This document summarizes research on identifying sound sources and propagation in a supersonic jet. It first decomposes the jet flowfield into acoustic, hydrodynamic and vortical modes using Momentum Potential Theory. This identifies a coherent axial acoustic wavepacket in the jet core and shows fluctuating hydrodynamics interacting with vorticity as the dominant sound source. A novel Synchronized Large-Eddy Simulation technique then analyzes perturbation evolution, showing intermittent wavefronts and shifts to lower frequencies downstream, consistent with experiments. Future work will combine these methods to further study sound source characteristics and evolution of modes from specific forcing locations in the jet.
International Journal of Computational Engineering Research(IJCER)ijceronline
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology
Uma equipe de astrônomos norte-americanos descobriu o par de buracos negros supermassivos mais próximos até agora no universo.
O par de buracos negros está localizado no centro do quasar chamado de PKS 1302-102, a aproximadamente 3.5 bilhões de anos-luz de distância.
Esses dois buracos negros estão separados de apenas uma semana-luz e estão num movimento espiral um em direção ao outro que deve acabar com uma colisão cataclísmica.
Em contraste, o par de buracos negros mais próximos descoberto até então estava separado de aproximadamente 20 anos-luz.
Ultrasonic guided wave techniques have great potential for structural health monitoring applications. Appropriate mode and frequency selection is the basis for achieving optimised damage monitoring performance.
In this paper, several important guided wave mode attributes are
introduced in addition to the commonly used phase velocity and group velocity dispersion curves while using the general corrosion problem as an example. We first derive a simple and generic wave excitability function based on the theory of normal mode expansion and the reciprocity theorem. A sensitivity dispersion curve is formulated based on the group velocity dispersion curve. Both excitability and sensitivity dispersion curves are verified with finite element simulations. Finally, a
goodness dispersion curve concept is introduced to evaluate the tradeoffs between multiple mode selection objectives based on the wave velocity, excitability and sensitivity.
International Journal of Computational Engineering Research(IJCER)ijceronline
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology
Uma equipe de astrônomos norte-americanos descobriu o par de buracos negros supermassivos mais próximos até agora no universo.
O par de buracos negros está localizado no centro do quasar chamado de PKS 1302-102, a aproximadamente 3.5 bilhões de anos-luz de distância.
Esses dois buracos negros estão separados de apenas uma semana-luz e estão num movimento espiral um em direção ao outro que deve acabar com uma colisão cataclísmica.
Em contraste, o par de buracos negros mais próximos descoberto até então estava separado de aproximadamente 20 anos-luz.
Ultrasonic guided wave techniques have great potential for structural health monitoring applications. Appropriate mode and frequency selection is the basis for achieving optimised damage monitoring performance.
In this paper, several important guided wave mode attributes are
introduced in addition to the commonly used phase velocity and group velocity dispersion curves while using the general corrosion problem as an example. We first derive a simple and generic wave excitability function based on the theory of normal mode expansion and the reciprocity theorem. A sensitivity dispersion curve is formulated based on the group velocity dispersion curve. Both excitability and sensitivity dispersion curves are verified with finite element simulations. Finally, a
goodness dispersion curve concept is introduced to evaluate the tradeoffs between multiple mode selection objectives based on the wave velocity, excitability and sensitivity.
RADAR - RAdio Detection And Ranging
This is the Part 1 of 2 of RADAR Introduction.
For comments please contact me at solo.hermelin@gmail.com.
For more presentation on different subjects visit my website at http://www.solohermelin.com.
Part of the Figures were not properly downloaded. I recommend viewing the presentation on my website under RADAR Folder.
This is for student of geophysics who want to know about basic of multi component seismic. For further detail or any query you can drop me mail, my mail id id bprasad461@gmail.com
Filtering in seismic data processing? How filtering help to suppress noises. Haseeb Ahmed
To enhance the signal-Noise ratio different techniques are used to remove the noises.
Types of Seismic Filtering:
1- Frequency Filtering.
2- Inverse Filtering (Deconvolution).
3- Velocity Filtering.
Modeling Beam forming in Circular Antenna Array with Directional EmittersIJRESJOURNAL
ABSTRACT: The article discusses the functioning of the radio direction-finding and beamforming methods in the system of circular antenna arrays formed from the designed radiators, directional factor which is not equal to 1. Evaluation of forming of spatial pattern of cylindrical antenna array using phased method is fulfilled. DolphChebyshev window is used to reduce the side lobe level.
Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. The term vibration is precisely used to describe mechanical oscillation. Familiar examples of oscillation include a swinging pendulum and alternating current.
