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Approximation concepts and dual-method algorithms are combined in method of minimum-weight design for structures. Approximation Concepts Code for Efficient Structural Synthesis (ACCESS3) program is powerful research tool in which mathematical programming and optimality criteria are coalesced in efficient structural weight-minimization method.
Equations are derived to demonstrate which distribution of lifting elements result in a minimum amount of aerodynamic drag. The lifting elements were arranged (1) in one line, (2) parallel lying in a transverse plane, and (3) in any direction in a transverse plane. It was shown that the distribution of lift which causes the least drag is reduced to the solution of the problem for systems of airfoils which are situated in a plane perpendicular to the direction of flight.
The adaptation of the law of the minimum (LOM) to wheat yield estimation is discussed. It is demonstrated through a trial application that the LOM concept is a valuable tool for model building when regression tools are inadequate.
For slow flapping motions it is found that the minimum energy loss occurs when the vortex wake moves as a rigid surface that rotates about the wing root - a condition analogous to that determined for a slow-turning propeller. The optimum circulation distribution determined by this condition differs from the elliptic distribution, showing a greater concentration of lift toward the tips. It appears that very high propulsive efficiencies are obtained by flapping.
The application of singular perturbation theory for deriving algorithms suitable for on board real time computation of optimal aircraft trajectory control was investigated. Minimum time intercept in three dimensions was selected as a pilot problem formulation, and data for an early version F-4 aircraft was used to represent aircraft aerodynamic and propulsion characteristics. Results include the derivation of nonlinear, near optimal feedback control laws that are readily implementable in an aircraft flight computer, performance results for a variety of initial conditions (including optimal intercept at short ranges), and a point mass three dimensional simulation suitable for representing fighter aircraft under closed loop optimal control.
Bounds on the minimum number of data transfers (i.e., loads, stores, copies) required by WFTA and FFT programs are presented. The analysis is applicable to those general-purpose computers with M general processor registers, where M is equal to or greater than 4 but much less than the transform length. It is shown that the 1008-point WFTA requires about 21 percent more data transfers than the 1024-point radix-4 FFT; on the other hand, the 120-point WFTA has about the same number of data transfers as the mixed radix (4 x 4 x 4 x 2) version of the 128-point FFT and 22 percent fewer than the radix-2 version. Finally, comparisons of the 'total' program execution times (multiplications, additions, and data transfers, but not indexing or permutations) are presented.
This study presents results from an analytic investigation to determine minimum-mass designs of stiffened Gr/Pi compression panels for a wide range of uniaxial compression loads. Four panel configurations are considered: (1) hat stiffened-laminated skin, (2) hat stiffened-honeycomb core sandwich skin, (3) blade stiffened-laminated skin and (4) blade stiffened-honeycomb core sandwich skin panels. Designs are generated by an automatic optimization computer code entitled PASCO (Panel Analysis and Sizing COde). The analysis portion of PASCO contains a generalized buckling analysis which calculates all critical modes without assuming any of them a priori. Mass-strength curves are presented for the four configurations along with specific designs generated for low, moderate and high values of compression load. A mass-strength curve for a titanium hat stiffened panel is provided for comparison. A 30% to 50% mass savings over titanium panels is shown for moderately and heavily loaded Gr/Pi panels.
The general solution to the bearing axis motor torque required to escape a minimum energy trap state is presented for oblate dual-spin spacecraft. A simplified, reduced order analysis of the bearing torque is then obtained for the case of small static imbalances, dynamic imbalances, and asymmetries on the rotor and the stator. This analysis is extended to include large asymmetry on one of the bodies. The results are applied to the design of the Galileo spacecraft.
The paper deals with a statistical analysis of the errors associated with a minimum variance analysis of directional discontinuities by use of an idealized model of these discontinuities and various simulations, and also by an examination of actual Mariner 10 interplanetary magnetic field data. An empirical expression is derived for the magnitude of the error in an estimated discontinuity normal component, relative to the total field across the directional discontinuity. The analysis was performed primarily to aid in differentiating between interplanetary tangential and rotational discontinuities observed by Mariner 10.
Resource inventories require samples with geographical scatter, sometimes not as widely spaced as would be hoped. A simple model of correlation over distances is used to create a minimum variance unbiased estimate population means. The fitting procedure is illustrated from data used to estimate Missouri corn acreage.
