Mach Wave

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John Douglas - One of the best experts on this subject based on the ideXlab platform.

  • Influence of super-shear on simulated near-source ground motion from the 1999 Izmit earthquake
    2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw7.4 Izmit, Turkey, earthquake, using a 3D finite difference method based on published finite source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of super-shear rupture propagation towards the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity, an important parameter in earthquake engineering. This is because the fault spatial heterogeneity is strong enough to mask the properties of super-shear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This study demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

  • Influence of super-shear earthquake rupture models on simulated near-source ground motion from the 1999 Izmit (Turkey) earthquake
    Bulletin of the Seismological Society of America, 2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw7.4 Izmit, Turkey, earthquake, using a 3D finite difference method based on published finite source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of super-shear rupture propagation towards the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity, an important parameter in earthquake engineering. This is because the fault's spatial heterogeneity is strong enough to mask the properties of super-shear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This study demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

  • Influence of Super-Shear Earthquake Rupture Models on Simulated Near-Source Ground Motion from the 1999 Izmit, Turkey, Earthquake
    Bulletin of the Seismological Society of America, 2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw 7.4 earthquake in Izmit, Turkey, using a 3D finite difference method based on published finite-source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of supershear rupture propagation toward the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity (PGV), an important parameter in earthquake engineering. This is because the fault's spatial heterogeneity is strong enough to mask the properties of supershear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This article demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

J Weertman - One of the best experts on this subject based on the ideXlab platform.

  • Transonic gliding edge dislocations/slip pulse near and on an interface/fault
    Journal of Geophysical Research, 2014
    Co-Authors: J Weertman
    Abstract:

    Three problems are solved in this paper that are related to transonic earthquakes. (1) The shear shock Mach Wave emanating from a transonic gliding edge dislocation which impacts an interface. (2) A transonic edge dislocation gliding parallel and near to an interface. (3) The transonic edge dislocation gliding on the interface itself. The dislocation is in uniform or quasi-uniform motion. The interface separates isotropic elastic material of slightly different properties. The first and last problems are essentially the same. The problems are solved with the building blocks of Mach Waves, with logarithmic and arctan distributions of infinitesimal shock Waves and with subsonic (with respect to longitudinal Wave velocities) glide edge and climb edge dislocations. The need for the smeared infinitesimal shock Wave distributions is an interesting feature of the solutions. Distributions of infinitesimal smeared Mach Waves will exist wherever physical discontinuities exist near a transonic dislocation. A slip pulse of infinitesimal moving edge dislocations can be self sharpening because of attractive forces between like sign dislocations in certain velocity ranges.

  • transonic gliding edge dislocations slip pulse near and on an interface fault
    Journal of Geophysical Research, 2014
    Co-Authors: J Weertman
    Abstract:

    Three problems are solved in this paper that are related to transonic earthquakes. (1) The shear shock Mach Wave emanating from a transonic gliding edge dislocation which impacts an interface. (2) A transonic edge dislocation gliding parallel and near to an interface. (3) The transonic edge dislocation gliding on the interface itself. The dislocation is in uniform or quasi-uniform motion. The interface separates isotropic elastic material of slightly different properties. The first and last problems are essentially the same. The problems are solved with the building blocks of Mach Waves, with logarithmic and arctan distributions of infinitesimal shock Waves and with subsonic (with respect to longitudinal Wave velocities) glide edge and climb edge dislocations. The need for the smeared infinitesimal shock Wave distributions is an interesting feature of the solutions. Distributions of infinitesimal smeared Mach Waves will exist wherever physical discontinuities exist near a transonic dislocation. A slip pulse of infinitesimal moving edge dislocations can be self sharpening because of attractive forces between like sign dislocations in certain velocity ranges.

Hideo Aochi - One of the best experts on this subject based on the ideXlab platform.

