Sharif Digital Repository

In this study a new SPH model for solving free surface and fluid-fluid interaction problems is presented. The numerical model is capable of simulating two dimensional hydraulic problems with arbitrary boundary and initial conditions and large number of particles. It has the ability to model multi-fluids domain with different densities and viscosities. Several corrections are implemented in SPH formulation such as treatment of free surface and correction of viscous term in order to conserve the angular momentum. Several examples are conducted in fluid-fluid domains to measure the capability of model in this area of study. This new model use Incompressible SPH method for more accurate... 

The propagation behavior of Love wave in functionally graded magneto-electro-elastic half-spaces with a quadratic variation is addressed. The magneto-electromechanical coupling factor, the dispersion relations, electric potential, magnetic potential and displacement are obtained analytically for both magneto-electrically open and short conditions. The effect of gradient coefficient on phase velocity, group velocity and magneto-electromechanical coupling factor are plotted and discussed. Research on the wave propagation in magneto-electro-elastic materials is still very limited. This work provides us with a theoretical foundation to design and practically apply SAW devices with high... 

This study presents a developed successive boundary element method to determine the sloshing natural frequencies, mode shapes and equivalent mechanical models for multi baffled 2D and axisymmetric containers with arbitrary geometries. The developed fluid model is based on the Laplace equation and Green's theorem. The governing equations of fluid dynamic and free surface boundary condition are also applied to proposed model. A zoning method is presented to model arbitrary arrangement of baffles in multi baffled axisymmetric tanks. The influence of each zone on neighboring zones is applied by introducing interface influence matrix which correlates the velocity potential of interfaces to their... 

The propagation of the surface waves in the piezoelectric (PE) and piezomagnetic (PM) layered media are studied. The surface BG waves in the PE half-spaces overlaid by a layer are considered and the closed-form dispersion relations for the open and short electromechanical surface boundary conditions are obtained. The numerical results for the phase velocities and the electromechanical coupling factor for PZT-2 and PZT-8 media are presented. Furthermore, the propagation of the Rayleigh waves in the PE-PM layered media is considered. The effects of the imperfect bonding between the half-space and the layer are discussed. Later, we study the propagation of the Rayleigh waves in 4 different... 

This paper was directed to recognize maneuver equations perfectly, and with regard to CFD method maneuver simulation is going to be done in form of two and three dimensional. Today, since CFD methods have been exerted in different works, further and more actual development of floating body's maneuver is going to be our special need. As numerical methods for floating body's maneuver simulation by RANS method are developing, more researches are being done about this field as well. This thesis is going to simulate primitively maneuver of one floating body by Smoothed Particle Hydrodynamic(SPH) method in order to be as the beginning of maneuver simulation by this method in which with regard to... 

Resonance acoustic spectroscopy (RAS) is one of the techniques used for monitoring the production quality and evaluation of mechanical properties of cylindrical components, due to their non-destructivity, high precision and quickness.
In this technique, the resonance effects are caused by the excitation of eigenvibrations of structure by an incident acoustic wave located in far-field. The resonance spectroscopy (isolation and identification of the resonance features) is performed on the far-field scattered pressure field which contains valuable information about the characteristics of the target. Appropriate exploitation of these resonance informations from the theoretical model and... 

In the present work, dynamic behavior of submerged slender bodies under external hydrodynamic forces with internal sloshing tanks is studied. The main application of this thesis is in submarines. For this purpose slender body theory is used for hydrodyanamics of body and unsteady hydrodynamics is used for the vehicle control fins. In submarines there are some water tanks that control the buoyancy, so that sloshing can be importatnt. An equivalent mechanical model is developed for simulating the dynamics of sloshing tanks. Assuming that a submarine is a slender body, elastic deformation of submarine body can affect dynamics of the whole system. Elastic behavior of the main body is simulated... 

Slosh phenomenon is described as the motion of the fluid’s free surface in a tank or partially-filled container. This motion can induce undesired forces that can change the path of a vehicle. In some liquid carrying vehicles these undesired changes is sensed by the driver or control system and can lead to instability. Some examples of this phenomenon are aircrafts, rockets, ships and fuel carrier trucks.
In this project, a coupling between the dynamics of the vehicle and the contained fluid is implemented for in depth understanding of the interactions. This is done by Co-Simulation. With the help of Co-Simulation, corrective control actions can be taken and the design of more powerful... 

In this thesis, sloshing of a rectangular container with perforated baffle is being analysed. Employing the linear sloshing theorem, we construct an accurate numerical and analytical approximation of natural sloshing mode in rectangular container with perforated baffle. Two dimensional irrotational flow of an ideal incompressible liquid is assumed. Finally the dissipated energy is being measured and equal viscous damping was calculated. So the perforation in which the damping is being maximized is determined and finally the results being compared with some experimental and analytical results from journal paper  

The propagation of love waves in a one-layered piezoelectric medium with slightly curved boundaries of sinusoidal type have been investigated in this study. Because of the widespread use of piezoelectric materials as surface acoustic wave (SAW) devices, sensors, actuators and in vibration control, the study of Love wave propagation in this Medias has been in the forefront of present studies in this era. But there always will be imperfection on surfaces. By employing the Taylor expansion up to the first order and using perturbation technic on the case with no irregularity and solving the problem, it has been found that along with the usual displacement components for stratified boundaries,... 

