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Passive vibration attenuation of modern mechanical structures is one of the most essential technologies applied to the arsenal of modern mechanical structures. In this thesis, dynamics analysis is performed on viscoelastic (VE) beam and plate sandwich structures. The proposed structures are composed of a VE core and aluminum face sheets as the substrate layers on both sides of the structure. The small-strain VE material is modeled based on the complex constant moduli model. In the modal analysis, the model effective mass analysis is performed to investigate its dominant mode shape and its sweet spot at resonance. Then, in the harmonic analysis, the resonance frequency is obtained to evaluate the performance of the VE sandwich structures via the maximum deformation. A comparison between the results of an analysis of viscoelastic sandwiched structures with subsequent done using FE models. A numerical application is accomplished to develop the integral shear finite element and modal assembly of the stiffness element and mass element established according to strain energy and the Hamilton principle. The harmonic analysis is done using ABAQUS® software with both C3D20RH®, CPS8R where C3D20RH indicates a 3- D element with 20 nodes with reduced integration technique and hybrid formulation and CPS8R indicates 2-D plane strain with eight nodes with reduced integration technique, the results are compared against analytical solutions form the literature, a parametric study is done on the beam’s core thickness to study the effect on the damping characteristics of the beam, the results showed that the modal developed in MATLAB® achieved the least error compared to the analytical solution from the literature and then comes the Abaqus® software solution, also the parametric study showed that the natural frequency of the beam does not change with the increase of the core thickness, however, the loss factor is directly proportional to the thickness of the viscoelastic layer of the beam. Keywords: Viscoelastic, Sandwich Beam/Plate, Dynamics Analysis, Complex Constant Moduli, Finite Element Method, Shear Deformation Theory
[Abstract Not Available]
The act of additive manufacturing (AM) entails layer by layer creation of a layered structure from the ground up. This competence allows for a sophisticated design to be carried out with geometries that are sometimes impossible to achieve and materialize with conventional manufacturing methods such as subtractive manufacturing, molding, foaming, etc. Fused filament fabrication (FFF) or sometimes addressed as fused deposition modeling (FDM) is among the AM methods which couples well with manufacturing composite materials. Fabricated composite materials using FFF has proven to be particularly useful in a plethora of industries, namely in the aerospace and aeronautics, automotive industry, therapeutic apparatuses, and sports goods. In general, invented parts with FFF method have excellent mechanical properties which make them worthy of further study. Performance under tensile tension and flexural (bending) tensions are particularly significant in composite materials. Therefore, a thorough finite element modeling (FEM) on tensile and flexural behavior of FFF fabricated continuous carbon fiber specimen in the COMSOL multi-physics® environment is executed while using layered shell elements to express the properties in a layered structure. The results gathered from the FEM was compared to other experimental and related empirical studies. Furthermore, the type of effects a composite material might have on tensile properties such as infill ratio, infill pattern, fiber content, layer orientation and stacking sequence will be put under scope. Based on the results provided under this new study, the tensile and flexural simulated specimen shown better maximum tensile and flexural capabilities, with 1490 [MPa] and 1240 [MPa] Max stress, while the tensile model underwent the boundary load of 559.9 MPa and the flexural model went through 302.70 N at two points to simulate the two-point flexure test.
Navigating a smart vehicle in an environment, determined or unknown, requires the localization of such vehicle in that environment using GPS, cameras, vision, laser or ultrasonic sensors, motion planning of the vehicle in free configuration space of the environment, and its ability to deviate from obstacles. In planning a path from a start to a goal configuration, the aim is to obtain the shortest path in less time while avoiding obstacles. Metaheuristic algorithms have been extensively applied to achieve this; while it exploits the environment from an initial solution, it also explores it to find a possible feasible path. Researchers in robotics and automation field have investigated and analysed the performance of population-based algorithms like Genetic Algorithm (GA), Ant Colony Optimization (ACO), Particle Swarm Optimization (PSO), Firefly Algorithm (FA), and Cuckoo Search Algorithm (CSA) to obtain a feasible shortest path. This research work investigates the performance of metaheuristic search algorithms like GA, PSO, FA, and CSA for path planning on four different benchmark problem maps (40 x 40m large, 20 x 20m maze, 20 x 20m rockpile and 20 x 20m pothole) and makes a comparative analysis based on computational time and path length. Furthermore, three sampling methods i.e., Random, Latin hypercube and pseudo-uniform sampling were used. It is observed that all the algorithms were able to achieve the optimal, although CSA performed poorly on path distance using GA and PSO on the maze and pothole map respectively, its performance on other two maps was relatively better both on shortest distance and computational time, however, it is concluded that no single algorithm is universally the best-performing algorithm for all maps. All simulations were performed on MATLAB R2022b. Keywords: Metaheuristic Algorithms, Path Planning, Navigation, Mobile Robot, Smart Vehicle
The concept of nanofluids refers to a new kind of heat transport fluids by suspending nano scaled metallic or nonmetallic particles in base fluids. The experimental results showed that the suspended nanoparticles increased convective heat transfer coefficient of the fluid. The properties and behavior of a nanofluid depend on a number of parameters including the properties of the base liquid and the dispersed phases, particle concentration, particle size and morphology, as well as the presence of dispersants and/or surfactants. From a macroscopic view, the properties of homogenous nanofluids that affect the heat transfer behavior include heat capacity, thermal conductivity, density and viscosity. Natural convective heat transfer is affected by a number of processes in parallel and/or series, including unsteady state heat conduction through the heating wall, conduction within the boundary layer and its development, as well as convection due to the variation of liquid density and the density difference between the nanoparticles and the liquid. In this experimental study, natural heat transfer of Nanofluid will be investigated. Nanofluid with different volume percentage will be put between walls of the cavity, and the natural heat transfer will be observed. As a result of the experimental readings, Nusselt number as a function of Rayleigh number (i.e. Nu= c Raⁿ) will be obtained.
