Temporal instability modes of supersonic round jets

2010 ◽  
Vol 662 ◽  
pp. 173-196 ◽  
Author(s):  
LUIS PARRAS ◽  
STÉPHANE LE DIZÈS
Keyword(s):  
A Priori ◽  
Temporal Stability ◽  
Jet Noise ◽  
Base Flow ◽  
Round Jets ◽  
Instability Modes ◽  
Theoretical Predictions ◽  
Mode Characteristics ◽  
The Impact ◽  
Good Agreement

In this study, a comprehensive inviscid temporal stability analysis of a compressible round jet is performed for Mach numbers ranging from 1 to 10. We show that in addition to the Kelvin–Helmholtz instability modes, there exist for each azimuthal wavenumber three other types of modes (counterflow subsonic waves, subsonic waves and supersonic waves) whose characteristics are analysed in detail using a WKBJ theory in the limit of large axial wavenumber. The theory is constructed for any velocity and temperature profile. It provides the phase velocity and the spatial structure of the modes and describes qualitatively the effects of base-flow modifications on the mode characteristics. The theoretical predictions are compared with numerical results obtained for an hyperbolic tangent model and a good agreement is demonstrated. The results are also discussed in the context of jet noise. We show how the theory can be used to determine a priori the impact of jet modifications on the noise induced by instability.

scholarly journals The Mainz profile algorithm (MAPA)

2019 ◽  
Vol 12 (3) ◽  
pp. 1785-1806 ◽  
Author(s):  
Steffen Beirle ◽  
Steffen Dörner ◽  
Sebastian Donner ◽  
Julia Remmers ◽  
Yang Wang ◽  
...  
Keyword(s):  
A Priori ◽  
Scaling Factor ◽  
Least Square ◽  
Trace Gas ◽  
Vertical Profiles ◽  
Mixing Ratios ◽  
Surface Mixing ◽  
Sensitivity Studies ◽  
The Impact ◽  
Good Agreement

Abstract. The Mainz profile algorithm (MAPA) derives vertical profiles of aerosol extinction and trace gas concentrations from MAX-DOAS measurements of slant column densities under multiple elevation angles. This paper presents (a) a detailed description of the MAPA (v0.98), (b) results for the CINDI-2 campaign, and (c) sensitivity studies on the impact of a priori assumptions such as flag thresholds. Like previous profile retrieval schemes developed at MPIC, MAPA is based on a profile parameterization combining box profiles, which also might be lifted, and exponential profiles. But in contrast to previous inversion schemes based on least-square fits, MAPA follows a Monte Carlo approach for deriving those profile parameters yielding best match to the MAX-DOAS observations. This is much faster and directly provides physically meaningful distributions of profile parameters. In addition, MAPA includes an elaborated flagging scheme for the identification of questionable or dubious results. The AODs derived with MAPA for the CINDI-2 campaign show good agreement with AERONET if a scaling factor of 0.8 is applied for O4, and the respective NO2 and HCHO surface mixing ratios match those derived from coincident long-path DOAS measurements. MAPA results are robust with respect to modifications of the a priori MAPA settings within plausible limits.

scholarly journals Numerical Investigation of the Impact of H2 Enrichment on Lean Biogas/Air Flames: An Analytical Modelling Approach

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 369
Author(s):  
Filipe M. Quintino ◽  
Edgar C. Fernandes
Keyword(s):  
Laminar Flame ◽  
A Priori ◽  
Kinetic Mechanism ◽  
Laminar Flame Speed ◽  
Independent Variables ◽  
New Correlation ◽  
Dilution Effects ◽  
The Impact ◽  
Good Agreement ◽  
Modelling Approach

The transition from natural gas to renewable gases such as biogas and hydrogen creates an interchangeability challenge. The laminar flame speed SL is a critical parameter in appliance design as it is a unique characteristic of the flame mixture. It is thus essential to evaluate the impact of renewable gases on SL. In this work, 1D simulations were conducted in Cantera with the USC-Mech 2.0 kinetic mechanism. The SL of three base biogas blends (BG100, BG90 and BG80) was computed for H2 enrichment up to 50% in volume, equivalence ratio 0.8≤ϕ≤1.0, p=1 atm and Tu=298 K. It was found that the effect of H2 enrichment is higher for base blends with higher CO2 content as the thermal-diffusive and dilution effects of carbon dioxide are mitigated by hydrogen. The introduction of H2 also increases the H radical pool, which is linked with the increase in SL. A new correlation to model the impact of H2 enrichment, SL(xH2)=ζ(ϕ)/SL′(xCO2)xH2exH2+SL′(xCO2), is proposed, which exhibits good agreement with the literature data and simulations. This equation can be directly used to estimate SL without the need for a priori adaptations of fit parameters as the contributions of CO2 and H2 are isolated in independent variables.

