NOAA NTHMP Mapping & Modeling Subcommittee Benchmarking Workshop: Tsunami Current NEOWAVE Validation Yefei Bai, Yoshiki Yamazaki, and Kwok Fai Cheung Department of Ocean and Resources Engineering University of Hawaii at Manoa Portland, Oregon February 9-10, 2015
NEOWAVE Model Introduction Prior Model Validation - 2011 Tohoku Tsunami Honolulu Coast Benchmark Cases BM1 BM2 BM5 Conclusions Outline
NEOWAVE Non-hydrostatic Evolution of Ocean Wave Governing Equations Depth-integrated, Non-hydrostatic Equations Weakly dispersive waves through non-hydrostatic pressure (Stelling and Zijlema, 2003; Yamazaki et al., 2009 & 2011) Numerical Schemes Semi-implicit, Finite Difference (FD) Model Explicit hydrostatic solution Implicit non-hydrostatic solution Two-Way, Grid-Nesting Scheme Standard grid refinement scheme for FD tsunami models Momentum Conserved Advection (MCA) Scheme Shock capturing scheme for FD models (Stelling and Duinmeijer, 2003; Yamazaki et al., 2009 & 2011)
Non-hydrostatic/Hydrostatic Hybrid Scheme Approximation of Energetic Breaking Waves as Bores Dispersive wave model generates artificial spike when wave front becomes steep at wave breaking or bore development Breaking region may consider hydrostatic for bore approximation - Hydrostatic pressure is main driving force - Non-hydrostatic pressure effects are negligible Check status of each cell every time step Breaking initiation Breaking termination 2 2 u v 0. 5 gd 2 2 u v 0. 15 gd Hydrostatic solution (TURN OFF non-hydrostatic) Non-hydrostatic solution (TURN ON non-hydrostatic) NO wave breaking
Prior Validation with 2011 Tohoku Tsunami Surface elevation time series (cm) Amplitude Spectrum Tide Gauge Kilo Nalu Velocity components time series (cm/s) Amplitude Spectrum Entrance ADCP Kilo Nalu High Sampling Rate Mea. Low Sampling Rate Mea. NEOWAVE
BM NO.1 Shallow-Water Flow around Submerged Conical Island (Lloyd and Stansby, 1997) 976 m (975cm) 152 cm 27 cm 500 cm 102 cm U0 = 11.5 cm/s 5.4 cm Manning coefficient =0.01 RIGHT boundary Open B.C.
BM NO.1 Close View of Conical Island with Three Resolutions 102 m left point 1.0-cm grid 27 cm center point 2.0-cm grid 5 cm 4.9 cm 5.4 cm 4.0-cm grid 75 cm
BM NO.1 Velocity Comparison center point Exp. 1cm 2cm 4cm left point
BM NO.1 Vortex Field Comparison Δx=1cm (977x153) Δt=0.0025s Δx=2cm (485x77) Δt=0.005s Δx=4cm (245x39) Δt=0.01s
BM NO. 1 Vortex Field Closeview Vortices are formed faster in finer grid Clear boundary between clockwise and counterclockwise vortex field 1cm 2cm 4cm
BM NO.2 Shallow-Water Flow around Hilo Bay BOTTOM boundary Wall B.C. LEFT boundary Wall B.C. u v Tide Gauge HA1126 HA1125 Control Point RIGHT boundary Wall B.C. : tide gauge or ADCP : initial wave extraction point TOP boundary Initiates solitary wave.
BM NO.2: DEM Data Modification Original NTHMP Hilo DEM Data - Induce Instability
BM NO.2: DEM Data Modification Modified NTHMP Hilo DEM Data - Remove Instability
BM NO.2 Tide Gauge Comparison record Mea. ed. 5m 5m 10m 10m 20m 20m (hour) Hilo Tide Gauge - Nested Grid spectrum amplitude 8 9 10 11 12 13 10 100 Mea. NEOWAVE
BM NO.2 Velocity Comparison Mea. 5m 10m 20m
BM NO.2 Velocity Comparison Mea. 5m 10m 20m
BM NO.2 Vortex Field Comparison Δt=0.025s Δx=5m (1401x1029) 2m/s Δt=0.05s Δx=10m (701x515) 2m/s Δt=0.1s Δx=20m (351x258) 2m/s
(a) Overview BM NO. 5 Shallow Shelf with a Conical Island Inundation Science & Engineering Cooperative (ISEC) Community Workshop Oregon State University, Corvallis, Oregon, July 8-10, 2009 (http://isec.nacse.org/workshop/isec_workshop_2009/) 45 m 25.9 m 19.1 m 10 m 7.5 m 8.4 m 17 m 12.5 m 12.5 m r=3 m 6.6 m 12.5 m 26 m (b) Side view 1 / 250 78 cm 45 cm 8 cm 1 / 3.57 28 cm 3 cm 22 cm 1 / 15
BM NO. 5 Model Setup Gird spaces: Δ x = Δ y = 5cm, 10cm, 25cm Time step: Δ t = 0.002s, 0.003s, 0.01s Manning coefficients: n = 0.012 (for finished concrete) TOP boundary Wall B.C. RIGHT boundary Wall B.C. Initial condition Solitary wave h = 78cm A = 0.5 h y x LEFT boundary Initiates solitary wave. BOTTOM boundary Wall B.C. : gesture gauge : wave gauge and ADV
BM NO.5 Surface Elevation Comparison at Gesture Gauges Exp. 5cm 10cm 25cm
BM NO.5 Velocity Components Comparison at ADVs Central Front Point Central Back Point Exp. 5cm Right Back Point 10cm 25cm
BM NO. 5 Vortex Field Comparison Vortices are generated in the wake and around the island Vortex strength is weaker in coarser grid but general pattern remains in all three grid sizes Runup process also involve vortex field 5cm 10cm 25cm
Conclusions NEOWAVE can reproduce the mean flow which is less sensitive to resolution Numerically generated vortex field depends on Spatial and temporal resolution Bottom friction Numerical scheme Generation mechanism Relation with physical vortex field