  • Influence of super-shear on simulated near-source ground motion from the 1999 Izmit earthquake
    2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw7.4 Izmit, Turkey, earthquake, using a 3D finite difference method based on published finite source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of super-shear rupture propagation towards the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity, an important parameter in earthquake engineering. This is because the fault spatial heterogeneity is strong enough to mask the properties of super-shear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This study demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

  • Influence of super-shear earthquake rupture models on simulated near-source ground motion from the 1999 Izmit (Turkey) earthquake
    Bulletin of the Seismological Society of America, 2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw7.4 Izmit, Turkey, earthquake, using a 3D finite difference method based on published finite source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of super-shear rupture propagation towards the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity, an important parameter in earthquake engineering. This is because the fault's spatial heterogeneity is strong enough to mask the properties of super-shear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This study demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

  • Influence of Super-Shear Earthquake Rupture Models on Simulated Near-Source Ground Motion from the 1999 Izmit, Turkey, Earthquake
    Bulletin of the Seismological Society of America, 2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw 7.4 earthquake in Izmit, Turkey, using a 3D finite difference method based on published finite-source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of supershear rupture propagation toward the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity (PGV), an important parameter in earthquake engineering. This is because the fault's spatial heterogeneity is strong enough to mask the properties of supershear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This article demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

Virginie Durand - One of the best experts on this subject based on the ideXlab platform.

  • Influence of super-shear on simulated near-source ground motion from the 1999 Izmit earthquake
    2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw7.4 Izmit, Turkey, earthquake, using a 3D finite difference method based on published finite source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of super-shear rupture propagation towards the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity, an important parameter in earthquake engineering. This is because the fault spatial heterogeneity is strong enough to mask the properties of super-shear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This study demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

  • Influence of super-shear earthquake rupture models on simulated near-source ground motion from the 1999 Izmit (Turkey) earthquake
    Bulletin of the Seismological Society of America, 2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw7.4 Izmit, Turkey, earthquake, using a 3D finite difference method based on published finite source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of super-shear rupture propagation towards the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity, an important parameter in earthquake engineering. This is because the fault's spatial heterogeneity is strong enough to mask the properties of super-shear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This study demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

  • Influence of Super-Shear Earthquake Rupture Models on Simulated Near-Source Ground Motion from the 1999 Izmit, Turkey, Earthquake
    Bulletin of the Seismological Society of America, 2011
    Co-Authors: Hideo Aochi, Virginie Durand, John Douglas
    Abstract:

    We numerically simulate seismic Wave propagation from the 1999 Mw 7.4 earthquake in Izmit, Turkey, using a 3D finite difference method based on published finite-source models obtained by Waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of supershear rupture propagation toward the east. Although the modeled ground motion does show a characteristic Mach Wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity (PGV), an important parameter in earthquake engineering. This is because the fault's spatial heterogeneity is strong enough to mask the properties of supershear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This article demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.

Kozo Fujii - One of the best experts on this subject based on the ideXlab platform.

  • Overexpansion Effects on Characteristics of Mach Waves from a Supersonic Cold Jet
    AIAA Journal, 2011
    Co-Authors: Taku Nonomura, Kozo Fujii
    Abstract:

    For predicting acoustic Waves emitted from a rocket plume, the overexpansion effects on Mach 3.0 supersonic jet acoustics are investigated using an implicit large eddy simulation. A Mach 2.0 supersonic free jet is computed for code validation, and the results show qualitatively good agreement with the experiments. Then, computations of three different jets (design Mach numbers 3.0, 3.5, and 4.0 with fully expanded jet Mach number 3.0) are conducted, and nondimensionalizations based on design parameters and fully expanded parameters are discussed. Acoustic far-field spectra show that nondimensionalization based on fully expanded parameters works well for the high-Mach-number overexpanded jets, as it does for the low-Mach-number underexpanded jets that were investigated in previous studies. This nondimensionalization improves the accuracy of prediction of the acoustic Waves emitted from rocket plumes because one parameter, the design Mach number, can be neglected for acoustic far fields. In addition, actual overexpansion effects after nondimensionalization are discussed. A comparison of the near flowfields and acoustic fields shows that Mach Wave sources move upstream because of the existence of Mach disks, which enhances shear-layer mixing. Meanwhile, the overexpanded jet, which possesses only a shock cell without Mach disks, exhibits the same Mach Wave generation characteristics as an ideally expanded jet.

