NOAA NTHMP Mapping & Modeling

Subcommittee Benchmarking Workshop:

Tsunami Current

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 Validation

• NEOWAVE Model Introduction

• Prior Model Validation - 2011 Tohoku Tsunami

– Honolulu Coast

• Benchmark Cases

– BM1

– BM2

– BM5

• Conclusions

Outline

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)

NEOWAVE

Non-hydrostatic Evolution of Ocean Wave

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

Non-hydrostatic solution(TURN ON non-hydrostatic)

Hydrostatic solution(TURN OFF non-hydrostatic)

Breaking initiation

gDvu 5.022

Breaking termination

gDvu 15.022

Check status of

each cell every

time step

NO wave breaking

Prior Validation with 2011

Tohoku Tsunami Tide Gauge

Kilo Nalu

Surface elevation time series (cm) Amplitude Spectrum

Entrance ADCPKilo Nalu

Velocity components time series (cm/s) Amplitude Spectrum

NEOWAVE

High Sampling Rate Mea.

Low Sampling Rate Mea.

BM NO.1Shallow-Water Flow around Submerged Conical Island

(Lloyd and Stansby, 1997)

RIGHT

boundary

Open B.C.

27 cm

5.4 cm

500 cm 102 cm

976 m (975cm)

152 cm

U0 = 11.5 cm/s

Manning coefficient =0 .01

1.0-cm grid

2.0-cm grid

4.0-cm grid

BM NO.1Close View of Conical Island with Three Resolutions

75 cm

102 m

5 cm

4.9 cm 5.4 cm

27 cm

center point

left point

1cm 2cm 4cmExp.

center point

left point

BM NO.1 – Velocity Comparison

BM NO.1 – Vortex Field Comparison

Δx=1cm (977x153)

Δx=2cm (485x77)

Δx=4cm (245x39)

Δt=0.0025s

Δt=0.005s

Δt=0.01s

BM NO. 1 – Vortex

Field Closeview 1cm

2cm 4cm

• Vortices are formed faster in

finer grid

• Clear boundary between

clockwise and

counterclockwise vortex field

BM NO.2Shallow-Water Flow around Hilo Bay

RIGHT boundary

Wall B.C.

TOP boundary

Initiates solitary wave.

: tide gauge or ADCP

: initial wave extraction point

BOTTOM boundary

Wall B.C.

LEFT boundary

Wall B.C.

Control Point

HA1125HA1126

Tide Gauge

u

v

BM NO.2: DEM Data ModificationOriginal NTHMP Hilo DEM Data - Induce Instability

BM NO.2: DEM Data ModificationModified NTHMP Hilo DEM Data - Remove Instability

5m 10m 20mrecord

ed.

BM NO.2 – Tide Gauge Comparison

(hour)

5m 10m 20mMea.

8 9 10 11 12 13 10 100

spectrum amplitudeHilo Tide Gauge - Nested Grid

NEOWAVEMea.

BM NO.2 – Velocity Comparison

5m 10m 20mMea.

5m 10m 20mMea.

BM NO.2 – Velocity Comparison

BM NO.2 – Vortex Field Comparison

Δt=0.025s

Δx=5m (1401x1029)

Δt=0.05s

Δx=10m (701x515)

Δt=0.1s

Δx=20m (351x258)2m/s2m/s 2m/s

(a) Overview

(b) Side view

BM NO. 5Shallow Shelf with a Conical Island

10 m 7.5 m

45 m

8.4 m

6.6 m 12.5 m12.5 m 12.5 m

25.9 m 19.1 m

26 m

r=3 m

17 m

1 / 3.57

1 / 15

1 / 250

78 cm

22 cm

28 cm

45 cm

3 cm

8 cm

• Inundation Science & Engineering Cooperative (ISEC)

Community Workshop

• Oregon State University, Corvallis, Oregon, July 8 - 10,

2009 (http://isec.nacse.org/workshop/isec_workshop_2009/)

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)

Initial condition

Solitary wave

h = 78cm

A = 0.5 h

BOTTOM boundary

Wall B.C.

RIGHT boundary

Wall B.C.

LEFT boundary

Initiates solitary wave.

TOP boundary

Wall B.C.

: gesture gauge

: wave gauge and ADV

BM NO. 5Model Setup

x

y

BM NO.5Surface

Elevation

Comparison at

Gesture Gauges

5cm

10cm

25cm

Exp.

5cm

10cm

25cm

Exp.

BM NO.5Velocity Components Comparison at ADVs

Central Front Point

Central Back Point

Right Back Point

BM NO. 5Vortex Field Comparison

5cm

10cm 25cm

• 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

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