Sharif Digital Repository

In this paper, a unified finite element formulation associated with saturated and unsaturated soils is presented. The finite element method is applied to the governing equations for the spatial discretization, followed by a generalized Newmark scheme used for the time domain discretization. Time stepping scheme is used in the fully implicit coupled method and a direct solution procedure is used for the coupled equation system. The framework of generalized plasticity is presented and the numerical results of three saturated-unsaturated earth and rockfill dams are demonstrated. A comparison is performed between the Pastor-Zienkiewicz and cap plasticity models through the dynamic analysis of... 

An active sliding mode controller is designed to synchronize three pairs of different chaotic systems (Lorenz-Chen, Chen-Lü, and Lü-Lorenz) in drive-response structure. It is assumed that the system parameters are known. The closed loop error dynamics depend on the linear part of the response systems and parameters of the controller. Therefore, the synchronization rate can be adjusted through these parameters. Analysis of the stability for the proposed method is derived based on the Lyapunov stability theorem. Finally, numerical results are presented to show the effectiveness of the proposed control technique. © 2005 Elsevier Ltd. All rights reserved  

Three different controllers, i.e., active controller, nonlinear controller, and active sliding mode controller are designed and examined for the synchronization of pairs of three different chaotic systems, i.e., Chen, Lü, and Lorenz. The synchronizing methods are then compared from various point of views including synchronizing error variance, convergence time, control effort, maximum and minimum values of the control signal. Our results indicate that the nonlinear controller synchronizes pairs of the different chaotic systems generally better than two other controllers according to the defined criteria. © 2006 Elsevier B.V. All rights reserved  

Laboratory triaxial compression tests were carried out in order to determine the stress-strain and dilation characteristics of geotextile-reinforced dry beach sand. The mechanical behavior of the composite material was investigated through varying the number of geotextile layers, type of geotextile, confining pressure, and geotextile arrangement. In order to study the effect of sample-size on the results, tests were performed on samples with two different diameters. The results demonstrated that geotextile inclusion increases the peak strength, axial strain at failure, and ductility. However, it reduces dilation. Such improvements in the behavior of reinforced sand are more pronounced for... 

The Class-E power amplifier has been widely studied and formulated in the literature. Although the majority of reported inductive coupling wireless power transfer (WPT) systems use a class-E power amplifier for driving the primary coil, still there is a lack of a comprehensive study on class-E circuit dedicated to WPT, providing a set of closed form design equations for proper class-E operation. This paper presents the required design equations needed to design a 'true' class-E circuit for WPT applications. Equations for the series-tuned secondary coil WPT system are presented, as well as two different design procedures for the parallel-tuned secondary coil. The derived equations have been... 

In modern wireless near-filed power and data telemetry systems such as Implantable Medical Devices (IMD), a data rate of several Mbps is required, while the power carrier frequency is limited to few MHz. Therefore, bit rate is comparable to carrier frequency, and the modulated power carrier signal has amplitude, frequency, or phase variation in every cycle. In this paper a very fast amplitude shift keying (ASK) demodulator circuit is presented. The proposed demodulator is able to demodulate a cycle by cycle ASK modulated signal, and a data-rate-to-carrier (DRC) ratio of 100% is achievable. The circuit extracts the clock by limiting the incoming ASK signal. Cycle by cycle demodulation is done... 

This paper presents a cycle by cycle Frequency Shift Keying (FSK) demodulator, able to demodulate a FSK signal with 1% frequency modulation index (MI), in a single cycle. Based on the proposed demodulation scheme, a high rate data transmission link can be established through a high-Q inductive coupling link, breaking the basic tradeoff between the power transfer efficiency (PTE) and data rate in single carrier wireless power and data transfer systems. Designed and simulated with 0.18μ m CMOS process, the proposed FSK demodulator, detects successfully a 5Mbps data with a carrier frequency of 5MHz. A test chip is fabricated in 180nm CMOS technology. Measurement results shows that the... 

Understanding of the effect of cementation on dynamic behaviour of cemented soil in an earthquake prone area could be crucial for earthquake resistance design. The major section of the city of Tehran has been developed on cemented coarse-grained alluvium. In order to understand the dynamic behaviour of this soil, a series of undrained cyclic triaxial tests were performed on uncemented and artificially calcite-cemented samples. In this paper, two dynamic parameters including dynamic shear modulus and damping ratio based on different definitions are investigated. In this regard the effects of cement content, confining pressure and cyclic deviatoric stress were studied as well. In general by... 

The behavior of an electrified liquid jet breakup and modes of disintegration were investigated at different flow rates and voltages. The current phenomenology belongs to a new injector introduced recently by Morad et al. (2016). This injector has proven to highly extend the stability and flow rate of electrospray particularly in the Taylor cone-jet mode. The experimental investigation was performed using a high-power light-emitting diode (LED) illumination as the light source. The light source was developed to operate in the pulsing condition when synchronized with a digital camera and was particularly designed to function properly in the presence of high electromagnetic interference (EMI).... 

The majority of the city of Tehran, Iran has been developed on cemented coarse-grained alluvium. In order to understand the mechanical behavior of this soil, a series of triaxial compression tests (CD, CU) were performed on uncemented and artificially cemented samples. Hydrated lime was used as the cementation agent for sample preparation to model the Tehran cemented deposit. The tests were performed on artificially cemented samples after an appropriate curing time. The effect of confining pressure, cement content and fine content is investigated in this research. The tests results show that peak shear strength is followed by strain softening for all cemented samples. Shear strength... 

