Second order waves before and after the floor work in the OEB in 2010 : Part B

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Second order waves before and after the floor work in the OEB in 2010 : Part B

Zaman, Hasanat; McKay, Shane; NRC Ocean, Coastal and River Engineering

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OCRE-TR-2013-004

NATIONAL RESEARCH COUNCIL CANADA OCEAN, COASTAL AND RIVER ENGINEERING

Second order waves before and after

the floor work in the OEB in 2010:

Part B

Technical Report - UNCLASSIFIED

Hasanat Zaman Shane McKay February, 2013

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REPORT NUMBER PROJECT NUMBER

DATE

SECURITY CLASSIFICATION DISTRIBUTION

TITLE

AUTHOR(S)

CORPORATE AUTHOR(S)/PERFORMING AGENCY(S) PUBLICATION (Journal or Conference name)

SPONSORING AGENCY(S)

RAW DATA STORAGE LOCATION(S)

PEER REVIEWED

MODEL # PROP

EMBARGO PERIOD

PROJECT (NPArC) GROUP (NPArC)

PROGRAM (NPArC) FACILITY (NPArC)

KEY WORDS PAGES TABLES FIGS.

SUMMARY

Report Documentation Page

OCRE - GOCF

2013 6 February

Wave quality, 2nd order waves, unwanted free waves i, 132, App 1-2 2

OCRE-TR-2013-004 _PJ2414-26 _UNCLASSIFIED _UNLIMITED

Second order waves before and after the floor work in the OEB in 2010: Part B

Hasanat Zaman and Shane McKay

NRC Ocean, Coastal and River Engineering

NRC-ST. JOHN’S

--- --- Research

--- St. John's: P.O. Box 12093, Arctic Ave, St. John's, NL A1B 3T5

This is a continuation of the work reported in TR-2013-003. In summer 2010, the south-west side trenches (0.3m x 0.4m) under and in front of the wave makers in the OEB have been permanently filled-up to provide a homogeneous bottom and uniform water depth all over the basin. This work is to understand the improvement of the wave quality after the floor work. Two sets of

experimental data comprised of mono- and bi-chromatic waves before and after the floor work are used to identify the impact of the development work on the generation of unwanted second order free waves in the OEB. In this report results are compared between the measured energies at different probe locations and also second order wave components before and after the floor work in the OEB. