scholarly journals Acoustic Modeling and Vibration Characteristics of Supersonic Inlet Buzz

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 2048
Author(s):  
Jianfeng Zhu ◽  
Wenguo Luo ◽  
Yuqing Wei ◽  
Cheng Yan ◽  
Yancheng You
Keyword(s):  
Numerical Simulations ◽  
Pressure Oscillation ◽  
Resonant Mode ◽  
Acoustic Model ◽  
Oscillation System ◽  
Nonlinear Simulation ◽  
Supersonic Inlet ◽  
Nonlinear Amplification ◽  
Oscillation Damping ◽  
The Ideal

The buzz phenomenon of a typical supersonic inlet is analyzed on the basis of numerical simulations and duct acoustic theory. Considering that the choked inlet could be treated as a duct with one end closed, a one-dimensional (1D) mathematical model based on the duct acoustic theory is proposed to describe the periodic pressure oscillation of the little buzz and the big buzz. The results of the acoustic model agree well with that of the numerical simulations and the experimental data. It could verify that the dominated oscillation patterns of the little buzz and the big buzz are closely related to the first and second resonant mode of the standing wave, respectively. The discrepancies between the numerical simulation and the ideal acoustic model might be attributed to the viscous damping in the fluid oscillation system. In order to explore the damping, a small perturbation jet is introduced to trigger the resonance of the buzz system and the nonlinear amplification effect of resonance might be helpful to estimate the damping. Through the comparison between the linear acoustic model and the nonlinear simulation, the calculated pressure oscillation damping of the little buzz and the big buzz are 0.33 and 0.16, which could be regarded as an estimation of real damping.

scholarly journals Pressure losses and oscillations in a compact valve of a steam turbine

2021 ◽  
Vol 345 ◽  
pp. 00027
Author(s):  
Václav Sláma ◽  
David Šimurda ◽  
Lukáš Mrózek ◽  
Ladislav Tajč ◽  
Jindřich Hála ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Pressure Oscillation ◽  
Operational Reliability ◽  
Operating Conditions ◽  
Steam Turbines ◽  
Valve Seat ◽  
Pressure Losses ◽  
Oscillation Analysis ◽  
Seat Angle ◽  
Wide Range

Characteristics of a new compact valve design for steam turbines are analysed by measuring pressure losses and oscillations on the valve model. It is the model of an intercept valve of the intermediate-pressure turbine part. This valve is relatively smaller hence cheaper than usual control and intercept valves. Besides, four different valve seat angles were tested in order to investigate the valve seat angle influence. In order to further clarify measured phenomena, the wide range of numerical simulations were also carried out. Measurements were performed in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences in an air test rig installed in a modular aerodynamic tunnel. Numerical simulations were performed in the Doosan Skoda Power Company using a package of ANSYS software tools. Measurement results are compared with numerical and generalized in the form of valve characteristics and pressure oscillation maps. As a result of the pressure loss analysis, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern compact valves are used. As a result of the pressure oscillation analysis, operating conditions at which dangerous flow instabilities can occur were identified. Thanks to this, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

Effects of Common Breaching Practices on the Overpressures Recorded Within the Stack

2014 ◽  
Author(s):  
Timothy J. Walilko
Keyword(s):  
Numerical Simulations ◽  
Free Field ◽  
Team Members ◽  
Current Limit ◽  
Blast Exposure ◽  
Total Impulse ◽  
Training Exercises ◽  
Operational Impact ◽  
Current Exposure ◽  
The Ideal

The objective of this paper is to provide useful information to both military and law enforcement dynamic entry teams for estimating the level of protection provided by their standard protective equipment and procedures. The procedures investigated include: the K-Equation for predicting safe standoff, the effects of stack spacing, and the effect of the orientation of the stack within the blast field on the breachers’ blast exposure. This investigation leveraged both experimental data gathered during explosive breaching training exercises (Breacher Consortium, 2011 - draft) and numerical simulations using the shock physics code CTH (McGlaun, 1990). The analysis revealed that the presence of objects within the blast range, including the other team members, significantly affected the individual’s exposure to the point that it sometimes exceeds current exposure recommendations. When each team member’s exposure was compared to the current limit of 4 psi (28 kPa), the average pressure from the gauges on the breacher helmets exceeded that level 43% of the time, and the averaged pressure at the shoulders exceeded the limit 50% of the time. In a comparison of the measured incident impulse energy to the maximum impulse energy predicted based on 4 psi peak pressure, the helmet impulse energy was exceeded 79% of the time and 64% of the time at the shoulders. Because the K-Equation was shown to be accurate in predicting the free-field pressure, these results and the output from the numerical simulations suggest that the stack and blanket do not provide the level of protection anticipated and that reducing the standoff distance, as prescribed by some protocols, is not justified. Ultimately, the operational impact of these results will depend on efforts to identify blast exposure injury thresholds. Since there is a direct relationship between the peak overpressure and total impulse to which the breaching team members in the stack are exposed, injury thresholds must reveal which component, pressure, impulse or a combination is more injurious. Based on whether pressure or impulse must be minimized, the ideal stack configuration can be calculated using the developed numerical model.

