Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 5 Articles
The paper describes a stalldetection criterion based on the use of symmetrised dot pattern (SDP) visual waveform analysis and\r\nthe stallwarning methodology based on a recently developed analysis. The experimental study explores the capability of the\r\nSDP technique to detect the stall incipience and evolution in the presence of low signal-to-noise ratios, that is, a noisy working\r\nenvironment. Moreover, the investigation presents a systematic analysis on the probe position�s influence with respect to the fan\r\nsection. As such, the SDP technique in combination with an acoustic measurement is able to create a visual pattern that one can\r\nuse to detect stall from potentially any location around the fan/duct system....
Atwo-node element is suggested for analyzing the stability and free vibration of Timoshenko beam.Cubic displacement polynomial\r\nand quadratic rotational fields are selected for this element.Moreover, it is assumed that shear strain of the element has the constant\r\nvalue. Interpolation functions for displacement field and beam rotation are exactly calculated by employing total beam energy\r\nand its stationing to shear strain. By exploiting these interpolation functions, beam elements� stiffness matrix is also examined.\r\nFurthermore, geometric stiffnessmatrix andmassmatrix of the proposed element are calculated by writing governing equation on\r\nstability and beam free vibration. At last, accuracy and efficiency of proposed element are evaluated through numerical tests. These\r\ntests show high accuracy of the element in analyzing beam stability and finding its critical load and free vibration analysis....
There are controversial requirements involved in developing numerical methodologies in order to compute the flow in industrial\r\nfans.The full resolution of turbulence spectrum in such high-Reynolds number flow configurations entails unreasonably expensive\r\ncomputational costs. The authors applied the study to a large unidirectional axial flow fan unit for tunnel ventilation to operate in\r\nthe forward direction under ambient conditions. This delivered cooling air to the tunnel under routine operation, or hot gases\r\nat 400�°C under emergency conditions in the event of a tunnel fire. The simulations were carried out using the open source\r\ncode OpenFOAM, within which they implemented a very large eddy simulation (VLES) based on one-equation SGS model to\r\nsolve a transport equation for the modelled (subgrid) turbulent kinetic energy. This subgrid turbulence model improvement is a\r\nremedial strategy in VLES of high-Reynolds number industrial flows which are able to tackle the turbulence spectrumâ��s well-known\r\ninsufficient resolution.TheVLES of the industrial fan permits detecting the unsteady topology of the rotor flow. This paper explores\r\nthe evolution of secondary flow phenomena and speculates on its influence on the actual load capability when operating at peakpressure\r\ncondition. Predicted noise emissions, in terms of sound pressure level spectra, are also compared with experimental results\r\nand found to agree within the uncertainty of the measurements....
Data from a low pressure air test facility are used to quantify the influence of the acoustic field in the main line on side branch\r\nresonance behavior. The main line of diameter D = 7.6 cm may accumulate acoustic energy broadcast from a resonating branch\r\nof diameter d = 1.9 cm (d/D = 0.25). The side branch resonance amplitude is a strong function of branch position along the main\r\nline with the normalized pressure rising to 1.2 in the most favorable branch positions with Strouhal number near 0.3. Large time\r\nvariation of the side branch andmain line resonance amplitude is apparent formost branch positions. Amoving window is used on\r\nthe time history to collect an array of power spectral densities (PSDs). Peak amplitude values from the PSD array are represented\r\nin a probability density function (PDF) that provides a repeatable characterization of data from the system....
This paper describes a resonance decay estimation for structural health monitoring in the presence of nonstationary vibrations.\r\nIn structural health monitoring, the structure�s frequency response and resonant decay characteristics are very important for\r\nunderstanding how the structure changes. Cumulative spectral analysis (CSA) estimates the frequency decay by using the impulse\r\nresponse. However, measuring the impulse response of buildings is impractical due to the need to shake the building itself. In a\r\nprevious study,we reported on system dampingmonitoring using cumulative harmonic analysis (CHA),which is based on CSA.The\r\ncurrent study describes scale model experiments on estimating the hidden resonance decay under non-stationary noise conditions\r\nby using CSA for structural condition monitoring....
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