scholarly journals Budgets of Disturbances Energy for Nozzle Flows at Subsonic and Choked Regimes

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Maxime Huet
Keyword(s):  
Acoustic Energy ◽  
Energy Budgets ◽  
Steady Flows ◽  
Test Rig ◽  
Transmission And Reflection Coefficients ◽  
Energetic Approach ◽  
Acoustic Fluctuations ◽  
Nozzle Flows ◽  
Transmission And Reflection ◽  
Good Agreement

The noise generated by the passage of acoustic and entropy perturbations through subsonic and choked nozzle flows is investigated numerically using an energetic approach. Low-order models are used to reproduce the experimental results of the hot acoustic test rig (HAT) of Deutsches Zentrum für Luft- und Raumfahrt (DLR), and energy budgets are performed to characterize the reflection, transmission, and dissipation of the fluctuations. Because acoustic and entropy perturbations are present in the flow in the general case, classical acoustic energy budgets cannot be used and the disturbances energy budgets proposed by Myers (1991, “Transport of Energy by Disturbances in Arbitrary Steady Flows,” J. Fluid Mech., 226, pp. 383–400.) are used instead. Numerical results are in very good agreement with the experiments in terms of acoustic transmission and reflection coefficients. The normal shock present in the diffuser for choked regimes is shown to attenuate the scattered acoustic fluctuations, either by pure dissipation effect or by converting a part of the acoustic energy into entropy fluctuations.

scholarly journals Budgets of Disturbances Energy for Nozzle Flows at Subsonic and Choked Regimes

2017 ◽  
Author(s):  
Maxime Huet
Keyword(s):  
Acoustic Energy ◽  
Energy Budgets ◽  
Acoustic Transmission ◽  
Test Rig ◽  
Transmission And Reflection Coefficients ◽  
Energetic Approach ◽  
Acoustic Fluctuations ◽  
Nozzle Flows ◽  
Transmission And Reflection ◽  
Good Agreement

The noise generated by the passage of acoustic and entropy perturbations through subsonic and choked nozzle flows is investigated numerically using an energetic approach. Low-order models are used to reproduce the experimental results of the Hot Acoustic Test rig (HAT) of DLR and energy budgets are performed to characterize the reflection, transmission and dissipation of the fluctuations. Because acoustic and entropy perturbations are present in the flow in the general case, classical acoustic energy budgets cannot be used and the disturbances energy budgets proposed by Myers (J. Fluid Mech. 226 (1991) 383–400) are used instead. Numerical results are in very good agreement with the experiments in terms of acoustic transmission and reflection coefficients. The normal shock present in the diffuser for choked regimes is shown to attenuate the scattered acoustic fluctuations, either by pure dissipation effect or by converting a part of the acoustic energy into entropy fluctuations.

scholarly journals Optically Transparent Metasurface Absorber Based on Reconfigurable and Flexible Indium Tin Oxide Film

Micromachines ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1032
Author(s):  
Lei Chen ◽  
Ying Ruan ◽  
Si Si Luo ◽  
Fu Ju Ye ◽  
Hao Yang Cui
Keyword(s):  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Air Permeability ◽  
Ultra Wideband ◽  
Reflection Coefficients ◽  
Transmission And Reflection Coefficients ◽  
Ito Film ◽  
Optically Transparent ◽  
Transmission And Reflection ◽  
Good Agreement

In this paper, we present a flexible, breathable and optically transparent metasurface with ultra-wideband absorption. The designed double layer of indium tin oxide (ITO) films with specific carved structure realizes absorption and electromagnetic (EM) isolation in dual-polarization, as well as good air permeability. Under the illumination of x- and y-polarization incidence, the metasurface has low reflectivity and transmission from about 2 to 18 GHz. By employing ITO film based on polyethylene terephthalate (PET), the presented metasurface also processes the excellent flexibility and optically transparency, which can be utilized for wearable device application. In addition, the dual-layer design enables mechanically-reconfigurable property of the metasurface. The transmission and reflection coefficients in two polarizations show distinct difference when arranging the different relevant positions of two layers of the metasurface. A sample with 14*14 elements is designed, fabricated and measured, showing good agreement with the simulation results. We envision this work has various potentials in the wearable costume which demands both EM absorption and isolation.

