Burnett equations for the ellipsoidal statistical BGK model

In order to discuss the agreement of the ellipsoidal statistical BGK (ES-BGK) model with the Boltzmann equation, Burnett equations are computed by means of the second-order Chapman-Enskog expansion of the ES-BGK model. It is found that the Burnett equations for the ES-BGK model with the correct Prandtl number are identical to the Burnett equations for the Boltzmann equation for Maxwell molecules (fifth-order power potentials). However, for other types of particle interaction, the Boltzmann Burnett equations cannot be reproduced from the ES-BGK model.Furthermore, the linear stability of the ES-BGK Burnett equations is discussed. It is shown that the ES-BGK Burnett equations are linearly stable for Prandtl numbers of and for , while they are linearly unstable for and .Received: 29 April 2003, Accepted: 20 June 2003PACS: 510.10.-y, 47.45.-n Correspondence to: Y. Zheng     

Some recent developments in vehicle—terrain interaction studies

This report presents a review of recent developments in the study of vehicle3-terrain interaction, based primarily on papers included in Session 2A of the 10th International Conference of ISTVS. Analytical studies of wheel-soil interaction using visco-elastic soil models and elasto-plastic and rigid-plastic finite element methods are reviewed. Results of experimental investigations of stress distributions on the wheel-soil interface as well as in the soil under various loading conditions are summarized. Various methods for predicting off-road vehicle performance are examined.     

A laboratory investigation of ground erosion and dust generation by air cushion vehicles

The erosion process which occurs when an air cushion vehicle (ACV) passes over certain types of surface material has been investigated. Experiments were conducted in laboratory apparatus which simulates conditions under the edge of an ACV skirt.

Tests were carried out on three samples of dry erodible materials for a variety of cushion parameters. Representative photographs and data on time rates of erosion are presented. The results indicate that erosion rates are proportional to cushion pressure to the power 3/2 and that skirt angle, hoverheight and time since start of a run are of secondary importance. The results and analysis indicate that erosion rates are independent of particle size when this exceeds about 0.1 mm.     

Spectrum analysis of road roughness for earthmoving machinery

The power spectral density functions of roughness of road surfaces for earthmoving machines such as tractors, scrapers and dumpers were determined by use of an accelerometer mounted on a towed fifth wheel of which the frequency-response function had previously been known. From obtained data, a range of power spectral density curves of the road roughness for these earthmoving machines was derived and expressed mathematically.     

Neural network optimization of material composition of a functionally graded material plate at arbitrary temperature range and temperature rise

Summary A neural network model is applied to optimization problems of material compositions for a functionally graded material plate with arbitrarily distributed and continuously varied material properties in the thickness direction. Unsteady temperature distribution is evaluated by taking into account the bounds of the number of the layers. Thermal stress components for an infinite functionally graded material plate are formulated under traction-free mechanical conditions. As a numerical example, a plate composed of zirconium oxide and titanium alloy is considered. In the optimization problem of minimizing the thermal stress distribution, the numerical calculations are carried out making use of the neural network. The optimum material composition is determined by taking into account the effect of temperature-dependence of material properties. The results obtained by neural network and ordinary nonlinear programming method are compared. Received 3 March 1998; accepted for publication 22 May 1998     

Experimental study of CHF in vertical and horizontal tubes cooled by freon-12

The influence of test section orientation and diameter on flow boiling crisis occurring in tubes has been studied experimentally using Freon-12 as a coolant. At low mass flux the critical heat flux (CHF) was lower in horizontal flow than in vertical. As either the liquid or vapour velocity, or both, were increased the vertical and horizontal CHF results converged. Above a mass flux of 4Mg · m⁻² · s⁻¹ the results were essentially identical.

The effect of tube diameter on boiling crisis in general depends crucially on the parameters which are maintained constant when the comparison is made.     

