AUT Journal of Mechanical Engineering
Year:2019 | Volume:3 | Issue:1|Papers Count:13

In this paper, Chebyshev spectral collocation method is used to solve the unsteady two-dimensional flow and heat transfer of Carreau nanofluid over a stretching sheet subjected to magnetic field, temperature dependent heat source/sink and viscous dissipation. Similarity transformations are used to reduce the systems of the developed governing partial differential equations to nonlinear third and second orders ordinary differential equations which are solved by the numerical method. Good agreements are established between the results of the present numerical solution and the results of Runge-Kutta coupled with shooting method. Using kerosene as the base fluid embedded with the silver (Ag) and copper (Cu) nanoparticles, the effects of pertinent parameters on reduced Nusselt number, flow and heat transfer characteristics of the nanofluid are investigated and discussed. From the results, it is established temperature field and the thermal boundary layers of Ag-Kerosene nanofluid are highly effective when compared with the Cu-Kerosene nanofluid. Heat transfer rate is enhanced by increasing in power-law index and unsteadiness parameter. Skin friction coefficient and local Nusselt number can be reduced by magnetic field parameter and they can be enhanced by increasing the aligned angle. Friction factor is depreciated and the rate of heat transfer increases by increasing the Weissenberg number. It is hope that the present work will enhance the study of the flow and heat transfer processes.

In this paper, the study of squeezing flow of sodium alginate (SA) a non-Newtonian fluid whose rate of shear is not constant with viscosity flows through a medium transporting nanoparticles of silver (Ag) and Alumina (Al2O3). The flow medium is a flat parallel plate arranged vertically against each other under steady flow condition. As the flow process arising from the mechanics can be described by ordinary nonlinear differential equation, the Adomian decomposition method been an effective, yet simple method is adopted to analyze the non-linear differential equation. This is used to investigate effect of squeezing flow and heat transfer on the nanofluid. Analytical results reported graphically depicts the effect of squeezing flow on heat transfer utilizing silver nanoparticles shows decreasing temperature distribution for plates coming together while as plates moves apart temperature distribution decreases further. Similar trend is observed adopting the alumina nanoparticle. However the silver nanoparticle having better thermal properties compared with alumina demonstrates higher heat transfer rate due to effect of varying fluid kinematic viscosity on heat exchange. Results generated from the study when compared with existing literature are in good agreement. Therefore study proves a good emphasis for the improvement of sodium alginate transport in biomedical, pharmaceuticals, manufacturing and chemical processes amongst others.

Critical heat flux has been recognized as the upper limit for the safe operation of many cooling systems which may lead to the occurrence of dryout causing a large temperature gradient in the heated wall. One way to increase the amount of the critical heat flux is to put in nanoparticles such as Al2O3 to the base fluid. The current research investigates the nanoparticles effect on dryout phenomenon using computational fluid dynamics. Boiling phenomena are simulated using the mechanistic model organized in Rensselaer Polytechnic Institute which is extended to analyze the critical heat flux by partitioning wall heat flux to liquid and vapor phases. It was shown that the dryout phenomenon can be delayed by increasing the nanoparticles concentration, and in certain concentration of nanoparticles (5 percent), dryout would not take place.

A numerical study is performed to investigate the effects of shaped multi-hole on film cooling effectiveness over a flat plate. Hence a single cylindrical film cooling hole with 11.1 mm diameter is replaced with the shaped multi-hole (14 holes with 2.97 mm diameter) while maintaining constant blowing ratio. Numerical simulations are performed at a fixed density ratio of 1.6, length-to-diameter of 4 and an inclined angle of 35o. Two configurations of hook and fan shapes are considered for multi-hole. The control-volume method with a semi-implicit method for pressure linked equations-consistent algorithm has been used to solve the steady-state Reynolds-averaged Navier–Stokes equations. The k-ε model is applied for modeling the turbulent flow and heat transfer field. It is found that replacing a single hole with the shaped multi-hole leads to a considerable increase in the film cooling effectiveness in both axial and lateral directions. Results of the present study show that for blowing ratio of 0.6, the hook shape and fan shape configurations of multi-hole, provide a higher area-averaged film cooling effectiveness by 48% and 58.2% more than the single hole respectively.