Oscillations occur not only in mechanical systems but also in dynamic systems in virtually every area of science: for example the beating of the human heart (for circulation), business cycles in economics, predator–prey population cycles in ecology, geothermal geysers in geology, vibration of strings in guitar and other string instruments, periodic firing of nerve cells in the brain, and the periodic swelling of Cepheid variable stars in astronomy. Contents
A powerpoint for explaining damped oscillations and the equations associated with it. Includes a sample question in the powerpoint. For physics 101 learning object 2.
RADAR - RAdio Detection And Ranging
This is the Part 1 of 2 of RADAR Introduction.
For comments please contact me at solo.hermelin@gmail.com.
For more presentation on different subjects visit my website at http://www.solohermelin.com.
Part of the Figures were not properly downloaded. I recommend viewing the presentation on my website under RADAR Folder.
This is for student of geophysics who want to know about basic of multi component seismic. For further detail or any query you can drop me mail, my mail id id bprasad461@gmail.com
Filtering in seismic data processing? How filtering help to suppress noises. Haseeb Ahmed
To enhance the signal-Noise ratio different techniques are used to remove the noises.
Types of Seismic Filtering:
1- Frequency Filtering.
2- Inverse Filtering (Deconvolution).
3- Velocity Filtering.
Modeling Beam forming in Circular Antenna Array with Directional EmittersIJRESJOURNAL
ABSTRACT: The article discusses the functioning of the radio direction-finding and beamforming methods in the system of circular antenna arrays formed from the designed radiators, directional factor which is not equal to 1. Evaluation of forming of spatial pattern of cylindrical antenna array using phased method is fulfilled. DolphChebyshev window is used to reduce the side lobe level.
Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. The term vibration is precisely used to describe mechanical oscillation. Familiar examples of oscillation include a swinging pendulum and alternating current.
Oscillations occur not only in mechanical systems but also in dynamic systems in virtually every area of science: for example the beating of the human heart (for circulation), business cycles in economics, predator–prey population cycles in ecology, geothermal geysers in geology, vibration of strings in guitar and other string instruments, periodic firing of nerve cells in the brain, and the periodic swelling of Cepheid variable stars in astronomy. Contents
A powerpoint for explaining damped oscillations and the equations associated with it. Includes a sample question in the powerpoint. For physics 101 learning object 2.
Karakteristik transistor disajikan dengan kurva karakteristik yang menggambarkan kerja transistor. Satu cara untuk melihat sebanyak mungkin detail adalah dengan grafik yang menggambarkan hubungan arus dan tegangan
P-Wave Onset Point Detection for Seismic Signal Using Bhattacharyya DistanceCSCJournals
In seismology Primary p-wave arrival identification is a fundamental problem for the geologist worldwide. Several numbers of algorithms that deal with p-wave onset detection and identification have already been proposed. Accurate p- wave picking is required for earthquake early warning system and determination of epicenter location etc. In this paper we have proposed a novel algorithm for p-wave detection using Bhattacharyya distance for seismic signals. In our study we have taken 50 numbers of real seismic signals (generated by earthquake) recorded by K-NET (Kyoshin network), Japan. Our results show maximum standard deviation of 1.76 sample from true picks which gives better accuracy with respect to ratio test method.
Directional Spreading Effect on a Wave Energy ConverterElliot Song
The results demonstrate the importance of tuning the WEC system for specific wave environments to harvest most energy and to avoid potential capsize due to hurricanes etc.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
Radio signal from extensive air showers EAS studied by the CODALEMA experiment have been detected by means of the classic short fat antennas array working in a slave trigger mode by a particle scintillator array. It is shown that the radio shower wavefront is curved with respect to the plane wavefront hypothesis. Then a new tting model (parabolic model) is proposed to fit the radio signal time delay distributions in an event-by-event basis. This model take
into account this wavefront property and several shower geometry parameters such as: the existence of an apparent localised radio-emission source located at a distance Rc from the antenna array of and the radio shower core on the
ground. Comparison of the outputs from this model and other reconstruction models used in the same experiment show:
1)- That the radio shower core is shifted from the particle shower core in a statistic analysis approach.
2)- The capability of the radiodetection method to reconstruct the curvature radius with a statistical error less than 50 g.cm−2 .
Finally a preliminary study of the primary particle nature has been performed based on a comparison between data and Xmax distribution from Aires Monte-Carlo simulations for the same set of events.
