The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
D M Hicks - One of the best experts on this subject based on the ideXlab platform.
-
the development of an automated Correction Procedure for digital photogrammetry for the study of wide shallow gravel bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated Correction Procedure for dealing with point errors associated with through-water photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The Procedure involves combining digital photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The Correction Procedure was applied to raw digital elevation models (DEMs) generated using digital photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that digital photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following Correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the Correction Procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
-
The development of an automated Correction Procedure for digital photogrammetry for the study of wide, shallow, gravel‐bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated Correction Procedure for dealing with point errors associated with through-water photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The Procedure involves combining digital photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The Correction Procedure was applied to raw digital elevation models (DEMs) generated using digital photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that digital photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following Correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the Correction Procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
Richard M Westaway - One of the best experts on this subject based on the ideXlab platform.
-
the development of an automated Correction Procedure for digital photogrammetry for the study of wide shallow gravel bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated Correction Procedure for dealing with point errors associated with through-water photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The Procedure involves combining digital photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The Correction Procedure was applied to raw digital elevation models (DEMs) generated using digital photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that digital photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following Correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the Correction Procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
-
The development of an automated Correction Procedure for digital photogrammetry for the study of wide, shallow, gravel‐bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated Correction Procedure for dealing with point errors associated with through-water photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The Procedure involves combining digital photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The Correction Procedure was applied to raw digital elevation models (DEMs) generated using digital photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that digital photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following Correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the Correction Procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
Stuart N Lane - One of the best experts on this subject based on the ideXlab platform.
-
the development of an automated Correction Procedure for digital photogrammetry for the study of wide shallow gravel bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated Correction Procedure for dealing with point errors associated with through-water photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The Procedure involves combining digital photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The Correction Procedure was applied to raw digital elevation models (DEMs) generated using digital photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that digital photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following Correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the Correction Procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
-
The development of an automated Correction Procedure for digital photogrammetry for the study of wide, shallow, gravel‐bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated Correction Procedure for dealing with point errors associated with through-water photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The Procedure involves combining digital photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The Correction Procedure was applied to raw digital elevation models (DEMs) generated using digital photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that digital photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following Correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the Correction Procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
Chunlei Liang - One of the best experts on this subject based on the ideXlab platform.
-
an efficient Correction Procedure via reconstruction for simulation of viscous flow on moving and deforming domains
Journal of Computational Physics, 2014Co-Authors: Chunlei Liang, Koji Miyaji, Bin ZhangAbstract:In this paper, we report the development of a new parallel solver using the Correction Procedure via Reconstruction (CPR) for viscous flows on moving and deforming grids. By employing an accurate treatment of flux derivatives for moving and deforming unstructured grids consisting of all quadrilateral cells, it is found that the Geometric Conservation Law is not explicitly required, the free-stream preservation is automatically satisfied. The CPR code is verified using a benchmark case for a moving inviscid vortex on moving and deforming grids. The optimal orders of accuracy are obtained. It is subsequently employed to study viscous flows on moving and deforming grids. The CPR method is faster than and nearly as accurate as the SD method for solving viscous flow problems with moving boundaries.
-
short note a comparison of computational efficiencies of spectral difference method and Correction Procedure via reconstruction
Journal of Computational Physics, 2013Co-Authors: Chunlei Liang, Christopher Cox, Michael W PlesniakAbstract:We report computational efficiencies of two types of numerical solvers. The first type uses the spectral difference (SD) method and the second one uses the Correction Procedure via reconstruction (CPR). In this paper, we employ the lumped g"2 scheme proposed by Huynh as an example of the CPR approach. The solvers deal with both inviscid Euler equations and Navier-Stokes equations on 2D unstructured grids which are comprised of all quadrilateral cells. Both types of solvers are programmed using Fortran 90 with similar management of data structures. We employ identical time marching schemes for both SD and CPR methods. Spatial 3rd and 4th order of accuracy for both methods is demonstrated by a study of a moving inviscid vortex. The comparisons were directed to measure the computational efficiency of both SD and CPR methods in spatial discretization. With respect to the fourth order methods, CPR is 27% faster than SD for inviscid flow, and more promisingly, CPR is over 40% faster than SD for viscous flow.
Hendrik Ranocha - One of the best experts on this subject based on the ideXlab platform.
-
stability of Correction Procedure via reconstruction with summation by parts operators for burgers equation using a polynomial chaos approach
Mathematical Modelling and Numerical Analysis, 2018Co-Authors: Philipp Öffner, Jan Glaubitz, Hendrik RanochaAbstract:In this paper, we consider Burgers’ equation with uncertain boundary and initial conditions. The polynomial chaos (PC) approach yields a hyperbolic system of deterministic equations, which can be solved by several numerical methods. Here, we apply the Correction Procedure via reconstruction (CPR) using summation-by-parts operators. We focus especially on stability, which is proven for CPR methods and the systems arising from the PC approach. Due to the usage of split-forms, the major challenge is to construct entropy stable numerical fluxes. For the first time, such numerical fluxes are constructed for all systems resulting from the PC approach for Burgers' equation. In numerical tests, we verify our results and show also the performance of the given ansatz using CPR methods. Moreover, one of the simulations, i.e . Burgers’ equation equipped with an initial shock, demonstrates quite fascinating observations. The behaviour of the numerical solutions from several methods (finite volume, finite difference, CPR) differ significantly from each other. Through careful investigations, we conclude that the reason for this is the high sensitivity of the system to varying dissipation. Furthermore, it should be stressed that the system is not strictly hyperbolic with genuinely nonlinear or linearly degenerate fields.
