Identification of thermoresistive solar radiation sensors

An identification procedure to estimate the parameters of a thermoresistive solar radiation sensor is presented. The proposed technique employs only electrical excitation for the sensor. The estimation algorithm is recursive and is applied to the sensor model derived from the thermodynamic equilibrium differential equations. The simulation and the experimental results demonstrate the validity of the proposed approach     

A note on the boundary value problem arising in free convection in porous media

By similarity transformation and governing equations of free convection on a heated vertical plate embedded in porous medium are reduced to coupled nonlinear equations. The equations are numerically integrated using the boundary conditions at the plate and at ‘infinity’. Assuming that the plate is subjected to a prescribed temperature [1–3] or to a prescribed heat flux [4, 5], the boundary value problems have been solved independently. These researchers seem to have not noted that the solutions for the two cases are dependent on each other. In the present note we consider yet another thermal boundary condition, namely, radiation boundary condition [6] at the plate and show that the solutions for the three cases are dependent and one can pass from one solution to the other easily.     

Reliability of MDOF-systems

To estimate the safety and reliability of nonlinear structural (MDOF)-systems subjected to random dynamic loading the response surface methodology (RSM) and Monte Carlo Simulation (MCS) respectively appear to be the most general approaches to calculate the failure probabilities of such systems. In an effort to reduce the number of computational time consuming simulations as generally required for direct MCS, only a small part of which is important for the assessment of failure rates, a new selective MCS technique named ‘Double and Clump’ (D&C) is suggested. The main idea of this procedure is to increase for each time step the relatively low number of response samples containing higher mechanical energy. The selective MCS procedure is tested by analysing nonlinear SDOF oscillators, for which exact analytical solutions exist. A good agreement between the distributions F(x) in the tails is obtained covering a wide range, i.e. 10⁻⁷ < F(x) < 1·0–10⁻⁷. The efficiency of selective MCS is demonstrated by applying it to a six-storey frame structure subjected to earthquake excitation. A comparison with results obtained by using the RSM is presented and discussed.     

Raising the accuracy of operative monitoring by using a variable pressure differential of the flow rate of material and energy carriers in the liquid and gaseous states

Means are considered for reducing the systematic errors in calculating the flow rate of material. For operative monitoring of the day- to- day flow rate, a comparative analysis is made of the numerical solution of the mass flow rate equation and the structure- generalized method for solving the equation.Translated from Izmeritel'naya Tekhnika, No. 5, pp. 37–39, May, 1994.     

Current decomposition in asymmetrical, unbalanced three-phasesystems under nonsinusoidal conditions

The most attractive theories found in the literature for the representation of the electrical systems under nonsinusoidal conditions can be divided to a great extent into those operating in the time domain and those operating in the frequency domain. When three-phase systems are concerned, the time-domain approach is mainly due to Akagi and Nabae under the name of “instantaneous power theory” or “p-q theory” and is based on the Park transformation. The frequency-domain approach is mainly due to Czarnecki. At a first reading, these two theories seem to be quite different. This paper shows how the application of some interesting properties of the Park transformation leads to a unified approach to the harmonic and sequence components and hence allows derivation of the frequency-domain current decomposition proposed by Czarnecki in a more straightforward way. Moreover, an extension of this decomposition to the case of asymmetrical supply voltages is considered     

The thermoelastic behaviour of semicrystalline and of glassy poly(ether-ether-ketone)

A thermoelastic evaluation, based on simultaneous measurements of the mechanical work and of the concomitant heat of deformation by a stretching micro calorimeter, was performed on semicrystalline and glassy PEEK. The objective of this study was to utilize the sensitive technique to detect differences that would account for observed effects of micro structure on mechanical performance. A clear difference was detected beyond a 0.6% strain, where the behaviour of glassy PEEK began to exhibit inelastic features such as yielding and plastic deformation. This difference between the glassy and the semicrystalline polymers was considered the reason for the superior mechanical fatigue and fracture properties produced by the latter micro structure.