As a means to achieve a minimum interference correction wind tunnel, a partially actively controlled test section was experimentally examined. A jet flapped wing with 0.91 m (36 in) span and R = 4.05 was used as a model to create moderately high lift coefficients. The partially controlled test section was simulated using an insert, a rectangular box 0.96 x 1.44 m (3.14 x 4.71 ft) open on both ends in the direction of the tunnel air flow, placed in the University of Washington Aeronautical Laboratories (UWAL) 2.44 x 3.66 m (8 x 12 ft) wind tunnel. A tail located three chords behind the wing was used to measure the downwash at the tail region. The experimental data indicates that, within the range of momentum coefficient examined, it appears to be unnecessary to actively control all four sides of the test section walls in order to achieve the near interference free flow field environment in a small wind tunnel. The remaining wall interference can be satisfactorily corrected by the vortex lattice method.
Several minimum-fuel, aerodynamically controlled, orbital plane change problems are formulated and solved as optimal control problems. A gradient projection algorithm is used to iteratively modify both the control functions, angle of attack and bank angle, and two control parameters to obtain the optimal trajectory. The atmospheric flight profile is combined with two Keplerian (two-body vacuum flight) arcs so that a complete orbit-to-orbit analysis results. The vehicle used in this investigation is the Space Transportation System Shuttle Orbiter. The effects of heat load constraint level and plane change angle are analysed.
A simple plasma convection model is combined with an ionospheric-atmospheric composition model in order to study the high-latitude winter F region at the solar minimum for low magnetic activity. The high latitude ionospheric features, such as the main trough, the ionization hole, the tongue of ionization, the aurorally produced ionization peaks, and the universal time effects are a natural consequence of the competition between the various chemical and transport processes known to be operating in the high-latitude ionosphere. In the polar hole, the F region peak electron density is below 300 km, and the dominant process at 300 km for NO(+) ions is diffusion.
A simple plasma convection model is combined with an ionospheric-atmospheric density model in order to study the ion composition in the high-latitude winter F-region at solar minimum for low geomagnetic activity. The numerical study produces time-dependent, three-dimensional ion density distributions for the ions NO(+), O2(+), N2(+), O(+), N(+), and He(+). The high-latitude ionosphere above 54 deg N magnetic latitude is covered at altitudes between 160 and 800 km for one complete day. Among the conclusions are the following: the ion composition varies significantly with latitude, local time, altitude, and universal time; the variations in the ion composition with latitude and local time are in good agreement with the Atmosphere Explorer measurements both quantitatively and qualitatively; and at times and at certain locations the molecular ion density can be comparable to the O(+) density at 300 km, and at 200 km the O(+) density can be comparable to the molecular ion density.
The modulator structure consisting of a single-input two-output sequential transducer whose output sequences control the modulated signal in the manner s(t) = x(i)p(t) + y(i)q(t) is considered. Here, iT is less than or equal to t, which is less than iT + T, where T is the modulation bit duration and where x(i) and y(i) take values in /+1, -1, 0/. The behavior of a sequential transducer is characterized by means of a 'trellis'. It is shown that, provided only that the 'carriers' p(t) and q(t) have the same energy in every bit interval, the optimum demodulator for the additive white Gaussian noise channel need process the received signal over only two bit intervals in making each data bit decision. It is demonstrated that particular choices of the sequential transducer yield differential minimum shift keying and differential staggered quadriphase shift keying. Possible generalizations of this approach are discussed.
In this paper, the problem of designing a matched filter for image correlation will be treated as a statistical pattern recognition problem. It is shown that, by minimizing a suitable criterion, a matched filter can be estimated which approximates the optimum Bayes discriminant function in a least-squares sense. It is well known that the use of the Bayes discriminant function in target classification minimizes the Bayes risk, which in turn directly minimizes the probability of a false fix. A fast Fourier implementation of the minimum Bayes risk correlation procedure is described.
A practical scheme is presented for generating fixed range, minimum fuel vertical flight profiles that also satisfy time-of-arrival constraints. The resulting algorithm is suitable for incorporation into an on-board flight management system. Example results show that such a capability can save up to 6% of fuel burned in flights subject to delays because of terminal area congestion.
A device is described which changes the Mach number capability of a wind tunnel without permanently altering the existing nozzle of the tunnel. An insert is removably attached to the wall of the existing nozzle expansion area thereby creating a second minimum section upstream of the model test section. The added insert may be removed without complicated and expensive changes to the basic wind tunnel. In one embodiment, a removable insert is disposed within wind tunnel nozzle walls with a portion of the flow boundary layer being bled off from the tunnel via passageway and tunnel exit to reduce the extent of separated flow normally occuring upstream of the insert contraction section.