Transformation of internal waves passing over a bottom step

2015 ◽  
Vol 768 ◽  
Author(s):  
Egor N. Churaev ◽  
Sergey V. Semin ◽  
Yury A. Stepanyants
Keyword(s):  
Internal Waves ◽  
Density Ratio ◽  
Numerical Data ◽  
Wave Transformation ◽  
Reflection Coefficients ◽  
Approximate Theory ◽  
Transmission And Reflection Coefficients ◽  
Transmission And Reflection ◽  
Good Agreement ◽  
Bottom Step

The transformation of small-amplitude internal waves on the oceanic shelf is studied numerically. The transmission and reflection coefficients are found for the simplified step-wise model of the oceanic shelf in a two-layer fluid. The approximate formulae are proposed for the transformation coefficients as functions of incident wavenumber, density ratio of layers, depth of the pycnocline and height of the bottom step. Results of direct numerical modelling of internal wave transformation are obtained and presented as functions of all aforementioned parameters. It is shown that there is a good agreement between the outcomes of approximate theory and numerical data. Both the theoretical and the numerical results agree well with the law of energy flux conservation.

Transmission and reflection of Rayleigh wave through a step

1977 ◽  
Vol 67 (5) ◽  
pp. 1277-1290
Author(s):  
L. Martel ◽  
M. Munasinghe ◽  
G. W. Farnell
Keyword(s):  
Rayleigh Wave ◽  
Phase Shifts ◽  
Body Waves ◽  
Reflected Wave ◽  
Homogeneous Half Space ◽  
Transmission And Reflection Coefficients ◽  
Group Delays ◽  
Seismic Models ◽  
Transmission And Reflection ◽  
Good Agreement

abstract The transmission and reflection of a Rayleigh wave through a step on a homogeneous half-space of Poisson's ratio σ = 0.253 have been investigated by a seismic models method. The experimental results show good agreement with numerical ones obtained by finite-difference calculations when the wave is incident onto a downward step. Phase shifts are given both for the upward and downward steps. The characteristics of the transmitted wave do not depend much on the direction of propagation but those of the reflected wave are clearly direction-dependent. In each case the transmission and reflection coefficients and phase shifts depend on the ratio of step height to wavelength. The group delays are calculated and they are positive or negative depending on the period. About 80 per cent of the incident energy is converted into body waves when the step is higher than 0.3 times the wavelength of the Rayleigh wave.

scholarly journals Transmission, Reflection and Dissipation of Microwaves in Magnetic Composites with Nanocrystalline Finemet-Type Flakes

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3499
Author(s):  
Anatoly B. Rinkevich ◽  
Dmitry V. Perov ◽  
Yuriy I. Ryabkov
Keyword(s):  
Composite Material ◽  
Microwave Absorption ◽  
Nanocrystalline Alloy ◽  
Reflection Coefficients ◽  
Magnetic Composites ◽  
Transmission And Reflection Coefficients ◽  
Wave Interference ◽  
Microwave Losses ◽  
Frequency Dependences ◽  
Transmission And Reflection

The microwave properties of a composite material containing flakes of finemet-type nanocrystalline alloy placed in the epoxy matrix have been investigated. Two compositions have been studied: with 15% and 30% flakes. Frequency dependences of transmission and reflection coefficients are measured in the frequency range from 12 to 38 GHz. The dielectric permittivity and magnetic permeability are obtained, and the microwave losses are calculated. The dependences of transmission and reflection coefficients have been drawn as functions of wave frequency and thickness of the composite material, taking into account the frequency dependences of permittivity and permeability. The regions of maximal and minimal microwave absorption have been defined. The influence of wave interference on the frequency dependence of microwave absorption is studied.

scholarly journals Experimental and Numerical Investigation about Small Clearance Journal Bearings under Static Load Conditions

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Carlo Alberto Niccolini Marmont Du Haut Champ ◽  
Fabrizio Stefani ◽  
Paolo Silvestri
Keyword(s):  
Three Dimensional ◽  
Journal Bearings ◽  
Radial Clearance ◽  
Small Scale ◽  
Test Rig ◽  
Small Clearance ◽  
Dimensional Simulation ◽  
Dynamic Loading Conditions ◽  
Static And Dynamic Loading ◽  
Good Agreement

