Acoustic pressure oscillations in the decay envelope of the initial shock radiated by an underwater explosion

2021 ◽  
Vol 150 (4) ◽  
pp. A114-A114
Author(s):  
Andrew R. McNeese ◽  
Preston S. Wilson ◽  
David P. Knobles ◽  
Peter H. Dahl ◽  
David Dall'Osto ◽  
...  
Keyword(s):  
Acoustic Pressure ◽  
Underwater Explosion ◽  
Pressure Oscillations ◽  
Initial Shock

scholarly journals Investigation on Acoustic Properties of Thruster Chamber with Coaxial Injectors and Plenum Chamber

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Dekun Gao ◽  
Jianxiu Qin ◽  
Huiqiang Zhang
Keyword(s):  
Acoustic Pressure ◽  
Rocket Engine ◽  
Pressure Oscillation ◽  
Acoustic Mode ◽  
Acoustic Properties ◽  
Pressure Oscillations ◽  
Plenum Chamber ◽  
Model Chamber ◽  
Pressure Peak ◽  
Tuning Frequency

Based on the URANS equation, a numerical simulation is carried out for acoustic properties of the thruster chamber with coaxial injectors and plenum chamber in a liquid rocket engine. Pressure oscillations with multiacoustic modes are successfully excited in the chamber by using the constant volume bomb method. FFT analysis is applied to obtain the acoustic properties of eigenfrequencies, power amplitudes, and damping rates for each excited acoustic mode. Compared with the acoustic properties in the model chamber with and without an injector as well as with and without the plenum chamber, it can be found that the injector with one open end and one half-open end still can work as a quarter-wave resonator. The power amplitudes of the acoustic mode can be suppressed significantly when its eigenfrequency is close to the tuning frequency of the injector, which is achieved by Cutting down the pressure Peak and Raising up the pressure Trough (CPRT). Compared with the acoustic properties in the model chamber with and without the plenum chamber, it can be found that 1L acoustic pressure oscillation is inhibited completely by the plenum chamber and other acoustic pressure oscillations are also suppressed in a different extent. The injector and plenum chamber have a little effect on the eigenfrequencies and damping rate of each acoustic mode. For multimode pressure oscillation, it is better for tuning frequency of the injector closing to the lower eigenfrequency acoustic mode, which will be effective for suppression of these multiacoustic modes simultaneously.

scholarly journals Role of Shear Layer Instability in Driving Pressure Oscillations in a Backward Facing Step Combustor

2016 ◽  
Author(s):  
Srinivas K. Kirthy ◽  
Santosh Hemchandra ◽  
Seunghyuck Hong ◽  
Santosh Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Stability Analysis ◽  
Shear Layer ◽  
Acoustic Pressure ◽  
Combustion Instability ◽  
High Amplitude ◽  
Open Loop ◽  
Hydrodynamic Modes ◽  
Pressure Oscillations ◽  
Layer Mode ◽  
Low Amplitude

This paper presents a global hydrodynamic stability analysis of flow fields in a backward facing step combustor, assuming weakly non-parallel flow. The baseline experiments in a ‘long’ combustor of length of 5.0 m shows the presence of two combustion instability states characterized by coherent low and high amplitude acoustic pressure oscillations. The analysis is performed for Propane-air mixtures at three values of ϕ = 0.63, 0.72 and 0.85 which correspond to quiet, low amplitude and high amplitude instability states in the long combustor experiments. Base flow velocity and density fields for the hydrodynamic stability analysis are determined from time averaged PIV measurements made after the length of the duct downstream of the step has been shortened to eliminate acoustic pressure oscillations. The analysis shows that the shear layer mode is self-excited for the ϕ = 0.72 case with an oscillation frequency close to that of the long combustor’s fundamental acoustic mode. We show from an analysis of the weakly forced, variable density Navier-Stokes equations that self-excited hydrodynamic modes can be weakly receptive to forcing — suggesting that the low amplitude instability in the long combustor is due to semi-open loop forcing of heat release oscillations by the shear layer mode. At ϕ = 0.85 the flow is hydrodynamically globally stable but locally convectively unstable. Spatial amplification of velocity disturbances by the convectively unstable flow causes high amplitude combustion instability in the long combustor case. These results show that combustion instability can be sustained by acoustic and hydrodynamic modes being either strongly coupled, resulting in fully closed loop forcing, or weakly coupled, resulting in semi-open loop forcing of the flame by a self-excited hydrodynamic mode.

Finite Element Analysis of Subsea Pipelines Subjected to Underwater Explosion

2013 ◽  
Author(s):  
F. Van den Abeele ◽  
P. Verleysen
Keyword(s):  
Shock Wave ◽  
Finite Element ◽  
Transient Response ◽  
Acoustic Pressure ◽  
Underwater Explosion ◽  
Structural Response ◽  
Added Mass ◽  
Radiation Damping ◽  
Time Response ◽  
Subsea Pipelines

