Vibrations and structureborne noise in space station

Analytical models were developed to predict vibrations and structureborne noise generation of cylindrical and rectangular acoustic enclosures. These models are then used to determine structural vibration levels and interior noise to random point input forces. The guidelines developed could provide preliminary information on acoustical and vibrational environments in space station habitability modules under orbital operations. The structural models include single wall monocoque shell, double wall shell, stiffened orthotropic shell, descretely stiffened flat panels, and a coupled system composed of a cantilever beam structure and a stiffened sidewall. Aluminum and fiber reinforced composite materials are considered for single and double wall shells. The end caps of the cylindrical enclosures are modeled either as single or double wall circular plates. Sound generation in the interior space is calculated by coupling the structural vibrations to the acoustic field in the enclosure. Modal methods and transfer matrix techniques are used to obtain structural vibrations. Parametric studies are performed to determine the sensitivity of interior noise environment to changes in input, geometric and structural conditions

Efficient Helicopter Aerodynamic and Aeroacoustic Predictions on Parallel Computers

This paper presents parallel implementations of two codes used in a combined CFD/Kirchhoff methodology to predict the aerodynamics and aeroacoustics properties of helicopters. The rotorcraft Navier-Stokes code, TURNS, computes the aerodynamic flowfield near the helicopter blades and the Kirchhoff acoustics code computes the noise in the far field, using the TURNS solution as input. The overall parallel strategy adds MPI message passing calls to the existing serial codes to allow for communication between processors. As a result, the total code modifications required for parallel execution are relatively small. The biggest bottleneck in running the TURNS code in parallel comes from the LU-SGS algorithm that solves the implicit system of equations. We use a new hybrid domain decomposition implementation of LU-SGS to obtain good parallel performance on the SP-2. TURNS demonstrates excellent parallel speedups for quasi-steady and unsteady three-dimensional calculations of a helicopter blade in forward flight. The execution rate attained by the code on 114 processors is six times faster than the same cases run on one processor of the Cray C-90. The parallel Kirchhoff code also shows excellent parallel speedups and fast execution rates. As a performance demonstration, unsteady acoustic pressures are computed at 1886 far-field observer locations for a sample acoustics problem. The calculation requires over two hundred hours of CPU time on one C-90 processor but takes only a few hours on 80 processors of the SP2. The resultant far-field acoustic field is analyzed with state of-the-art audio and video rendering of the propagating acoustic signals

Clientelistic networks and local corruption: Evidence from Western Crete DIMITRIOS CHRISTOPOULOS

In this article, the attitudes and interaction of local political and business elites in western Crete are examined by means of an attitudinal survey, triangulated with data from in-depth interviews, conducted between July and October 1991. The data examined indicate that the endemic prevalence of clientelistic networks creates the background for corruption, although evidence of corrupt practice is not strong. In this analysis it is presumed that the attitudes and perceptions of key actors are affected by a definition of corruption that is relevant to their particular civil society alone. Data analyzed here suggest that local élite attitudes towards corruption are not perceived to affect the standards of conduct at the local level. It can also be deduced that if corruption is linked to the problems of administrative efficiency and economic development of the region, these can be related to vertical clientelistic networks with the national centre

Aerodynamic aspects and cooling techniques of turbine blade; numerical studies using URANS and LES

Numerical investigations of turbine blade are carried out using unsteady Reynolds-averaged Navier-Stokes (URANS) and large eddy simulation (LES) techniques. The goal of the present studies is to investigate the turbine blade aerodynamics and blade cooling techniques. The simulations are performed for a Reynolds number, Re = 1.3 x 106, based on the chord, c, of the airfoil and free-stream velocity. The computational results reveal the dissipative nature, of URANS, associated with the turbulence modeling. © 2011 by Marcel Ilie

Reduction of helicopter BVI noise using active flow control; the case of vortex street interactions

A novel technique regarding the reduction of helicopter blade-vortex interaction noise is proposed. The proposed technique is based on the idea of injecting air at the leading edge of the blade to alter the vortex characteristics (strength and core size). The numerical investigations are performed using the large-eddy simulation (LES) approach. The simulations were performed for a Reynolds number, Re = 1.3 × 106, based on the NACA0012 airfoil chord and free-stream velocity. The present study shows that by injecting air at the leading edge of the blade, the influence of blade-vortex interaction on the aerodynamic coefficients and aeroacoustic noise is significantly reduced. © 2011 by Marcel Ilie