Low-grade heat (LGH) sources, here defined as those below 500 oC, are a group of abundant energy sources available as industrial waste heat, solar thermal, and geothermal which are not used to their full advantages. For example, they are not adequately for conversion to power because of low efficiency energy conversion. The utilization of LGH can become advantageous for achieving to the highest thermal efficiency. Technologies that allow the efficient conversion of low-grade heat into mechanical and electrical power need to be developed. Various studies have been carried out to appraise the potential of using supercritical carbon dioxide (S-CO2) in a closed Brayton cycle using LGH source for power generation. In this study, the objective of research is to perform a thermodynamic analysis on five different configurations of S-CO2 Brayton cycle. Different configurations are examined among which recompression and partial cooling have been found very promising. The main part of this study is focused on carbon dioxide Brayton cycle. CO2 Brayton cycle has wide range of applications such as heat and power generation and in automotive and aircraft industry. Proposed configurations of each carbon dioxide Brayton cycle performance simulation are conducted and subsequently compared with other power cycles utilizing LGH sources. The CO2 transcritical power cycle (CDTPC) utilizing LGH is also studied. The models are developed by using the Engineering Equation Solver (EES) for several different Brayton cycle configurations. The choice was made to pursue Brayton cycle with regeneration configuration for further, due to its simplicity and high efficiency. Keywords: Supercritical CO2 Brayton cycle, transcritical CO2 cycle, simulation, low-grade heat.
The motivation of this research project was in response to issues of increasing energy demand and the surge in energy scarcity and environmental problem. Various form of fuel like oil, natural gas, wood, and coal etc. can be used for drying process but they are not cheap, and most of them are not environmentally friendly. Renewable energies are one of the promising ways to tackle this global challenge. This work is centered on the investigation solar drying process. A mix-mode solar dryer was designed for drying fruits, vegetables, and biomass. The dryer is made up of a flat plate solar collector, duct fan, two drying chamber module glazed from the top. The flat plate collector of length 200 cm, width 100 cm and height 20 cm was use to preheat the air before entering the drying chamber. The collector is made up of 3mm thick double layer of glass, V-corrugated sheet metal with 60° groove angle. A duct fan is used to provide air circulation. The drying chamber is manufactured from steel, wood, and glass. Different tests were carried out to evaluate the performance of the dryer. The dryer was used to dry apple, banana, grapes and chili pepper. For the different tests carried out the temperature, humidity and solar radiation was recorded to enable evaluation for the performance parameters such as moisture content at the end of each day, drying rate, and drying efficiency. The moisture content of apple, banana, grapes and chili pepper was reduced to their final moisture content within two days of sunshine hours. The average drying rate for apple, banana, chili pepper, and grapes were found to be 30.2 g/h, 82 g/h, 67.8 g/h and 98 g/h respectively per kg of each specimen. Keywords: Solar drying, mix-mode solar dryer, food crop and drying chamber
ABSTRACT: Heat transfer behavior of Cu-water nanofluid in a two dimensional (infinite depth) rectangular duct is studied numerically for laminar flow, where the nanofluid has been considered as a Newtonian fluid. The governing continuity, momentum, and energy equations are discretized using finite volume approach and solved using SIMPLE method. The viscosity and thermal conductivity of nanofluid are determined by models proposed by Brinkman and Patel et al. Study has been conducted for a wide range of Reynolds number from 10 to 1500, for solid volume fractions between 0% and 5%. Top and bottom walls are considered for two cases of constant temperature and constant wall heat flux, while results for both uniform and parabolic entrance velocities are considered in each case. It has been observed that the rate of heat transfer increases with increase in solid volume fraction as well as increase in flow rate. Besides, higher heat transfer is observed for uniform entrance velocity compared to channel with parabolic inlet velocity. Keywords: Nanofluid, Rectangular duct, Laminar flow, Newtonian. …………………………………………………………………………………………………………………………
