Sharif Digital Repository

Recently, the multi-model controllers design was proposed in the literature based on integrating of the stability and performance criteria. Although these methods overcome the redundancy problem, the decomposition step is very complex and time consuming. In this paper, a cascade design of multi-model control is presented that is made from two sequential steps. In the first step, the nonlinear system is decomposed into a set of linear subsystems by just considering the stability criterion. In this step, the gap metric is used as a smart tool to measure the distance between linear subsystems. While the closed-loop stability is gained through the first step, the performance is improved in the... 

A numerical modeling procedure was used to quantify calibration chamber size and boundary effects for cone penetration testing in sand. In the numerical analyses, chamber diameter and boundary conditions were varied to investigate the effects of chamber size and boundary conditions on cone tip resistance. These analyses show that, for loose sand, a chamber-to-cone diameter ratio of 33 is sufficient for the boundaries to have no influence on the cone tip measurements. However, for very dense sand, the numerical analyses show that the chamber-to-cone diameter ratio should be more than 100 to ensure that boundaries have no influence on cone tip measurements. Numerical analysis indicates that,... 

A numerical analysis is presented to model the cone penetration test (CPT) tip resistance in layered soil. Analyses are performed for two-layer soils composed of either sands with different relative densities or different materials (sand and clay). Parametric numerical modeling is used to determine the distance that a cone senses a new upcoming soil layer interface or a layer interface behind. Analyses are also carried out for a thin sand layer embedded in soft clay. It is seen that the full tip resistance may not be reached in thin stiff layers. This is especially true for penetration in thin dense sand layers interbedded in softer clay. A correction factor is suggested to correct the cone... 

In the present study, exergoeconomic optimization of a trigeneration system for cooling, heating and power purposes has been carried out. The system is made up of air compressor, combustion chamber, gas turbine, dual pressure heat recovery steam generator and absorption chiller in order to produce cooling, heating and power. The design parameters of this study are selected as: air compressor pressure ratio, gas turbine inlet temperature, pinch point temperatures in dual pressure heat recovery steam generator, pressure of steam that enters the generator of absorption chiller, process steam pressure and evaporator of the absorption chiller chilled water outlet temperature. The economic model... 

Analytical treatment of a linear elastic isotropic bi-material full-space reinforced by an interfacial thin film under axisymmetric normal loading is addressed. The thin film is modeled as an extensible membrane perfectly bonded to the half-spaces. By virtue of Love's potential function and Hankel integral transform, elastic fields of the system are explicitly written in the form of semi-infinite line integrals. The analytical results are verified by the special cases corresponding to the surface stiffened half-space and classical bi-material problem. The limiting cases of reinforced homogeneous full-space and inextensible membrane are presented and discussed. The proposed formulation is... 

This study deals with the elastodynamic response of a surface-stiffened transversely isotropic half-space subjected to a buried time-harmonic normal load. The half-space is reinforced by a Kirchhoff thin plate on its surface. By virtue of a displacement potential function and appropriate time-harmonic Green’s functions of transversely isotropic half-spaces, a robust solution corresponding to two plate-medium bonding assumptions, namely (a) frictionless interface, and (b) perfectly bonded interface is obtained for the first time. All elastic fields of the problem are expressed explicitly in the form of semi-infinite line integrals. Results of some limiting cases including isotropic materials,... 

Finesmigration is a noticeable problem in petroleum-production engineering. Plugging of throats in porous media occurs because of detachment of fine particles from sand surfaces. Thus, the study of interactions between fines and pore surfaces and the investigation of governing forces are important factors to consider when describing the mechanism of the fines-release process. The main types of these forces are electric double-layer repulsion (DLR) and London-van der Waals attraction (LVA). It may be possible to alter these forces with nanoparticles (NPs) as surface coatings. In comparison with repulsion forces, NPs increase the effect of attraction forces. In this paper, we present new... 

Background: Archaeological metallic artefacts buried in soils deteriorate by means of various environmental as well as internal factors and mechanisms over time such as change in composition and microstructure of metal and corrosive factors due to long-term burial environment. Corrosion in metals occurs in different morphologies and results in different types of corrosion products based on soil composition. Identification of corrosion mechanisms and morphology in archaeological metals can help conservators to characterize deterioration occurred in metals and make decisions to protect artefacts about preventing further deterioration. In archaeological bronzes, different layers may form on the... 

