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Joseph Majdalani - One of the best experts on this subject based on the ideXlab platform.
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nonlinear rocket motor stability prediction Limit Amplitude triggering and mean pressure shift
Physics of Fluids, 2007Co-Authors: Gary Flandro, Sean R Fischbach, Joseph MajdalaniAbstract:High-Amplitude pressure oscillations in solid propellant rocket motor combustion chambers display nonlinear effects including: 1) Limit cycle behavior in which the fluctuations may dwell for a considerable period of time near their peak Amplitude, 2) elevated mean chamber pressure (DC shift), and 3) a triggering Amplitude above which pulsing will cause an apparently stable system to transition to violent oscillations. Along with the obvious undesirable vibrations, these features constitute the most damaging impact of combustion instability on system reliability and structural integrity. The physical mechanisms behind these phenomena and their relationship to motor geometry and physical parameters must, therefore, be fully understood if instability is to be avoided in the design process, or if effective corrective measures must be devised during system development. Predictive algorithms now in use have Limited ability to characterize the actual time evolution of the oscillations, and they do not supply the motor designer with information regarding peak Amplitudes or the associated critical triggering Amplitudes. A pivotal missing element is the ability to predict the mean pressure shift; clearly, the designer requires information regarding the maximum chamber pressure that might be experienced during motor operation. In this paper, a comprehensive nonlinear combustion instability model is described that supplies vital information. The central role played by steep-fronted waves is emphasized. The resulting algorithm provides both detailed physical models of nonlinear instability phenomena and the critically needed predictive capability. In particular, the true origin of the DC shift is revealed.
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On Nonlinear Combustion Instability in Liquid Propellant Rocket Motors
40th AIAA ASME SAE ASEE Joint Propulsion Conference and Exhibit, 2004Co-Authors: Joseph Majdalani, Gary A. Flandro, J. D. SimsAbstract:All liquid propellant rocket instability calculations in current use have Limited value in the predictive sense and serve mainly as a correlating framework for the available data sets. The well-known n-t model first introduced by Crocco and Cheng in 1956 is still used as the primary analytical tool of this type. A multitude of attempts to establish practical analytical methods have achieved only Limited success. These methods usually produce only stability boundary maps that are of little use in making critical design decisions in new motor development programs. Recent progress in understanding the mechanisms of combustion instability in solid propellant rockets"' provides a firm foundation for a new approach to prediction, diagnosis, and correction of the closely related problems in liquid motor instability. For predictive tools to be useful in the motor design process, they must have the capability to accurately determine: 1) time evolution of the pressure oscillations and Limit Amplitude, 2) critical triggering pulse Amplitude, and 3) unsteady heat transfer rates at injector surfaces and chamber walls. The method described in this paper relates these critical motor characteristics directly to system design parameters. Inclusion of mechanisms such as wave steepening, vorticity production and transport, and unsteady detonation wave phenomena greatly enhance the representation of key features of motor chamber oscillatory behavior. The basic theoretical model is described and preliminary computations are compared to experimental data. A plan to develop the new predictive method into a comprehensive analysis tool is also described.
Gary Flandro - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Combustion Instability Prediction
2010Co-Authors: Gary FlandroAbstract:The liquid rocket engine stability prediction software (LCI) predicts combustion stability of systems using LOX-LH2 propellants. Both longitudinal and transverse mode stability characteristics are calculated. This software has the unique feature of being able to predict system Limit Amplitude.
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nonlinear rocket motor stability prediction Limit Amplitude triggering and mean pressure shift
Physics of Fluids, 2007Co-Authors: Gary Flandro, Sean R Fischbach, Joseph MajdalaniAbstract:High-Amplitude pressure oscillations in solid propellant rocket motor combustion chambers display nonlinear effects including: 1) Limit cycle behavior in which the fluctuations may dwell for a considerable period of time near their peak Amplitude, 2) elevated mean chamber pressure (DC shift), and 3) a triggering Amplitude above which pulsing will cause an apparently stable system to transition to violent oscillations. Along with the obvious undesirable vibrations, these features constitute the most damaging impact of combustion instability on system reliability and structural integrity. The physical mechanisms behind these phenomena and their relationship to motor geometry and physical parameters must, therefore, be fully understood if instability is to be avoided in the design process, or if effective corrective measures must be devised during system development. Predictive algorithms now in use have Limited ability to characterize the actual time evolution of the oscillations, and they do not supply the motor designer with information regarding peak Amplitudes or the associated critical triggering Amplitudes. A pivotal missing element is the ability to predict the mean pressure shift; clearly, the designer requires information regarding the maximum chamber pressure that might be experienced during motor operation. In this paper, a comprehensive nonlinear combustion instability model is described that supplies vital information. The central role played by steep-fronted waves is emphasized. The resulting algorithm provides both detailed physical models of nonlinear instability phenomena and the critically needed predictive capability. In particular, the true origin of the DC shift is revealed.
Kristina Todorović - One of the best experts on this subject based on the ideXlab platform.