The energy demand all over the world has been continuously increased. The ever increasing cost, limited resources and possible environmental risks of using conventional energy resources have increased the renewable energy utilization. Solar energy is considered the most promising, inexhaustible and plentiful renewable source of energy. Solar collectors are employed in converting solar energy into thermal energy. The energy consumption of space heating in residential and industrial sector is considerable. In solar energy utilization direct use for space heating could be achieved by employing solar air heaters (SAHs). Technical feasibility has been achieved for SAHs. One of the main concerns is providing economic feasibility. The present study consists of three series of experiments. First, three SGSAHs with different bed heights (7 cm, 5 cm, and 3 cm) were fabricated with multiple glass panes used for glazing. The length, width, and thickness of each pane were 131 cm, 6 cm and 0.4 cm respectively. The mass flow rate was varied between (0.014 and 0.057) kg/s. The second series of experiments had been conducted to investigate the effect of the width of glass panes, the distance between the slits and mass flow rates on the efficiencies of the three SGSAHs. A glass pane with the length of 131 cm and thickness 0.4 cm was studied for three different glass pane widths: 6 cm, 5 cm, and 4 cm. In addition, the bed height of duct in the second series of experiments was fixed at 7 cm. The ambient air was continuously withdrawn through the gaps between the glass panes by fans. In the first and second series, the experiments were conducted for four different gap distances between the glass panes (i.e., 0.5 mm, 1 mm, 2 mm and 3 mm). Finally, the third series of experiments had been carried out on a SGSAH and a UTC to compare their efficiencies. The mass flow rates in the second and third series of experiments were varied between (0.014 and 0.029) kg/s. In the first series of experiments the highest efficiency obtained was 82% where the bed height was 7 cm, glass pane gap distance was 0.5 mm, and the mass flow rate was 0.057 kg/s. The air temperature difference between the inlet and outlet (∆T) was maximum (27˚C) at the lowest mass flow rate (i.e., 0.014 kg/s) for the same SGSAH. The results demonstrated that for mass flow rates lower than 0.036 kg/s and gap distances greater than 2 mm, the performance of the SGSAH with 3 cm bed height was better compared to the SGSAHs having 5 cm and 7 cm bed heights. However, for flow rates equal or higher than 0.036 kg/s, the SGSAH with 7 cm bed height performed better for all different gap distances compared to the other two SGSAHs. The experimental results of the second series indicated that the maximum thermal efficiency of 75% was obtained when the gap distance was 0.5 mm, slit width was 4 cm and the mass flow rate was 0.029 kg/s. The maximum rise in air temperature was noted as 28℃ at the lowest mass flow rate where the gap distance and slit widths were 0.5 mm and 4 cm respectively. The experimental results obtained from the last series indicated that the thermal efficiency of the SGSAH was 16% higher than the UTC’s efficiency. Keywords: Slit glazed solar air heater, thermal efficiency, unglazed transpired collector, bed height
Energy is one of leading problem all around the world. Increasing urbanization and industrialization, improving life conditions and standards and increasing world population have been creating a dramatic rise of energy demand. As a consequence of population growth, this resulted in high rate fossil fuel consumption. Besides, use of fossil fuels creating irrecoverable environmental damages such as global warming. Renewable energy and its storage systems are most promising solutions to overcome this problem. North Cyprus is an island good and suitable candidate for renewable energy utilization and its storage applications. Particularly, solar energy is abundant throughout year in North Cyprus and it represents a high potential to be used for building space heating. The main barrier is the imbalance between the heating demand and solar energy availability. Due to the cyclic nature of it, there is no solar radiation available at nighttime once the heat losses increasing. This condition indicates the need of utilizing thermal energy storage coupled with solar collector systems to store the solar energy once it is available to be used later when it is needed. Despite latent and sensible heat storage systems have been researched widely for this purpose, they have some major drawbacks such as low energy storage density and high heat losses limiting the storage potential and duration. A new thermal energy storage method; thermochemical heat storage, based on reversible sorption-desorption cycles is purposed in this study. Such thermal energy storage system could provide higher heat storage density and long-term heat storage potential making it attractive for solar thermal applications. From this point of view, aim of the presented study is; to develop a prototype thermochemical heat storage system and to test it under laboratory conditions. A novel composite sorption material; CaCl2–Vermiculite was synthesized and used as the heat storage material. Three different cycles (discharging-charging) with the same flow rate were carried out. Throughout the testing, some optimal results were obtained. For charging temperature between 80-90 °C, discharging average temperature lift of air between 15-20 °C was obtained. Besides, cumulative energy output in the range of 1.6-1.8 kWh was attained, corresponding to an energy storage density between 200-230 kWh. Observed results in this experimental study demonstrated that, for both long and short term heat storage, thermochemical process using V-CaCl2 sorbent is satisfactorily promising and a good candidate to be utilized in solar thermal applications in buildings for sustainable space heating.