Since the solar energy is from the most well-known and important sources of clean energies, the solutions to absorb solar energy play significant role in the effectiveness of thermal collector system. The present study aims to investigate the experimental analysis of solar volume collector’s performance for usage in domestic solar water heater and using graphene oxide nanoplatelets nanofluid based deionized water. The weight percentage of graphene oxide/deionized water has been chosen with the percentages of 0. 005, 0. 015 and 0. 045, respectively. The used collector has been tested according to the standard of EN 12975-2 in different temperatures of inlet fluid and in flow rates of 0. 0075, 0. 015 and 0. 225 kg/s. The results of this experiment determine that with the increase of nanofluid’s weight percentage, the collector efficiency is increased and collector efficiency in its highest level in the flow rate of 0. 015kg/s and in the weight percentages of 0. 005, 0. 015 and 0. 045 are 63. 28, 72. 59 and 75. 07 respectively, which this amount for the base fluid is 58/25.

Optimization and design of new configurations in the field of engineering became faster and more accurate by improving three dimension modeling software and computational fluid dynamics methods. Exhaust manifold of the marine diesel engine, which transfers hot gases from cylinders to the turbocharger, has a problem with extreme thermal gradients and crack creation. In order to improve the heat transfer and prevent crack occurrence at the detected critical points, new configurations in geometrics design for exhaust manifold were studied in this paper. Flow simulation of thermal analysis was performed in ANSYS CFX by using Rensselaer Polytechnic Institute wall boiling model for subcooled boiling at the low pressure. Analysis indicated the single channel configuration, performed by removing output-separating wall on hot gases side, provide more uniform temperature distribution in the manifold body. Results showed the correct operation of new manifold geometry that reduces the maximum temperature of the body up to 27.36% and controls the extreme (amount of) thermal gradients.

 In the present paper, a mathematical model has been provided for a magneto-electro-elastic plate to investigate its energy harvesting in nonlinear transverse vibration. The nonlinear equations of motion of a magneto-electro-elastic plate have been used based on the Kirchhoff plate theory. These equations have been reduced to an ordinary deferential equations using Airy stress function and Galerkin Method. The equivalent electrical circuit of the structure is developed. A closed form solution has been obtained for the output power of the harvester using the method of multiple scales. The obtained results are compared with those of finite element method and a good agreement observed between the results of displacement and voltage. By introducing an analytical relation for the power as cost function, the Genetic Algorithm method is applied to optimize the best parameters of the harvester which gives the maximum power. The effect of various parameters of the harvester, such as dimension and thickness, on the power is investigated and the results are discussed.

In the current study, a finite element method is developed using the principle of total potential energy based on nonlocal integral elasticity theory to investigate the free vibration behavior of nano-scaled plates. The classical plate theory is considered for deriving the formulations of the plate. The eigenvalue problem is extracted by using the variational principle and corresponding natural frequencies of free vibration are obtained. Different boundary conditions and various geometries can now be appropriately analyzed by using the nonlocal finite element method proposed in the current article. The results of the current study are compared with those available in the literature. Then the effects of nonlocal parameters, geometrical parameters, various boundary conditions and surface effects on the free vibration behavior of nano-scaled plates are investigated.

 In this paper, the stretching stiffness of a rippled graphene is studied using the molecular dynamics simulation. The uneven surface of the rippled graphene is modeled by a random function with different amplitudes and frequencies. Two models of the rippled graphene are simulated. In the first model, it is supposed that the graphene has random wrinkles with different amplitudes and frequencies. It can be regarded as an opened crumpled graphene. In the second model, the uneven surface of the rippled graphene is modeled by the trigonometric sine shapes. The adaptive intermolecular reactive bond order potential function is utilized to model the covalence bonding of the carbon atoms and the Nose-Hoover thermostat is used to control temperature of the system. It is implemented in the software package large scale atomic/molecular massively parallel simulator in order to simulate covalent bond formation between carbon atoms in the structure of graphene layer. Results are presented for both zigzag and armchair rippled graphene sheets with different initial surfaces. It is concluded that the failure strain of a rippled graphene under uniaxial tensile loading is less than that of a flat one. It is also demonstrated that the rippled graphene has softening stretching behavior due to its uneven surface.