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Dynamics of landslide model with time delay and periodic parameter perturbations
Communications in Nonlinear Science and Numerical Simulation, 2014Co-Authors: Srđan Kostić, Nebojša Vasović, Igor Franović, Dragutin Jevremović, David Mitrinovic, Kristina TodorovićAbstract:Abstract In present paper, we analyze the dynamics of a single-block model on an inclined slope with Dieterich–Ruina friction law under the variation of two new introduced parameters: time delay T d and initial shear stress μ . It is assumed that this phenomenological model qualitatively simulates the motion along the infinite creeping slope. The introduction of time delay is proposed to mimic the memory effect of the sliding surface and it is generally considered as a function of history of sliding. On the other hand, periodic perturbation of initial shear stress emulates external triggering effect of long-distant earthquakes or some non-natural vibration source. The effects of variation of a single observed parameter, T d or μ , as well as their co-action, are estimated for three different sliding regimes: β β = 1 and β > 1, where β stands for the ratio of long-term to short-term stress changes. The results of standard local bifurcation analysis indicate the onset of complex dynamics for very low values of time delay. On the other side, numerical approach confirms an additional complexity that was not observed by local analysis, due to the possible effect of global bifurcations. The most complex dynamics is detected for β T d , or the co-action of both parameters T d and μ . These results correspond well with the previous experimental observations on clay and siltstone with low clay fraction. In the same regime, the perturbation of only a single parameter, μ , renders the oscillatory motion of the block. Within the velocity-independent regime, β = 1, the inclusion and variation of T d generates a transition to equilibrium state, whereas the small oscillations of μ induce oscillatory motion with decreasing Amplitude. The co-action of both parameters, in the same regime, causes the decrease of block’s velocity. As for β > 1, highly-frequent, Limit-Amplitude oscillations of initial stress give rise to oscillatory motion. Also for β > 1, in case of perturbing only the initial shear stress, with smaller Amplitude, velocity of the block changes exponentially fast. If the time delay is introduced, besides the stress perturbation, within the same regime, the co-action of T d ( T d μ induce the onset of deterministic chaos.
Sean R Fischbach - One of the best experts on this subject based on the ideXlab platform.
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nonlinear rocket motor stability prediction Limit Amplitude triggering and mean pressure shift
Physics of Fluids, 2007Co-Authors: Gary Flandro, Sean R Fischbach, Joseph MajdalaniAbstract:High-Amplitude pressure oscillations in solid propellant rocket motor combustion chambers display nonlinear effects including: 1) Limit cycle behavior in which the fluctuations may dwell for a considerable period of time near their peak Amplitude, 2) elevated mean chamber pressure (DC shift), and 3) a triggering Amplitude above which pulsing will cause an apparently stable system to transition to violent oscillations. Along with the obvious undesirable vibrations, these features constitute the most damaging impact of combustion instability on system reliability and structural integrity. The physical mechanisms behind these phenomena and their relationship to motor geometry and physical parameters must, therefore, be fully understood if instability is to be avoided in the design process, or if effective corrective measures must be devised during system development. Predictive algorithms now in use have Limited ability to characterize the actual time evolution of the oscillations, and they do not supply the motor designer with information regarding peak Amplitudes or the associated critical triggering Amplitudes. A pivotal missing element is the ability to predict the mean pressure shift; clearly, the designer requires information regarding the maximum chamber pressure that might be experienced during motor operation. In this paper, a comprehensive nonlinear combustion instability model is described that supplies vital information. The central role played by steep-fronted waves is emphasized. The resulting algorithm provides both detailed physical models of nonlinear instability phenomena and the critically needed predictive capability. In particular, the true origin of the DC shift is revealed.
Srđan Kostić - One of the best experts on this subject based on the ideXlab platform.
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Dynamics of landslide model with time delay and periodic parameter perturbations
Communications in Nonlinear Science and Numerical Simulation, 2014Co-Authors: Srđan Kostić, Nebojša Vasović, Igor Franović, Dragutin Jevremović, David Mitrinovic, Kristina TodorovićAbstract:Abstract In present paper, we analyze the dynamics of a single-block model on an inclined slope with Dieterich–Ruina friction law under the variation of two new introduced parameters: time delay T d and initial shear stress μ . It is assumed that this phenomenological model qualitatively simulates the motion along the infinite creeping slope. The introduction of time delay is proposed to mimic the memory effect of the sliding surface and it is generally considered as a function of history of sliding. On the other hand, periodic perturbation of initial shear stress emulates external triggering effect of long-distant earthquakes or some non-natural vibration source. The effects of variation of a single observed parameter, T d or μ , as well as their co-action, are estimated for three different sliding regimes: β β = 1 and β > 1, where β stands for the ratio of long-term to short-term stress changes. The results of standard local bifurcation analysis indicate the onset of complex dynamics for very low values of time delay. On the other side, numerical approach confirms an additional complexity that was not observed by local analysis, due to the possible effect of global bifurcations. The most complex dynamics is detected for β T d , or the co-action of both parameters T d and μ . These results correspond well with the previous experimental observations on clay and siltstone with low clay fraction. In the same regime, the perturbation of only a single parameter, μ , renders the oscillatory motion of the block. Within the velocity-independent regime, β = 1, the inclusion and variation of T d generates a transition to equilibrium state, whereas the small oscillations of μ induce oscillatory motion with decreasing Amplitude. The co-action of both parameters, in the same regime, causes the decrease of block’s velocity. As for β > 1, highly-frequent, Limit-Amplitude oscillations of initial stress give rise to oscillatory motion. Also for β > 1, in case of perturbing only the initial shear stress, with smaller Amplitude, velocity of the block changes exponentially fast. If the time delay is introduced, besides the stress perturbation, within the same regime, the co-action of T d ( T d μ induce the onset of deterministic chaos.