A REVIEW OF FLOW ACOUSTIC EFFECTS ON A COMMERCIAL AUTOMOTIVE EXHAUST SYSTEMBarhm Mohamad
Acoustic simulation methods are being increasingly used for practical exhaust system design of automotive. In many practical applications, the sound source emits, partly, a low frequency sound spectrum comprised of superposed discrete tones and partly, a higher frequency broadband spectrum. The turbulent vortices that develop in the boundary layer between the duct wall and the flowing medium are said to generate a self-excited noise, that noise is broadband character. The self-excitation is enhanced when the flow is disturbed by irregularities in the duct wall. Unsteady compressible fluid flow through a duct is often encountered in many engineering applications and has been investigated by many researchers. When a pressure wave generated inside a duct is discharged from an open end of the duct, an impulsive wave that is usually characterized by high sound pressure level of short duration forms at the vicinity of the exit of the duct. Acoustic simulations solve the equations for motion, mass, momentum, and energy and can be divided into two methods, linear and non-linear. Through that literature review, we can analyse the methods and the latest development done on exhaust systems with regard to acoustic performance. The basic theory behind both approaches is explained as well as a source characterization technique that can be used to link the two methods. Some acoustic software tool has been applied to a variety of exhaust systems.
Periodic material-based vibration isolation for satellitesIJERA Editor
The vibration environment of a satellite is very severe during launch. Isolating the satellitevibrations during
launch will significantly enhance reliability and lifespan, and reduce the weight of satellite structure and
manufacturing cost. Guided by the recent advances in solid-state physics research, a new type of satellite
vibration isolator is proposed by usingperiodic material that is hence called periodic isolator. The periodic
isolator possesses a unique dynamic property, i.e., frequency band gaps. External vibrations with frequencies
falling in the frequency band gaps of the periodic isolator are to be isolated. Using the elastodynamics and the
Bloch-Floquet theorem, the frequency band gaps of periodic isolators are determined. A parametric study is
conducted to provide guidelines for the design of periodic isolators. Based on these analytical results, a finite
element model of a micro-satellite with a set of designed periodic isolators is built to show the feasibility of
vibration isolation. The periodic isolator is found to be a multi-directional isolator that provides vibration
isolation in the three directions.
Periodic material-based vibration isolation for satellitesIJERA Editor
The vibration environment of a satellite is very severe during launch. Isolating the satellitevibrations during
launch will significantly enhance reliability and lifespan, and reduce the weight of satellite structure and
manufacturing cost. Guided by the recent advances in solid-state physics research, a new type of satellite
vibration isolator is proposed by usingperiodic material that is hence called periodic isolator. The periodic
isolator possesses a unique dynamic property, i.e., frequency band gaps. External vibrations with frequencies
falling in the frequency band gaps of the periodic isolator are to be isolated. Using the elastodynamics and the
Bloch-Floquet theorem, the frequency band gaps of periodic isolators are determined. A parametric study is
conducted to provide guidelines for the design of periodic isolators. Based on these analytical results, a finite
element model of a micro-satellite with a set of designed periodic isolators is built to show the feasibility of
vibration isolation. The periodic isolator is found to be a multi-directional isolator that provides vibration
isolation in the three directions.
APPLICATION OF TAGUCHI METHOD FOR PARAMETRIC STUDIES OF A FUNNEL SHAPED STRUC...ijmech
In this paper, attempt has been made to minimize sound reflection from the wall by using Taguchi’s method and to find optimal structure for the suggested test-section inside the cavitation tunnel. The suggested structure which was added to the test-section is funnel-shaped with a performance like a check valve. In order to obtain approximate values of five independent parameters, three levels were taken into account for each parameter. By combining parameters of different levels, 27 tests were designed using Taguchi’s method and Minitab Software. Different acoustic analyses were conducted in COMSOL Multiphysics software, and defined parameter of general reflection coefficient was obtained for 21 observer points. Applying the general reflection coefficients to Minitab Software and drawing the SNR graph, approximate values of the parameters were obtained. However, these values did not produce enough accuracy to design the optimal structure. For this reason, five levels around optimal values, obtained from the previous analysis, were considered for each parameter. Same steps were repeated again for the parameters at five
levels and optimal values were obtained. Optimal structure was modelled and analyzed. Consequently, appropriate defined parameters of general and local reflection coefficients were extracted which represented an optimal structure for the intended test section.
International Journal of Computational Engineering Research(IJCER)ijceronline
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology.
