Sharif Digital Repository

Thermal optimization of the vertical continuous casting process is considered in the present study. The goal is to find the optimal distribution of the temperature and interfacial heat transfer coefficients corresponding to the primary and secondary cooling systems, in addition to the pulling speed, such that the solidification along the main axis of strand approaches to the unidirectional solidification mode. Unlike many thermal optimization of phase change problems in which the desirable (target) temperature, temperature gradient, or interface position are assumed to be a priori known, a desirable shape feature of the freezing interface (not its explicit position) is assumed to be known in... 

Heavy-duty gas turbines are usually devised in power plants to generate electrical energy. Sudden failure in any of its parts or subdivisions will result in a decrement of the efficiency of the system or emergency shutdown of the system. The highest risk of failure in these turbines is subjected to the hot gas path (HGP) of the turbine. Due to the existence of uncertainty in diagnosing process or damage growth, in this research, a modified risk-based probabilistic failure analysis model using Bayesian networks (BN) was developed. First, a failure model was developed using the Fault Tree Analysis, and then it is transformed into a BN model. This model is capable of predicting and diagnosing... 

This paper presents a new probabilistic framework for seismic hazard assessment and hazard sensitivity analysis. Hazard in this context means the probability of exceeding a measure of ground shaking intensity, such as peak ground acceleration and spectral acceleration. The main components of the proposed framework include structural reliability methods to estimate exceedance probabilities and their sensitivities, and multiple probabilistic models for earthquake occurrence, magnitude, location, and ground motion. This paper presents two analysis approaches. The first approach utilizes the first- and second-order reliability methods and importance sampling. This approach efficiently yields the... 

In this study, a review of the overlay/index methods served for delineation of vulnerable zones in coastal aquifers affected by SWI is provided. Then, a more realistic presentation of the vulnerability mapping of coastal aquifers to SWI through modified GALDIT index method by incorporating the influential factors on SWI is established. The modifications on GALDIT method including incorporating the seaward hydraulic gradient (i) instead of the height of groundwater level above sea level (L) (so-called GAiDIT), and considering hydraulic gradient (i) as an additional parameter to the GALDIT (so-called GALDIT-i). Three GALDIT, GAiDIT, and GALDIT-i methods were evaluated with data from three... 

Natural convection in a porous enclosure in the presence of thermal dispersion is investigated. The Fourier–Galerkin (FG) spectral element method is adapted to solve the coupled equations of Darcy’s flow and heat transfer with a full velocity-dependent dispersion tensor, employing the stream function formulation. A sound implementation of the FG method is developed to obtain accurate solutions within affordable computational costs. In the spectral space, the stream function is expressed analytically in terms of temperature, and the spectral system is solved using temperature as the primary unknown. The FG method is compared to finite element solutions obtained using an in-house code... 

In this study, the effect of distance-dependent dispersion coefficients on density-driven flow is investigated. The linear asymptotic model, which assumes that dispersivities increase linearly with distance from the source of contamination and reach asymptotic values at a large asymptotic distance, is employed. An in-house numerical model is adapted to handle distance-dependent dispersion. The effect of asymptotic-dispersion on aquifer contamination is analyzed for two tests: (i) a seawater intrusion problem in a coastal aquifer and (ii) a leachate transport problem from a surface deposit site. Global Sensitivity Analysis (GSA) combined with the Polynomial Chaos Expansion (PCE) surrogate... 

Utilizing ground-based measurements to obtain water budget components, especially in large scale basins, is challenging due to the limitation in the spatiotemporal availability of in-situ data. In this paper, we propose a probabilistic framework for estimating water budgets in low runoff regions using remote sensing products. By studying water budgets in the Central Basin of Iran (CBI) over 8 years period (2009–2016), we investigate the locations and time scales at which the water budget calculated from satellite products provides most closure. To this end, we use precipitation from the Tropical Rainfall Measuring Mission (TRMM), evapotranspiration from the Water Productivity Open Access... 

This paper presents a probabilistic approach to reveal the negative consequences of overlooking code calibration when adopting the provisions of nonindigenous building codes in design. A taxonomy of the national building codes of various countries whose provisions are adopted from one or more original standards is first presented. Next, the reliability-based approach to quantify the lack of safety that may arise due to the absence of code calibration is presented. This approach is then applied to the case study of the National Building Code of Iran, whose load and resistance factors are directly adopted from ASCE/SEI 7. To this end, seven steel building archetypes with various structural...