmic models have been devised by establishing between the optimization task and events occurring in nature. While, Darwin&amp / #8217 / s survival of the fittest theory is mimicked by GAs, annealing process of physical systems are employed to SA. On the other hand, dome structures are among the most preferred types of structures for large unobstructed areas. Domes have been of a special interest in the sense that they enclose a maximum amount of space with a minimum surface. This feature provides economy in terms of consumption of constructional materials. So merging these two concepts make it possible to obtain optimum designs of dome structures. This thesis is concerned with the use of GAs and SA in optimum structural design of dome structures, which range from some relatively simple problems to the problems of increased complexity. In this thesis, firstly both techniques are investigated in terms of their practicality and applicability to the problems of interest. Then numerous test problems taken from real life conditions are studied for comparing the success of the proposed GA and SA techniques with other discrete and continuous optimization methods. The results are discussed in detail to reach certain recommendations contributing to a more efficient use of the techniques in optimum structural design of pin-jointed 3-D dome structures.

iv The primary objective of this study is to understand the mechanism, the hydraulics and the characteristics, of the two-phase flow in horizontal annuli. While achieving this goal, both theoretical and experimental works have been conducted extensively. The METU-PETE-CTMFL (Middle East Technical University, Petroleum and Natural Gas Engineering Department, Cuttings Transport and Multiphase Flow Laboratory) multiphase flow loop consists of 4.84 m long eccentric horizontal acrylic pipes having 0.1143m inner diameter (I.D) acrylic casing - 0.0571m outer diameter (O.D) drillpipe and 0.0932m I.D acrylic casing - 0.0488m O.D drillipipe geometric configurations. During each experiment, differential pressure loss data obtained from digital and analog pressure transmitters at a given liquid and gas flow rate were recorded. The flow patterns were identified visually. Meanwhile a mechanistic model has been developed. The flow pattern identification criteria proposed originally for twophase flow through pipes by Taitel and Dukler1 has been inherited and modified for the eccentric annular geometry. The complex geometry of eccentric annuli has been represented by a new single diameter definition, namely representative diameter dr. The representative diameter has been used while calculating the pressure losses. A computer code based on the algorithm of the proposed mechanistic model has been developed in Matlab 7.0.4. Both the flow pattern prediction and the frictional pressure loss estimation are compared with the gathered experimental data. Moreover, friction factor correlations have been developed for each flow pattern using experimental data and statistical methods. The performance of the proposed model and the friction factor correlations has been evaluated from experimental data. The mechanistic model developed in this study accurately predicts flow pattern transitions and frictional pressure losses. The model&rsquo / s pressure loss estimations are within &plusmn / 30% for two different annular flow geometries.

Past studies on sands have shown that the shear strength measured in plane strain tests was higher than that measured in triaxial tests. It was observed that this difference changed with the friction angle &amp / #966 / cv at constant volume related to the mineralogical composition. In order to investigate the difference in strength measured in the wedge shear test, which approaches the plane strain condition, in the triaxial test, and in the shear box test, Anatolian sands were obtained from different locations in Turkey. Mineralogical analyses, identification tests, wedge shear tests (cylindrical wedge shear tests (cylwests) and prismatic wedge shear tests (priswests)), triaxial tests, and shear box tests were performed on these samples. In all shear tests, the shear strength measured was found to increase with the inclination &amp / #948 / of the shear plane to the bedding planes. Thus, cylwests (&amp / #948 / = 60o) iii yielded higher values of internal friction &amp / #966 / by about 3.6o than priswests (&amp / #948 / = 30o) under normal stresses between 17 kPa and 59 kPa. Values of &amp / #966 / measured in cylwests were about 1.08 times those measured in triaxial tests (&amp / #948 / &amp / #8776 / 65o), a figure close to the corresponding ratio of 1.13 found by past researchers between actual plane strain and triaxial test results. There was some indication that the difference between cylwest and triaxial test results increased with the &amp / #966 / cv value of the samples. With the smaller &amp / #948 / values (30o and 40o), priswests yielded nearly the same &amp / #966 / values as those obtained in triaxial tests under normal stresses between 20 kPa and 356 kPa. Shear box tests (&amp / #948 / =0o) yielded lower values of &amp / #966 / than cylwests (by about 7.9o), priswests (by about 4.4o), and triaxial tests (by about 4.2o) under normal stresses between 17 kPa and 48 kPa. It was shown that the shear strength measured in shear box tests showed an increase when &amp / #948 / was increased from 30o to 60o / this increase (about 4.2o) was of the order of the difference (about 3.6o) between priswest (&amp / #948 / = 30o) and cylwest (&amp / #948 / = 60o) results mentioned earlier. Shear box specimens with &amp / #948 / = 60o, prepared from the same batch of any sample as the corresponding cylwests, yielded &amp / #966 / values very close to those obtained in cylwests.