This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete (SFRC) under the four point bending test (FPBT). All the force components at the beam section (before and after cracking) are formulated by applying these assumptions: a realistic stress-strain model is used for concrete behavior in compression, a linear response is considered for the uncracked tension region in a concrete constitutive model, and an exponential relationship is proposed as a stress-crack opening in the crack region which requires two parameters. Then the moment capacity of the critical cracked section is calculated by using these forces and satisfying equilibrium law at the... 

Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares different geometries for numerical investigation of the 3D flow in the runner of a Francis turbine, and presents an optimum geometry with least computational effort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis Turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal flows, 1989) in which the geometry and detailed best efficiency... 

A numerical modeling procedure is presented to evaluate cone tip resistance in sand. The procedure involves a moving boundary simulating cone penetration. The soil is modeled as a Mohr-Coulomb elastic-plastic material with stress-dependent parameters. The procedure is verified by comparing predicted numerical values of cone tip resistance with published experimental measurements from calibration chamber tests. The selected database. consists of 59 calibration chamber tests on Ticino sand with different relative densities, overconsolidation ratios, stresses, and boundary conditions. Several applications of the modeling procedure are also presented. The computer program FLAC is used to carry... 

The overall success in launching discovered drugs is tightly restricted to the high rate of late-stage failures, which ultimately inhibits the distribution of medicines in markets. As a result, it is imperative that methods reliably predict the effectiveness and, more critically, the toxicity of medicine early in the drug development process before clinical trials be continuously innovated. We must stay up to date with the fast appearance of new infections and diseases by rapidly developing the requisite vaccinations and medicines. Modern in vitro models of disease may be used as an alternative to traditional disease models, and advanced technology can be used for the creation of... 

Purpose: In this paper, the joint replenishment problem is modeled for a two-level supply chain consisting of a single supplier and multiple retailers that use the vendor-managed inventory (VMI) policy for several products. This paper aims to find the optimal number of products to order in both policies, the optimal times at which each retailer orders the products in the traditional policy and the optimal times at which the supplier orders the product in the VMI policy. Design/methodology/approach: The problem is first formulated into the framework of a constrained integer nonlinear programming model; then, the problem is solved using a teacher-learner based optimization algorithm. As there... 

Millimeter-wave radars are essential for automotive sensing, medical imaging, and safety- monitoring applications. Among different architectures, frequency-modulated continuous-wave (FMCW) radars are particularly suited for miniature integration targeting portable consumer applications with detection ranges up to a few tens of meters. This translates to a relatively low requirement of transmitter (TX) output peak power and hence is well suited for implementation using low-supply-voltage CMOS processes. To avoid saturating the receiver (RX) under CW operation, FMCW radars must achieve high TX-to-RX isolation in the front-end. Typically, at least 40dB of isolation is necessary for W-band (75... 

For the efficient removal of some anionic dyes, a novel adsorbent was developed. The adsorbent was prepared by coating a synthetic polymer on magnetite nanosphere surface as a magnetic carrier. The synthesized nano-adsorbent was fully characterized using Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer, X-ray diffractometer, scanning electron microscope, and transmission electronic microscopy measurements. The synthesized nano-adsorbent showed high adsorption capacity towards removal of some anionic dyes (221.4, 201.6, and 135.3 mg g-1 for reactive red 195, reactive yellow 145, and reactive blue 19 dye, respectively) from aqueous samples. The dye adsorption was... 

The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: solar heating and absorption cooling (SHAC), solar heating and ejector cooling (SHEC), and heating and solar vapor compression cooling (HSVC). First, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated. The systems are parametrically analyzed with the weather conditions of Tehran, Iran. The results show that the life cycle costs (LCC) of the SHAC and HSVC systems are alike and much lower than those of the SHEC system. The HSVC system exhibits the best performance from... 

The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: solar heating and absorption cooling (SHAC), solar heating and ejector cooling (SHEC), and heating and solar vapor compression cooling (HSVC). First, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated. The systems are parametrically analyzed with the weather conditions of Tehran, Iran. The results show that the life cycle costs (LCC) of the SHAC and HSVC systems are alike and much lower than those of the SHEC system. The HSVC system exhibits the best performance from...