The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
H T Goldrein - One of the best experts on this subject based on the ideXlab platform.
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measurement of dynamic large strain deformation maps using an automated Fine Grid technique
Optics and Lasers in Engineering, 1999Co-Authors: P J Rae, H T Goldrein, N K Bourne, W G Proud, L C Forde, M LiljekvistAbstract:Automatic analysis of the dynamic deformation of a Fine Grid ruled onto a specimen's surface has allowed whole-field measurement of both in-plane displacement components. A high-speed camera was used to capture images of impacts at velocities of over 500 m/s. The Fourier transform method and phase unwrapping were used to calculate planes of phase coordinates which deform with the specimen. An iterative search algorithm yields the displacements directly by searching for the shifted location of each set of phase coordinates in the image of the deformed specimen. This paper describes the application of a previously proven analysis technique to dynamic deformation. Simple sample preparation and experimental operation make this technique ideal for the dynamic regime.
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automated Fine Grid technique for measurement of large strain deformation maps
Optics and Lasers in Engineering, 1995Co-Authors: H T Goldrein, S J P Palmer, J M HuntleyAbstract:Abstract The Fine Grid technique has been a standard engineering tool for measuring large strains for many years. The sample surface is marked with a Grid, and the deformation of this Grid allows the deformation of the sample to be monitored. However, it has never been easy quantitatively to analyse the strain across the whole of a specimen's surface. We describe here an automated approach in which digitised images of a sample prepared with a Grid are analysed by the Fourier transform method. This provides phase maps which, when unwrapped, yield planes representing the two in-plane specimen coordinates. An iterative technique follows these deforming planes from one frame to the next as the specimen deforms, allowing displacement fields to be calculated. Numerical differentiation gives strains across the specimen surface. Gerchberg iteration is used to provide immunity to errors resulting from holes or tears in the specimen surface. The method is demonstrated on a propellant simulant containing burn holes (a cylinder of diameter 10 mm; Grid pitch = 76 μm), loaded in compression across a diameter. All in-plane components of strain are calculated up to strains of approximately one-third. Displacement accuracy is of order 1 μm.
J M Huntley - One of the best experts on this subject based on the ideXlab platform.
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automated Fine Grid technique for measurement of large strain deformation maps
Optics and Lasers in Engineering, 1995Co-Authors: H T Goldrein, S J P Palmer, J M HuntleyAbstract:Abstract The Fine Grid technique has been a standard engineering tool for measuring large strains for many years. The sample surface is marked with a Grid, and the deformation of this Grid allows the deformation of the sample to be monitored. However, it has never been easy quantitatively to analyse the strain across the whole of a specimen's surface. We describe here an automated approach in which digitised images of a sample prepared with a Grid are analysed by the Fourier transform method. This provides phase maps which, when unwrapped, yield planes representing the two in-plane specimen coordinates. An iterative technique follows these deforming planes from one frame to the next as the specimen deforms, allowing displacement fields to be calculated. Numerical differentiation gives strains across the specimen surface. Gerchberg iteration is used to provide immunity to errors resulting from holes or tears in the specimen surface. The method is demonstrated on a propellant simulant containing burn holes (a cylinder of diameter 10 mm; Grid pitch = 76 μm), loaded in compression across a diameter. All in-plane components of strain are calculated up to strains of approximately one-third. Displacement accuracy is of order 1 μm.
Hyam Abboud - One of the best experts on this subject based on the ideXlab platform.
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a full discretization of the time dependent navier stokes equations by a two Grid scheme
Mathematical Modelling and Numerical Analysis, 2008Co-Authors: Hyam Abboud, Toni SayahAbstract:We study a two-Grid scheme fully discrete in time and space for solving the Navier-Stokes system. In the first step, the fully non-linear problem is discretized in space on a coarse Grid with mesh-size H and time step k. In the second step, the problem is discretized in space on a Fine Grid with mesh-size h and the same time step, and linearized around the velocity u H computed in the first step. The two-Grid strategy is motivated by the fact that under suitable assumptions, the contribution of u H to the error in the non-linear term, is measured in the L 2 norm in space and time, and thus has a higher-order than if it were measured in the H 1 norm in space. We present the following results: if h = H2 = k, then the global error of the two-Grid algorithm is of the order of h , the same as would have been obtained if the non-linear problem had been solved directly on the Fine Grid.
M Liljekvist - One of the best experts on this subject based on the ideXlab platform.
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measurement of dynamic large strain deformation maps using an automated Fine Grid technique
Optics and Lasers in Engineering, 1999Co-Authors: P J Rae, H T Goldrein, N K Bourne, W G Proud, L C Forde, M LiljekvistAbstract:Automatic analysis of the dynamic deformation of a Fine Grid ruled onto a specimen's surface has allowed whole-field measurement of both in-plane displacement components. A high-speed camera was used to capture images of impacts at velocities of over 500 m/s. The Fourier transform method and phase unwrapping were used to calculate planes of phase coordinates which deform with the specimen. An iterative search algorithm yields the displacements directly by searching for the shifted location of each set of phase coordinates in the image of the deformed specimen. This paper describes the application of a previously proven analysis technique to dynamic deformation. Simple sample preparation and experimental operation make this technique ideal for the dynamic regime.
Toni Sayah - One of the best experts on this subject based on the ideXlab platform.
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a full discretization of the time dependent navier stokes equations by a two Grid scheme
Mathematical Modelling and Numerical Analysis, 2008Co-Authors: Hyam Abboud, Toni SayahAbstract:We study a two-Grid scheme fully discrete in time and space for solving the Navier-Stokes system. In the first step, the fully non-linear problem is discretized in space on a coarse Grid with mesh-size H and time step k. In the second step, the problem is discretized in space on a Fine Grid with mesh-size h and the same time step, and linearized around the velocity u H computed in the first step. The two-Grid strategy is motivated by the fact that under suitable assumptions, the contribution of u H to the error in the non-linear term, is measured in the L 2 norm in space and time, and thus has a higher-order than if it were measured in the H 1 norm in space. We present the following results: if h = H2 = k, then the global error of the two-Grid algorithm is of the order of h , the same as would have been obtained if the non-linear problem had been solved directly on the Fine Grid.
