Papers by Mohammad Tawfik
Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic for... more Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness, and inertia forces on a structure. In an aircraft, as the speed of the flow increases, there may be a point at which the structural damping is insufficient to damp out the motion which is increasing due to aerodynamic energy being added to the structure. This vibration can cause structural failure, and therefore considering flutter characteristics is an essential part of designing an aircraft. Scientists and engineers studied flutter and developed theories and mathematical tools to analyze the phenomenon. Strip theory aerodynamics, beam structural models, unsteady lifting surface methods (e.g., Doublet-Lattice) and finite element models expanded analysis capabilities. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called " stop-bands ". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. This may reduce the vibration level of the structure, and hence improve its dynamic performance. In this paper, for the first time, we analyze the flutter characteristics of a wing with a periodic change in its sandwich construction. The new technique preserves the external geometry of the wing structure and depends on changing the material of the sandwich core. The periodic analysis and the vibration response characteristics of the model are investigated using a finite element model for the wing. Previous studies investigating the dynamic bending response of a periodic sandwich beam in the absence of flow have shown promising results.
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The main energy source for the cube satellite in the space is the photovoltaic panels (PV) that c... more The main energy source for the cube satellite in the space is the photovoltaic panels (PV) that convert the sun irradiance to current .It is important to get the maximum output power from the PV panels by using the Maximum Power Point Tracking Technique (MPPT) to maximize energy harvesting from the sun, to supply the high power requirements of the powerful on-board computer .The PV panels' output power depends on the incident irradiance. When the cube satellite's orientation changes, the incident irradiance varies, consequently the output power from PV panels changes. The variation of the incident irradiance makes the global maximum peak (GMP) tracking difficult, which decreases the efficiency of the PV panels. This paper presents the implementation of an analog maximum power point tracking technique to save size inside cube satellite and to save the tracking power consumption. The main goal of this analog technique is to maximize the output power of the PV systems.
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For many years, several crack detection attempts have been using measurements of the structure's ... more For many years, several crack detection attempts have been using measurements of the structure's modal parameters. One of the easiest is to measure and correlate the change in natural frequencies to cracks. The direct and inverse problem have been discussed in literature. However, the inverse problem, being addressed in this paper, is a challenging one, where it starts by measuring certain structural properties and estimate the corresponding crack location and size. Unlike previous studies that utilizing natural frequencies from one direction, both axial and bending natural frequencies are used together to determine crack size and location, without prior estimation of natural frequencies of the intact beam. The results obtained showing promising capabilities in crack detection .
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Multi-copter or Multi-rotor is a new field and most of the modeling and control research points a... more Multi-copter or Multi-rotor is a new field and most of the modeling and control research points are interested to improve the performance of the multi-rotors to do its work with no effort and in best way. Here Quadcopter system was proposed due its wide usage. Quadcopters as it is known as quadrotor has been involved in many applications due to its facilitations and speed. They have been used in Search and rescue, Building Inspection after Earth Quicks, Precision Agriculture, Remote farming, Mapping of building, Transportation, Motivation and mine detection. Modeling of the Quadcopter is the most important part of designing as we see all the characteristics of the system and depend on this observations we determine the controller which sustain all the requirements. We investigate two different methods for modeling first one is modeling which depend on the system of equations describing the system motion and performance, the second method using the neural network using NARX model proposed here[5]. The results will show the difference between those two methods.
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Modeling of dynamic systems using system identification became an important discipline as it over... more Modeling of dynamic systems using system identification became an important discipline as it overrides the errors that may be introduced by traditional modelling techniques. There are two methodologies for identification of systems' models; statistical and deterministic methods. Identification algorithms are proposed in this paper using deterministic neural network and compare the results with regression method. Here we are interested in identifying the input output relation of many dynamic systems such as satellites, UAV, Quadcopters etc…. The neural network we talk about is a NARX based model with back-propagation learning technique which allows the network to learn from the system response and the excitations at every time step with time delay. Meanwhile, the regression used the least square method for determining the relations between the response at any time step and the previous time step response and excitation. We implemented our algorithms on embedded board to verify its operation. The results were verified using data obtained from a numerical integration solver and others obtained from real sensors on different dynamic systems. Our results showed that the algorithms were able to predict the performance of the dynamic systems tested to a very good degree of accuracy.
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ABSTRACT Flexible manipulators have received wide attention being more realistic than their rigid... more ABSTRACT Flexible manipulators have received wide attention being more realistic than their rigid counterparts in many practical conditions. The control of the motion and vibration of an elastic model has inspired many studies in the past decades. A modified genetic algorithm (MGA) is proposed to optimize the feedback gains of a proportional derivative (PD) controller used for the control of the position and vibration of a flexible arm. It has been shown that the new algorithm results in faster convergence and higher accuracy over the simple genetic algorithm (SGA). Also, MGA solves the problem of premature convergence and stagnation that is caused by SGA. Three different objective functions based on minimizing the error function were tested and compared. Multi-objective error fitness function combined with the proposed GA has given the best system response which encourages for further research into various control applications.
