The Experts below are selected from a list of 75 Experts worldwide ranked by ideXlab platform

Thomas E Boothby - One of the best experts on this subject based on the ideXlab platform.

  • strength of Spandrel walls in masonry arch bridges
    Transportation Research Record, 2004
    Co-Authors: Ece Erdogmus, Thomas E Boothby
    Abstract:

    Previous research on the strength of masonry arch bridges has focused on the carrying capacity of the arch barrel in the Span Direction. Although the results of a Spandrel wall collapse may be very serious, the transverse strength of masonry arch bridges has not been widely addressed. Recent experience, however, has shown that the transverse behavior and the strength of the Spandrel walls are at least as important as the behavior in the Span Direction. Although complex computer analysis methods have been proposed for examining the masonry arch bridge as a three-dimensional structure, these methods are not suitable for everyday practical application. An approximate analytical method for the prediction of the strength of masonry Spandrel walls is developed based on the conventional analysis of fills supported by retaining walls. The method is based on the determination of loads by Coulomb-Rankine analysis and the determination of resistance by the fracture line method, similar to the yield line method for reinforced concrete slabs. A table that further increases the simplicity and speed of the method is also provided. The proposed method allows the practicing engineer to calculate a factor of safety for the transverse strength of a Spandrel wall for different situations, such as moist soil, cracked wall, effect of live load for shallow fill bridges, or existence of parapet walls. Results of these conventional, simplified analyses compare favorably with observed bridge distress and results of a previously validated finite element analysis method.

  • Transverse behaviour of masonry arch bridges
    The Structural engineer, 2001
    Co-Authors: Thomas E Boothby, B. J. Roberts
    Abstract:

    Research efforts in the assessment of masonry arch bridges have concentrated on the strength of the arch in the Span Direction. However, experience with these structures indicates that masonry arch bridges more often fail by sliding or overturning of the Spandrel walls perpendicular to the roadway centreline, or by the development of longitudinal cracks in the arch barrel and eventual separation of the Spandrels from the remainder of the arch barrel. The present paper reports results of a 3-dimensional non-linear finite element (FE) model of an arch bridge that uses a Drucker-Prager material for the fill and a brittle material for the masonry. The model predicts that most truck-loaded stone arch bridges will exhibit a premature failure due to lateral effects rather than a mechanism collapse. The predicted lateral failure modes include local Spandrel wall failures, overturning of the Spandrel walls, edge failure of the arch barrel, and local punching of the arch. Stone bridges with thin arches or bridges with very low tensile strengths were predicted to be significantly weakened by such lateral effects. (A)

Reza S Abhari - One of the best experts on this subject based on the ideXlab platform.

  • comparison of predicted and experimental nusselt number for a film cooled rotating blade
    International Journal of Heat and Fluid Flow, 1997
    Co-Authors: Vijay K Garg, Reza S Abhari
    Abstract:

    Abstract The predictions from a three-dimensional (3-D) Navier-Stokes code have been compared to the Nusselt number data obtained on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film-cooling holes covering the entire Span. This is the only film-cooled rotating blade on which experimental heat transfer data are available for the present comparison. Over 2.25 million grid points are used to compute the flow over the blade. Usually, in a film cooling computation on a stationary blade, the computational domain is just one Spanwise pitch of the film-cooling holes, with periodic boundary conditions in the Span Direction. However, for a rotating blade, the computational domain consists of the entire blade Span from hub to tip, as well as the tip clearance region. As far as the authors know, the present work is the first comparison of the prediction of surface heat transfer using a 3-D Navier-Stokes code with film injection and the measured heat flux on a fully film-cooled rotating transonic turbine blade. A reasonably good comparison with the measured data is obtained on the suction surface, particularly near the hub section. On the pressure surface, however, the comparison between the data and the prediction is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects caused by stator-rotor interaction in the experiments, which are not modeled in the present numerical computations.

  • comparison of predicted and experimental nusselt number for a film cooled rotating blade
    ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition, 1996
    Co-Authors: Vijay K Garg, Reza S Abhari
    Abstract:

    The predictions from a three-dimensional Navier-Stokes code have been compared to the Nusselt number data obtained on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film cooling holes covering the entire Span. This is the only film-cooled rotating blade over which experimental heat transfer data is available for the present comparison. Over 2.25 million grid points are used to compute the flow over the blade. Usually in a film cooling computation on a stationary blade, the computational domain is just one Spanwise pitch of the film-cooling holes, with periodic boundary conditions in the Span Direction. However, for a rotating blade, the computational domain consists of the entire blade Span from hub to tip, as well as the tip clearance region.As far as the authors are aware of, the present work offers the first comparison of the prediction of surface heat transfer using a three dimensional CFD code with film injection and the measured heat flux on a fully film-cooled rotating transonic turbine blade. In a detailed comparison with the measured data on the suction surface, a reasonably good comparison is obtained, particularly near the hub section. On the pressure surface, however, the comparison between the data and the prediction is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects due to stator-rotor interaction in the experiments which are not modeled in the present numerical computations.Copyright © 1996 by ASME

Ece Erdogmus - One of the best experts on this subject based on the ideXlab platform.