The aim of the present research is to characterize both experimentally and numerically journal bearings with low radial clearances for rotors in small-scale applications (e.g., microgas turbines); their diameter is in the order of ten millimetres, leading to very small dimensional clearances when the typical relative ones (order of 1/1000) are employed; investigating this particular class of journal bearings under static and dynamic loading conditions represents something unexplored. To this goal, a suitable test rig was designed and the performance of its bearings was investigated under steady load. For the sake of comparison, numerical simulations of the lubrication were also performed by means of a simplified model. The original test rig adopted is a commercial rotor kit (RK), but substantial modifications were carried out in order to allow significant measurements. Indeed, the relative radial clearance of RK4 RK bearings is about 2/100, while it is around 1/1000 in industrial bearings. Therefore, the same original RK bearings are employed in this new test rig, but a new shaft was designed to reduce their original clearance. The new custom shaft allows to study bearing behaviour for different clearances, since it is equipped with interchangeable journals. Experimental data obtained by this test rig are then compared with further results of more sophisticated simulations. They were carried out by means of an in-house developed finite element (FEM) code, suitable for thermoelasto-hydrodynamic (TEHD) analysis of journal bearings both in static and dynamic conditions. In this paper, bearing static performances are studied to assess the reliability of the experimental journal location predictions by comparing them with the ones coming from already validated numerical codes. Such comparisons are presented both for large and small clearance bearings of original and modified RKs, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance 8/1000), as expected. In comparison with two-dimensional lubrication analysis, three-dimensional simulation improves prediction of journal location and correlation with experimental results.

Analytical Study of Cylindrical P-Wave Propagation across Jointed Rock Masses

2014 ◽  
Vol 988 ◽  
pp. 502-507 ◽  
Author(s):  
Shao Bo Chai ◽  
Jian Chun Li ◽  
Hai Bo Li ◽  
Ya Qun Liu
Keyword(s):  
Wave Propagation ◽  
Rock Joint ◽  
Jointed Rock ◽  
P Wave ◽  
Displacement Discontinuity ◽  
Linear Elastic ◽  
Transmission And Reflection Coefficients ◽  
Conservation Of Momentum ◽  
Elastic Rock ◽  
Transmission And Reflection

According to the displacement discontinuity method and the conservation of momentum at the wave fronts, analysis for cylindrical P-wave propagation across a linear elastic rock joint is carried out. Considering the energy variation for wave propagation in one medium, the wave propagation equation was derived and expressed in an iterative form. The transmission and reflection coefficients are then obtained from the equation. By verification, the results agree very well with those from the existing results.

Structural Source Identification from Acoustic Measurements Using an Energetic Approach

2017 ◽  
Vol 34 (4) ◽  
pp. 431-441 ◽  
Author(s):  
A. Samet ◽  
M. A. Ben Souf ◽  
O. Bareille ◽  
M. N. Ichchou ◽  
T. Fakhfakh ◽  
...  
Keyword(s):  
Energy Method ◽  
Numerical Test ◽  
Acoustic Energy ◽  
Vibration Source ◽  
Radiated Noise ◽  
Acoustic Cavity ◽  
Energetic Approach ◽  
Structural Force ◽  
Noise Measurements ◽  
Acoustic Energy Density

AbstractAn inverse energy method for the identification of the structural force in high frequency ranges from radiated noise measurements is presented in this paper. The radiation of acoustic energy of the structure coupled to an acoustic cavity is treated using an energetic method called the simplified energy method. The main novelty of this paper consists in using the same energy method to solve inverse structural problem. It consists of localization and quantification of the vibration source through the knowledge of acoustic energy density. Numerical test cases with different measurement points are used for validation purpose. The numerical results show that the proposed method has an excellent performance in detecting the structural force with a few acoustical measurements.

Study of a synchronizer mechanism through multibody dynamic analysis

2018 ◽  
Vol 233 (6) ◽  
pp. 1601-1613 ◽  
Author(s):  
Ali Farokhi Nejad ◽  
Giorgio Chiandussi ◽  
Vincenzo Solimine ◽  
Andrea Serra
Keyword(s):  
Dynamic Model ◽  
Three Dimensional ◽  
Time Estimation ◽  
Test Rig ◽  
Operational Conditions ◽  
Multibody Dynamic ◽  
Dynamic Analyses ◽  
Single Cone ◽  
Good Agreement ◽  
Numerical Approaches

The synchronizer mechanism represents the essential component in manual, automatic manual, and dual-clutch transmissions. This paper describes a multibody dynamic model for analysis of a synchronizer mechanism subjected to different operational conditions. The three-dimensional multi-dynamic model is developed to predict the dynamic response of synchronizer, especially for calculation of synchronization time. For the purpose of validation, three different synchronizers (single-cone, double-cone, and triple-cone synchronizers) were used on the test rig machine. For the purpose of synchronizing time estimation, an analytical formulation is proposed. The results of the analytical and multibody dynamic analyses were compared with the experimental data, showing a good agreement. The results of analytical and numerical approaches show that the predicted time of synchronization is more precise than previous works. A sensitivity analysis was performed on the single-cone synchronizer, and the effect of tolerance dimension on the dynamic behavior of the synchronizer was reported.

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