33,931 research outputs found
A Wake Model for Free-Streamline Flow Theory, Part II. Cavity Flows Past Obstacles of Arbitrary Profile
In Part I of this paper a free-streamline wake model was introduced to treat the fully and partially developed wake flow or cavity flow past an oblique flat plate. This theory is generalized here to investigate the cavity flow past an obstacle of arbitrary profile at an arbitrary cavitation
number. Consideration is first given to the cavity flow past a polygonal obstacle whose wetted sides may be concave towards the flow and may also possess some gentle convex corners. The general case of curved walls is then obtained by a limiting process. The analysis in this general case leads to a set of two functional equations for which several
methods of solution are developed and discussed.
As a few typical examples the analysis is carried out in detail for the specific cases of wedges, two-step wedges, flapped hydrofoils, and inclined circular arc plate. For these cases the present theory is found in good agreement with the experimental results available
A wake model for free-streamline flow theory. Part 2. Cavity flows past obstacles of arbitrary profile
In Part 1 of this paper a free-streamline wake model mas introduced to treat the fully and partially developed wake flow or cavity flow past an oblique flat plate. This theory is generalized here to investigate the cavity flow past an obstacle of arbitrary profile at an arbitrary cavitation number. Consideration is first given to the cavity flow past a polygonal obstacle whose wetted sides may be concave
towards the flow and may also possess some gentle convex corners. The general case of curved walls is then obtained by a limiting process. The analysis in this general case leads to a set of two funnctional equations for which several methods of solutioii are developed and discussed.
As a few typictbl examples the analysis is carried out in detail for the specific cases of wedges, two-step wedges, flapped hydrofoils, and inclined circular arc plates. For these cases the present theory is found to be in good agreement with the experimental results available
An Approximate Numerical Scheme for the Theory of Cavity Flows Past Obstacles of Arbitrary Profile
Recently an exact theory for the cavity flow past an obstacle of arbitrary profile at an arbitrary cavitation number has been developed by adopting a free-streamline wake model. The analysis in this general case leads to a set of two functional equations for which several numerical methods have been devised; some of these methods have already been successfully carried out for several typical cases on a high speed electronic computer.
In this paper an approximate numerical scheme, somewhat like an engineering principle, is introduced which greatly shortens the computation of the dual functional equations while still retaining a high degree of accuracy of the numerical result. With such drastic simplification, it becomes feasible to carry out this approximate mrmerical scheme even with a hand computing machine
Small-Time Behavior of Unsteady Cavity Flows
A perturbation theory is applied to investigate the small-time behavior of unsteady cavity flows in which the time-dependent part of the flow may be taken as a small-time expansion superimposed on an established steady cavity flow of an ideal fluid. One purpose of this paper is to study the effect of the initial cavity size on the resulting flow due to a given disturbance. Various existing steady cavity-flow models have been employed for this purpose to evaluate the initial reaction of a cavitated body in an unsteady motion. Furthermore, a physical model is proposed here to give a proper representation of the mechanism by which the cavity volume may be changed with time; the initial hydrodynamic force resulting from such change is calculated based on this model
The rare decay B --> X_s l^+ l^- to NNLL precision for arbitrary dilepton invariant mass
We present a new phenomenological analysis of the inclusive rare decay . In particular, we present the first calculation of the NNLL
contributions due to the leading two-loop matrix elements, evaluated for
arbitrary dilepton invariant mass. This allows to obtain the first NNLL
estimates of the dilepton mass spectrum and the lepton forward-backward
asymmetry in the high region, and to provide an
independent check of previously published results in the low region. The numerical impact of these NNLL corrections in the
high-mass region () amounts to -13% in the
integrated rate, and leads to a reduction of the scale uncertainty to .
The impact of non-perturbative contributions in this region is also discussed
in detail.Comment: 40 pages, 12 figures. v2: extended phenomenological discussion;
results unchanged; published versio
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Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems
Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion
An efficient method for computing the Thouless-Valatin inertia parameters
Starting from the adiabatic time-dependent Hartree-Fock approximation
(ATDHF), we propose an efficient method to calculate the Thouless-Valatin
moments of inertia for the nuclear system. The method is based on the rapid
convergence of the expansion of the inertia matrix. The accuracy of the
proposed method is verified in the rotational case by comparing the results
with the exact Thouless-Valatin moments of inertia calculated using the
self-consistent cranking model. The proposed method is computationally much
more efficient than the full ATDHF calculation, yet it retains a high accuracy
of the order of 1%.Comment: 16 pages, 3 figure
Transient response under ultrafast interband excitation of an intrinsic graphene
The transient evolution of carriers in an intrinsic graphene under ultrafast
excitation, which is caused by the collisionless interband transitions, is
studied theoretically. The energy relaxation due to the quasielastic acoustic
phonon scattering and the interband generation-recombination transitions due to
thermal radiation are analyzed. The distributions of carriers are obtained for
the limiting cases when carrier-carrier scattering is negligible and when the
intercarrier scattering imposes the quasiequilibrium distribution. The
transient optical response (differential reflectivity and transmissivity) on a
probe radiation and transient photoconductivity (response on a weak dc field)
appears to be strongly dependent on the relaxation and recombination dynamics
of carriers.Comment: 9 pages, 8 figure
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