Khaled A. Alnefaie

A refined nonlocal thermoelasticity theory for the vibration of nanobeams induced by ramp-type heating

For small volumes at the micrometer and nanometer level, classical continuum mechanics cannot be used to capture experimentally observed phenomena, such as size effects. Moreover, dissipation is much less pronounced than that in the case of macroscopic volume elements. To remedy the situation, generalized continuum mechanics theories should be used as an alternative to molecular dynamics simulations which do provide physical insight, but may not be suitable for engineering applications and the formulation of related boundary value problems. The present contribution is an example in this direction. An Euler-Bernoulli beam model is constructed to study the vibration of a nanobeam subjected to ramp-type heating. A generalized thermoelasticity theory with non-local deformation effects and dual-phase-lag (DPL) or time-delay thermal effects is used to address this problem. An analytical technique based on Laplace transform is employed. The inverse of Laplace transform is computed numerically using Fourier expansion techniques. The effects of nonlocality, DPLs, and the ramping-time parameter on the lateral vibration, the temperature, the displacement and the flexural moment of the nanobeam are discussed. The results are shown quantitatively in corresponding graphs.

Free Transverse Vibrations of a Double-Walled Carbon Nanotube: Gradient and Internal Inertia Effects

This is a modest contribution on higher-order continuum theory for predicting size effects in small-scale objects. It relates to a preceding article of the journal by the same authors (AMSS, 2013, 26: 9–20) which considered the longitudinal dynamical analysis of a gradient elastic fiber but, in addition to an internal length, an internal time parameter is also introduced to model delay/acceleration effects associated with the underlying microstructure. In particular, the free transverse vibration of a double-walled carbon nanotube (DWNT) is studied by employing gradient elasticity with internal inertia. The inner and outer carbon nanotubes are modeled as two individual elastic beams interacting with each other through van der Waals (vdW) forces. General explicit expressions are derived for the natural frequencies and the associated inner-to-outer tube amplitude ratios for the case of simply supported DWNTs. The effects of internal length (or scale) and internal time (or inertia) on the vibration behavior are evaluated. The results indicate that the internal length and time parameters of the adopted strain gradient-internal inertia generalized elasticity model have little influence on the lower order coaxial and noncoaxial vibration modes, but a significant one on the higher order modes.

Nonlocal Thermoelasticity Theory for Thermal-Shock Nanobeams with Temperature-Dependent Thermal Conductivity

In this work, a model of nonlocal generalized thermoelasticity with one thermal relaxation time is used to consider the vibration behavior of an Euler-Bernoulli (E-B) nanobeam. The thermal conductivity of the nanobeam is assumed to be temperature-dependent. The nonlocality brings in an internal length scale in the formulation and, thus, allows for the interpretation of size effects. The governing partial differential equations are solved in the Laplace transform domain by adopting the state-space approach of modern control theory. The inverse of Laplace transforms are numerically computed using Fourier expansion techniques. The distributions of the lateral vibration, the temperature, the axial displacement and the bending moment of the nanobeam are determined. The effect of thickness and variability of thermal conductivity, as well as the influence of the nonlocal parameter are investigated.

A Comparative Study of Almond Biodiesel-Diesel Blends for Diesel Engine in Terms of Performance and Emissions

This paper investigates the opportunity of using almond oil as a renewable and alternative fuel source. Different fuel blends containing 10, 30, and 50% almond biodiesel (B10, B30, and B50) with diesel fuel (B0) were prepared and the influence of these blends on emissions and some performance parameters under various load conditions were inspected using a diesel engine. Measured engine performance parameters have generally shown a slight increase in exhaust gas temperature and in brake specific fuel consumption and a slight decrease in brake thermal efficiency. Gases investigated were carbon monoxide (CO) and oxides of nitrogen (NOx). Furthermore, the concentration of the total particulate and the unburned fuel emissions in the exhaust gas were tested. A blend of almond biodiesel with diesel fuel gradually reduced the engine CO and total particulate emissions compared to diesel fuel alone. This reduction increased with more almond biodiesel blended into the fuel. Finally, a slight increase in engine NOx using blends of almond biodiesel was measured.

