Automatic measurement method of large scale satellite antenna in planar near-field test

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

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Study on Measurement Method of Electromagnetic Interference from Large-scale Electric Equipment/System

2020 IEEE Asia-Pacific Microwave Conference (APMC) ◽

10.1109/apmc47863.2020.9331509 ◽

2020 ◽

Author(s):

Tatsuru Itsukaichi ◽

Koji Igari ◽

Shinobu Ishigami ◽

Ken Kawamata ◽

Yasutoshi Yoshioka

Keyword(s):

Electromagnetic Interference ◽

Measurement Method ◽

Large Scale ◽

Electric Equipment ◽

Equipment System

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Ultrasonic measurement of clamping force for injection molding machine

Journal of Polymer Engineering ◽

10.1515/polyeng-2018-0268 ◽

2019 ◽

Vol 39 (4) ◽

pp. 388-396 ◽

Cited By ~ 6

Author(s):

Peng Zhao ◽

Yao Zhao ◽

Jianfeng Zhang ◽

Junye Huang ◽

Neng Xia ◽

...

Keyword(s):

Injection Molding ◽

Measurement Method ◽

Large Scale ◽

Force Measurement ◽

Low Cost ◽

Ultrasonic Method ◽

Injection Molding Process ◽

Propagation Time ◽

Clamping Force ◽

Molding Process

AbstractAn online and feasible clamping force measurement method is important in the injection molding process and equipment. Based on the sono-elasticity theory, anin situclamping force measurement method using ultrasonic technology is proposed in this paper. A mathematical model is established to describe the relationship between the ultrasonic propagation time, mold thickness, and clamping force. A series of experiments are performed to verify the proposed method. Experimental findings show that the measurement results of the proposed method agree well with those of the magnetic enclosed-type clamping force tester method, with difference squares less than 2 (MPa)2and errors bars less than 0.7 MPa. The ultrasonic method can be applied in molds of different thickness, injection molding machines of different clamping scales, and large-scale injection cycles. The proposed method offers advantages of being highly accurate, highly stable, simple, feasible, non-destructive, and low-cost, providing significant application prospects in the injection molding industry.

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Instability wave models for the near-field fluctuations of turbulent jets

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.401 ◽

2011 ◽

Vol 689 ◽

pp. 97-128 ◽

Cited By ~ 172

Author(s):

K. Gudmundsson ◽

Tim Colonius

Keyword(s):

Flow Field ◽

Large Scale ◽

Microphone Array ◽

Near Field ◽

Turbulent Jets ◽

Instability Wave ◽

Mean Flow ◽

Velocity Fluctuations ◽

The Mean ◽

Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

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The ‘preferred mode’ of the axisymmetric jet

Journal of Fluid Mechanics ◽

10.1017/s0022112081000608 ◽

1981 ◽

Vol 110 ◽

pp. 39-71 ◽

Cited By ~ 200

Author(s):

A. K. M. F. Hussain ◽

K. B. M. Q. Zaman

Keyword(s):

Reynolds Number ◽

Reynolds Stress ◽

Coherent Structure ◽

Large Scale ◽

Near Field ◽

Saddle Points ◽

Initial Boundary ◽

Phase Average ◽

Background Turbulence ◽

Time Average

The ‘preferred mode’ of an incompressible axisymmetric free jet has been organized through controlled perturbation, and spatial distributions of time-average as well as phase-average flow properties in the near field are documented. The excitation produces noticeable changes in the time-average measures of the jet, although these changes are less dramatic than those for the excitation producing stable vortex pairing. For different stages in the evolution of the preferred-mode coherent structure, the phase-average vorticity, coherent Reynolds stress, and incoherent turbulence intensities and Reynolds stress have been educed through phase-locked hot-wire measurements, over the spatial extent of the structure and without invoking the Taylor hypothesis. For a particular stage of the evolution (i.e. when the structure is centred at x/D ≃ 3) the distributions of these quantities have been compared for both initially laminar and fully turbulent exit boundary layers, and for four jet Reynolds numbers. The relative merits of the coherent structure streamline and pseudo-stream-function patterns, as compared with phase-average velocity contours, for structure boundary identification have been discussed. The structure shape and size agree closely with those inferred from the average streamline pattern of the natural structure educed by Yule (1978).These data as well as τ-spectra show that even excitation at the preferred mode cannot sustain the initially organized large-scale coherent structure beyond eight diameters from the jet exit. The background turbulence is organized by the coherent motions in such a way that the maximum rate of decrease of the coherent vorticity occurs at the structure centres which are the saddle points of the background-turbulence Reynolds-stress distributions. The structure centres are also the locations of peak phase-average turbulence intensities. The evolving shape of the structure as it travels downstream helps explain the transverse variations of the wavelength and convection velocity across the mixing layer. The coherent structure characteristics are found to be independent of whether the initial boundary layer is laminar or turbulent, but depend somewhat on the jet Reynolds number. With increasing Reynolds number, the structure decreases in the streamwise length and increases in the radial width and becomes relatively more energetic, and more efficient in the production of coherent Reynolds stress.

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