  • Effects of shear-layer characteristic on the Feedback-loop Mechanism in supersonic open cavity flows
    49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011
    Co-Authors: Taku Nonomura, Kozo Fujii
    Abstract:

    Supersonic cavity flows with laminar and turbulent inflow conditions are numerically studied by implicit large-eddy simulations and the effects of shear-layer characteristic on the feedback-loop mechanism are investigated. The feedback compression Wave is generated by the reflection of Mach Wave at the rear wall in the simulation of cavity flow with laminar inflow, which is clarified by the visualization of phase-averaged flowfields. However, the Mach Wave reflection does not occur in the cavity flow with turbulent inflow. This is because the shear-layer behavior is much different from laminar case. In the laminar inflow case, highly two-dimensional shedding vortex is present in the shear-layer, which leads to intense Mach Wave radiation. The intense Mach Wave travels downstream with the vortex and reflects at the rear wall. However, when turbulent inflow is imposed, the shear-layer consists of plenty of small-scale vortical structures with highly three-dimensional characteristics. Although large-scale shear-layer motions are observed, no intense Mach Wave radiates from the shear-layer. Further discussion on the generation mechanism of feedback compression Waves are conducted using phase-averaged flowfields. Results show that the vortex impingement itself does not lead to feedback-compression-Wave radiation. Instead, low-pressure region associated with vortex and high-pressure region in the connection of two adjacent vortices alternatively/intermittently impinge on the trailing edge, which results in pressure pulses. These pressure pulses are probably the generation mechanism of feedback compression Waves. This mechanism also includes the cavity flows with laminar inflow condition in which intense Mach Wave radiation and its reflection are observed, since the Mach Wave is the interface of low-pressure region and high-pressure region.

  • POD of Aeroacoustic Fields of a Jet Impinging on an Inclied Plate
    16th AIAA CEAS Aeroacoustics Conference, 2010
    Co-Authors: Taku Nonomura, Kozo Fujii
    Abstract:

    Proper orthogonal decomposition (POD) analysis of a supersonic jet impinging on an inclined flat plate is presented. We process data of flow fields and acoustic fields obtained in the previous study in which we found that three kinds of aeroacoustic Waves are generated; (i) Mach Waves from the main jet, (ii) acoustic Waves from the impingement region and (iii)Mach Waves from the supersonic flow downstream of the impingement region. For the two-dimensional pressure distribution in acoustic fields by a impinging jet, POD analysis with Fourier transformation is conducted. POD results illustrate locations of the acoustic Waves (ii) and Mach Waves (iii). Also POD results show that acoustic Waves (ii) and Mach Waves (iii) are observed in the same POD mode. Thus, the result shows that the acoustic Wave (ii) and Mach Wave (iii) have the strong relation each other.

  • Computational Analysis of Characteristics of Mach Wave Sources in Supersonic Free-jets
    47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009
    Co-Authors: Taku Nonomura, Kozo Fujii
    Abstract:

    For the prediction of acoustic Waves from a rocket plume, source characteristics of Mach Waves are investigated with using high resolution schemes. Four ideally-expanded supersonic jets, M=2.0 cold jet, M=3.0 cold jet, M=2.0 hot jet and M=3.0 hot jet, are computed and analyzed. With regard to computation, the seventh order weighted compact non-linear scheme and the tenth order compact scheme are used for the fluid analysis and near fields acoustics propagation, respectively. Source positions are investigated with the focused array method and the visualization of sources. The results of the focused array methods show that the high frequency sources are located at the upstream region, while the low frequency sources are located at the downstream region. In addition, Mach Waves emitted from the high frequency sources are propagated with the large angle to the axis, while that from the low frequency sources are propagated with the small angle. Mach Wave sources are located in the ambient supersonic region, in which fluid-velocity is higher than the sound speed of the ambient. The almost same features are obtained with using the visualization of sources. Then the normalization of the source frequency is investigated. Using the shear layer thickness and the velocity at the axis, we can normalize the source frequency of various supersonic jets well without the temperature effects. Finally our computational results show that the lowest frequency of Mach Waves is determined by the ambient supersonic region length and the potential core length.

  • Numerical Study of Pressure Waves Generated by H-IIA Launch Vehicle at Lift-off
    2008
    Co-Authors: Seiji Tsutsumi, Taro Shimizu, Ryoji Takaki, Eiji Shima, Kozo Fujii
    Abstract:

    Generation mechanisms of pressure Waves from the H-IIA launch vehicle are analyzed numerically. The Mach Wave radiated downstream from wavy shear-layer of supersonic exhaust plume is revealed to be the dominant noise source. Reflecting from the constructions of the launch-pad, the Mach Wave turns to propagate to the vehicles. It was also found that the fluctuating supersonic plume entering into the flame duct is the dominant noise source that appears in the flame duct. Then, the pressure Wave propagates through the flame duct and is ejected outside to the vehicle.