scholarly journals Experiment and Analysis on the Free Dynamics of a Shallow Arch After an Impact Load at the End

2005 ◽  
Vol 72 (1) ◽  
pp. 54-61 ◽  
Author(s):  
Jen-San Chen ◽  
Chun-Yi Liao
Keyword(s):  
Transient Response ◽  
Impact Load ◽  
Minimum Energy ◽  
The Other ◽  
Initial Speed ◽  
Attached Mass ◽  
Shallow Arch ◽  
Theoretical Predictions ◽  
The Impact ◽  
Good Agreement

In this paper we consider a sinusoidal arch with one end pinned in space while the other end attached to a mass and supported by a spring. The supporting wall of the spring is moved a distance quasi-statically to initiate preload in the arch and the spring. The assembly is then set in motion by an impact at the attached mass. The condition under which the arch may snap to the other side dynamically depends on the initial speed of the attached mass due to impact. Sufficient condition on the initial speed against dynamic snap-through is formulated based on the concept of minimum energy barrier. The effects of damping on the transient response of the assembly are also discussed. An experimental setup is designed to measure the transient response of the arch following the impact and the critical initial speed of the attached mass. The experimental results are in good agreement with theoretical predictions.

Safety considerations on teenage pedestrian–bus impact

2019 ◽  
Vol 233 (14) ◽  
pp. 3839-3856
Author(s):  
Salvatore Golfo ◽  
Gabriele Virzì Mariotti ◽  
Filippo Carollo ◽  
Antonella Argo ◽  
Gabriele Barbaraci
Keyword(s):  
Thoracic Trauma ◽  
A Priori ◽  
Chest Injury ◽  
Abbreviated Injury Scale ◽  
Head Injury Criterion ◽  
Vehicle Mass ◽  
Biomechanical Parameters ◽  
Safety Considerations ◽  
The Impact ◽  
Good Agreement

This work studies the impact conditions between the adolescent pedestrian and the bus focusing on head and chest injury. The injury to the head is analyzed using both the Head Injury Criterion (HIC) 36 and the HIC15 parameters as established by the most advanced legislation and comparing the risk probability Abbreviated Injury Scale (AIS3+) and AIS4+. The parameter HIC15 gives a higher probability of risk with lower values, and therefore it can be considered more conservative. Moreover, the study of chest injury is performed with two different biomechanical parameters: the Thoracic Trauma Index (TTI) and the TTI(d); the last neglects the pedestrian mass. The results indicate that the parameters are equivalent for the assessment of chest injury. Instead the front pedestrian collision is characterized by 3 ms criterion. The results comparison with those obtained previously with other types of vehicles shows that, in all cases, the impact with the bus is most dangerous for the teenage pedestrian because of the higher values of the biomechanical parameters. Finally, the influence of the vehicle mass has been investigated, emphasizing how it cannot be neglected a priori. Numerical analysis results are in very good agreement with the results carried out experimentally, from several authors, in real accidents where buses are involved.

Movement characteristics analysis of bi-directional friction linear micro-motor driven by a set of micro-actuator

2021 ◽  
pp. 2140013
Author(s):  
Zhenlu Wang ◽  
Jiue Zhang ◽  
Shuxia Ma ◽  
Guangqiao Liu
Keyword(s):  
Driving Frequency ◽  
Dynamics Model ◽  
Motion Direction ◽  
Movement Characteristics ◽  
Theoretical Predictions ◽  
Characteristics Analysis ◽  
Directional Motion ◽  
The Impact ◽  
Theoretical Results ◽  
Good Agreement

In this paper, a bi-directional friction linear micro-motor (BFLM) driven by a set of micro-actuators was introduced and analyzed. The BFLM was fabricated using PolyMUMPs process. The impact dynamics model for the BFLM was established, and its motion equation was also derived that takes into account the friction and contact. The relative motion between the driving head and the slider, as well as forward or backward movement of the slider were analyzed in detail. The forward and backward movement displacement of the slider was measured, and the experimental results were in good agreement with theoretical predictions. The theoretical results show that the motion direction of the slider can be changed by controllable driving frequency to the BFLM. It was feasible to use a set of actuators to drive the slider in bi-directional motion.

scholarly journals The Mainz Profile Algorithm (MAPA)

2018 ◽  
Author(s):  
Steffen Beirle ◽  
Steffen Dörner ◽  
Sebastian Donner ◽  
Julia Remmers ◽  
Yang Wang ◽  
...  
Keyword(s):  
A Priori ◽  
Scaling Factor ◽  
Trace Gas ◽  
Aerosol Extinction ◽  
Vertical Profiles ◽  
Mixing Ratios ◽  
Surface Mixing ◽  
Sensitivity Studies ◽  
The Impact ◽  
Good Agreement

