Effect of residual surface stress on parametrically excited nonlinear dynamics and instability of double-walled nanobeams: an analytical study

Engineering with Computers - A class of nonlinear Mathieu–Hill equation is established to determine the bifurcations and the regions of nonlinear dynamic instability of a short double-walled...     

A Simple Method to Enhance Gain and Isolation of MIMO Antennas Simultaneously Based on Metamaterial Structures for Millimeter-Wave Applications

Journal of Infrared, Millimeter, and Terahertz Waves - In this paper, a multiple-input and multiple-output (MIMO) antenna with high gain and high isolation based on the metamaterial concept is...     

Natural convection heat transfer enhancement of different nanofluids by adding dimple fins on a vertical channel wall

In this numerical study, natural flow and heat transfer of nanofluids with Al_2O_3, TiO_2, Cu and CNT nanoparticles in a vertical channel with dimpled fins at Rayleigh number(Ra) of Ra = 3.25 × 10~7 to Ra = 1 × 10~8 are investigated by using the finite volume method. The obtained results revealed that, using CNT in volume fractions of 2% and 4%leads to significant heat transfer and at φ = 6%, using TiO_2 nanoparticles has a great effect on Nu number enhancement. Also, using solid nanoparticles in base fluid causes more uniform heat transfer distribution,especially in areas close to heated surface and by adding more volume fraction in base fluid, temperature level reduces. In general, according to temperature contours, reduction of wall temperature depends on the increase of Ra and volume fraction and the type of solid nanoparticles.     

Target recognition and discrimination based on multiple-frequencies LFM signal with subcarrier hopping

Multidimensional Systems and Signal Processing - An anti-deception jamming technique is proposed for moving target indication in a pulse-Doppler (PD) radar. The deceive targets are produced by...     

Development of a nonlinear conical spring bracing system for framed structures subjected to dynamic load

In this study, a nonlinear conical spring bracing (NCSB) system that can be applied as a lateral resistance component in framed structures was developed to mitigate the vibration effects of earthquake and wind. The NCSB device consists of two solid telescopic conical springs attached to steel wire ropes. The application of NCSB in framed structures, particularly moment-resisting steel frame (MRSF), improves the seismic behavior of the frame because of the variable action of the NCSB device. NCSB stiffness is not considerable in the low to medium vibration range compared with structural stiffness. Therefore, the inherent ductility of MRSF is unaffected because of the addition of the NCSB device to the frame. However, with its large displacement value, NCSB stiffness increases and prevents excessive displacement in structures. A mathematical model of the NCSB device that considers the effect of cable stiffness is developed and implemented in program code. Furthermore, the seismic behavior of eight types of NCSB applications in frames subjected to different earthquake accelerations is evaluated in terms of displacement, velocity, and acceleration, as well as compared with bare and brace frames. Results reveal the reduction influences of the NCSB device on framed structures. The best geometric configuration for the NCSB system is also determined by using the proposed numerical analysis.     

Magnetic field effects on buckling characteristics of smart flexoelectrically actuated piezoelectric nanobeams based on nonlocal and surface elasticity theories

Microsystem Technologies - This study employs the nonlocal and surface elasticity theories to explore the buckling characteristics of piezoelectric nanobeams incorporating flexoelectricity effects....     

A new framework for evaluation of rock fragmentation in open pit mines

The main purpose of blasting in open pit mines is to produce the feed for crushing stage with the optimum dimensions from in situ rocks. The size distribution of muck pile indicates the efficiency of blasting pattern to reach the required optimum sizes. Nevertheless, there is no mature model to predict fragmentation distribution to date that can be used in various open pit mines. Therefore, a new framework to evaluate and predict fragmentation distribution is presented based on the image analysis approach. For this purpose, the data collected from Jajarm bauxite mine in Iran were used as the sources in this study. The image analysis process was performed by Split-Desktop software to find out fragmentation distribution, uniformity index and average size of the fragmented rocks. Then, two different approaches including the multivariate regression method and the decision-making trial and evaluation laboratory (DEMATEL) technique were incorporated to develop new models of the uniformity index and the average size to improve the Rosin-Rammler function. The performances of the proposed models were evaluated in four blasting operation sites. The results obtained indicate that the regression model possesses a better performance in prediction of the uniformity index and the average size and subsequently the fragmentation distribution in comparison with DEMATEL and conventional Rosin-Rammler models.     

Three-dimensional pore network model of biofilter treating toluene: A study of the effect of the pore space morphology

Treatment of polluted air stream with toluene in a biofilter under quasi-steady-state condition is described with a three-dimensional (3-D) pore network model. The efficiency of the process depends on the pore structure of the biofilter media. The previous models for the process, considered transport and reaction equations mostly in the continuum systems. They cannot show the effect of pore spaces’ morphology, different pore size distributions and connectivity types. We used the 3-D pore network model to simulate the pore structure and to study the effects of biofilm growth on pore size distribution and pore connectivity on the biofilter performance. This model predicts the toluene conversion, pressure drop profiles, biofilm thickness and clogging in the biofilter. Our developed model assumes a nonlinear kinetic for the biodegradation reaction of toluene in the biofilm. The differential equations of the model are solved numerically. Model results indicated that biofilter media with smaller mean pore size and higher connectivity have a higher toluene conversion. To investigate the validity of the model, we compared the model results with experimental data and found satisfying similarities.     

Investigating the thermal environment effects on geometrically nonlinear vibration of smart functionally graded plates

An analytical solution for a sandwich circular FGM plate coupled with piezoelectric layers under one-dimensional heat conduction is presented. All materials of the device may be of any functional gradients in the direction of thickness. The solution exactly satisfies all the equilibrium conditions and continuity conditions for the stress, displacement and electric displacement as well as electric potential on the interfaces between adjacency layers. A nonlinear static problem is solved first to determine the initial stress state and pre-vibration deformations of the FG plate that is subjected to in-plane forces and applied actuator voltage in thermal environment in the case of simply supported boundary conditions. By adding an incremental dynamic state to the pre-vibration state, the differential equations that govern the nonlinear vibration behavior of pre-stressed piezoelectric coupled FGM plates are derived. The role of thermal environment as well as control effects on nonlinear static deflections and natural frequencies imposed by the piezoelectric actuators using high input voltages are investigated. Numerical examples are provided and simulation results are discussed. Numerical results for FGM plates with a mixture of metal and ceramic are presented in dimensionless forms. The good agreement between the results of this paper and those of the finite element (FE) analyses validated the presented approach. In a parametric study the emphasis is placed on investigating the effect of varying the applied actuator voltage and thermal environment as well as gradient index of FG plate on the dynamics and control characteristics of the structure.