Investigation of electronic switches for analog and hybrid computation technical note no. 6

Analog switching circuits for analog and hybrid computer

Low-frequency sound propagation modeling over a locally-reacting boundary using the parabolic approximation

There is substantial interest in the analytical and numerical modeling of low-frequency, long-range atmospheric acoustic propagation. Ray-based models, because of frequency limitations, do not always give an adequate prediction of quantities such as sound pressure or intensity levels. However, the parabolic approximation method, widely used in ocean acoustics, and often more accurate than ray models for lower frequencies of interest, can be applied to acoustic propagation in the atmosphere. Modifications of an existing implicit finite-difference implementation for computing solutions to the parabolic approximation are discussed. A locally-reacting boundary is used together with a one-parameter impedance model. Intensity calculations are performed for a number of flow resistivity values in both quiescent and windy atmospheres. Variations in the value of this parameter are shown to have substantial effects on the spatial variation of the acoustic signal

Passive and active seismic isolation for gravitational radiation detectors and other instruments

Some new passive and active methods for reducing the effects of seismic disturbances on suspended masses are described, with special reference to gravitational radiation detectors in which differential horizontal motions of two or more suspended test masses are monitored. In these methods it is important to be able to determine horizontal seismic accelerations independent of tilts of the ground. Measurement of changes in inclination of the suspension wire of a test mass, relative to a direction defined by a reference arm of long period of oscillation, makes it possible to carry this out over the frequency range of interest for earth-based gravitational radiation detectors. The signal obtained can then be used to compensate for the effects of seismic disturbances on the test mass if necessary. Alternatively the signal corresponding to horizontal acceleration can be used to move the point from which the test mass is suspended in such a way as to reduce the effect of the seismic disturbance and also damp pendulum motions of the suspended test mass. Experimental work with an active anti-seismic system of this type is described

Numerical analysis of flow non-uniformity in the hot gas manifold of the Space Shuttle main engine

Three-dimensional viscous flow in a conceptual hot gas manifold (HGM) for the Space Shuttle Main Engine High Pressure Fuel Turbopump (SSME HPFTP) was numerically analyzed. A finite difference scheme was used to solve the Navier-Stokes equations. The exact geometry of the SSME HGM was modeled using boundary fitted curvilinear coordinates and the General Interpolants Method (GIM) code. Slight compressibility of the subsonic flow was modeled using a linearized equation of state with artificial compressibility. A time relaxation method was used to obtain a steady state solution. The feasibility and potential usefulness of computational methods in assisting the design of SSME components which involves the flow of fluids within complex geometrical shapes is demonstrated

A study of the optimization of ethylene production in a tubular reactor

The pyrolysis of ethane is a complex reaction involving six individual reactions in a reactant mixture of thirteen components. It is further complicated by the deposition of carbon along the reactor walls. The carbon buildup eventually necessitates reactor shutdown, During the intermediate stages the reactor experiences a gradual increase in inlet pressure which affects the reaction conditions, Optimum temperature profiles exist because the yield goes up with increasing temperature, but, consequently, the reactor must be shut down and cleaned out with increasing frequency. The combined effect causes the yearly production of ethylene to go through an optimum. To find this optimum a computer program was developed with the ability of handling 25 simultaneous reactions involving up to 25 components, It calculates the carbon deposition profile and the changing pressure profiles, as a function of a predetermined reaction gas temperature profile. The reactor will remain in production until the inlet pressure exceeds eight atmospheres. The average yearly production rate is calculated, assessing a reactor shut down penalty of 24 and 48 hours required for the cleaning of the clogged pyrolysis tubes. The optimum exit temperature for the 24 hour penalty was 1127°K with a corresponding 57% one pass ethane conversion. The 48 hour penalty lowers the optimum exit temperature to 1124°K and a 50.5% ethane conversion. The practice of increasing pressure to compensate for carbon buildup results in accelerated carbon deposition and is detrimental to overall production scheme. The program given here is immediately applicable to any plug flow system, the only additional requirement being the physical and thermodynamic constants for the additional components. The program could, for example, be used to calculate the production of acetylene

High field CdS detector for infrared radiation

New and highly sensitive method of detecting infrared irradiation makes possible solid state infrared detector which is more sensitive near room temperature than usual photoconductive low band gap semiconductor devices. Reconfiguration of high field domains in cadmium sulphide crystals provides basis for discovery

Effect of gas temperature gradients and radiant heat transmission on kinetic model behavior

Satisfactory methods to predict radiant heat transmission in enclosures containing a radiating gas at uniform temperature are available. These methods have been traditionally used in solutions of kinetic models. Kinetic models are strongly temperature dependent with a difference of 10°K able to double the reaction rate. In the present investigation, calculation techniques which make allowance for the non-uniformity of gas temperatures in an enclosure are applied to the kinetic models. The furnace problem considers only the radiation section with the assumption that detailed knowledge of combustion and fluid flow pattern within the enclosure is available. If the gas space in the enclosure and the bounding walls are divided into zones, a zone being taken small enough so that it may be considered isothermal, then for steady-state operation one can write an energy balance on each zone. For any specific problem, every term in these equations with the exception of the net wall fluxes may be written as a function of unknown temperatures only; furthermore the number of equations is exactly equal to the number of unknown temperatures and wall fluxes so that a solution is possible, though exceedingly difficult due to the existing non-linearities. The net wall fluxes are calculated by the kinetic model, the flux at any point being a function of the overall heat transfer coefficient, the extent of reaction, and the temperature of the reacting gases, each of which in turn is a complex function of reaction gas composition and velocity. The chief problem of this investigation was one of evaluating the emission from both a gas zone and a surface zone and the radiant interchange between all zones, making due allowance for absorption along every path from one zone to another. The primary result of this dissertation has been the application of radiant dominant heat transmissions in enclosures (which make allowances for temperature non-uniformity in gas mass) to a pyrolysis reactor. The result of this reactor-furnace hybrid model is the ability to determine optimum tube placement, furnace size, and fuel consumption, while accounting for the effect of carbon deposition in the reactor. The methods developed in this dissertation were instrumented on an IBM 370-15 computer. This machine made it possible to make parametoric studies which predict the effect of changing furnace and reactor variables. The high severity steam cracking furnace results in the greatest production per pound of fuel consumed. A yield of 73% represents maximum fuel economy. However, the associated problems of coke formation and high tube metal temperature must first be overcome Wore these yields can be realized

Cylindrical, periodic surface lattice — theory, dispersion analysis, and experiment

A two-dimensional surface lattice of cylindrical topology obtained via perturbing the inner surface of a cylinder is considered. Periodic perturbations of the surface lead to observation of high-impedance, dielectric-like media and resonant coupling of surface and non-propagating volume fields. This allows synthesis of tailored-for-purpose "coating" material with dispersion suitable, for instance, to mediate a Cherenkov type interaction. An analytical model of the lattice is discussed and coupled-wave equations are derived. Variations of the lattice dispersive properties with variation of parameters are shown, illustrating the tailoring of the structure's electromagnetic properties. Experimental results are presented showing agreement with the theoretical model