The Experts below are selected from a list of 615 Experts worldwide ranked by ideXlab platform

Shigeru Obayashi - One of the best experts on this subject based on the ideXlab platform.

  • Sonic Boom Variability Due to Homogeneous Atmospheric Turbulence
    2010
    Co-Authors: Hiroshi Yamashita, Shigeru Obayashi
    Abstract:

    This study describes the Nondeterministic Effect of homogeneous atmospheric turbulence on sonic boom propagation. The Sears–Haack body was calculated in three dimensions by computational fluid dynamics in inviscid flow (Euler) mode to create the near-field pressure wave. The homogeneous atmospheric turbulence field was represented by the finite sum of discrete Fourier modes based on the von Karman and Pao energy spectrum. The sonic boom signature was then calculated by the modified waveform parameter method, considering a random velocity of homogeneous atmospheric turbulence. The results of this study indicated that atmospheric turbulence has a marked influence on sonic boom overpressure during its propagation to the ground. In comparison to the noturbulence condition, we found that the sonic boom decreased in 59 % of the cases and increased in 41 % of the cases. Thus, homogeneous atmospheric turbulence seems to favor a decrease, rather than an increase, in boom overpressure. In addition, we found that turbulence has a small Effect on the propagation path from the flight altitude to the ground. Nonetheless, this small change in the propagation path may result in a variability, of the point at which the sonic boom reaches the ground, of up to 1820 ft in the north–south direction (flight direction) and 115 ft in the east–west direction. Nomenclature AL = body reference length in fee

  • Sonic Boom Variability Due to Homogeneous Atmospheric Turbulence
    Journal of Aircraft, 2009
    Co-Authors: Hiroshi Yamashita, Shigeru Obayashi
    Abstract:

    This study describes the Nondeterministic Effect of homogeneous atmospheric turbulence on sonic boom propagation. The Sears-Haack body was calculated in three dimensions by computational fluid dynamics in inviscid flow (Euler) mode to create the near-field pressure wave. The homogeneous atmospheric turbulence field was represented by the finite sum of discrete Fourier modes based on the von Karman and Pao energy spectrum. The sonic boom signature was then calculated by the modified waveform parameter method, considering a random velocity of homogeneous atmospheric turbulence. The results of this study indicated that atmospheric turbulence has a marked influence on sonic boom overpressure during its propagation to the ground. In comparison to the no-turbulence condition, we found that the sonic boom decreased in 59 % of the cases and increased in 41 % of the cases. Thus, homogeneous atmospheric turbulence seems to favor a decrease, rather than an increase, in boom overpressure. In addition, we found that turbulence has a small Effect on the propagation path from the flight altitude to the ground. Nonetheless, this small change in the propagation path may result in a variability, of the point at which the sonic boom reaches the ground, of up to 1820 ft in the north-south direction (flight direction) and 115 ft in the east-west direction.

Hiroshi Yamashita - One of the best experts on this subject based on the ideXlab platform.

  • Sonic Boom Variability Due to Homogeneous Atmospheric Turbulence
    2010
    Co-Authors: Hiroshi Yamashita, Shigeru Obayashi
    Abstract:

    This study describes the Nondeterministic Effect of homogeneous atmospheric turbulence on sonic boom propagation. The Sears–Haack body was calculated in three dimensions by computational fluid dynamics in inviscid flow (Euler) mode to create the near-field pressure wave. The homogeneous atmospheric turbulence field was represented by the finite sum of discrete Fourier modes based on the von Karman and Pao energy spectrum. The sonic boom signature was then calculated by the modified waveform parameter method, considering a random velocity of homogeneous atmospheric turbulence. The results of this study indicated that atmospheric turbulence has a marked influence on sonic boom overpressure during its propagation to the ground. In comparison to the noturbulence condition, we found that the sonic boom decreased in 59 % of the cases and increased in 41 % of the cases. Thus, homogeneous atmospheric turbulence seems to favor a decrease, rather than an increase, in boom overpressure. In addition, we found that turbulence has a small Effect on the propagation path from the flight altitude to the ground. Nonetheless, this small change in the propagation path may result in a variability, of the point at which the sonic boom reaches the ground, of up to 1820 ft in the north–south direction (flight direction) and 115 ft in the east–west direction. Nomenclature AL = body reference length in fee

