Sharif Digital Repository

The existence of the important similarities between gelation and glass transition makes it hard to distinguish between the two types of nonergodic states experimentally. Here, we report on a stochastic analysis of the scattered light intensity through a colloidal particles suspension during the gel and glass formation. In this analysis, we exploit the methods developed for complex hierarchical systems, such as turbulence. Using the multiplicative log-normal cascade models, we provide a criterion to distinguish gels from glasses  

We report the observation of the oscillatory and irregular motion of solid spheres settling under the influence of gravity in a thixotropic yield-stress fluid, namely, a suspension of Laponite. The size of the ball and the aging time of the Laponite suspension are found to be two important parameters that determine whether oscillations occur. The irregular motion may be related to the existence of an unstable flow region and shear banding as is concluded from comparisons with rheological measurements, namely, the flow curve and creep tests, using the same Laponite suspensions. © 2017 The Japan Society of Applied Physics  

We present a quantitative analysis on the response of a dilute active suspension of self-propelled rods (swimmers) in a planar channel subjected to an imposed shear flow. To best capture the salient features of the shear-induced effects, we consider the case of an imposed Couette flow, providing a constant shear rate across the channel. We argue that the steady-state behavior of swimmers can be understood in the light of a population splitting phenomenon, occurring as the shear rate exceeds a certain threshold, initiating the reversal of the swimming direction for a finite fraction of swimmers from down- to upstream or vice versa, depending on the swimmer position within the channel.... 

This paper proposes a novel method to design an H∞-optimal Fractional Order PLD (FOPLD) controller with ability to control the transient, steady-state response and stability margins characteristics. The method uses particle swarm optimization algorithm and operates based on minimizing a general cost function. Minimization of the cost function is carried out subject to the H∞-norm; this norm is also included in the cost function to achieve its lower value. The method is applied to a phase-locked-loop motor speed system and an electromagnetic suspension system as two examples to illustrate the design procedure and verify performance of the proposed controller. The results show that the... 

An application of a new controller order reduction technique with stability and performance preservation based on linear matrix inequality optimization to an active suspension system is presented. In this technique, the rank of the residue matrix of a proper rational approximation of a high-order H∞controller subject to the H∞-norm of a frequency-weighted error between the approximated controller and the high-order H∞ controller is minimized. However, because solving this matrix rank minimization problem is very difficult, the rank objective function is replaced with a nuclear-norm that can be reduced to a semidefinite program so that it can be solved efficiently. Application to the active... 

Using passenger cars for daily traveling include advantages and disadvantages simultaneously; this daily traveling causes variety of road excitations in the form of vibration with different amplitude and acceleration to be imposed on body. Exceeding the standard limitations of these parameters results in fatigue, restlessness, and health problems. In this paper, a quarter-car model with semi-active suspension system is considered and three control approaches are applied to reduce these parameters in the limit of standard. Results show adaptive fuzzy optimal controller has better performance compared to others in controlling the critical health parameters, and can be easily used in future... 

The accuracy of multi dimensional simulation of vehicle dynamics has been significantly increased for both passive and active vehicles which are equipped with advanced electronic components. Recently, one of the subjects that has been considered is increasing the car safety in design. Therefore, many efforts have been done to increase vehicle stability especially during the turn. It is also very important in three wheel car. One of the most important efforts is adjusting the camber angle in the car suspension system. Camber angle as well as the vehicle stability has major effects on the wheel slip, reducing rubber abrasion, acceleration and braking. Since the increase or decrease in the... 

A new rheological model is developed to predict viscous and elastic behavior of concentrated suspensions of short fiber and one dimensional nanoparticles in steady and transient shear flows, simultaneously. The previously presented models cannot predict such rheological behavior with a set of parameters. The reduced strain closure (RSC) model in spite of its ability to successfully reproduce the slow kinetics of orientation growth observed in concentrated short-fiber suspensions is not able to predict both the shear viscosity and the normal stress difference data together, which could be possibly due to the fact that an orientation model with a scalar interaction coefficient cannot predict... 

The secondary suspension of most new EMU and DMU rail vehicles is equipped with air springs, to offer a good ride comfort to passengers. Air springs are a very important isolating component, which guarantees good ride comfort during the trip. In most rail-vehicle models developed by researchers, the thermo-dynamical effects of air springs in the rail-vehicle dynamics are not considered and secondary suspension is modeled by simple springs and dampers. As the performance of suspension components, especially for air springs, have significant effects on railvehicle dynamics and the ride comfort of passengers, a complete nonlinear thermo-dynamical air spring model, which is a combination of two... 

This paper presents an active suspension system for passenger cars, using adaptive critic-based neurofuzzy controller. The model is described by a system with seven degrees of freedom. The car is subjected to excitation from a rode surface and wheel unbalance. The main superiority of the proposed controller over previous analogous fuzzy logic controller designed approaches, e.g., genetic fuzzy logic controller, is its online tuning characteristic and remarkable reduced amount of computations used for parameter adaptation, which makes it desirable for real time applications. Considering the simplicity of this controller and its independence from the system model, this control method has the... 

