Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

DSD-INT 2018 Validation test of a solitary wave over an erodible sloped beach for XBeach in Non-Hydrostatic mode - Mancini

322 views

Published on

Presentation by Giulia Mancini, University of Nottingham, UK, at the XBeach User Day 2018, during Delft Software Days - Edition 2018. Thursday, 15 November 2018, Delft.

Published in: Software
  • Be the first to comment

  • Be the first to like this

DSD-INT 2018 Validation test of a solitary wave over an erodible sloped beach for XBeach in Non-Hydrostatic mode - Mancini

  1. 1. Validation test of a solitary wave over an erodible sloped beach for XBeach in Non-Hydrostatic mode Giulia Mancini, Riccardo Briganti, Nicholas Dodd University of Nottingham, UK Fangfang Zhu University of Nottingham Ningbo, China Environmental Fluid Mechanics and Geoprocesses Research Group
  2. 2. • Introduction and Motivation • Aim and Objectives • Methodology • Results • Conclusions
  3. 3. Introduction and Motivation The non-hydrostatic version of XBeach model allows to simulate the propagation of individual waves in the nearshore region up to the shoreline and bed changes However, modelling of the intra-swash sediment transport and, in turn, morphodynamic evolution of beaches needs further investigation x=44.5m x=75.86m Simulated and measured velocity and suspended sediment concentration in the swash zone Bichromatic broad-banded wave condition
  4. 4. Aim and Objectives Aim: Improve the modelling of intra-swash processes in wave resolving models • Simulation of a solitary wave over an erodible beach Single swash event without the complexity of swash-swash interaction present in wave groups • Comparison with the high accuracy numerical solution obtained by Zhu and Dodd (2015) Analytical solution used as a benchmark for assessing XBeach response Objectives
  5. 5. Methodology Zhu and Dodd (2015): XBeach in Non-hydrostatic mode (“XBeachX BETA” release): • 1D - Non Linear Shallow Water Equations including bed shear stress • 𝜕𝑧 𝑏 𝜕𝑡 + ξ 𝜕𝑞 𝑏 𝜕𝑥 = ξ(𝐷 − 𝐸) • 𝜕ℎ𝐶 𝜕𝑡 + 𝜕ℎ𝑢𝐶 𝜕𝑥 = 𝑚 𝑒 𝑢2 𝑢0 − 𝑤𝑠C = E − D (suitable for swash zone flow, but unlike XBeach frequency dispersion is not modelled) + (Pritchard and Hogg, 2005) • 1D - Non Linear Shallow Water Equations + Non-hydrostatic pressure term (comparable to SWASH one single layer version) Governing equations: • 𝜕ℎ𝐶 𝜕𝑡 + 𝜕ℎ𝑢𝐶 𝜕𝑥 + 𝑑𝑖𝑓𝑓 = ℎ𝐶 𝑒𝑞−ℎ𝐶 𝑇𝑠 = 𝐸 − 𝐷 • 𝜕 𝑧 𝑏 𝜕𝑡 + ξ 𝜕𝑞 𝑏 𝜕𝑥 = ξ(D − E) + (Galappatti and Vreugdenhil, 1985) Governing equations: (solved by means of method of characteristics)
  6. 6. Methodology - Bed load (Van Thiel – Van Rijn) Equilibrium concentration: - Suspended load (Van Thiel – Van Rijn) As all waves are resolved in extended NLSWE, in the non- hydrostatic solver all intra-wave velocities are currently included in “u” term (thus, urms is null) 𝜕ℎ𝐶 𝜕𝑡 + 𝜕ℎ𝑢𝐶 𝜕𝑥 + 𝑑𝑖𝑓𝑓 = ℎ𝐶𝑒𝑞 − ℎ𝐶 𝑇𝑠 = E − D 𝐶𝑒𝑞 = max min 𝐶𝑒𝑞,𝑏, 1 2 𝐶 𝑚𝑎𝑥 + min 𝐶𝑒𝑞,𝑠, 1 2 𝐶 𝑚𝑎𝑥 , 0 𝐶𝑒𝑞,𝑏 = 𝐴 𝑠𝑏 ℎ 𝑢2 + 0.64𝑢 𝑟𝑚𝑠 2 − 𝑈𝑐𝑟 1.5 𝐶𝑒𝑞,𝑠 = 𝐴 𝑠𝑠 ℎ 𝑢2 + 0.64𝑢 𝑟𝑚𝑠 2 − 𝑈𝑐𝑟 2.4 XBeach in Non-hydrostatic mode: sediment transport formulation implemented were originally validated only for the wave-averaged framework
