Quasi-static operation

Another key issue is the sensitivity of the mass flux or burning rate and surface temperature to the independent variables, P, To, qr. The sensitivity of burning rate to pressure and initial temperature is obviously important for internal ballistics and rocket motor performance prediction for quasi-static operation. The sensitivity of surface temperature is not quite as obvious but is related to the unsteady combustion behavior through Zeldovich-Novozhilov (ZN) theory. The sensitivity parameters are derivatives of the steady equations as defined in the nomenclature. Equation (15) or (16) can be differentiated with respect to initial temperature (To), pressure (Dg), and radiative flux (qr) to give... 

Comments The entropy generation is higher compared to the previous example, implying that there are more irreversible features when the flow rate is increased. How so The net result of the increased flow rate is that the temperature of the hot stream remains constant at its high value, 500 °C. As a result, the temperature difference between the hot and cold streams is higher than it was in the previous example, where the temperature of the hot stream was allowed to drop and get closer to that of the colder stream. By increasing the flow rate, the process was further removed from the assumptions of quasi-static operation and thus became more irreversible. 

However, even in quasi-static operation the actual displacement and desired displacement usually do not correspond. Internal imperfections such as complex hysteretic nonlinearities described by the operator Ia in Fig. 6.6 and external influences such as load reactions via the surrounding mechanical... 

Following a principle used in piezoelectric ultrasonic motors [60], T. Aku-ta [61] has built the first magnetostrictive friction motor. This stator is made of pairs of orthogonal actuators excited with sinusoidal 90° phase-shift currents, which produce an elliptical vibration. The modeling of such magnetostrictive stators [42] has shown that in quasi-static operation a good elliptical motion is produced. It has also been shown that there are many coupled modes, but none of them provides a satisfactory elliptical motion. Therefore, unlike piezoelectric motors, this motor cannot operate at resonance. As a consequence and in relation to the previous analysis of power (Fig. 6.34), the efficiency is comparatively weak. Its other characteristics are a speed of 40°/s and a torque of 1.8 Nm [62]. 

Abstract The theoretical basis for the quantum time evolution of path integral centroid variables is described, as weU as the motivation for using these variables to study condensed phase quantum dynamics. The equihbrium centroid distribution is shown to be a well-defined distribution function in the canonical ensemble. A quantum mechanical quasi-density operator (QDO) can then be associated with each value of the distribution so that, upon the application of rigorous quantum mechanics, it can be used to provide an exact definition of both static and dynamical centroid variables. Various properties of the dynamical centroid variables can thus be defined and explored. Importantly, this perspective shows that the centroid constraint on the imaginary time paths introduces a non-stationarity in the equihbrium ensemble. This, in turn, can be proven to yield information on the correlations of spontaneous dynamical fluctuations. This exact formalism also leads to a derivation of Centroid Molecular Dynamics, as well as the basis for systematic improvements of that theory. 

SFM s can be also classified according to static and dynamic operating modes. Under quasi-static conditions, the microscope measures the instantaneous response of the cantilever when it interacts with the sample. Dynamic SFM enables separation of the elastic and inelastic component in the cantilever deflection when the sample surface is exposed to a periodically varying stress field. The dynamic modes are useful for investigation of viscoelastic materials such as polymers and results in additional improvements in the signal-to-noise ratio. 

The ratio concentration for 12 months symmetric static PV concentrator operation is from 3.5-14. For Northern countries application during 9 month of polar summer the static symmetric concentrator has the ratio concentration from 5-20. Quasi-static symmetric PV concentrator module with ratio concentration 7.5-30 needs correction of position every 6 months. 

Cyclic chip formation refers to the periodic chip formation process of birth, growth, and final breaking of chips. The study of cyclic chip formation is important because in practice chip formation is rarely a imiquely defined process that can be represented by a quasi-static condition, but rather a cyclically repeated application of a time-dependent process involving chip formation, chip-form development, and chip fracture. Even if the cycles are not exactly repeatable, they indicate the history of chip formation and trace back important information to connect with the process mechanics. One of the earliest discoveries of cyclic chip formation in turning operations was reported by Jawahir (1986). This work was followed by an extensive experimental analysis... 

The quasi-static process is an idealization that allows us to associate a path drawn on the thermodynamic plane with an actual process. It is a mental device that we use to draw connections between mathematical operations on the thermodynamic plane and real processes that can be conducted experimentally. Since this is a mental exercise, we are not concerned as to whether this is a practical way to run the process. In fact, this is a rather impractical way of doing things Gradients are desirable because they increase the rate of a process and decrease the time it takes to perform the task. This does not mean that the quasi-static concept is irrelevant in real life. When mathematics calls for an infinitesimal change, nature is satisfied with a change that is small enough. If an actual process is conducted in a way that does not upset the equilibrium state too much, it can then be treated as a quasi-static process. 

We next operated the DSC dynamically and obtained the indicated temperatures for melting on lid and bottom for the four metals. In each case the difference between the observed melting points for lid and bottom was found to be a linear function of T. The slopes of these fits for the four metals were the same, to within experimental accuracy. Tlie least squares fits to the data for the bottom melting for each standard yielded the values for the constants in Eq.(l). The extrapolations of the least squares fits to the data for each metal to T 0 agreed very well with the quasi-static values obtained as described above. 

Instead of applying the fundamental conservation equations, as described above, another modeling approach is to characterize gas turbine performance by utilizing real steady state engine performance data, as in (Hung, 1991). It is assumed that transient thermodynamic and flow processes are characterized by a continuous progression along the steady state performance curves. This is known as the quasi-static assumption. The dynamics of the gas turbine, e.g. combustion delay, motor inertia, fuel pump lag etc. are then represented as lumped quantities separate from the steady-state performance curves. Very simple models result if it is further assumed that the gas turbine is operated at all times close to rated speed (Rowen, 1983). 

Movement relative to Adhesive layer thickness and sealing joint width Thermal movement (e.g. very slow quasi-static) Loading and unloading Slight accident, infrequent incidents (e.g. derailment) Normal service operation (dynamic, fast)... 

Parris et al adopted a continuous mode of operation (Figure 193), in which quasi-static thermal and chemical regimes could be maintained. This method offers advantages over the pulsed mode in terms of control of decomposition, volatilization, and atomization of the analyte. 

Ultrasound reflects from a layer of oil between two bearing surfaces. The response of the oil film can be modelled using a quasi-static spring model. The proportion of the wave reflected depends on the stiffness of the oil film and its acoustic properties. Experiments have shown this spring model approach to be valid for the thickness of oil films typically encountered in the operation of hydrodynamic bearings. 

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