Mohamed Gaith

Smart structures: modeling, analysis, and control with different strategies

Weight optimization of structures can result in lower stiffness and less internal damping, causing the structure to become excessively prone to vibration. To overcome this problem, active or smart materials are implemented. The coupled electromechanical properties of smart materials, used in the form of piezoelectric ceramics in this work, make these materials well-suited for being implemented as distributed sensors and actuators to control the structural response. The smart structure proposed in this paper is composed of a cantilevered steel beam, an adhesive or bonding layer, and a piezoelectric actuator. The static deflection of the structure is derived as function of the piezoelectric voltage, and the outcome is compared to theoretical and experimental results from literature. The relation between the voltage and the piezoelectric moment at both ends of the actuator is also investigated and a reduced finite element model of the smart structure is created and verified. Finally, different linear controllers are implemented and its ability to attenuate the vibration due to the first Eigen frequency is demonstrated.

Rated wind speed reality or myth for optimization in design of wind turbines

The rotor design procedure of wind turbines starts first with adopting a rated output power and a rated wind speed. There is lack of modelling to determine an optimized rated wind speed and no evidences are observed to suggest the best rated wind speed to produce maximum output power annually. For example in the market of small wind turbines, it is frequently observed that the rated wind speed is taken from small value of 8 m/s to large value of 20 m/s. To examine overall performance of these wind turbines, it is required to develop mathematical models to relate the annual power production of the wind turbines to the given rated wind speeds. By examining power curves of some small European wind turbines from 100 to 900 Watt with constant speed generators, a simplified mathematical model for power curves is introduced and combined with Weibull distribution of wind speeds. Results of the model based on a capacity factor are presented versus the rated wind speed using wind characteristics of an optional region. It is observed that between the cut-in and cut-out wind speeds, there is an optimum rated wind speed above which the annual output power production of the wind turbine remains unchanged.

Mathematical modelling of the Marsh Funnel for measuring rheological properties of drilling nanofluids for energy efficient environment

The oil and gas industry has recognized the use of nanofluids for improving production rates and also reducing energy demands. Nanofluids function in oil well drilling is to modify rheological and heat transfer properties of the base fluid. Skin friction is reduced by nanofluids which in turn reduces drilling torque and the corresponding power consumption. This also mitigates wear on drilling equipments. The lubrication effects of nanofluids are achieved through enhanced surface energy absorption and ball bearing effects. Marsh Funnel is the practical method to measure viscosity of the drilling fluids with or without nanoparticles. The discharge time is the only measured parameter during operation. In this study, a new mathematical model is introduced for determining discharge flow rate of the Marsh Funnel. Results of the present method are validated against some available experimental data for Newtonian fluids. The present method can be equally applied for nanofluids. Marsh funnel volume discharge rate and the corresponding time are two important measureable parameters that can be used to determine different rheological parameters of nanofluids. The oil well drilling nanolubricants may be promising in an energy efficient operational environment.

External flows on entry of a hybrid wind catcher-wind turbine system

A new concept in wind power harnessing is recently developed under INVELOX (Increasing VELocity) by the company Sheerwind in USA. It is claimed that the new concept can significantly outperforms traditional wind turbines in terms of reducing the diameter of wind turbine, improve aerodynamic characteristics under the same wind conditions, and delivers significantly higher output at reduced cost. The innovative feature of the wind turbine is the elimination of tower-mounted turbines. It is believed that the entry of such systems is crucially important because external flows over nozzle or diffuse devices are different from classically known internal flows. Shrouded wind turbines and wind catcher systems are normally use a diffuser shape at entry, however, the INVELOX concept suggest using a nozzle at entry. In this paper, two different simpler systems than INVELOX are designed with nozzle or diffuser at the entry using general methods in design of blower wind tunnels. In the first phase of this work, CFD (computational fluid dynamics) method is applied to solve external flows around nozzle and diffuser flows by solving the modelled RANS (Reynolds average Navier-Stokes) equations. The initial results indicate that the wind speed retarded at the entry of nozzle while wind speed accelerated at entry of a diffuser device.

Heat losses from human body in weather condition of Amman city

It is wrongly anticipated that the amount of fats burn in human body is related to the amount of sweating, particularly in hot months of the year. In this study, heat losses from human body are studied based on clothing habit, weather condition in Amman city, and the bio-heat transfer mechanisms. The heat losses from human body include breathing (evaporation), conduction, convection, and radiation mechanisms. It is shown that heat losses are largely prevailed by conduction and radiation compared with convection and breathing mechanisms in all months of the year. It is also realized that the heat loss by breathing air is totally depends on the dry bulb temperature of the ambient. The heat loss by convection mechanism depends on many parameters such as clothes temperature, Nusselt number, and heat convection coefficient. The heat loss by radiation mechanism depends mainly on temperature differences between clothes surface and ambient. From the results of this study, the human body losses more heat in spring and winter than summer and autumn. It is also concluded that human body burns more fats during winter and spring seasons than summer and autumn.