Underwater mines and explosives, left in ports and harbours after World War II, can still pose a threat to subsea pipelines. In case of an accidental explosion, or even during controlled detonation, such explosives can cause significant damage to subsea pipelines. To assess the safety of pipelines exposed to an underwater explosion, finite element analyses are performed to predict the transient response of the pipeline to an acoustic pressure shock wave. This type of problem is characterized by a strong coupling between the structural response of the pipe and the acoustic pressure on the wetted interface between the pipe surface and the surrounding seawater. The spherical pressure wave induced by an underwater explosion is characterized by a very steep wave front, where the maximum pressure is attained over an extremely short rise time. The pressure then drops off exponentially over a significantly longer period of time. As a result, the structural behaviour is a combination of a long time response, dominated by an added mass effect (low frequency), a short time response, governed by radiation damping (high frequency), and an intermediate time-frequency response, where both added mass and radiation damping effects are present. In this paper, a finite element model is presented to simulate the transient response of a subsea pipeline subjected to an underwater explosion. The close coupling between acoustic pressure and structural response gives rise to numerical challenges like the accurate formulation and representation of the shock wave, the mesh requirements for the acoustic domain, and the position of the surface based absorbing radiation boundaries. An explicit dynamic solver is used to tackle these challenges, and to predict the behaviour of subsea pipelines exposed to an underwater explosion. The numerical results are compared to published experimental data, and can be used to assess the safety of submerged pipelines in the vicinity of explosives.

scholarly journals Measuring the phase between fluctuating pressure and flame radiation intensity in a cylindrical combustion chamber

2019 ◽  
Author(s):  
S. Gröning ◽  
J.S. Hardi ◽  
D. Suslov ◽  
M. Oschwald
Keyword(s):  
Energy Transfer ◽  
Phase Shift ◽  
Heat Release ◽  
Acoustic Pressure ◽  
Dynamic Pressure ◽  
Rocket Engine ◽  
Pressure Sensors ◽  
Pressure Oscillations ◽  
Flame Radiation ◽  
Rate Oscillations

The energy transfer from the heat release of the combustion to the acoustic pressure oscillations is the driving element of combustion instabilities. This energy transfer is described by the Rayleigh criterion and depends on the phase shift between the pressure and heat release rate oscillations. A research rocket engine combustor, operated with the propellant combination hydrogen/oxygen, was equipped with dynamic pressure sensors and fibre optical probes to measure the flame radiation. This setup has been used for a phase shift analysis study which showed that unstable operation is characterized by a phase shift leading to an energy transfer from the heat release to the acoustic pressure oscillations.

scholarly journals Methane hydrogen laminar burning velocity blending laws in horizontal open-ended flame tube rig

2022 ◽  
Vol 1217 (1) ◽  
pp. 012013
Author(s):  
N A Amaludin ◽  
M Morrow ◽  
R Woolley ◽  
A E Amaludin
Keyword(s):  
Flame Propagation ◽  
Acoustic Pressure ◽  
Burning Velocity ◽  
Horizontal Tube ◽  
Hydrogen Gas ◽  
Hydrogen Fuel ◽  
Laminar Burning Velocity ◽  
Pressure Oscillations ◽  
Fuel Blends ◽  
Kinetics Of

Abstract Different fuel properties and chemical kinetics of two different fuels would make it challenging to predict the combustion parameters of a binary fuel. Understanding the effect of blending methane and hydrogen gas is the main focus of this paper. Utilizing a horizontal tube combustion rig, methane-hydrogen fuel blends were created using blending laws from past literature, over a range of equivalence ratios from 0.6 – 1.2 were studied, while keeping one combustion parameter constant, the theoretical laminar burning velocity. The selected theoretical laminar burning velocity for all the mixtures tested were kept constant at 0.6 ms−1. Different factors affected the flame propagation across the tube, including acoustic pressure oscillations, heat loss from the rig, and obvious difference in hydrogen percentage in the fuel blends. The average experimental laminar burning velocity of all the flames was 0.368 ms−1, compared to the expected value of 0.6 ms−1. In an attempt to keep the theoretical laminar burning velocity constant for different mixtures, it was discovered that this did not promise the same flame propagation behaviour for the tested mixtures. Further experimentation and analysis are required in order to better understand the underlying interaction of the fuel blends.

Acoustodynamics of the Longitudinal Collinear Impact of Finite Elastic Cylinders

1977 ◽  
Vol 99 (1) ◽  
pp. 144-150 ◽  
Author(s):  
G. Y. Matsumoto ◽  
W. J. Simpson
Keyword(s):  
Acoustic Pressure ◽  
Natural Frequencies ◽  
Acoustic Radiation ◽  
Pressure Measurements ◽  
Acceleration Response ◽  
Pressure Oscillations ◽  
Noise Pattern ◽  
Elastic Cylinders ◽  
The Impact ◽  
Free Plane

The acoustodynamics of finite elastic cylinders is examined both experimentally and theoretically to investigate the sources of noise generation associated with longitudinal, collinear impact. Analytical predictions are based on the assumption that the acoustic radiation is predominately derived from the acceleration response of the free, plane-end surfaces of the colliding bodies and consists of rigid-body deceleration and vibration “ringing” components. Those predictions are in excellent agreement with structural acceleration and acoustic pressure measurements obtained experimentally from two separate cylinder impact configurations, except for the presence of a single dominant noise pattern originating from the proximity of the impact surfaces. This unexpected noise consists of damped pressure oscillations at a frequency unrelated to any natural frequencies of the test apparatus. Its source can be traced to the injection of air into the region between the impact surfaces just following impact separation.

Sign in / Sign up

Export Citation Format

Share Document