  7. 7. Methodology Zhu and Dodd (2015): • Initial condition along the x-domain (t=0s, x) • Solitary wave simulated by means of 1st order theory of cnoidal waves by Mei (1990) XBeach: • Boundary condition located at x=-20 m • Time series of u(t) and η(t) provided by Zhu and Dodd (2015)
  8. 8. Results • Initial shoreline position located at x = 5m, where the bore collapses • In the uprush sediment is entrained in the water column and transported onshore • In the backwash sediment is entrained in the water column and moved offshore • Bed step formation due to collision of backwash bore and still water mass
  9. 9. Results Hydrodynamics: 𝑡/ ℎ0/𝑔 𝑡/ ℎ0/𝑔 𝑢/𝑔ℎ0𝑢/𝑔ℎ0𝑢/𝑔ℎ0
  10. 10. Results Bed step Bed step Erosion Erosion Bed changes: 0 𝑡/ℎ0/𝑔 Deposition Bed step Erosion Deposition
  11. 11. Results • 𝜕ℎ𝐶 𝜕𝑡 + 𝜕ℎ𝑢𝐶 𝜕𝑥 = 𝐸 − 𝐷 • 𝜕 𝑧 𝑏 𝜕𝑡 + ξ 𝜕𝑞 𝑏 𝜕𝑥 = −ξ(E − D) Sediment transport equation: Exner equation: x=6m x=12m Source term Source term
  12. 12. Results x = 6m XBeachZhu and Dodd (2015) 𝑡/ ℎ0/𝑔 𝑡/ ℎ0/𝑔 Flow reversal • The advection term dominates on the source term • The source term has the same order of magnitude as the advection term
  13. 13. Results x = 6m XBeachZhu and Dodd (2015) 𝑡/ ℎ0/𝑔 𝑡/ ℎ0/𝑔 0 𝑡/ℎ0/𝑔 Exner equation
  14. 14. Results x = 12m XBeachZhu and Dodd (2015) 𝑡/ ℎ0/𝑔 𝑡/ ℎ0/𝑔 • The advection term dominates on the source term • The source term has the same order of magnitude as the advection term Flow reversal
  15. 15. Results x = 12m XBeachZhu and Dodd (2015) 𝑡/ ℎ0/𝑔 𝑡/ ℎ0/𝑔 0 𝑡/ℎ0/𝑔 Exner equation
  16. 16. Conclusions Ongoing work: inclusion of further sediment transport formulation (Pritchard and Hogg, 2005) and testing of multiple events • Despite the different governing equations, results highlight a good agreement between the two models in terms of hydrodynamics response 0 • The main qualitative difference is noticed in the uprush suspended sediment transport and morphodynamic response Sediment transport formulation implemented were originally validated only for the wave-averaged framework 𝑡/ ℎ0/𝑔 𝑡/ℎ0/𝑔 Flow reversal
  17. 17. Thank you for your attention! Giulia Mancini Email: evxgm7@nottingham.ac.uk References: XBeach model: • D. Roelvink, et al. XBeach model description and manual. Unesco-IHE Institute for Water Education, Deltares and Delft University of Technology, 2010 • P. Smit, G. Stelling, J.A. Roelvink , J. Van Thiel de Vries, R. McCall, A. van Dongeren, C. Zwinkels, R. Jacobs. XBeach: Non-hydrostatic model: Validation, verification and model description. Delft University of Technology, 2010 CoSSedM-HYDRALAB IV project: • J.M. Alsina, E.M. Padilla, I. Cáceres. Sediment transport and beach profile evolution induced by bi-chromatic wave groups with different group periods. Coastal Engineering 114: 325-340, 2016 • G. Ruffini, R. Briganti, J. Alsina, M. Brocchini, N. Dodd, R. McCall. Manuscript under review Zhu and Dodd (2015) model: • F. Zhu and N. Dodd. The morphodynamics of a swash event on an erodible beach. Journal of Fluid Mechanics, 762:110–140, 2015 • D. Pritchard and A. J. Hogg. On the transport of suspended sediment by a swash event on a plane beach. Coastal Engineering, 52(1):1–23, 2005

×