Dense underflows are continuous currents, which move down the slope due to the fact that, their density are heavier than ambient water. In turbidity currents the density differences arises from suspended solids. Vicinity of the wall make density currents and wall jets similar in some sense but Variation of density cause this flows more complex than wall jets. An improved form of 'near-wall' k-ε turbulence model is chosen which preserve all characteristics of both density and wall jet currents and a compression is made between them. Then the outcomes from low Reynolds number k-ε model is compared with v2̄-f model which show similarity. Also results show good agreement with experimental data... 

Patterns formed by the flow of an inhomogeneous fluid (suspension) over a smooth inclined surface were studied. It was observed that fractal patterns form. There exists a threshold angle for the inclination above which global fractal patterns are formed. This angle depends on the particle size of the suspension. We observed that there are two fractal dimensions for these patterns, depending on the area from which the pattern is extracted. If the pattern is taken from the top which only consists of the beginning steps of the pattern forming, one finds two fractal dimensions, i.e. 1.35-1.45 and 1.6-1.7, in which the first one is dominant while, if the entire pattern is taken, then a fractal... 

The dynamic interaction problem of moving vehicles on uniform suspension bridges is studied. The resulting variable moving loads acting on the bridge are of great practical importance to both bridge and automotive engineers. The vehicle, including the occupants, is modelled as a planar half-car with six degrees of freedom, and the bridge is assumed to obey the Euler-Bernoulli beam theory with arbitrary conventional boundary conditions. However, the numerical simulations presented here are for the case of a vehicle travelling at a constant speed on a bridge with simply supported end conditions. Owing to the continuously moving location of the loads on the bridge, the governing differential... 

This paper concerns molecular weight control of a batch polymerization reactor where suspension polymerization of methyl methacrylate(MMA) takes place. For this purpose, a cascade control structure with two control loops has been selected. The slave loop is used for temperature control using on-line temperature measurements, and the master loop controls the average molecular weights based on its estimated values. Two different control algorithms namely proportional-integral(PI) controller and globally linearizing controller (GLC) have been used for temperature control. An estimator, which has the structure of an extended Kalman filter (EKF), is used for estimating monomer conversion and... 

This paper concerns non-linear state estimation in a batch polymerization reactor where suspension polymerization of methyl methacrylate takes place. A kinetic model proposed in the literature is selected and its validity has been verified through an experimental set-up. Based on this model monomer conversion and average molecular weights of the polymer are estimated using only one output measurement (reactor temperature). The performance of the estimator, which has the structure of an extended Kalman filter, is examined through simulation and experimental studies in the presence of different levels of parameter uncertainties. The effects of adding 'fictitious noise' and parameter state' to... 

A manipulator mounted on a moving vehicle is called a mobile manipulator. A mobile manipulator with an appropriate suspension system can pass over uneven surfaces, thus having an infinite workspace. If the manipulator could operate while the vehicle is traveling, the efficiency concerning with the time and energy used for stopping and starting will be increased. This paper presents the kinematic and dynamic modeling of a one degree of freedom manipulator attached to a vehicle with a two degrees of freedom suspension system. The vehicle is considered to move with a constant linear speed over an uneven surface while the end effector tracks a desired trajectory in a fixed reference frame. In... 

In this paper, a complete four axle rail vehicle model with 70 Degrees Of Freedom (DOFs) is addressed, which includes; a carbody, two bogies and four axles. In order to include track irregularity effects on vehicle behavior, a simplified track model for a straight line is proposed. As the performance of the suspension components, especially for air springs, has significant effects on rail-vehicle dynamics and the ride comfort of passengers, a complete nonlinear thermo-dynamical air spring model which is a combination of two different models is introduced and then implemented in the complete rail-vehicle dynamics. By implementing the Presthus formulation [1], the thermo-dynamical parameters... 

The fabrication of strong photocatalysts applied to the degradation of organic pollutants is necessary in environmental applications. In a single-stage method, acetate precursor and poly vinyl pyrolydine are used to produce ZnO nanostructures with various morphologies in annealing temperatures ranging from 300 °C to 900 oC. The physical properties of the prepared nanostructures were characterized by SEM, XRD and PL spectroscopy. The SEM images exhibit a variety of the as-prepared hexagonal zinc oxides including wires, rods, particles and porous network of welded particles of ZnO nanoparticles. The results of the photocatalytic degradation of methylene blue as an organic dye in aqueous... 

Functionally-graded NiO-8. mol % YSZ composite films were prepared by a controlled voltage-decay electophoretic deposition (EPD) process. The films consisted of three layers with varying NiO concentrations and porosities. Effects of different parameters including the type of the organic media, solid concentration, NiO:YSZ ratio, and iodine on the stability of EPD suspensions and deposition kinetics were studied. A stable NiO-YSZ suspension was attained in isopropanol with NiO-YSZ ratio of 60:40 and iodine concentration of 0.5. mM. The composite film contained varying NiO concentration from 46. wt.% near the substrate to 32. wt.% close to the electrolyte with 42. wt% NiO in the intermediate...