Effect o f boundary layer and rotor speed on broadband noise from horizontal ...vasishta bhargava
In this paper, the effect of rotor speed and boundary layer on the broadband noise from wind turbines are discussed. The results from the computations have been validated using the far field acoustic measurements from a similar sized turbine
This study deals with the active control of the dynamic response of a string with fixed ends and mass
loaded by a point mass. It has been controlled actively by means of a feed forward control method. A point mass of a
string is considered as a vibrating receiver which be forced to vibrate by a vibrating source being positioned on the
string. By analyzing the motion of a string, the equation of motion for a string was derived by using a method of
variation of parameters. To define the optimal conditions of a controller, the cost function, which denotes the dynamic
response at the point mass of a string was evaluated numerically. The possibility of reduction of a dynamic response
was found to depend on the location of a control force, the magnitude of a point mass and a forcing frequency
This project is about the seismic wave signal Parameter enhancement with vibration analysis and
geomagnetic signal anomalies. In this project, we are going to detect the seismic signal using seismograph. The
ghosting effects were occurring and it will be suppressed using the filters. We propose to show the benefit of 1D
convolutional filter, to remove all the non-energetic wave-field in order to provide a better imaging of the
reflecting wave-field. In this paper, wave signals are decomposed into intrinsic (characteristic) modes via Discrete
Wavelet Transform [4] (DWT), Empirical Mode Decomposition [1] (EMD) and the relationship between seismic
activities are investigated.
Time domain sound spectrum measurements in ducted 2 cm
RESEARCHSTATEMENT_2016
1. Noise source-identification and propagation in a supersonic jet
1 Introduction
Jet noise is a major nuisance, especially near airports and on aircraft carriers. Sustained exposure
to high noise levels constitute health hazards to crew and results in environmental impact and dis-
ruption of the community near airports. Despite decades of research, the fundamental mechanism
by which the turbulent energy is filtered into acoustic energy through non-linear processes remains
unknown. This is a physical ramification of the non-linearity in the governing laws of fluid flows -
the Navier–Stokes equations (NSE). A satisfactory theory of sound genesis will provide scientific
insight and aid exploration of control techniques.
In order to better understand these non-linear interactions and identify sound sources, we an-
alyze a jet by decomposing its flowfield into the constituent modes – acoustic, hydrodynamic and
vortical, the results of which are discussed in Section 2. For this, we use the Momentum Potential
Theory (MPT), put forward by Doak (1989). Further, to understand the transport of acoustic en-
ergy into the farfield of the jet, we characterize the evolution of small perturbations in this turbulent
flow using a novel technique called Synchronized Large-Eddy Simulation (SLES) which solves the
full 3D, compressible, unsteady Navier-stokes equations (Section 3). Results to date have analyzed
a supersonic cold air-jet with a nozzle-exit Mach number of 1.3.
2 Mode decomposition and sound-sources of the jet – MPT
The flowfield of the turbulent jet is highly complex, with a broad range of spatio-temporal scales,
as can be seen in Fig. 1(a). The governing NSE do not split the different forms of energy, which
1
2. Figure 1: (a) Complex flowfield of the jet, (b) Hydrodynamic mode, (c) Acoustic mode with
wavepacket-nature, (d) Radiation from the acoustic wavepacket.
inhibits clarity in understanding the acoustic dynamics. To resolve this, we have applied for the
first time (Unnikrishnan and Gaitonde (2016a)), the decomposition proposed by Doak (1989). The
momentum density of the jet ρu, (where ρ is the fluid-density and u is the particle velocity vector)
is split as; ρu = B+B − ψA − ψT . B is the mean hydrodynamic, B is the fluctuating hydro-
dynamic component and, − ψAand − ψT are the fluctuating acoustic and thermal components
respectively. The hydrodynamic component is defined as the divergence-free part of ρu and the
acoustic and thermal components are irrotational.
The magnitude of the hydrodynamic mode (||B ||) in (b) highlights the shear-layer growth of
the jet and the roll-up of vortices. The acoustic-mode component (−∂ψA/∂x) in (c) captures (for
the first time in published literature) a well-defined axial wavepacket in the highly turbulent core
of the jet. This coherent form of the acoustic mode is significant, since the acoustic dynamics of
the jet are better represented here and this wavepacket can be reproduced to model sound radiation.
The highly-directional downstream sound radiation induced by this wavepacket is shown in (d).