Abstract. The Mainz profile algorithm MAPA derives vertical profiles of aerosol extinction and trace gas concentrations from MAX-DOAS measurements of slant column densities under multiple elevation angles. This manuscript presents (a) a detailed description of the MAPA algorithm v0.98, including the flagging scheme for the identification of questionable or dubious results, (b) results for the CINDI-2 campaign, and (c) sensitivity studies on the impact of a-priori assumptions such as flag thresholds. MAPA is based on a profile parameterization combining box profiles, which also might be lifted, and exponential profiles. The profile parameters yielding best match to the MAX-DOAS observations are derived by a Monte Carlo approach, making MAPA much faster than previous parameter-based inversion schemes, and directly providing distributions of profile parameters. The AODs derived with MAPA for the CINDI-2 campaign show good agreement to AERONET if a scaling factor of 0.8 is applied for O4, and the respective NO2 and HCHO surface mixing ratios match those derived from coincident long-path DOAS measurements. MAPA results are robust to modifications of the a-priori MAPA settings within plausible limits.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Instability and Collapse in Discrete Wave Equations

2005 ◽  
Vol 5 (3) ◽  
pp. 223-241
Author(s):  
A. Carpio ◽  
G. Duro
Keyword(s):  
Continuum Limit ◽  
Wave Equations ◽  
Numerical Solutions ◽  
Blow Up ◽  
Theoretical Predictions ◽  
Initial States ◽  
The Impact ◽  
The Continuum

AbstractUnstable growth phenomena in spatially discrete wave equations are studied. We characterize sets of initial states leading to instability and collapse and obtain analytical predictions for the blow-up time. The theoretical predictions are con- trasted with the numerical solutions computed by a variety of schemes. The behavior of the systems in the continuum limit and the impact of discreteness and friction are discussed.

The Impact of Competitive Quasi-Market on Service Delivery in Benue State University, Makurdi Nigeria

GIS Business ◽  
2019 ◽  
Vol 14 (4) ◽  
pp. 85-98
Author(s):  
Idoko Peter
Keyword(s):  
Service Delivery ◽  
A Priori ◽  
Least Square ◽  
Secondary Source ◽  
State University ◽  
Ordinary Least Square ◽  
Negative Effect ◽  
The Impact ◽  
The Relationship

This research the impact of competitive quasi market on service delivery in Benue State University, Makurdi Nigeria. Both primary and secondary source of data and information were used for the study and questionnaire was used to extract information from the purposively selected respondents. The population for this study is one hundred and seventy three (173) administrative staff of Benue State University selected at random. The statistical tools employed was the classical ordinary least square (OLS) and the probability value of the estimates was used to tests hypotheses of the study. The result of the study indicates that a positive relationship exist between Competitive quasi marketing in Benue State University, Makurdi Nigeria (CQM) and Transparency in the service delivery (TRSP) and the relationship is statistically significant (p<0.05). Competitive quasi marketing (CQM) has a negative effect on Observe Competence in Benue State University, Makurdi Nigeria (OBCP) and the relationship is not statistically significant (p>0.05). Competitive quasi marketing (CQM) has a positive effect on Innovation in Benue State University, Makurdi Nigeria (INVO) and the relationship is statistically significant (p<0.05) and in line with a priori expectation. This means that a unit increases in Competitive quasi marketing (CQM) will result to a corresponding increase in innovation in Benue State University, Makurdi Nigeria (INVO) by a margin of 22.5%. It was concluded that government monopoly in the provision of certain types of services has greatly affected the quality of service experience in the institution. It was recommended among others that the stakeholders in the market has to be transparent so that the system will be productive to serve the society effectively

Dynamic model for high-speed rotors based on their experimental characterization

2017 ◽  
Vol 2 (4) ◽  
pp. 25
Author(s):  
L. A. Montoya ◽  
E. E. Rodríguez ◽  
H. J. Zúñiga ◽  
I. Mejía
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Experimental Characterization ◽  
Rotating Systems ◽  
Computing Performance ◽  
The Impact ◽  
Stiffness Distribution ◽  
Good Agreement

Rotating systems components such as rotors, have dynamic characteristics that are of great importance to understand because they may cause failure of turbomachinery. Therefore, it is required to study a dynamic model to predict some vibration characteristics, in this case, the natural frequencies and mode shapes (both of free vibration) of a centrifugal compressor shaft. The peculiarity of the dynamic model proposed is that using frequency and displacements values obtained experimentally, it is possible to calculate the mass and stiffness distribution of the shaft, and then use these values to estimate the theoretical modal parameters. The natural frequencies and mode shapes of the shaft were obtained with experimental modal analysis by using the impact test. The results predicted by the model are in good agreement with the experimental test. The model is also flexible with other geometries and has a great time and computing performance, which can be evaluated with respect to other commercial software in the future.

Sign in / Sign up

Export Citation Format

Share Document