Numerical Study of Self-Complementary Antenna Characteristics on Substrate Lenses at Terahertz Frequency

This paper presents a numerical study of self-complementary antennas on substrate lenses made of high-permittivity dielectric material. Bowtie, logarithmically periodic, and logarithmic spiral antennas with the same outer and inner dimensions were selected for study, and their overall performances were compared in the terahertz band at frequencies up to 5.0?THz. The resonance and radiation characteristics of the three antennas were investigated in terms of input impedance, directivity, and radiation efficiency, using a full electromagnetic simulator. This study provides useful guidelines and partially solves the difficult problems of choosing the proper feed and optimizing the lens structure for a THz broadband integrated lens antenna.     

An experimental study of a confined and submerged impinging jet heat transfer using Al2O3-water nanofluid

An experimental investigation was performed to study the heat transfer performance of a 36 nm-Al₂O₃-particle–water nanofluid in a confined and submerged impinging jet on a flat, horizontal and circular heated surface. The tests were realized for the following ranges of the governing parameters: the nozzle diameter is 3 mm and the distance nozzle-to-heated-surface was set to 2, 5 and 10 mm; the flow Reynolds number varies from 3800 to 88 000, the Prandtl number from 5 to 10, and the particle volume fraction is ranging from 0 to 6%. Experimental data, obtained for both laminar and turbulent flow regimes, have clearly shown that, depending upon the combination of nozzle-to-heated surface distance and particle volume fraction, the use of a nanofluid can provide a heat transfer enhancement in some cases; conversely, for other combinations, an adverse effect on the convective heat transfer coefficient may occur. Within the experimental parameters used, it has been observed that highest surface heat transfer coefficients can be achieved using an intermediate nozzle-to-surface distance of 5 mm and a 2.8% particle volume fraction nanofluid. Nanofluids with high particle volume fractions, say 6% or higher, have been found not appropriate for the heat transfer enhancement purpose under the confined impinging jet configuration. On the other hand, for a very small and a large distance of nozzle-to-heated-surface, it has been observed that the nanofluid use does not provide a perceptible heat transfer enhancement and has, for some particular cases, produced a clear decrease of the convective heat transfer coefficient while compared to that obtained using distilled water.     

Thickness effect on interdiffusion of Fe/Pt multilayers

The effect of thickness on interdiffusion in Fe/Pt multilayer thin films was studied using rapid thermal annealing. [Fe(1 nm)/Pt(1 nm)]₂₀ and [Fe(3 nm)/Pt(3 nm)]₁₀ multilayers were prepared via DC magnetron sputtering and subsequently annealed at temperatures of 523 K to 603 K in an argon atmosphere in an infrared lamp furnace for a very short time. X-ray diffraction yielded the interdiffusion coefficients from the slopes of the satellite peak versus annealing time. The temperature dependence of interdiffusion in the range of 523 K to 603 K can be described by D(t)=3.42×10⁻¹⁵ exp(−0.83 eV/k_BT) (m²/s) for [Fe(1 nm)/Pt(1 nm)]₂₀ and D(t) =7.85×10⁻¹⁶ exp(−0.62 eV/k_BT) (m²/s) for [Fe(3 nm)/Pt(3 nm)]₁₀. The activation energy Q=0.83 eV for [Fe(1 nm)/Pt(1 nm)]₂₀ is higher than that of Q=0.62 eV for [Fe(3 nm)/Pt(3 nm)]₁₀. This phenomenon suggests that the atoms in the thicker film can move more easily in the interface and the lattice, which results in lower activation energy and higher diffusivity.     

Finite Element Method Simulations to Improve Press Formability of Door Hinge

Door hinges are a key product in the automotive industry. The function of automotive door hinge is not only to close, open, and keep the open angle of the door but also to reduce traumas for passengers in the car when it is hit by another car. However, concentrated stress and strain occur at the corner of this product during forming, which can cause a crack if the shape of this area of the blank is not carefully designed. Accordingly, this article proposes a method for improving the press formability of a door hinge by changing the shape of the concerned area of the blank based on finite element method (FEM) simulations using the explicit dynamic code ABAQUS, version 6.5. The resulting optimized solution for robust forming was a corner radius of 7 mm, protrusion length of 18 mm, and protrusion height of 5 mm.     