  • strength of Spandrel walls in masonry arch bridges
    Transportation Research Record, 2004
    Co-Authors: Ece Erdogmus, Thomas E Boothby
    Abstract:

    Previous research on the strength of masonry arch bridges has focused on the carrying capacity of the arch barrel in the Span Direction. Although the results of a Spandrel wall collapse may be very serious, the transverse strength of masonry arch bridges has not been widely addressed. Recent experience, however, has shown that the transverse behavior and the strength of the Spandrel walls are at least as important as the behavior in the Span Direction. Although complex computer analysis methods have been proposed for examining the masonry arch bridge as a three-dimensional structure, these methods are not suitable for everyday practical application. An approximate analytical method for the prediction of the strength of masonry Spandrel walls is developed based on the conventional analysis of fills supported by retaining walls. The method is based on the determination of loads by Coulomb-Rankine analysis and the determination of resistance by the fracture line method, similar to the yield line method for reinforced concrete slabs. A table that further increases the simplicity and speed of the method is also provided. The proposed method allows the practicing engineer to calculate a factor of safety for the transverse strength of a Spandrel wall for different situations, such as moist soil, cracked wall, effect of live load for shallow fill bridges, or existence of parapet walls. Results of these conventional, simplified analyses compare favorably with observed bridge distress and results of a previously validated finite element analysis method.

Vijay K Garg - One of the best experts on this subject based on the ideXlab platform.

  • comparison of predicted and experimental nusselt number for a film cooled rotating blade
    International Journal of Heat and Fluid Flow, 1997
    Co-Authors: Vijay K Garg, Reza S Abhari
    Abstract:

    Abstract The predictions from a three-dimensional (3-D) Navier-Stokes code have been compared to the Nusselt number data obtained on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film-cooling holes covering the entire Span. This is the only film-cooled rotating blade on which experimental heat transfer data are available for the present comparison. Over 2.25 million grid points are used to compute the flow over the blade. Usually, in a film cooling computation on a stationary blade, the computational domain is just one Spanwise pitch of the film-cooling holes, with periodic boundary conditions in the Span Direction. However, for a rotating blade, the computational domain consists of the entire blade Span from hub to tip, as well as the tip clearance region. As far as the authors know, the present work is the first comparison of the prediction of surface heat transfer using a 3-D Navier-Stokes code with film injection and the measured heat flux on a fully film-cooled rotating transonic turbine blade. A reasonably good comparison with the measured data is obtained on the suction surface, particularly near the hub section. On the pressure surface, however, the comparison between the data and the prediction is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects caused by stator-rotor interaction in the experiments, which are not modeled in the present numerical computations.

  • comparison of predicted and experimental nusselt number for a film cooled rotating blade
    ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition, 1996
    Co-Authors: Vijay K Garg, Reza S Abhari
    Abstract:

    The predictions from a three-dimensional Navier-Stokes code have been compared to the Nusselt number data obtained on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film cooling holes covering the entire Span. This is the only film-cooled rotating blade over which experimental heat transfer data is available for the present comparison. Over 2.25 million grid points are used to compute the flow over the blade. Usually in a film cooling computation on a stationary blade, the computational domain is just one Spanwise pitch of the film-cooling holes, with periodic boundary conditions in the Span Direction. However, for a rotating blade, the computational domain consists of the entire blade Span from hub to tip, as well as the tip clearance region.As far as the authors are aware of, the present work offers the first comparison of the prediction of surface heat transfer using a three dimensional CFD code with film injection and the measured heat flux on a fully film-cooled rotating transonic turbine blade. In a detailed comparison with the measured data on the suction surface, a reasonably good comparison is obtained, particularly near the hub section. On the pressure surface, however, the comparison between the data and the prediction is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects due to stator-rotor interaction in the experiments which are not modeled in the present numerical computations.Copyright © 1996 by ASME

Charles R Farrar - One of the best experts on this subject based on the ideXlab platform.

  • structural health monitoring of wind turbines method and application to a hawt
    Wind Energy, 2011
    Co-Authors: Douglas E Adams, Jonathan White, Mark A Rumsey, Charles R Farrar
    Abstract:

    Structural health monitoring in the context of a Micon 65/13 horizontal axis wind turbine was described in this paper as a process in statistical pattern recognition. Simulation data from a calibrated model with less than 8% error in the first 14 natural frequencies of vibration was used to study the operational response under various wind states as well as the effects of three types of damage in the blade, low speed shaft and yaw joint. It was shown that vertical wind shear and turbulent winds lead to different modal contributions in the operational response of the turbine suggesting that the sensitivity of operational data to damage depends on the wind loads. It is also shown that there is less than a 4% change in the wind turbine natural frequencies given a 25% reduction in the stiffness at the root of one blade. The modal assurance criterion was used to analyse the corresponding changes in modal deflections, and this criterion exhibited nearly orthogonal changes because of the three damage scenarios suggesting that the modal deflection determines which damage is observable at a given frequency for a given wind state. The' modal contribution is calculated as a damage feature, which changes as much as 100% for 50% reductions in blade root stiffness, but only the blade damage is detected using this feature. Operational data was used to study variations in the forced blade response to determine the likelihood that small levels of damage can be detected amidst variations in wind speed across the rotor plane. The standard deviation in measured data was shown to be smallest for the Span and edge-wise measurements at 1P due to gravity, which provides the dominant forcing function at this frequency. A 3% change in the response in the Span and edge-wise Directions because of damage is required to detect a change of three standard deviations in contrast to the 90% change in flap Direction response that is required to detect a similar change because of damage. The dynamic displacement in the Span Direction is then used to extract a damage feature from the simulation data that provides the ability to both locate and quantify the reduction in stiffness in the blade root. Copyright © 2011 John Wiley & Sons, Ltd.