ON THE LOW-TEMPERATURE BEHAVIOR OF THE INFINITE-VOLUME IDEAL BOSE GAS

2010 ◽  
Vol 13 (01) ◽  
pp. 39-63
Author(s):  
KARL-HEINZ FICHTNER ◽  
KEI INOUE ◽  
MASANORI OHYA
Keyword(s):  
Low Temperature ◽  
Numerical Simulations ◽  
Bose Gas ◽  
Temperature Behavior ◽  
Infinite Volume ◽  
Position Distribution ◽  
Bounded Volume ◽  
Ideal Bose Gas ◽  
The Ideal

In Ref. 11 clustering representations of the position distribution of the ideal Bose gas were considered. In principle that gives rise to possibilities concerning simulations of the system of positions of the particles. But one has to take into account that in case of low temperature the clusters are very large and their origins are far from a fixed bounded volume. For that reason we will consider some estimations of the influence of these clusters on the behavior of the subsystem of particles located in a fixed bounded volume. All points in the fixed bounded volume come from a bigger volume which the estimation (5.2) in Theorem 5.2 gives on average. Several numerical simulations in dimension two are shown in Sec. 5.

Damping of Acoustic Waves in Pipelines due to End Conditions

2013 ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Acoustic Waves ◽  
Wave Amplitude ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Structural Vibration ◽  
Acoustic Model ◽  
Simplified Models ◽  
Physical Behaviour ◽  
End Conditions ◽  
Simple Equations

Acoustic waves in pipelines are of concern because they can cause failure due to structural vibration and fatigue. The maximum wave amplitude that can be generated is limited by damping; a good understanding of damping is therefore vital. The damping considered here is due to the loss of energy from a resonant mode at a reflecting boundary. This type of damping is straightforward to analysis and consequently simple equations for damping are developed. A further aspect of damping is that it considerably modifies the description of acoustic resonance. The use of damped acoustic modes is shown to be problematic because they are complex and do not satisfy orthogonally conditions. A further and more significant observation is that damping prevents modes from being uncoupled and considered as independent. An uncoupled configuration is always found in undamped modes and is useful in forming simplified models however such uncoupling does not, in general, extend to damped modes. A condition for determining if modes can be uncoupled is derived. If a damped mode, which is not uncoupled, is used in an acoustic model it can generate energy as well as absorb energy. This non-physical behaviour greatly complicates the analysis of acoustic systems with damping.

Structures of reconnection layers based on the ideal magnetohydrodynamic equations

1994 ◽  
Vol 51 (3) ◽  
pp. 381-398
Author(s):  
Wenlong Dai ◽  
Paul R. Woodward
Keyword(s):  
Numerical Simulations ◽  
Quantitative Agreement ◽  
Mhd Equations ◽  
Riemann Solver ◽  
Magnetohydrodynamic Equations ◽  
One Dimensional ◽  
Ideal Mhd ◽  
Ideal Magnetohydrodynamic ◽  
The One ◽  
The Ideal

A Riemann solver is used, and a set of numerical simulations are performed, to study the structures of reconnection layers in the approximation of the one- dimensional ideal MHD equations. Since the Riemann solver may solve general Riemarin problems, the model used in this paper is more general than those in previous investigations on this problem. Under the conditions used in the previous investigations, the structures we obtained are the same. Our numerical simulations show quantitative agreement with those obtained through the Riemann solver.

