14,233 research outputs found
Application of the generalized reduced gradient method to conceptual aircraft design
The complete aircraft design process can be broken into three phases of increasing depth: conceptual design, preliminary design, and detail design. Conceptual design consists primarily of developing general arrangements and selecting the configuration that optimally satisfies all mission requirements. The result of the conceptual phase is a conceptual baseline configuration that serves as the starting point for the preliminary design phase. The conceptual design of an aircraft involves a complex trade-off of many independent variables that must be investigated before deciding upon the basic configuration. Some of these variables are discrete (number of engines), some represent different configurations (canard vs conventional tail) and some may represent incorporation of new technologies (aluminum vs composite materials). At Lockheed-Georgia, the sizing program is known as GASP (Generalized Aircraft Sizing Program). GASP is a large program containing analysis modules covering the many different disciplines involved fin defining the aricraft, such as aerodynamics, structures, stability and control, mission performance, and cost. These analysis modules provide first-level estimates the aircraft properties that are derived from handbook, experimental, and historical sources
Homogeneity and isotropy in a laboratory turbulent flow
We present a new design for a stirred tank that is forced by two parallel
planar arrays of randomly actuated synthetic jets. This arrangement creates
turbulence at high Reynolds number with low mean flow. Most importantly, it
exhibits a region of 3D homogeneous isotropic turbulence that is significantly
larger than the integral lengthscale. These features are essential for enabling
laboratory measurements of turbulent suspensions. We use quantitative imaging
to confirm isotropy at large, small, and intermediate scales by examining one--
and two--point statistics at the tank center. We then repeat these same
measurements to confirm that the values measured at the tank center are
constant over a large homogeneous region. In the direction normal to the
symmetry plane, our measurements demonstrate that the homogeneous region
extends for at least twice the integral length scale cm. In the
directions parallel to the symmetry plane, the region is at least four times
the integral lengthscale, and the extent in this direction is limited only by
the size of the tank. Within the homogeneous isotropic region, we measure a
turbulent kinetic energy of ms, a dissipation
rate of ms, and a Taylor--scale Reynolds
number of . The tank's large homogeneous region, combined with
its high Reynolds number and its very low mean flow, provides the best
approximation of homogeneous isotropic turbulence realized in a laboratory flow
to date. These characteristics make the stirred tank an optimal facility for
studying the fundamental dynamics of turbulence and turbulent suspensions.Comment: 18 pages, 9 figure
Formulation of a dynamic analysis method for a generic family of hoop-mast antenna systems
Analytical studies of mast-cable-hoop-membrane type antennas were conducted using a transfer matrix numerical analysis approach. This method, by virtue of its specialization and the inherently easy compartmentalization of the formulation and numerical procedures, can be significantly more efficient in computer time required and in the time needed to review and interpret the results
Sectoral productivity and spillover effects of FDI in Latin America
Empirical studies analysing productivity effects of inward FDI in Latin America (LA) are inconclusive. We argue that investigating aggregate FDI masks interesting effects of FDI that take place within and across sectors. Moreover, the potential of FDI to generate productivity effects differs across sectors. For these reasons and because sectoral FDI intensities vary significantly among LA countries and change over time, we investigate the productivity effects of FDI in eight different sectors including the primary sector, manufacturing and services. Besides FDI, sector-specific institutional factors, education and a sector‘s export share are considered as control variables. Given the likely endogeneity of variables, a GMM system estimation approach is used. The results indicate that positive productivity effects can be found in all sectors, although they may depend on specific conditions or are limited to a certain time period. Direct productivity effects are highest in the primary sector (agriculture, mining and petroleum production) and in financial services. In contrast, FDI in manufacturing and in transport and telecommunications generates productivity spillovers to nearly all other sectors.FDI, productivity, sector level, Latin America
Polymer chain in a quenched random medium: slow dynamics and ergodicity breaking
The Langevin dynamics of a self - interacting chain embedded in a quenched
random medium is investigated by making use of the generating functional method
and one - loop (Hartree) approximation. We have shown how this intrinsic
disorder causes different dynamical regimes. Namely, within the Rouse
characteristic time interval the anomalous diffusion shows up. The
corresponding subdiffusional dynamical exponents have been explicitly
calculated and thoroughly discussed. For the larger time interval the disorder
drives the center of mass of the chain to a trap or frozen state provided that
the Harris parameter, , where is a
disorder strength, is a Kuhnian segment length, is a chain length and
is the Flory exponent. We have derived the general equation for the non -
ergodicity function which characterizes the amplitude of frozen Rouse
modes with an index . The numerical solution of this equation has
been implemented and shown that the different Rouse modes freeze up at the same
critical disorder strength where the exponent
and does not depend from the solvent quality.Comment: 17 pages, 6 figures, submitted to EPJB (condensed matter
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