A finite element modeling-based approach to predict vibrations transmitted through different body segments of the operator within the workspace of a small tractor

Agricultural tractor drivers are subjected to high levels of whole-body vibrations and hand arm vibrations during most part of the farm activities due to unevenness of field surface, uneasy posture, improper workplace design, moving parts of the tractor, and other unavoidable circumstances. The comfort level of the operator inside a dynamic tractor is dependent on the level of vibration generated inside the different human body segments. In the present study, a finite element modeling was proposed to predict vertical vibrations (Z-axis) and frequencies at the different body segments of the seated small tractor operator. The forces required for different controls of the tractor were measured to be used as input parameters in the finite element modeling. The maximum mean forces of the brake (172.8 N) and clutch (153.2 N) were used as the input parameters for the simulation study. The simulated results were validated with the field measured values of vertical accelerations at selected body segments of the operator. The simulation could successfully predict vertical vibrations at selected points of interest (i.e., foot, leg, thigh, lower arm, upper arm, back, and head) except the chest of the body, as the buttock of the operator model was fixed (degree of freedom is equal to zero) in the simulation. The obtained results were compared with the international standards ISO 2631-1 (1985/1997) and ISO 5349-1 (2001) to assess the vibration characteristics at the different body segments of the operator. The foot, leg, lower arm, and upper arm of the operator were subjected to vertical vibration frequencies from 10 to 200 Hz. Most of the resonance of vertical accelerations occurred in one-third octave bands of 20–80 Hz frequencies. The thigh, chest, back, and head of the operator were exposed to vibration frequencies below 40 Hz during field operation. At these parts of the body, the vertical acceleration resonated at lower frequencies, between 2 and 8 Hz.     

Lattice Boltzmann method simulation of electroosmotic stirring in a microscale cavity

The suitable surface modification of microfluidic channels can enable a neutral electrolyte solution to develop an electric double layer (EDL). The ions contained within the EDL can be moved by applying an external electric field, inducing electroosmotic flows (EOFs) that results in associated stirring. This provides a solution for the rapid mixing required for many microfluidic applications. We have investigated EOFs generated by applying a steady electric field across a square cavity that has homogenous electric potentials along its walls. The flowfield is simulated using the lattice Boltzmann method. The extent of mixing is characterized for different electrode configurations and electric field strengths. We find that rapid mixing can be achieved by using this simple configuration which increases with increasing electric field strength. The mixing time for water-soluble organic molecules can be decreased by four orders of magnitude by suitable choice of wall zeta potential and electric field. We dedicate this paper to the memory of our colleagues Professors Kevin Granata and Liviu Librescu who fell tragically on April 16, 2007 while answering their call to serve higher education. They continue to inspire us. AM gratefully acknowledges support from Jadavpur University under the World Bank funded Technical Education Quality Improvement Programme of the Government of India and the hospitality of the Virginia Tech ESM Department where he conducted a portion of this work.     

Deformation Behavior and Evolution of Microstructure and Texture During Hot Compression of AISI 304LN Stainless Steel

Deformation behavior of hot-rolled AISI 304 LN austenitic stainless steel was studied by hot axisymmetric compression tests at 1173 K, 1273 K, and 1373 K (900 °C, 1000 °C, and 1100 °C) at strain rates of 0.01, 0.1, and 1 s^?1. The flow curves were examined to understand the deformation characteristics. The influence of Zener–Holloman parameter was analyzed using appropriate constitutive models. The activation energy for deformation was found to be 473 kJ/mol. Quantitative microstructural analysis was carried out using Electron backscattered diffraction. Compression at 1173 K (900 °C) at all true strain rates gave rise to partially dynamic recrystallized microstructure with strong α-fiber texture. The deformation texture is characterized by the formation of Brass component, and partial dynamic recrystallization (DRX) led to the development of Goss, S, and ube components. Necklace structure of small equiaxed recrystallized grains could be observed surrounding the large, elongated deformed grains. Compressions at 1273 K and 1373 K (1000 °C and 1100 °C) resulted in fully recrystallized microstructure consisting of mostly Σ3 and Σ9 coincidence site lattice high-angle boundaries. Compression at 1273 K (1000 °C) leads to the formation of low-intensity diffused α-fiber. DRX was confirmed by the presence of Goss, S, Cube, and rotated Cube components. Compression performed at 1373 K (1100 °C) resulted in nearly random texture with traces of α-fiber and prominent Cube/rotated Cube components. The microstructures of the 1173 K (900 °C)-compressed samples were partitioned using grain size and misorientation criteria to quantify DRX.     