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ABSTRACT
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Crack detection in structures has attracted the researchers for many years. Several crack detecti... more Crack detection in structures has attracted the researchers for many years. Several crack detection attempts use measurements of the structure's modal parameters, like the natural frequencies and mode shapes. One of The easiest parameter among them to measure and correlate to cracks is the natural frequencies. Several approaches focused on crack detection in beams and bars using the changes in the natural frequencies. The direct problem has been addressed, but the inverse problem is a challenging one, where it starts by measuring certain structural properties and estimate the crack location and size. In most research works, the natural frequencies of the intact structure or historical measurements have to be known in advance. Another feature in similar studies is to handle the beam action and bar action separately. The inverse problem of an Euler-Bernoulli beam with an open crack is addressed here. Unlike these models, the present model utilizes the first axial and transverse na...
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Flexible manipulators have received wide attention because they are more realistic than their rig... more Flexible manipulators have received wide attention because they are more realistic than their rigid counterparts in many practical conditions. The control of the motion and vibration of an elastic model has inspired many studies in the past decades. In this paper, a finite element model is developed and used for the modeling of the single-link flexible arm. A new adaptive genetic algorithm (AGA) is proposed to optimize the feedback gains of a proportional derivative (PD) controller for the control of the motion and vibration of the flexible arm. The proposed technique is based on a new adaptive mutation operator to adjust the probability of mutation of each chromosome based on the average fitness value at each generation. The results are compared with those obtained by applying simple GA and a direct evaluation of the objective function in the domain. It has been shown that the new developed adaptive mechanism is faster in convergence and the obtained solutions are of higher fitness...
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This paper presents an investigation into a new optimization technique based on genetic algorithm... more This paper presents an investigation into a new optimization technique based on genetic algorithm (GA). A dynamically-changed mutation value approach is introduced to increase the diversity in the search space and avoid premature convergence caused by simple genetic algorithm (SGA). The enhanced genetic algorithm (EGA) is used to tune the feedback gains of a PD controller which controls both the position and vibration of a single-link flexible arm. The dynamic model of the system is derived using Hamilton’s principle and modeled using the finite element method (FEM). A multi-objective function is defined and altered to reach a range of specified system responses and therefore it is shown to be able to satisfy different objectives. Adaptive Genetic Algorithm (AGA) and Cloud Model Based Adaptive Genetic Algorithm (CAGA) techniques are used to challenge the proposed technique. Results obtained show that EGA creates significant improvement in the speed of convergence compared to other t...
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In the past decades, many numerical and experimental investigations on the capabilities of period... more In the past decades, many numerical and experimental investigations on the capabilities of periodic structures for vibration attenuation and band localization were performed, and proved those capabilities for different simple structures. Earlier investigation of such phenomenon in periodic plates was not promising due to different factors. A parametric study is a systematic way to vary a number of model parameters and have the system run for one or several analyses for each combination of parameters. In this research, investigation of the effect of varying different parameters on the attenuation bands location and width of four different patterns of periodic plates will be discussed.
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The undesirable vibrations in all structures types (buildings, vehicles, machines and electronics... more The undesirable vibrations in all structures types (buildings, vehicles, machines and electronics) affect the durability, performance and the control of these structures. Damping of these vibrations is the concern of many researches using smart materials. The super-elastic behavior of shape memory alloys (SMA) may be utilized in the active damping of structures vibrations. SMA wire was obtained for this research but we had to calibrate it to get load-elongation-heat relations. In the process of SMA calibrating, an experimental device was designed to measure different loadings and the corresponding elongations at different heating conditions. To control the temperature an electric direct current was used.
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In the previous decades, many numerical and experimental investigations on the capabilities of pe... more In the previous decades, many numerical and experimental investigations on the capabilities of periodic structures for vibration attenuation and band localization were performed and proved those capabilities for different simple structures. Earlier investigation of such phenomenon in peri-odic plates was not promising due to different factors. In this research, experimental and numerical investigations of the vibration response of different periodic plates are investigated to examine simi-lar behaviour of periodic plates. Three different periodic configurations were tested under 'almost' free support boundary conditions. This work is an important development over that performed by Tawfik [3] . Milled plates are used to avoid the damping effect of the adhesive material which was used by Tawfik. The experiments involved excitation from one corner of the square plate and meas-uring the response at three other corners. The results were compared to those of a similar size plain p...
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Papers by Mohammad Tawfik