Sharif Digital Repository

The equations of motion for a beam on a flying support for EulerBernoulli and Timoshenko Beam Theories is derived. In modeling and attempting to have an accurate model at high speeds, a stretch variable instead of conventional axial deformation is used. For a planar rotating beam and a spatial rotating beam, equations of motion are lineralized and verified. Finite element and Newmark direct integration methods are employed for numerical simulations  

Structural systems will normally fail as a consequence of a chain of different components failure es. In this paper, fatigue reliability of fixed offshore platforms is investigated by analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, it is divided into a finite number of sub-scenarios. All combinations of time sequences are generated for a given sequence of failures, using a specially developed program. In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. A large number of sub-scenarios should be analyzed, therefore implementing time... 

Cone penetration tests have long been used to characterize snowpack stratigraphy. With the development of sophisticated digital penetrometers such as the SnowMicroPen, vertical profiles of snow hardness can now be measured at a spatial resolution of a few micrometers. By using small penetrometer tips at this high vertical resolution, further details of the penetration process are resolved, leading to many more stochastic signals. An accurate interpretation of these signals regarding snow characteristics requires advanced data analysis. Here, the failure of ice connections and the pushing aside of separated snow grains during cone penetration lead to a combination of (a) diffusive noise, as... 

Accurate prediction of static and dynamic response of nano structures under external excitations has been one of the interests of scientists in the last decade. Several applications of nano machines make it necessary to analyze their components, such as nano bearing, precisely. In this paper, the static and vibrational behavior of a fullerene as a sensitive part of nano bearing under external forces is simulated by a newly designed spherical super element. This super element is designed in such a way that the user can select as many numbers of nodes as desired, so that it can be implemented in different desired precisions. In this study, a 228-node super element, which is similar to a hollow... 

For traditional calculations of relative phase permeability (Kr) from coreflood Steady-State Test (SST), the capillary pressure (Pc) is required. Usually, Pc is determined from a separate test, using a centrifuge or porous-plate methods. However, during SSTs, water cut and pressure drop are measured during the transition period between two sequential fractional-flow steps. We developed a novel method for simultaneous determination of Kr and Pc from SST by using both steady-state and transient data. In the proposed method, the transition data on the pressure drop across the core are used instead of the traditionally utilised Pc-curve. The main idea is that the stabilisation period during each... 

The accuracy of Reynolds Averaged Navier-Stokes (RANS) turbulence models to predict the behavior of 2-D density currents has been examined. In this work, a steady density current is simulated by the k - ε, k - ε RNG, two-layer k - ε and modified v̄2 - f model, all of which are compared with the experimental data. Density currents, with a uniform velocity and concentration, enter a channel via a sluice gate into a lighter ambient fluid and move forward down-slope. The eddy-viscosity concept cannot accurately simulate this flow because of two stress production structures found within it. Results show that all isotropic models have a weak outcome on this current, but by improving the ability of... 

Research on the reliable characterization of saturated permeability has received great yet necessary attention globally. However, most studies were carried out on soils with a volumetric tendency being almost insensitive to water saturation or at least with this hidden assumption. This is clearly not the case when dealing with the two broad categories of problematic soils, including collapsible and expansive soils. As confirmed by previous research, at least one-fifth of the planet comprises of these soils with a relatively fair distribution. Therefore, the main objective of this study is to introduce a low-compliance double cell/burette permeameter to track all volumetric changes during the... 

Irrigated agriculture is the principal consumer of fresh water resources. Most countries do not have a precise measurement of water consumption for irrigation. In this study, an innovative approach is proposed that allows for estimation of irrigation water use at the catchment scale based on satellite soil moisture data. To this end, the SM2RAIN algorithm, which had been originally developed for estimation of rainfall from the soil moisture observations, is adopted. The satellite soil moisture observations obtained from Advanced Microwave Scanning Radiometer 2 (AMSR2) along with different rainfall and evapotranspiration (ET) products in the period 2012–2015 are used as the input to the... 

This paper presents the results of parametric analyses of the yielding moment (My) of Bolted Flush Endplate Beam (BFEB) splice connections using Finite Element Modeling (FEM) tools. The connection components were modeled using three-dimensional brick elements, while contact between the endplates was modeled using Coulomb friction. Materials for beam, endplate and bolts were considered to behave non-linearly. Finite element results with three experimental and numerical studies were compared, and all indicated good agreement, which is also briefly reviewed in this paper. Using verified FEM, fairly large parametric studies, based on the practical configuration of BFEB connections, were carried... 

Certain stratified charge divided chamber engines have a very small pre-chamber, equipped with a spark plug and a main chamber connected to the pre-chamber through nozzles, A theoretical model is presented in this research to predict ignition delay and initiation of combustion in the pre-chamber. It considers flame progress in the pre-chamber up to the point where the flame penetrates the main chamber through the connecting nozzles. Step by step calculations then continue in the main chamber and the mass fraction burned and the energy release rate are calculated. The process continues to the point where all the fuel is burned. At each step, due to a one degree rotation of the crank shaft,... 