Forecasting industrial employment figures in Southern California: A Bayesian vector autoregressive model

In this paper, we construct a Bayesian vector autoregressive model to forecast the industrial employment figures of the Southern California economy. The model includes both national and state variables. The root mean squared error (RMSE) and the Theil's U statistics are used in selecting the Bayesian prior. The out-of-sample forecasts derived from each model and prediction of the turning points show that the Bayesian VAR model outperforms the ARIMA and the unrestricted VAR models. At longer horizons the BVAR model appears to do relatively better than alternative models. A prior that becomes increasingly looser produces more accurate forecasts than a tighter prior in the BVAR estimations. Received: March 1999/Accepted: November 1999     

A tamper detection suitable fragile watermarking scheme based on novel payload embedding strategy

Multimedia Tools and Applications - Intentional tampering in digital image content is one of the common malpractices in the current digital arena. So in this paper, the authors have proposed a...     

Local jet pattern: a robust descriptor for texture classification

Multimedia Tools and Applications - Methods based on locally encoded image features have recently become popular for texture classification tasks, particularly in the existence of large intra-class...     

Wave structure in Stokes' second problem for a dipolar fluid with nonclassical heat conduction

Summary The classical heat conduction law of Fourier associates an infinite speed of propagation to a thermal disturbance in a material body. Such behavior is a violation of the causality principle. In recent years, several modifications of Fourier's heat law have been proposed. In this work, a modified form of Fourier's heat law, based on the Maxwell-Cattaneo-Fox (MCF) model, is used to analyze the heat conduction effects in Stokes' second problem for a dipolar fluid. The structure of the waves and the influence of the dipolar constants on the velocity field is investigated. These results are then compared to the viscous fluid case. In addition, the displacement thickness and skin friction at the plate are determined.     

Modelling non-Newtonian two-phase flow in conventional and helical-holding tubes

Summary The research described in this communication was undertaken to test the hypothesis that the fluid mechanics and heat-transfer aspects involved in aseptic processing could be modelled. In order to do this, a finite difference FORTRAN program (using the fourth-order, four-stage explicit Runge–Kutta method) was written by the authors to compute the velocity of fluid elements and particles during fully 3-dimensional flow in conventional and helical-holding tubes. The effect of particles on the fluid-flow field and the interaction between particles was taken into account during the modelling. Simulation results showed that an increase in specific gravity, tube diameter or coil diameter resulted in an increase in the residence time of the particles, while an increase in the flow rate decreased the residence time of the particles. An increase in the particle diameter or the flow rate narrowed the Residence Time Distribution (RTD) of the particles, while an increase in specific gravity or the tube diameter increased the RTD of the particles.     

Numerical modeling—A new tool for understanding shotcrete

The analytical flow simulation of fresh concrete is a recent challenge to researchers. Due to its heterogeneity, the concrete mix shows neither a perfectly viscous nor perfectly particulate behavior. However, the particulate behavior of fresh concrete flow like arching and blocking in pipes and in complex boundary conditions, is very common. This is further magnified due to high pressure in the case of shotcreting. For the first time in shotcrete research, authors propose the application of the Distinct Element Method [1] (DEM) to predict particle behavior and amount of rebound loss, and to assess the quality of the shotcrete analytically. Also, the effect of an accelerating agent, the way its effect is modeled, effects of gradual change in shooting pressure, the resulting rebound is shown. The void of the attached concrete is also compared with that of normal cast concrete in an analytical way.