Separation of heart rate variability components of the autonomic nervous system by utilizing principal dynamic modes

This work introduces a modified Principal Dynamic Modes (PDM) methodology using eigenvalue/eigenvector analysis to separate individual components of the sympathetic and parasympathetic nervous contributions to heart rate variability. We have modified the PDM technique to be used with even a single output signal of heart rate variability data, whereas the original PDMs required both input and output data. This method specifically accounts for the inherent nonlinear dynamics of heart rate control, which the current method of power spectrum density (PSD) is unable to do. Propranolol and atropine were administered to normal human volunteers intravenously to inhibit the sympathetic and parasympathetic activities, respectively. With separate applications of the respective drugs, we found a significant decrease in the amplitude of the waveforms that correspond to each nervous activity. Furthermore, we observed near complete elimination of these dynamics when both drugs were given to the subjects. Comparison of our method to the conventional low/high frequency ratio of PSD shows that PDM methodology provides much more accurate assessment of the autonomic nervous balance by separation of individual components of the autonomic nervous activities. The PDM methodology is expected to have an added benefit that diagnosis and prognostication of a patient's health can be determined simply via a non-invasive electrocardiogram.     

Obtaining the shear stress shear rate relationship and yield stress of liquid foods from Couette viscometry data

A method based on Tikhonov regularisation is used to convert the Couette viscometry data of a number of liquid foods into shear stress vs shear rate relationships. For liquid foods that have a yield stress and if the viscometry data cover the appropriate range of shear stress, Tikhonov regularisation is used to compute simultaneously the yield stress. The versatility of Tikhonov regularisation is demonstrated by applying it to process data from wide as well as narrow gap Couette viscometers. The results generated by Tikhonov regularisation are compared against that obtained by methods currently employed by rheologists.     

Dynamic compression-shear response of brittle materials with specimen recovery

A new configuration for compression-shear soft-recovery experiments is presented. This technique is used to investigate various failure mechanisms during dynamic multiaxial loading of an Al₂O₃/SiC nanocomposite and TiB₂. Velocity profiles of the target surface are measured with a variable sensitivity displacement interferometer, yielding normal and transverse velocity-time histories. A dynamic shear stress of approximately 280 MPa is obtained, in the Al₂O₃/SiC nanocomposite, for an imposed axial stress of about 3.45 GPa on a 540 m thick sample. This dynamic shear stress is well below the value predicted by elastic wave propagation theory. This could be the result of stress-induced damage and inelasticity in the bulk of the sample or inelasticity on the sample surface due to frictional sliding. To gain further insight into the possible failure mechanisms, an investigation of compression-shear recovery techniques, with simultaneous trapping of longitudinal and lateral release waves, is conducted.     

Moving shocks through metallic grids: their interaction and potential for blast wave mitigation

Numerical simulations and laboratory measurements have been used to illuminate the interaction of a moving shock wave impacting on metallic grids at various shock strengths and grid solidities. The experimental work was carried out in a large scale shock tube facility while computational work simulated the flow field with a time-dependent inviscid and a time-dependent viscous model. The pressure drop measured across the grids is a result of two phenomena which are associated with the impact of the shock on the metallic grids. First are the reflection and refraction of the incoming shock on the grid itself. This appears to be the main inviscid mechanism associated with the reduction of the strength of the transmitted shock. Second, viscous phenomena are present during the reflection and refraction of the wave as well as during the passage of the induced flow of the air through the grid. The experimental data of pressure drop across the grid obtained in the present investigation are compared with those obtained from computations. The numerical results slightly overpredict the experimental data of relative pressure drop which increases substantially with grid solidity at fixed flow Mach numbers. The processes of shock reflection and refraction are continuous and they can be extended in duration by using thicker grids that will result in lower compression rates of the structural loading and increase the viscous losses associated with these phenomena which will further attenuate the impacting shock. Preliminary theoretical analysis suggests that the use of a graded porosity/solidity material will result in higher pressure drop than a constant porosity/solidity material and thus provide effective blast mitigation.