The problem of the Rayleigh wave propagation in a piezoelectric layer overlying a piezoelectric half space by an imperfect interface is investigated. These days because of widespread use of the piezoelectric materials in sensors and transducers based on surface waves, the study of wave propagation in these medias is paid attention by many researchers. In this study, imperfection between layer and half-space idealized by springs which have determine values. If the stiffness of springs approaches to infinity, the interface will be perfect. Also, zero stiffness of springs indicates that there is no continuity between layer and half space. With the use of potential functions for displacement... 

In the this study, a numerical simulation of two-dimensional incompressible sloshing flow in a rectangular tank with baffle(s), using Lattice Boltzmann Method (LBM) is presented. Finite difference LBM and two-phase "Lee" model were used. The potential form of intermolecular forces is utilized to guarantee the stability of the numerical scheme and the discretization of the solution domain is performed by a two dimensional structured grid. Two different distribution functions are applied to obtain pressure, momentum, and composition of the particles. Furthermore, the Boltzmann transport equation is discretized, by using standard D2Q9 method. The "dropl" test case is simulated by the present... 

Lorentz reciprocity theorem is one of the most fundamental concepts in electromagnetism. Although, in specific conditions, for example in nonlinear systems or systems with broken time-reversal symmetry it can be violated. In recent years, many interests have been attracted towards such systems. With a proper design, they can support nonreciprocal or at specific conditions unidirectional propagation behavior. For example, despite ordinary dielectrics, in ferrite layers, the propagation constant of surface waves on ferrite edge, depends on the direction of propagation with respect to magnetization direction. Furthermore, in the specific interval of frequencies, ferrite structures allow... 

This work focuses on developing a theoretical approach for the calculations of the surface elastic constants for (100) planes of fcc crystals. Using this method, the surface elastic constants, as well as the surface residual stress of the (100) planes of Al, Ag, Ni, Pt, and Cu fcc crystals, are evaluated using quantum calculations and VASP code. Surface effects are important in nanostructures and the considered metals are the most applicable ones in nanostructures especially in optic and electronic fields. For verification of the obtained values for surface elastic constants and residual stress, other surface parameters including the equilibrium lattice parameter, the energy per atom of the... 

In this research, the feasibility of the usage of the Wells turbine for direct conversion of the hydro-mechanical energy of the surface waves is studied via analytical and numerical methodologies. The results produced, showed for the first time that the Wells turbine can be employed for such waves directly and the performance variables are quite reasonable and even efficient considering low cost of HKWT system and abundant availability of those waves. For the low-frequency waves, the turbine is tested for different wave velocities to discover the best angular velocity of the rotor in terms of performance and the rotational velocity of 300 RPM has been found to be the optimum amount. Further,... 

The issue of fluid sloshing in vessels is of paramount importance in aerospace engineering. To suppress sloshing Baffles are used and one kind of baffles is “Perforated Baffle” that is good in weight efficiency. When fluid passes through Perforated Baffle, the energy dissipates and sloshing induces. The purpose of this study is to develop a model for linear sloshing in presence of a Perforated Baffle in the vessel. In this project, the flow is modeled by potential function. The Flow may be rotational in the nearby of baffle due to viscosity when it passes through-out perforations, so Laplace's equation for the velocity potential is useless in this region. To simulate the flow in such zones,... 

In its most general form, analysis of macroscopic electromagnetic behaviour of a medium must include the dependence of magnetic flux density on the electric field and electric flux density on the magnetic filed. This new degree of freedom can lead to new propagation phenomena and result in novel microwave and optical devices. In recent years, numerous theoritical and exprimental studies have been carried out to fabricate these bi-anisotropic materials and understand their behaviour. A particular class of bi-anisotropic materials is electromagnetically equivalent to an anisotropic medium with gyrotropic permittivity and permeability tensors that operate on pseudo-electromagnetic fields. In... 

This experimental study investigates the interaction between surface waves and flexible stems in aquatic environments, focusing on the case where the wave frequency is close to the natural frequency of the stems. Aquatic plants have significant structural and ecological effects on aquatic environments, inducing various changes in the flow passing through them. In this research, a polyurethane stem model is used, which is submerged and randomly placed in water. The oscillation amplitude and pollutant dispersion are investigated. The experiments were conducted at four frequencies of 0.7, 0.83, 1, and 1.125 Hz, two wave heights of 2 and 3 cm, and two densities of 0.8 and 1.2%. Image processing... 

Motivated by the role of interfacial instabilities in sediment resuspension, this paper provides quantitative measurements of the long-time behavior of the interfacial waves and the changes in vertical density during motion of a surface wave over a muddy bed. After an initial fluidization process, a 3D quasi-standing interfacial wave was observed at the interface as a result of a resonant wave interaction with the surface wave. In the process, the quasi-standing wave started growing exponentially at a rate of 0.052-0.081 1/s and then reached a maximum amplitude (kexpb=0.77-0.83). The interfacial wave then took a downward trend in the transition stage and approached a steady state...