Construction over problematic soils is a common problem in many parts of the world, and one of the effective procedures to tackle this problem is soil stabilization. Accordingly, the current study provides the finding of a laboratory investigation into the effect of three kinds of nanomaterials, including nano-silica (NS), nano-clay (NC) and nano-calcium carbonate (NCC) on the properties of a loessial collapsible soil. To accomplish this issue, reconstituted samples of the stabilized loessial soil were prepared for unconfined compression and consolidation tests. The results illustrated that an insignificant amount of nanomaterials (less than 1% of the total dry weight of the soil when is... 

A constitutive model is developed for a cemented gravelly sand. The model is based on the separation of the cemented soil to the uncemented part and cemented bonds and combining the mechanical behaviour of each part using consistency and energy equilibrium equations. The uncemented part was modelled using the Pastor et al. (1985) model for sands. A new model was developed and proposed for the cemented bonds. Combination of these parts resulted in the modelling of cemented soil behaviour with a very good consistency both in drained and undrained conditions. The pore pressure in undrained conditions and the volumetric strains in the drained state were also modelled successfully using this... 

Construction over problematic soils is a common problem in many parts of the world, and one of the effective procedures to tackle this problem is soil stabilization. Accordingly, the current study provides the finding of a laboratory investigation into the effect of three kinds of nanomaterials, including nano-silica (NS), nano-clay (NC) and nano-calcium carbonate (NCC) on the properties of a loessial collapsible soil. To accomplish this issue, reconstituted samples of the stabilized loessial soil were prepared for unconfined compression and consolidation tests. The results illustrated that an insignificant amount of nanomaterials (less than 1% of the total dry weight of the soil when is... 

Liquefaction of loose and saturated soils during earthquakes and strong ground motions has been a major cause of damage to buildings and earth embankments as well as other civil engineering structures. In order to evaluate the liquefaction potential and steady state characteristics of gravely sand of south west Tehran, a subsoil exploration program conducted dividing the region into 10 zones. In each zone of 500 m × 500 m a borehole of 20 m deep was drilled. SPT was performed at one meter intervals in each borehole and a total of 200 samples were recovered. Soils of similar grain size distribution have been considered to have similar steady state characteristics,therefore consolidated... 

In this paper a new approach is introduced for structural health monitoring of offshore jacket platforms. The procedure uses the measured ambient vibration responses and the corresponding readable natural frequencies and mode shapes of the structural system. Since offshore platforms are composed of heavy topsides supported by jacket structures, participation of the first mode is dominant in each direction in the response of the structure under field excitations. Moreover, ambient vibrations such as wave loads and boat impacts only excite the first modes of the structure. Therefore, it is difficult to find higher modes and the pertinent frequencies by use of accelerometers data. The... 

In this paper, by introducing a new general state-space form for uncertain linear time-invariant fractional-order systems subjected to interval and polytopic uncertainties, two problems including robust stability analysis and robust stabilization of the presented systems are investigated. Subsequently, two sufficient conditions in terms of several linear matrix inequalities for the problems mentioned are concluded as two separate theorems. It is assumed that the fractional order α is a known constant belonging to 0 < α < 1. Simulation results of two different numerical examples demonstrate that the provided sufficient conditions are applicable and effective for tackling robust stability and... 

The volume change that occurs due to membrane penetration into peripheral voids of gravelly specimens during hydrostatic compression test in a conventional triaxial apparatus is studied by performing a set of hydrostatic compression tests on gravelly specimens with different initial relative densities. During the isotropic loading on the specimens, the total volume changes of the specimens were determined by measuring the amount of water seeping out of the specimens at different loading steps. Image processing technique was implemented simultaneously to determine the skeletal volume changes of the specimens. In this regard specimens were compressed to isotopic pressures from 10 to 500 kPa... 

Adaptive Model Predictive Transmission Control Protocol (AMP-TCP) as a new TCP delay-based congestion control algorithm is introduced. Both aspects of design and implementation of the algorithm are described using simulations on the ns-2 network simulator. The design stage is composed of two steps. First, a recursive system identification approach is proposed to capture the network delay dynamics from TCP source view. Second, the proposed modeling is employed to develop an adaptive model predictive TCP congestion control strategy in the absence of any explicit congestion notification. The characteristics and performance of AMP-TCP are investigated using several network simulations. Finally a... 

Transmission Control Protocol (TCP) uses multiple timers to do its work. The most important of these is the retransmission timer. In this paper, the TCP retransmission timer adjustment mechanism is approached from a system point of view and a new mechanism is proposed. A simple recursive system identification algorithm is used to capture both time variant and time invariant Internet behavior. Also a dynamic model-based Round-Trip Time (RTT) predictor was provided. Based on network simulation and real Internet data collection, it was observed that when the retransmission timer is adjusted by the proposed predictor instead of the traditional RTT estimator, performance increased significantly  

To characterize the role of specimen disturbance and structure in the hydromechanical behavior of collapsible soils, two sets of wetting-induced collapse and suction-controlled triaxial tests were conducted on intact and reconstituted specimens of a loessial soil taken from a loess deposit in Gorgan, a city in the northeastern Golestan province of Iran. The testing approach used an advanced triaxial testing device that was specifically modified to control pressures applied to a soil specimen and to monitor and measure the amount of changes in volume and water content of the soil specimens during testing using highly sensitive digital sensors with an accuracy of 60.01 cm3. Results of the...