Representative Parameter Values Research Articles

Forced Convection Heat Transfer from a Shrouded Fin Array with and without Tip Clearance

An analysis is made of the laminar heat transfer characteristics of an array of longitudinal fins with an adiabatic shroud situated adjacent to the fin tips. The analysis involves the solution of the velocity field in the inter-fin space and in the shroud clearance gap beyond the tips, after which the governing energy equations for the fluid and the fins are solved simultaneously. Solutions are obtained for representative values of dimensionless parameters which describe the system geometry and the fin conductance. For the fin, the results show that the heat loss is a minimum adjacent to the base and increases along the fin in the direction of the tip. The maximum fin heat loss occurs either at the tip or intermediate between the base and the tip, depending on whether or not there is clearance between the fin tips and the shroud. The calculated heat transfer coefficients vary along the fin and, in some cases, take on negative values. Heat loss variations are also encountered along the base surface, the extent of which depends on the fin conductance, the inter-fin spacing, and the extent of the clearance gap. With regard to the overall heat loss, the fin is, on a unit area basis, a more efficient transfer surface than is the base. The results demonstrate that the conventional uniform heat transfer coefficient model is inapplicable to shrouded fin arrays.

A Comparison of Information Policies for Minimum Delay Routing Algorithms

The problem of routing in a computer networks is dealt with by separating the information problem and the control problem. Several classes of information policies are examined, and numerical comparisons are made of their performance, using representative values of network parameters. Routing based on the expected values of delay, rather than actual values of delay, is shown to be superior to the other algorithms considered.

Dual-Polarized Channel Outages During Multipath Fading

A statistical model for outages that occur in a dual-polarized-frequency radio channel during periods of multipath fading is proposed, and an analytical expression for outage time obtained. The model, which results in Rice-Nakagami statistics for the cochannel interference signal, describes channel outage time as a function of several environmental and radio-system parameters. The formulation obtained allows for efficient parameteric studies to evaluate the importance of these parameters to channel outage time and to examine parameter sensitivity questions. Results of practical significance relative to hardware xpd requirements, maximum hop length, system gain, dependence on geographic environment, and digital terminal performance characteristics are obtained for present 11-GHz QCPSK (quaternary-coherent-phase-shift-keyed) digital radio systems. Estimates of dual-polarized-frequency channel outage time are obtained for a variety of representative system parameter values and compared with expected outage times for a conventional channel. Particular attention is given to the mechanism of channel outages during multipath fading, and several potential means for control and/or reduction of channel outage time are discussed.

An economic analysis of fuel gas production from solid waste

An engineering analysis was carried out to establish the economics of methane production by anaerobic digestion of municipal solid waste. A plant processing 907,000 kg/day (1000 ton/day) and serving a metropolitan area of about 500,000 population was specified on the basis of known characteristics of waste handling, rates of gas generation, and specific equipment costs. A quantitative description of the process was formulated to account for the broadest possible scope of relevant factors, including capital costs based on engineering selection of equipment, credits and penalties associated with waste consumption and residue disposal, realistic financing and operating charges, and the most complete description of operating characteristics available. Representative values of operating and cost parameters were selected and utilized to establish a base-line process description. Confidence in the values selected was attained by conferring with recognized researchers, engineers, equipment manufacturers, and engineering design firms to verify and document the information and selections. The cost of gas produced by the base-line process was then calculated. A sensitivity study was conducted in order to determine the effect of variations from base-line conditions on gas cost. The effect on gas cost of the financing options available in government or private ownership were investigated. Through computer-aided optimization of the calculated cost of a privately owned plant, it was found that methane can be produced at a base-line cost of $0.074 per cubic meter ($2.09/Mcf). This cost is economically acceptable when compared with projected costs of natural or synthetic gas. Operating energy requirements of the process consume the equivalent of only 37.5% of the gas produced, and the community obtains a storable fuel of versatile applicability.

Baroclinic instability at the winter stratopause

AbstractBaroclinic instability is examined in an idealized model of the winter stratopause. The upper stratosphere is more stably stratified than the lower mesosphere, and instability can occur when the zonal flow has westerly shear., Using representative parameter values, a maximum doubling time of 2 days is found for a disturbance with zonal wavelength 4000 km and vertical scale 10 km, moving with a velocity within 2ms−1 of that of the zonal wind at the stratopause. Newtonian cooling reduces growth‐rates by some 80% of the damping rate, and becomes important for relaxation times of less than 7 days.

Acoustic radiation from a spherical source embedded eccentrically within a fluid sphere

The radiation from a spherical source vibrating with an arbitrary, axisymmetric, time-harmonic velocity distribution while positioned at an arbitrary point within a fluid sphere, which is embedded in another infinite fluid medium, is computed. This configuration is an idealization of a spherical acoustic lens, with focal point inside the lens, when used as a sound projector. The translational addition theorem for spherical wave functions is used to express series of wave modes centered at one sphere in terms of modes centered at the other, thereby facilitating the task of satisfying the boundary conditions. The radiation load on the source and the farfield directivity pattern are evaluated for representative values of the many parameters that characterize the problem, such as the wavelength size of the lens and source, the relative characteristic impedances and sound velocities of the two fluid media, the position of the source, and the velocity distribution on the source sphere. In general, no great increase in the radiation resistance is noted when the source is at the focal point of the lens. The focal points for monopole and dipole sources are usually not coincident. The size of the source has little effect upon the farfield directivity pattern.