Nonlinear response of pressure-loaded functionally graded cylindrical panels with temperature effects

This paper presents an analytical approach to investigate nonlinear response of functionally graded cylindrical panels under uniform lateral pressure with temperature effects are incorporated. Material properties are assumed to be temperature-independent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. Equilibrium and compatibility equations for cylindrical panels are derived by using the classical shell theory with both geometrical nonlinearity in von Karman–Donnell sense and initial geometrical imperfection are taken into consideration. The resulting equations are solved by Galerkin method to determine explicit expressions of nonlinear load-deflection curves. Stability analysis for a simply supported panel shows the effects of material and geometric parameters, in-plane restraint and temperature conditions, and imperfection on the nonlinear response of the panel.     

Parametric analysis of runway stone lofting mechanisms

The influence of various factors affecting the severity of runway debris lofting mechanisms was investigated by performing numerical simulations and drop-weight impact experiments to assess the likelihood of a stone impact. Geometrical characterisation of stones collected from airfields led to a generic model of a tyre rolling over stones of various shape with different overlaps, orientations, and densities. In numerical simulations of a 0.4 m diameter aircraft tyre rolling at 70 m/s, a 10 mm diameter spherical stone was lofted at a maximum vertical speed of 35 m/s. For equivalent mass prolate spheroid stones, the loft speeds were 11–34% lower depending on the stone orientation. Objects with flat surfaces exhibited different lofting mechanisms and lower angular velocities. The conditions most conducive to stone lofting were very stiff, small diameter, sharp cornered tyres rolling on ground with a high friction coefficient over spherical stones such that just under half the stone diameter was covered by the tyre. The stone loft speed was approximately proportional to the square root of the tyre tread stiffness. Finally, tyre tread grooves could throw stones upwards at the tyre-ground separation speed, which was 17 m/s for the conditions mentioned earlier.     

Preparation of chitosan/magnetite composite beads and their application for removal of Pb(II) and Ni(II) from aqueous solution

A simple and effective process has been proposed to prepare chitosan/magnetite nanocomposite beads with saturation magnetization value as high as uncoated Fe₃O₄ nanoparticles (ca. 54 emu/g). The reason was that the coating chitosan layer was so thin that it did not affect magnetic properties of these composite beads. Especially, chitosan on the surface of the magnetic Fe₃O₄ nanoparticles is available for coordinating with heavy metal ions, making those ions removed with the assistance of external magnets. Maximum adsorption capacities for Pb(II) and Ni(II), occurred at pH 6 and under room temperature were as high as 63.33 and 52.55 mg/g respectively, according to Langmuir isotherm model. These results permitted to conclude that chitosan/magnetite nanocomposite beads could serve as a promising adsorbent not only for Pb(II) and Ni(II) (pH = 4–6) but also for other heavy metal ions in wastewater treatment technology.     

Fuzzy sliding-mode controllers with applications

This paper concerns the design of robust control systems using sliding-mode control that incorporates a fuzzy tuning technique. The control law superposes equivalent control, switching control, and fuzzy control. An equivalent control law is first designed using pole placement. Switching control is then added to guarantee that the state reaches the sliding mode in the presence of parameter and disturbance uncertainties. Fuzzy tuning schemes are employed to improve control performance and to reduce chattering in the sliding mode. The practical application of fuzzy logic is proposed here as a computational-intelligence approach to engineering problems associated with sliding-mode controllers. The proposed method can have a number of industrial applications including the joint control of a hydraulically actuated mini-excavator as presented in this paper. The control hardware is described together with simulated and experimental results. High performance and attenuated chatter are achieved. The results obtained verify the validity of the proposed control approach to dynamic systems characterized by severe uncertainties     

A cohesive model of fatigue crack growth

We investigate the use of cohesive theories of fracture, in conjunction with the explicit resolution of the near-tip plastic fields and the enforcement of closure as a contact constraint, for the purpose of fatigue-life prediction. An important characteristic of the cohesive laws considered here is that they exhibit unloading-reloading hysteresis. This feature has the important consequence of preventing shakedown and allowing for steady crack growth. Our calculations demonstrate that the theory is capable of a unified treatment of long cracks under constant-amplitude loading, short cracks and the effect of overloads, without ad hoc corrections or tuning.     

Wall temperature experimental investigation in a thermally driven channel

Direct local wall temperature has been measured, in a steady state, along a vertical air channel asymmetrically heated with uniform fluxes. In the range of high Grashof numbers that was investigated, the flow regime probably remained laminar. A radiative part has been analysed with two extreme values of internal surface emissivity corresponding to unpainted metal and black painted wall. A correlation has been proposed for the calculation of a characteristic channel outlet value of the Nusselt number referred to air spacing. A local Nusselt number over the height has been developed in a power law scheme.