  • Sonic Boom Variability Due to Homogeneous Atmospheric Turbulence
    Journal of Aircraft, 2009
    Co-Authors: Hiroshi Yamashita, Shigeru Obayashi
    Abstract:

    This study describes the Nondeterministic Effect of homogeneous atmospheric turbulence on sonic boom propagation. The Sears-Haack body was calculated in three dimensions by computational fluid dynamics in inviscid flow (Euler) mode to create the near-field pressure wave. The homogeneous atmospheric turbulence field was represented by the finite sum of discrete Fourier modes based on the von Karman and Pao energy spectrum. The sonic boom signature was then calculated by the modified waveform parameter method, considering a random velocity of homogeneous atmospheric turbulence. The results of this study indicated that atmospheric turbulence has a marked influence on sonic boom overpressure during its propagation to the ground. In comparison to the no-turbulence condition, we found that the sonic boom decreased in 59 % of the cases and increased in 41 % of the cases. Thus, homogeneous atmospheric turbulence seems to favor a decrease, rather than an increase, in boom overpressure. In addition, we found that turbulence has a small Effect on the propagation path from the flight altitude to the ground. Nonetheless, this small change in the propagation path may result in a variability, of the point at which the sonic boom reaches the ground, of up to 1820 ft in the north-south direction (flight direction) and 115 ft in the east-west direction.

Michael Butler - One of the best experts on this subject based on the ideXlab platform.

  • External and internal choice with event groups in Event-B
    Formal Aspects of Computing, 2012
    Co-Authors: Michael Butler
    Abstract:

    Abrial’s Event-B formalism for refinement-based system development is influenced by Back’s action system approach. Morgan has defined a CSP-like failures-divergence semantics for action systems that distinguishes internal and external choice of actions. Morgan’s semantics has the characteristic that the choice between enabled actions is external while internal choice is represented less directly through Nondeterministic Effect of actions. Practical experience with Event-B has demonstrated the need to be able to represent both internal and external choice between enabled events more explicitly. In this paper, Morgan’s failures semantics for action systems is modified to allow both internal and external choice to be represented directly. This is achieved by grouping events so that external choice is between event groups and internal choice is within event groups. This leads to a refinement rule for preservation of choice between event groups while allowing for reduction of choice within event groups. We also provide a refinement rule for splitting event groups in order to increase external choice. The refinement rules are justified in terms of failures refinement.

Zhang Dongmo - One of the best experts on this subject based on the ideXlab platform.

  • Dealing with the ramification problem in the extended propositional dynamic logic
    Singapore World Scientific, 2002
    Co-Authors: Foo N. Y. Y.), Zhang Dongmo
    Abstract:

    This paper presents a solution to the ramification problem in the presence of Nondeterministic Effect and Nondeterministic choice of actions based on the extended propositional dynamic logic. We first show that the causation-based approach can be re-coded in the extended dynamic logic. Then by taking advantage of the extra expressive power of dynamic logic for compound actions and programs, any complex ramifications involved in an automatic system can be expressed and specified. Specially, Thielscher's and Shanahan's benchmark examples can be more Effectively elaborated

Foo N. Y. Y.) - One of the best experts on this subject based on the ideXlab platform.

  • Dealing with the ramification problem in the extended propositional dynamic logic
    Singapore World Scientific, 2002
    Co-Authors: Foo N. Y. Y.), Zhang Dongmo
    Abstract:

    This paper presents a solution to the ramification problem in the presence of Nondeterministic Effect and Nondeterministic choice of actions based on the extended propositional dynamic logic. We first show that the causation-based approach can be re-coded in the extended dynamic logic. Then by taking advantage of the extra expressive power of dynamic logic for compound actions and programs, any complex ramifications involved in an automatic system can be expressed and specified. Specially, Thielscher's and Shanahan's benchmark examples can be more Effectively elaborated