The effect of fillers on relaxation phenomena of vulcanized styrene–butadiene elastomers

Standard recipe mixtures, based on styrene/butadiene rubber SBR 1500 and oil-extended SBR 1712, with varying amounts of carbon black, silica, or kaoline fillers were prepared and the stress relaxation curves of vulcanized samples were determined. The measurements were restricted to slow relaxation phenomena, observed after 50% initial elongation. Three λ-processes and a fourth ?-process, existing only in filled rubbers, were observed. The relaxation times and activation energies, determined graphically, reflect the amount and activity of the fillers. All relaxation times are lower for filled vulcanizates and decrease with increasing temperature; however, the type of filler does not affect the activation energy. The higher parameters observed for the ?-processes are discussed in terms of filler particle mobilities and rearrangements and of filler/rubber contact layer phenomena. © 1994 John Wiley & Sons, Inc.     

Robust adaptive control using a combined approach

Direct control, indirect control and variable structure methods are combined with high-gain feedback in this paper for the robust adaptive control of first-, second- and third-order plants with increasing levels of uncertainty. The latter include external disturbance, unmodelled dynamics, time delay and sensor noise. A judicious combination of the methods is found to result in satisfactory response in most cases.     

Performance evaluation of the coupling of a desktop personalized ventilation air terminal device and desk mounted fans

The performance of a coupled system of the Desktop Personalized Ventilation Air Terminal Device (DPV ATD) and desk mounted fans (DMF) was examined in a field environmental chamber. Cooling effect was evaluated using manikin-based equivalent temperature (Teq,), of each of the 26 body segments of a breathing thermal manikin (BTM) and personal exposure effectiveness (PEE) was used as an indicator for effectiveness of ventilation. Computational fluid dynamics (CFD) was used to examine the velocity field generated around BTM to provide better understanding of the relationship between air patterns generated and convective cooling effect on each of the body segments produced by DPV ATD coupled with DMF. Four different positions of DPV ATD were examined: two positions each in front and on the side of the BTM. Measurements were conducted at ambient temperature of 26 °C and PV air temperature of 23 °C at a flow rate of 10 L/s. The results indicate that coupling of DPV ATD and DMF distributes cooling more uniformly across BTM surfaces and therefore has the potential to reduce risk of draft discomfort as compared to usage of DPV ATD alone. Personalized exposure effectiveness was increased in 3 of the positions examined when the coupled system was used.     

Evaluation of the loading capacity of a pair of three-phase high voltage cable systems using the finite-element method

A finite-element model is developed for the analysis of the heating of a pair of three-phase 110 kV underground cable systems in normal and emergency conditions. The main contribution of the paper is the inclusion of the solar emission and radiation in the evaluation of the ampacity of cables and the analysis of their effects. In addition, alternative approaches in dealing with emergency cases are studied providing a reference for future applications in practice. The model developed is used for the study of a practical case being under construction in Belgrade city area.     

Modeling of chemorheology of thermoset cure by modified WLF equation

An analysis of chemorheology of cure of a formulation composed of diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin and a mixture of aromatic amines was performed. A series of kinetic and rheological tests were run, and the experimentally obtained results were checked against the proposed model. A modified form of the classical Williams–Landel–Ferry (WLF) equation was used to model the chemorheology of the formulation. To arrive at the appropriate form of the modified WLF equation, expressions were developed for (i) the cure kinetics, (ii) the glass transition temperature as a function of the degree of cure, and (iii) the changes in parameters C₁ and C₂ as a function of temperature. By using these correlations in conjunction with the WLF equation, good agreement between predicted and experimental findings was observed.     

A comparative analyze of fundamental noise in cantilever sensors based on lateral and longitudinal displacement: case of thermal infrared detectors

The performance of novel cantilever-based sensors approaches the limit posed by thermo-mechanical fluctuations, which is the currently accepted fundamental detection barrier for micro- and nanomechanical sensors. At the same time, the sensitivity of a high-level measurement techniques used for readout of the cantilever displacement nears the value of 10^?14 m/Hz^½. However, the thermo-mechanical noise of some cantilever sensors based on bimaterial structures is considerably higher than imposed by the fundamental limit. Moreover, the signal-to-noise ratio of some sensors based on contemporary MEMS technologies falls behind the characteristics of older types of mechanical sensors, fabricated using macroscopic production technologies. To investigate the cause of this situation, we perform a comparative analysis of the performance limits for two classes of cantilever sensors: the bimaterial cantilevers where the output signal is the transversal (lateral) displacement of the cantilever tip and the simple cantilever sensors where the signal is the longitudinal displacement along the cantilever axis. As a starting point of our analysis we established a correspondence between the parameters of a bimaterial cantilever and the simple cantilever. In a general case these two structures are not directly comparable, since the deformation of the bimaterial cantilever depends on 14 variables, while the longitudinal elongation of the simple cantilever depends on seven parameters only. However, under certain conditions analyzed in this paper a partial correspondence between the parameters of these two structures can be established. Our analysis shows that in certain applications a cantilever with longitudinal elongation has potentially better performance than the corresponding bimaterial element.     

Three-dimensional analysis of the effect of human movement on indoor airflow patterns

Human activity is known to leave significant effects on indoor airflow patterns. These patterns are carefully designed for many facilities such as cleanrooms, pharmaceutical settings, and healthcare environments, where human-induced wakes contribute to the transport of contaminants. Therefore, the knowledge about these wakes as it relates to indoor air quality is critical. As a result, a series of experiments were conducted in a controlled chamber to study the three-dimensional effects of true human walking on airflow. Experiments were designed to capture the effect of human walking under three different flow conditions, and for two different walking schemes. The results show that the effect of walking on the airflow is not negligible and can sustain up to 10 seconds after the moving body has passed. Walking on a straight line creates significant change in the velocity normal to the walking path and vertical to the plane of walking movement. These changes were detectable till 1.0 m away from the walking track. Also, the similarity between airflow patterns of walking once and twice illustrated a promising opportunity of predicting the flow patterns of random walk from a set of base cases.     

Principal features of structural relaxation in glassy polymers. A Review

The principal features of models of structural relaxation in the glassy state were reviewed. The concepts of fictive temperature as the structural parameter and nonexponentiality and nonlinearity of structural relaxations were described. Various expressions for the structural relaxation time were presented and compared. One particular model was selected and utilized in a parametric optimization study of structural relaxation. Model predictions were checked against experimental results obtained by volumetric and calorimetric measurements.     

Erlangen pipe flow: the concept and DNS results for microflow control of near-wall turbulence

The concept of a micropatterned surface morphology capable of producing self-stabilization of turbulence in wall-bounded flows is considered in pipes of non-circular cross-sections which act to restructure fluctuations towards the limiting state where these must be entirely suppressed. Direct numerical simulations of turbulence in pipes of polygon-shaped cross-sections with straight and profiled sides were performed at a Reynolds number $Re_\tau \simeq {\mathrm 300}$ based on the wall shear velocity and the hydraulic diameter. Using the lattice Boltzmann numerical algorithm, turbulence was resolved with up to ${\mathrm 540\times 10^6}$ grid points ( ${\mathrm 8,192\times 257 \times 256}$ in the x ₁, x ₂ and x ₃ directions). The DNS results show a decrease in the viscous drag around corners, resulting in a reduction of the skin-friction coefficient compared with expectations based on the well-established concept of hydraulic diameter and the use of the Blasius correlation. These findings support the conjecture that turbulence might be completely suppressed if the pipe cross-section is a polygon consisting of a sufficient number of profiled sides of the same length which intersect at right angles at the corners.