Dynamic Analysis of a Gradient Elastic Polymeric Fiber

A dynamic analysis of an elastic gradient-dependent polymeric fiber subjected to a periodic excitation is considered. A nonlinear gradient elasticity constitutive equation with strain-dependent gradient coefficients is first derived and the dispersive wave propagation properties for its linearized counterpart are briefly discussed. For the linearized problem a variational formulation is also developed to obtain related boundary conditions of both classical (standard) and non-classical (gradient) type. Analytical solutions in the form of Fourier series for the fiber’s displacement and strain fields are provided. The solutions depend on a dimensionless scale parameter (the diameter to length radio d = D/L) and, therefore, size effects are captured.

The First Solar Power Tower System in Saudi Arabia

This article is about designing and building a small scale prototype tower system to gather solar energy and store it in a molten salt tank. The system consists of several heliostats directing incident solar rays to a receiver at the top of a tower. It is intended to establish highly reputable research and development facility in solar thermal energy systems. A thorough investigation in the field of building and utilizing solar tower system was conducted. The authors studied and presented the current state of art of the technological developments concerning the solar tower systems and an assessment of their advantages and disadvantages. The adaptability of CSP (Concentrating Solar Power) power systems to Saudi Arabia climate was closely investigated. A scheme for a pilot solar power plant that it most suited to the conditions of Saudi Arabia was proposed. The next stage will be building, fabrication, and constructing the various subsystems; heliostats, tower, receiver, and storage tank.

A Small Concentrating Solar Power Tower System

A small scale prototype of functional R&D solar tower system (about 10 kW) to gather solar energy and store it in a molten salt tank will be designed, developed and built. The prototype tower system will be built at King Abdulaziz University in Jeddah, Saudi Arabia where direct irradiation is very high. Collectors of large mirrors (called heliostats) will be used to track the incident sunrays. The heliostats focus the energy flow towards solar receivers, where energy is transferred to a working thermal fluid. The proposed system consists of several heliostats directing incident solar rays to a tower of height about 20 meters. A solar receiver will be installed at the top of the tower to collect solar energy reflected from the heliostats. The heat transfer fluid (HTF) re-circulated in the receiver transfers the collected heat in the receiver to a storage tank. The storage tank contains molten salts.

Conceptual Design of Solar Powered Unmanned Arial Vehicle

The solar-powered aircraft represents a major step forward in environmentally friendly vehicle technology. An unmanned aircraft vehicle (UAV) was designed to fly for 24 hours continuously to achieve surveillance at low altitude. It is a lightweight, solar-powered, remotely piloted flying wing aircraft that is demonstrating the technology of applying solar power for long-duration and low-altitude flight. Several programs and codes were used in the designing process of the UAV and generating its layout. A MATLAB computer programming code was written to optimize on various values of aspect ratio (AR) and wingspan (b) after setting the mission requirements and estimating the technological parameters. A program called Java Foil was used to calculate the lift. Another program called RDS was used to obtain the final layout of the aircraft. The great benefit is that the design is general enough to be applied to different values of aspect ratio and wingspan. Moreover, the analytical form of the method allows identifying clear some general principles like the optimization on various values of aspect ratio and wingspan, and the calculation of the lift.

Construction and Building of an Experimental Prototype of Solar Power Tower Plant

In this paper it is aimed to present the detailed design procedure of the first solar power system in Jeddah. A prototype of solar power tower system was built at King Abdulaziz University in Jeddah, Saudi Arabia where direct irradiation is very high. Heliostats were used to track the incident sun rays and focus the energy flow towards a solar receiver. The system consists of 10 heliostats directing incident solar rays to a tower of height about 7 meters. Two motors were used to control the heliostat rotational and elevation movements. A solar receiver made of alloy steel is installed at the top of the tower to collect solar energy reflected from the heliostats. A molten salt fluid consists of sodium and potassium nitrates (60/40) re-circulated in the receiver transfers the collected heat in the receiver to a storage tank. A cylindrical vessel with height of 1 m and diameter of 1.5 m was adopted for each of the cold and hot tanks. The design thermal power was 13 kW. The percentage error in the thermal power obtained is about 5.3%.

Bio-Diesel from Almond Oil as an Alternative Fuel for Diesel Engines

Different fuel blends containing 10, 30 and 50% almond oil with diesel fuel were prepared and the influence of these blends on emissions and some performance parameters were inspected using a diesel engine. The blends and the diesel fuel were examined under various load conditions and the results showed that almond-blended fuels have slightly different properties than diesel fuel. Measured engine performance parameters have generally showed a slight increase in exhaust gas temperature and in brake specific fuel consumption, and a slight reduction in brake thermal efficiency. Blending of almond oil with diesel fuel reduced the engine CO and increased NOx percentages.