Real world models of seawater intrusion (SWI) require high computational efforts. This creates computational difficulties for the uncertainty propagation (UP) analysis of these models due the need for repeated numerical simulations in order to adequately capture the underlying statistics that describe the uncertainty in model outputs. Moreover, despite the obvious advantages of moment-independent global sensitivity analysis (SA) methods, these methods have rarely been employed for SWI and other complex groundwater models. The reason is that moment-independent global SA methods involve repeated UP analysis which further becomes computationally demanding. This study proposes the use of... 

This paper presents a new combined method for accurate upscaling of two-phase displacements in highly heterogeneous reservoirs. The method has the capability to retain its high performance for various flow regimes, from viscous to gravity dominant displacements, without the need for further modifications and computational steps. Two different grids are incorporated for simulation. The grid on fine scale is used to recognize the complicated physics of flow which depends on dominated driving forces and their interaction with heterogeneity. However, to achieve a fast simulation, the global flow calculation is performed on the coarse scale grid using upscaled equivalent properties. The... 

Bolted Column Base Plate (BCBP) connections are widely used to connect steel columns to the concrete foundations. This paper conducts a parametric study on the initial stiffness of bolted base plate with Square Hollow Section (SHS) column connection, through an extended 3-D Finite Element Modeling (FEM). Different features of the connection such as material behavior, geometric details, typical contact phenomena and large displacements are also considered in the modeling. A comparison between experimental test and FEM is carried out to illustrate the ability of the numerical method to simulate the connection behavior. An analytical explanation on the initial stiffness of the connection is... 

The process of coarsening the detailed geological model of a reservoir to simulation models is known as upscaling. There are two fundamental steps in the procedure of upscaling, i.e., defining the coarse grid geometry and calculating the average properties for the generated coarse grid. In this paper, the focus will be on investigating the applicability of optimization in the context of coarse grid geometry definition. To do so, different objective function candidates will be defined, and their behavior in terms of predicting the two-phase flow accuracy of coarse grids will be analyzed to determine the proper objective function. A modified objective function employing the idea of analytical... 

A recent method in the seismic assessment of structures is Endurance Time Analysis (ETA). ETA is a time-history-based dynamic pushover procedure, in which structures are subjected to gradually intensifying acceleration functions called Endurance Time Acceleration Functions (ETAFs), and their performances are evaluated based on the equivalent intensity level that they can endure while satisfying required performance goals. In this paper, the accuracy of the ETA in the seismic assessment of steel moment resisting frames is compared with the Time History Analysis (THA) and Incremental Dynamic Analysis (IDA) methods. For this purpose, a set of mid-rise and high-rise frames were selected as a... 

A new exponential model to depict the moment-rotation (M-θ) relationship of Bolted Endplate Connections (BEC) is proposed. The proposed model represents an approach to the prediction of M-O curves, taking into account the possible failure modes and the deformation characteristics of the connection elements. The presented model has three physical parameters, along with two curve-fitted factors. These physical parameters are generated from dimensional details of the connection, as well as the material properties. By employing simplified connection behavioral models to estimate the connection M-θ behavior, analytical expressions for evaluating major connection parameters, such as initial... 

Fractional-pixel accuracy Motion Estimation (ME) has been shown to result in higher quality reconstructed image sequences in hybrid video coding systems. However, the higher quality is achieved by notably increased Motion Field (MF) bitrate and more complex computations. In this paper, new half-pixel block matching ME algorithms are proposed to improve the rate-distortion characteristics of low bitrate video communications. The proposed methods tend to decrease the required video bandwidth, while improving the motion compensation quality. The key idea is to put a deeper focus on the search origin of the ME process, based on center-bias characteristics of low bitrate video MFs. To employ the... 

Remote sensing is an effective tool for capturing spatial and temporal variations of water surface temperature (WST) in large lakes. The WST of Urmia Lake in northwestern Iran was examined from 2007 to 2010, using MODIS land surface temperature (LST) products. Spatial and temporal (diurnal, monthly, seasonal and inter-annual) variations of Urmia Lake WST were also investigated. Results indicate that the MODIS-derived WSTs are in a good agreement with the in situ data (R2=0.92 and bias=-0.27). Spatial analysis of WST revealed that there are three thermal zones along the lake: the shallow region in barriers of the causeway, islands and the shoreline; the south part; and the deep north parts.... 

A large number of offshore platforms of various types have been installed in deep or shallow waters throughout the world. These structures are mainly made of tubular members which are interconnected by using tubular joints. In tubular frames, joints may exhibit considerable flexibility in both elastic and plastic range of response. The resulting flexibility may have marked effects on the overall behavior of offshore platforms.This paper investigates the effects of joint flexibility on local and global behavior of tubular framed structures in linear range of response. A new joint flexibility element is developed on the basis of flexibility matrix and implemented in a finite-element program to... 

The rotational and translational motions of nanocars and nanotrucks as well as their motion regimes at different temperatures are investigated. In recent years, few similar types of molecular machines have been simulated. In contrast to previous studies, which have used the Rigid-Body Molecular Dynamics (RBMD) method, an all-atom model and classic atomistic dynamics have been employed in this paper to achieve better accuracy. Our results demonstrated that the exibility of the chassis and its attachment to the gold surface played an important role in the motion of a nanocar. In fact, a heavier and more exible nanocar chassis reduces its speed compared to a nanotruck. In addition, the results...