2
3. Figure 2: (a) Schematic of sound-source mechanism, (b) Time-averaged behavior of sound-source.
Upon further analyzing Doak’s theory, the interaction of the fluctuating hydrodynamic mode
B with fluctuating Coriolis acceleration (ω × u) , (where ω = × u is the vorticity, defined
as the curl of velocity vector) was found to be the most significant acoustic source mechanism
of the jet. The schematic in Fig. 2(a) summarizes this source mechanism; whenever rolled-up
vortices from the shear-layer of the jet intrude into its high-speed core, the local total-enthalpy H
(H = cpT + u.u/2, where cp is the specific heat at constant pressure and T is the temperature)
surges, and these fluctuations in total enthalpy H , are carried away by the momentum fluctuations
(ρu) , resulting in the acoustic-energy-flux from the jet. The time-averaged behavior of this source
mechanism, −B .(ω×u) in (b) identifies the prominent sound-source region to be within the
lipline of the jet (marked by the dotted line). The peak source-values are observed along the
center-region of the inner shear-layer, between two to seven jet-diameters in the axial direction.
Significance of the method: By focusing on the decomposed fields, this analysis has identified
the prominent features of the acoustic mode, and how it derives its energy to radiate sound.
3 Perturbation evolution in the turbulent jet – SLES
As mentioned in the introduction, the identification of sound-source mechanism was followed by
development of a novel technique to study small-perturbation evolution in the jet. The idea is
3
4. Figure 3: (a) Forcing location in the twin simulation, Instantaneous visualization of (b) Basline,
(c) Twin and (d) Perturbation-field of the jet.
to understand how the turbulence filters and modulates signals from the core of the jet to yield
its observed acoustic signature. Traditional methods study propagation of perturbations in a time-
invariant mean base flow by linearizing the NSE. Here, we use two synchronous full Navier-Stokes
simulations - a baseline and a twin, to propagate the perturbations in the time-dependent evolving
turbulent flow (Unnikrishnan and Gaitonde (2016b)). The twin simulation is forced at a select
location using the signal from the baseline at the corresponding location and the difference between
the two simulations is obtained. This difference-field (denoted perturbation-field) shows the effect
of the forcing on the instantaneous flow, yielding insight into jet-noise directivity and intermittency.
Several insights were obtained by studying perturbations evolving from the core of the jet.
Figure 3(a) schematically shows the forcing location of the twin, point A. The background contours
of time-averaged streamwise velocity show the high-speed jet-core and the developing shear-layer
surrounding it. An instantaneous snapshot of the baseline and twin simulations are shown in (b)
and (c) respectively. Although they appear similar at this level, their difference in (d) indicates how
the forcing at point A evolved into the perturbation-field in the turbulent flow.
Looking at more details, the perturbation-field in Fig. 4(a) shows the effects of forcing at
4
5. Figure 4: (a) Perturbation field of the jet, Time-frequency analysis of the perturbation field at P1
(b) and P2 (c).
point A, leading to intermittent wavefronts in the nearfield of the jet, and secondary downstream
amplification (between x = 15 and x = 20). An analysis of the time-frequency properties of the
perturbation-field at two points P1 (sideline) in (b) and P2 (downstream) in (c) indicates well-
defined intermittent events. (St, Strouhal is the non-dimensional frequency). For e.g., the sideline
signals are dominated by high-frequency content as marked by the dotted curve in (b). Conversely,
high-energy shifts to lower frequencies in the downstream direction which shows peak acoustic
radiation in jets. These results are consistent with experimental observations (Tam, 1995; Tam et
al., 2008). Significance of the method: The current technique provides information on sound
directivity and farfield signature without simplifications associated with mean-flow analyses and
localizes the effect of specific regions in the core on the acoustic signature of the jet.
Future work will combine the two methods described above– MPT and SLES to study evolution
of each mode from specific forcing locations in the jet, by applying Doak’s decomposition to
the perturbation-field obtained from SLES. The sound-source and nearfield characteristics of the
modes have to be then analyzed using statistical tools. Finally, these techniques would be applied
to subsonic, heated and coaxial jets, which mimic real-life aircraft-engine-exhaust configurations.
5
6. References
Doak, P. E. (1989). Momentum potential theory of energy flux carried by momentum fluctuations.
Journal of sound and vibration, 131(1), 67–90.
Tam, C. K. W. (1995). Supersonic jet noise. Annual Review of Fluid Mechanics, 27(1), 17–43.
Tam, C. K. W., Viswanathan, K., Ahuja, K. K., & Panda, J. (2008). The sources of jet noise:
experimental evidence. Journal of Fluid Mechanics, 615, 253–292.
Unnikrishnan, S., & Gaitonde, D. V. (2016a). Acoustic, hydrodynamic and thermal modes in a
supersonic cold jet. Journal of Fluid Mechanics, 800, 387–432.
Unnikrishnan, S., & Gaitonde, D. V. (2016b). A high-fidelity method to analyze perturbation
evolution in turbulent flows. Journal of Computational Physics.
6