GMS, SMS, and WMS User Forum

# Harris

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1. ## CGWAVE: output time series / spectrum

Hi all, Does anyone know whether CGWAVE can output the wave spectrum at a an output point? or, alternatively, is it possible to modify the time step and length of the output time series? I want to use a white noise spectrum as input, say in the band from 20Hz to 200Hz, in order to determine the resonance frequencies of a harbour. If the first component of input spectrum is the T=20sec component, the time interval of the output time series is 1sec and the duration 20sec. If the longest duration component (T=200sec) is first, the time interval is 10sec and the duration 200sec. It appears that the time series outplot plot corresponds to the first component of the input spectrum. Fot this example, to be effective, the output time series should be at least 200sec long and the time interval 1/400sec. In both cases the provided time series is not sufficient to determine the wave spectrum at an output point. Thanks, Harris
2. ## Infragravity Wave Modeling with CGWAVE

Hi, I am trying to model the wave agitation within a harbour basin caused by infra-gravity (IG) waves. These long period (20 - 200sec) waves are formed under the windsea wave groups and are bound to them, hence, their propagation characteristics (celerity and direction)are those of the wave group. Moreover, their "shoaling" characteristics differ from the free gravity waves. The IG waves are released and can propagate as free gravity waves when the wave group formation ceases to exist, either due to depth induced breaking along the breaker zone or due to diffraction at the harbour entrance. Hence, in order to model the wave penetration into a harbour with CGWAVE, the input wave characteristics at the offshore boundary should be such that the resulting characteristics (amplitude and direction)at the harbour entrance are approximately those of the IG characteristics when they are released from the group at that area. Due to the very long period that the IG waves exhibit, the CGWAVE model region must extend far away form the the harbour entrance. If we provide the free IG wave characteristics at the offshore boundary, the nearshore characteristics (amplitude and direction) would differ from the actual nearshore charcateristics at the zone of their release. My question is how to setup the model region for IG waves. In addition, it seems to me that the "Infragravity Wave Toolbox" that may be used to create the IG wave spectrum at a specific water depth for a specified windsea spectrum, outputs the components' spectral density rather than amplitude and therefore the IG wave height at the boundary is unrealistic. Thank you. Harris
3. ## Infra-gravity wave toolbox

I tried to create the IG wave spectrum based on a windsea standard directional spectrum defined in SMS, utilizing the IG Wave Toolbox of CGWAVE under SMS 9.2. However, the wave energy of the generated IG spectrum seems to be too high. The input windsea spectrum is a TMA spectrum characterized by Hs=3.0m and Tp=7.0sec (gamma=3.3 and nn=4) with 30 frequency and 30 directional components. The correponding *.spf file was created at the IG Wave Toolbox by selecting the above spectrum. The followind data were entered in the IG Wave Toolbox: Offshore water depth: 50m Nearshore water depth: 6.0m Lower long wave period cutoff: 20sec Upper long wave period cutoff: 120sec Number of frequency components: 30 Max wave direction: 130 deg Min wave direction: 130 deg Number of wave directions: 1 The frequency interval of the generated IG spectrum is constant. The number of the frequency components is 40 rather than 30, while the resulting IG wave energy (mo=1/2 * sum of squares of amplitudes) is 4.95 m2 which corresponds to an Hs about 8.9m! I would very much appreciate your comments / assistance in the correct implementation of the IG wave toolbox.
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