In this research paper, an improved theory is used for buckling analysis of sandwich truncated conical shells with thick core and thin functionally graded material face sheets and homogeny core and with temperature-dependent properties. Section displacements of the conical core are assumed by cubic functions, and displacements of the functionally graded material face sheets are assumed by first-order shear displacements theory. The linear variations of temperature are assumed in the through thick. According to a power-law and exponential distribution the volume fractions of the constituents of the functionally graded material face sheets are assumed to be temp-dependent by a third-order and vary continuously through the thickness. In other words to get the strain components, the nonlinear Von-Karman method and his relation is used. The equilibrium equations are obtained via minimum potential energy method. Analytical solution for simply supported sandwich conical shells under axial compressive loads and thermal conditions is used by Galerkin’s solution method. Analysing the results show that the critical dimensionless axial loads are affected by the configurations of the constituent materials, compositional profile variations, thermal condition, semi-vertex angle and the variation of the sandwich geometry. Numerical modeling is made by ABAQUS finite element software. The comparisons show that the present results are in the good and better agreement with the results in the literature and the present finite element modelling.

The applications of aluminum alloys are limited due to the low formability at ambient temperature. To overcome such limitations, hot metal gas forming is developed as a new process. In this paper, the hot metal gas forming for production of cylindrical step tubes from 6063 aluminum alloy is studied experimentally. For this purpose, Taguchi method of experimental design was used to optimize the process parameters such as axial feed, forming temperature and gas pressure. Seamless tubes with an outer diameter of 25 mm and 1.3 mm thickness were used. After deformation, the specimens were cut and the die filling and thickness distribution were measured. At a constant temperature, with increasing pressure at low axial feed, the specimens burst, while with increasing axial feed at low pressure the specimens were wrinkled. The results indicate that if the axial feed increases in proportion to the pressure, the risk of bursting and wrinkling decreases. The analysis of variance indicated that from the three parameters studied, the effect of axial feeding on filling percentage was of prime importance and the gas pressure and forming temperature were respectively in the second and third rank. The main effects plots for signal-to-noise ratio showed that the optimum arrangement of parameters were at 580°C, 0.6 MPa and an axial feed of 14 mm. In this condition, the die filling of 92% and maximum thinning less than 10% were achieved.

Piezoelectric cantilevers are mostly used for vibration energy harvesting. Changing the shape of the cantilevers could affect the generated output power and voltage. In this work, vibration energy harvesting via piezoelectric resonant unimorph cantilevers is considered. Moreover, a new design to obtain more wideband piezoelectric energy harvester is suggested. This study also provides a comprehensive analysis of the output voltage relationships and deducing an essential precise rule of thumb to calculate resonance frequency in cantilever-type unimorph piezoelectric energy harvesters using the Rayleigh-Ritz method. The analytical formula is then analyzed and verified by experiment on a fabricated prototype. The analytical data was found in an agreement with the experimental results. An important finding is that among all the unimorph tapered cantilever beams with uniform thickness, the triangular cantilever, can lead to highest resonance frequency and by increasing the ratio of the trapezoidal bases, the resonance frequency decreases. It is concluded that the shape can have a significant effect on the output voltage and therefore maximum output power density. Some triangular cantilever energy harvesters can arrange in pizza form using cantilever arrays. This arrangement decreases the occupied space and can lead to increasing the power density and also operating bandwidth.

This paper investigates the effect of road quality on the control strategies of active suspension system integrated with anti-lock braking system in a quarter-car vehicle model. To this aim, two optimal control laws for active suspension system and anti-lock braking system are analytically designed using the responses prediction of a continuous 4 degree of freedom non-linear vehicle model including longitudinal and vertical dynamics. The optimal feature of the suspension controller provides the possibility of adjusting the weighting factors to meet the ride comfort and road holding criteria on roads with various qualities. It is shown that, regulating the tire deflection in a constant value to increase the tire normal load leads to instability of suspension system. Therefore, the active suspension system cannot influence on the anti-lock braking system performance on flat roads in a quarter car model. The same effect is observed for hard braking on irregular roads with good quality. In this condition, the active suspension system should be focused on the ride comfort as its first aim. However, for braking on irregular roads with poor quality, decreasing the variation of tire deflection to avoid the tire from jumping is effective in reducing the stopping distance.