-
Correction Procedure via Reconstruction Using Summation-by-Parts Operators
Theory Numerics and Applications of Hyperbolic Problems II, 2018Co-Authors: Philipp Öffner, Hendrik Ranocha, Thomas SonarAbstract:The Correction Procedure via reconstruction (CPR, also known as flux reconstruction), is a high-order numerical scheme for conservation laws introduced by Huynh (2007), unifying some discontinuous Galerkin, spectral difference and spectral volume methods. A general framework of summation-by-parts (SBP) operators with simultaneous approximation terms (SATs) is presented, allowing semidiscrete stability for Burgers’ equation using nodal bases without boundary nodes or modal bases. The linearly stable schemes of Vincent et al. (2011, 2015) are embedded within this general kind of semidiscretisation. The contributed talk Artificial Viscosity for Correction Procedure via Reconstruction Using Summation-by-Parts Operators given by Philipp Offner extends these results.
-
Artificial Viscosity for Correction Procedure via Reconstruction Using Summation-by-Parts Operators
Theory Numerics and Applications of Hyperbolic Problems II, 2018Co-Authors: Jan Glaubitz, Hendrik Ranocha, Philipp Öffner, Thomas SonarAbstract:We focus on spectral viscosity in the framework of Correction Procedure via reconstruction (CPR, also known as flux reconstruction) using summation-by-parts (SBP) operators. In Ranocha et al. (J Comput Phys 342:13–28, 2017), [10], Ranocha et al. (J Comput Phys 311:299–328, 2016), [9], the authors used SBP operators in the CPR framework and were able to recover and extend some results of Gassner (SIAM J Sci Comput 35(3):A1233–A1253, 2013), [1] and Vincent et al. (Comput Methods Appl Mech Eng 296:248–272, 2015), [12]. In this contribution, we introduce a viscosity term for a scalar conservation law and analyse this new setting in the context of CPR methods using SBP operators. We derive conditions on the viscosity term and the basis, which allow us to prove conservation and stability in the semidiscrete setting. Next, we extend semidiscrete stability results to fully discrete stability by an explicit Euler method. Numerical tests are presented, which verify our results (Ranocha, Enhancing stability of Correction Procedure via reconstruction using summation-by-parts operators I: artificial dissipation, 2016, [8]). This is an extension of the contribution Correction Procedure via Reconstruction Using Summation-by-parts Operators by Hendrik Ranocha (J Comput Phys 342:13–28, 2017), [10], Ranocha et al. (J Comput Phys 311:299–328, 2016), [9].
-
Summation-by-Parts and Correction Procedure via Reconstruction
Lecture Notes in Computational Science and Engineering, 2017Co-Authors: Hendrik Ranocha, Philipp Öffner, Thomas SonarAbstract:The Correction Procedure via reconstruction (CPR, also known as flux reconstruction), is a framework of high order methods for conservation laws, unifying some discontinuous Galerkin, spectral difference and spectral volume methods. These methods are embedded in the framework of summation-by-parts (SBP) operators with simultaneous approximation terms (SATs), recovering the linearly stable methods of Vincent et al. (J Comput Phys 230(22): 8134–8154, 2011; J Sci Comput 47(1):50–72, 2011; Comput Methods Appl Mech Eng 296:248–272, 2015). The introduction of new Correction terms enables stability for Burgers’ equation using nodal bases not including boundary nodes, i.e. Gauss nodes. Extended notions of SBP operators and split-forms are used to obtain stability.
-
stability of Correction Procedure via reconstruction with summation by parts operators for burgers equation using a polynomial chaos approach
arXiv: Numerical Analysis, 2017Co-Authors: Philipp Öffner, Jan Glaubitz, Hendrik RanochaAbstract:In this paper, we consider Burgers' equation with uncertain boundary and initial conditions. The polynomial chaos (PC) approach yields a hyperbolic system of deterministic equations, which can be solved by several numerical methods. Here, we apply the Correction Procedure via reconstruction (CPR) using summation-by-parts operators. We focus especially on stability, which is proven for CPR methods and the systems arising from the PC approach. Due to the usage of split-forms, the major challenge is to construct entropy stable numerical fluxes. For the first time, such numerical fluxes are constructed for all systems resulting from the PC approach for Burgers' equation. In numerical tests, we verify our results and show also the advantage of the given ansatz using CPR methods. Moreover, one of the simulations, i.e. Burgers' equation equipped with an initial shock, demonstrates quite fascinating observations. The behaviour of the numerical solutions from several methods (finite volume, finite difference, CPR) differ significantly from each other. Through careful investigations, we conclude that the reason for this is the high sensitivity of the system to varying dissipation. Furthermore, it should be stressed that the system is not strictly hyperbolic with genuinely nonlinear or linearly degenerate fields.