Exergy analysis of reactive combustion processes in gas heaters

In this study, exergy analysis and second law efficiency of gas heaters with reactive combustion processes are considered. The reactive combustion of natural gas is modeled via a chain of eight chemical reactions along with first and second law of thermodynamics. The main constitutional elements react in combustion chamber is considered at constant pressure and temperature of the basic elements hydrogen, carbon, oxygen, and nitrogen from the fuel and air. Heat transfer is modeled assuming free convection and radiation mechanisms from gas heater outer surfaces. The governed equations were solved using Engineering Equation Solver (EES) software tool. Results of this study reveal that preheating of air will considerably increase the second law efficiency of combustion process. Excessive air is effective up to 40 percent to prevent incomplete combustion; however, excessive air more than 80 percent is not recommended from exergy stand point of view in gas heaters.

Neural Network usage in structural crack detection

Artificial Neural Network is becoming an efficient tool in online structural health monitoring. ANN enables, due to its promising inherent capabilities, to predict existence of undesirable effects such as cracks within the structure. Natural frequencies of the structure particularly the first three vibration modes are the most pronounced features of the structure to be evaluated for the health monitoring tasks. Crack in the structure make it weaker and under certain loads it may extend to complete fracture and sometimes to catastrophic failure. In this paper, the ANSYS software which employs finite element (FE) techniques is used to generate data for solid cantilever beams and simply supported beams. Natural frequencies are obtained for the first three vibration modes taking into account that the structure is linear for the healthy and the cracked structures. For different crack locations and crack depths, the ANSYS data on natural frequencies and vibration modes show lower values compared with healthy structure. These are good indicators to be used for training the Artificial Neural Network (ANN) tools. Results of ANSYS software is first verified with some available theoretical solutions and then results of the trained artificial neural network (ANN) for defected structure are compared with ANSYS solutions. The findings of this study suggest high accuracy of ANN on structural health monitoring with robust prediction of size and location of cracks.

Computational Study of Hemodynamic Effect of False Lumen Partial Thrombosis of Type B Aortic Dissection for various Tear Size and Configuration

N simulation of interaction between fluid flow and particle motion demands sophisticated algorithms due to the motion of particles and difficulty in creating the grid system. We developed, during past decades, numerical solution methods to tackle this problem and applied the methods to several branches of engineering applications of small scales. The method is based on the Lattice Boltzmann Method (LBM). In this presentation, we demonstrate three kinds of numerical solutions provided by the methods. First, we developed the simulation code for the problem of translocation of a biopolymer through a nano–pore driven by an external electric field. A theoretical formula is also used to calculate the net electrophoretic force acting on the part of the polymer residing inside the pore. Next, we simulated the motion of microscopic artificial swimmer. The swimmer consists of an artificial filament composed of super–paramagnetic beads connected by elastic linkers and an externally oscillating magnetic field is used to actuate the filament, and we have found that there is an optimum sperm number at which the filament swims with maximum velocity. Then, we computed the fluid flow generated inside a micro -channel by an array of beating elastic cilia. We have found that there exists a maximum flow rate at an optimum sperm number. We also simulated the motion of particles caused by fluid flow of cilia actuation.T Magnus effect is the phenomenon whereby a rotating body experiences an asymmetric force due to its rotation. Historically researchers (Benjamin Robins and Gustav Magnus) investigated this effect using spherical bodies. A simplified investigation later followed by limiting attention to two dimensions, reducing the sphere to a circle was performed. Potential flow theory was capable of describing this situation by superposing a uniform stream upon a collocated doublet/vortex flow. Integrating Euler’s equation along the surface of the resulting “rotating” circle yielded an asymmetric force. Experimental verification of this theoretical result was undertaken by approximating the two dimensional circle by a circular cylinder that spanned either a water or wind tunnel. Potential flow theory was taken by Ludwig Prandtl and expanded to describe the lifting flow about a three dimensional surface. Prandtl and his colleague Max Munk used this theory to derive the optimum distribution of vortex flow (hence, circulation) along the span of a lifting body. The elliptical distribution is the optimum in order to reduce induced drag. Given that optimum, Munk was able to solve for the optimum chord distribution for a fixed wing. The extension from two dimensional to three dimensional investigation for airfoils/fixed wings has outpaced that for rotating bodies. The majority of the work on rotating bodies to date has remained two dimensional. The author has taken the optimum circulation distribution and applied it to a rotating cylindrical body. The theoretically optimum three dimensional geometry has been derived and will herein be described.Like most accredited mechanical engineering programs, the undergraduate curriculum at California State University Chico includes a required course in Finite Element Analysis (FEA). Historically, the primary focus of the class has been the underlying theory of the method and its formulation from fundamental governing equations with little to no instruction in commercial software designed specifically for the purpose. Students were taught the traditional theoretical methods (Stiffness, Galerkin, Virtual Work, Castigliano, etc.) and were given assignment problems with rigorous hand-work such as assembling stiffness matrices. They were taught computer based solution methods through non-specific computational software such as Excel and MATLAB®. Feedback from advisory boards, capstone project sponsors, senior exit surveys, and other evidence clearly indicated a problem with the curriculum’s approach to finite element analysis. While program graduates were well versed in the theory of the method, there was strong evidence that they were not skilled its proper application via commercial FEA software, a very common task in the workplace. Observations included poorly posed problems, unnecessary computational rigor, meaningless results, or indeed the inability to obtain a solution at all. In response, the FEA course was redesigned to include basic instruction in the proper use of commercial FEA software while still maintaining sufficient theory for understanding the inherent assumptions and limitations of the method. Segments of theory-based discussion and traditional assignments are now followed with exploration of the same concepts in the context of commercial software. Emphasis is placed on its proper use, underlying assumptions, limitations, and validity of results.