Oscillation Damping Enhancement via Coordinated Design of PSS and FACTS-Based Stabilizers in a Multi-Machine Power System Using PSO

2010 ◽  
Vol 1 (3) ◽  
pp. 1-18 ◽  
Author(s):  
M. A. Abido ◽  
Saleh M. Bamasak
Keyword(s):  
Power System ◽  
Damping Ratio ◽  
Oscillation Mode ◽  
Low Frequency ◽  
Pso Algorithm ◽  
System Stability ◽  
Nonlinear Simulation ◽  
Low Frequency Power ◽  
Oscillation Damping ◽  
Power System Oscillations

This paper investigates the enhancement of power system stability via coordinated design of Power System Stabilizers (PSSs), Thyristor Controlled Series Capacitor (TCSC)-based stabilizer, and Static Var Compensator (SVC)-based stabilizer in a multi-machine power system. The design problem of the proposed stabilizers is formulated as an optimization problem. Using the developed linearized power system model, the particle swarm optimization (PSO) algorithm is employed to search for optimal stabilizer settings that maximize the minimum damping ratio of all system oscillating modes. The proposed stabilizers are evaluated on a two-area weakly-connected multi-machine power system with unstable interarea oscillation mode. The nonlinear simulation results and eigenvalue analysis show the effectiveness of the proposed coordinated stabilizers in damping low frequency power system oscillations and enhancing the system stability.

scholarly journals Regular and non-regular solutions of the Riemann problem in ideal magnetohydrodynamics

2012 ◽  
Vol 79 (3) ◽  
pp. 335-356 ◽  
Author(s):  
K. TAKAHASHI ◽  
S. YAMADA
Keyword(s):  
Numerical Simulations ◽  
Riemann Problem ◽  
Regular Solution ◽  
Initial Condition ◽  
Regular Solutions ◽  
Arbitrary Initial Condition ◽  
Standard Problem ◽  
Ideal Mhd ◽  
Ideal Magnetohydrodynamics ◽  
The Ideal

AbstractWe have built a code to numerically solve the Riemann problem in ideal magnetohydrodynamics (MHD) for an arbitrary initial condition to investigate a variety of solutions more thoroughly. The code can handle not only regular solutions, in which no intermediate shocks are involved, but also all types of non-regular solutions if any. As a first application, we explored the neighborhood of the initial condition that was first picked up by Brio and Wu (1988) (Brio, M. and Wu, C. C. 1988 An upwind differencing scheme for the equation of ideal magnetohydrodynamics. J. Comput. Phys. 75, 400–422) and has been frequently employed in the literature as a standard problem to validate numerical codes. Contrary to the conventional wisdom that there will always be a regular solution, we found an initial condition for which there is no regular solution but a non-regular one. The latter solution has only regular solutions in its neighborhood and actually sits on the boundary of regular solutions. This implies that the regular solutions are not sufficient to solve the ideal MHD Riemann problem and suggests that at least some types of non-regular solutions are physical. We also demonstrate that the non-regular solutions are not unique. In fact, we found for the Brio and Wu initial condition that there are uncountably many non-regular solutions. This poses an intriguing question: Why a particular non-regular solution is always obtained in numerical simulations? This has important ramifications to the discussion of which intermediate shocks are really admissible.

scholarly journals Geothermal response of a geothermal system for energy piles in a typical Brazilian tropical soil

2020 ◽  
Vol 205 ◽  
pp. 05005
Author(s):  
Roberto Pimentel de Sousa Júnior ◽  
Renato Pinto Cunha ◽  
Rideci de Jesus da Costa Farias
Keyword(s):  
Heat Exchange ◽  
Numerical Simulations ◽  
Federal District ◽  
Tropical Soil ◽  
Geothermal System ◽  
High Demand ◽  
Energy Piles ◽  
Long Time ◽  
Pile Caps ◽  
The Ideal

For a long time ago energy piles systems have been used for heating and/ or cooling purposes. The proposal of a conditioning system for closed environments that is economical and sustainable has drawn attention in Brazil, a country that is experiencing energy difficulties and have a high demand for thermal conditioning in most of its territory. Different configurations of foundation blocks were simulated, and an extensive geological-geotechnical survey of the soil chosen as representative of the Federal District, allowed the calculation of the thermal parameters of this soil. With these parameters the next step were the numerical simulations, the aim of this paper, which varied the foundations with the number of pile caps, piles diameter and turns in the pipe, seeking the best configuration for the region studied. As a result of this work, it was concluded that for blocks with pile diameters of 30 and 40 cm, the ideal is the use of only two turns in the pipes for blocks with 4 or more piles, while for piles of 60 cm three turns in the pipe generates a maximum exchange of heat. It is also concluded that the soil of the Federal District has a high potential for heat exchange.

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