Radiation from a Spherical Source Eccentrically Positioned in a Fluid Sphere

Acoustic Radiation from a spherical source eccentrically positioned within a fluid sphere embedded in another fluid is evaluated. This configuration is an idealization of a spherical acoustic lens used as a sound projector. To effect a solution, the translational addition theorem for spherical wavefunctions is used to express series of wavemodes centered at one sphere in terms of modes centered at the other, thereby facilitating the task of satisfying the boundary conditions. Because spherical wavefunctions centered at one point are not orthogonal over the surface of a sphere centered elsewhere, each mode associated with the first sphere couples into every one of the modes associated with the other. Hence, the evaluation of the modal coefficients in the series for the radiated pressure necessitates solving an infinite set of equations. Approximate solutions are obtained by truncating the set to finite size and solving numerically. The source radiation impedance and farfield directivity have been calculated for representative values of the many parameters that characterize the problem, such as wavelength size of fluid sphere and source, relative characteristic impedances and sound velocities of the two fluids, and position and velocity distribution of the source. [Research was supported by the Ordnance Research Laboratory under contract with the U. S. Naval Ordance Systems Command.]

Theoretical proton velocity distributions in the flow around the magnetosphere

Relations from kinetic theory are combined with results from fluid calculations to determine a microscopic interpretation of the properties of the solar wind as it flows around the magnetosphere. Proton velocity distributions are presented as a function of the particle speed and direction for several points in space for representative values of the solar wind parameters. The results illustrate how the velocity distribution is highly collimated in the incident stream, is completely isotropic at the magnetosphere nose, and the degree to which it changes back to that of a highly collimated stream along the flanks of the magnetosphere. Except for a very small region in the vicinity of the magnetosphere nose, the number of particles that move in the upstream direction is insignificantly small compared with the number that move in the direction of the bulk velocity. The most probable speed of the protons, as viewed in a frame fixed in the Earth, is always in the direction of the local bulk velocity, and tends to be relatively constant throughout the flow in spite of substantial changes in temperature and bulk velocity. The paper concludes with a discussion of the relation of these results to the measurements that would be made by various types of instruments commonly used to observe plasma flows in space.

A Method of Estimating Demand

A method is presented for the estimation of a "probable" annual maximum collective demand in kva (kilovolt-amperes) for a set of heterogeneous residential electric appliances. The method considers diversity between appliances of different types as well as diversity among those of the same type. It is based on a probable model of appliance behavior using parameters obtained from observed operation. The accuracy of the method and its application are examined, and representative parameter values are presented but not derived. A sample calculation is included.

A high voltage, high speed, three terminal P-N-P-N switch

The design of high voltage, high speed, three terminal silicon P v PN switches for high pulse current applications is discussed. The resistivity of the v region and the minimum base widths are determined by the minimum breakover voltage requirement. The dependence of the delay and turn times and trigger requirements the two base widths is then analyzed. It is pointed out that the breakover voltage, speed, and peak current requirement in combination with the desire for a low on drop necessitates stringent control of the resistivity of the v material during processing. The emitter area and emitter contact sheet resistance are determined by the peak current requirement. Other design features of the device are also discussed. Representative values of the device parameters are given for various designs. In typical applications, the devices are capable of switching from 500 volts to 50 amperes with turn-on times of .05 µsec.

The effect of multipath distortion on the choice of operating frequencies for high-frequency communication circuits

Harmful multipath distortion on high-frequency facsimile services and telegraphic services operating at high speeds occurs when the received signal is composed of two or more components arriving by different modes over the same great-circle path with comparable intensities, but having travel times which differ by an amount equal to an appreciable fraction of the duration of a signal element. The dependence of multipath distortion on the relationship of the operating frequency to the MUF is discussed and a new term, the multipath reduction factor (MRF), is introduced which permits calculation in terms of the MUF of the lowest frequency which can be used to provide a specified measure of protection against multipath distortion. The MRF has a marked path-length dependence and is calculated as a function of path length for representative values of the other parameters involved by making use of an ionospheric model. It is then shown how the MRF can be used in connection with world-wide MUF prediction material to determine the minimum number of frequencies which must be assigned to a high-frequency communication service of continuous availability operating at high speed. Some comparisons with observations are discussed, and finally conclusions are drawn concerning manner of operation and choice of operating frequencies to reduce or to eliminate harmful multipath distortion.

An Analytical Theory of Landing-Shock Effects on an Airplane Considered as an Elastic Body

Abstract An analytical method of determining the accelerations at any point P (x, y, z) of an airplane during landing is given. The method is applicable to any type airplane with either tricycle or conventional landing gear. The shock-strut forces are determined by a method previously published. A criterion for the mechanism of a broken spar is sought. Calculations are carried out for no particular airplane, but representative values of parameters for four-engined transports are employed.