Transient State Analyses Research Articles

Power system transient and harmonic studies using wavelet transform

This paper presents the application of wavelet transforms in power system transient and harmonic analyses. Based on the discrete time domain approximation, the system components such as resistors, inductors and capacitor are modeled respectively in the discrete wavelet domain for the purpose of transient and steady state analyses. Since the power system is described by a set of ordinary differential equations, an initial value of the state variable is considered for the transient analysis, while a periodic condition is applied to the state variable for the steady state analysis. The wavelet domain impedance is set up, and the equivalent circuit is thus built for system simulation. This method can be implemented by any kind of orthogonal wavelet transform. Numerical results from an arc furnace system are also presented for the transient, harmonic and time-frequency analyses.

Imperfect boundaries: thermal response of the cathode surface of a potted heater-cathode assembly

This paper extends the thermal analysis of the potted heater-cathode assembly described in our earlier paper [1] to show the effect of non-ideal interfaces formed during fabrication of the potted structure. The present analysis also accounts for the variable thermo-physical properties of the various materials used. The results of steady- and transient-state analyses are presented for some typical values of the interface heat transfer coefficient. Our results reaffirm the superiority of the pancake heater performance when considered for thermal response to the cathode surface but in the case where uniformity of surface temperature is desired, a helical heater is still preferred even in the situation of nonideal interfaces. Co-axial heat shield calculation with reference to the Spectra-Mat 600 ion source design has also been modified by taking into account the possible imperfections at the respective interfaces.

Three‐dimensional transient thermo‐elastic analyses by the BIE method

AbstractThe proposed method is the direct boundary integral equation (BIE) method applied to three‐dimensional transient heat transfer analyses and to corresponding elastostatic analyses under thermal loading. The mechanical and thermal problems are decoupled. For those not familiar with the BIE method, a short survey of the basic principles is given to help them understand the mathematical treatment, which is performed in the frame of distribution theory. The tempered elementary solution of the transient heat transfer problem contains time and space variables. The numerical treatment of the thermal equation is performed analytically with respect to time and numerically with respect to space in the same way as for steady state equations. Great care is paid to space integration in order to compute the values of the kernels precisely enough on the surface and inside the volume. The computational treatments of both problems are realized in such a way as to minimize computing time. Differences between transient and steady state analyses, on the one hand, and between elastostatic analyses with and without thermal loading, on the other, are emphasized. Finally, an analytical example shows the good behaviour of the proposed method to solve singular thermal problems and an industrial example shows the accuracy of the results obtained by using the BIE method to solve three‐dimensional thermo‐elastic problems.

Actions of glucagon on flux rates in perfused rat liver. 1. Kinetics of the inhibitory effect on glycolysis and the stimulatory effect on glycogenolysis.

Changes in the rates of glucose, lactate and pyruvate production following infusion of glucagon were studied in isolated livers from fed or fasted rats perfused with non-recirculating Krebs-Henseleit bicarbonate buffer. Evidence was presented that under these experimental conditions, the release of lactate plus pyruvate into the perfusate represents 80-90% of the total glycolytic flux; oxidation of pyruvate derived from glucose and/or glycogen accounts for the remaining 10-20%, whereas recycling of pyruvate to glucose is negligible. In the presence of glucagon, rates of lactate plus pyruvate production were diminished to less than 30% in the fed state (glycogen as substrate) and to less than 10% in the fasted state (glucose as substrate). Rates of pyruvate oxidation were unchanged. Although recycling of pyruvate to glucose was enhanced, it could account for not more than 20% of the decrease in lactate plus pyruvate production. The data indicate a strong inhibition of the substrate flux through glycolysis. The glucagon concentration for half-maximal inhibition of glycolysis was 0.2 nM, independent of the substrate (glucose or glycogen) and the nutritional state. The effective concentrations were within the physiological range of glucagon concentrations reported for portal venous blood. Transient state analyses indicated that the inhibition of glycolysis precedes the stimulation of glycogenolysis. When after a delay glycogenolysis was accelerated, it was followed by a transient stimulation of glycolysis. The stimulatory component in the glucagon effect on glycolysis was diminished in glycogen-depleted livers and when glucose was the main substrate. The coordinated control of glycolysis and glycogenolysis by glucagon and the interaction of the two processes in the transient state are discussed.

Electrical properties of normal and dysgenic mouse skeletal muscle in culture.

AbstractElectrical properties of normal and dysgenic mouse skeletal muscle were studied by intracellular recording from embryonic cells developing in vitro. Passive membrane constants were determined from records of transmembrane potential responses to hyperpolarizing pulses of current using two types of analyses, assuming the tubes to be finite cylinders: the off transient and steady state analyses. The following properties of normal and dysgenic fibers were also studied. (a) membrane potentials (b) acetylcholine sensitivity (c) α‐Bungarotoxin binding and (d) maximum rate of rise, overshoot and one‐half fall time of the action potential. Rare electrotonic coupling between fibroblasts and myotubes was noted. An anomalous type of rectification Was observed in some fibers in which the transmembrane potential responses possessed under and overshoots. These responses may have affected the values of membrane constants as derived by the off transient analysis. In all parameters studied, including membrane constants derived by the steady state analysis, the cultured mouse cells resembled adult denervated mammalian muscle rather than innervated muscle. There were no differences between normal and dysgenic fibers with respect to any of the parameters studied. Dysgenic fibers did not contract although they displayed passive and active membrane properties like those in normal, non‐dysgenic fibers.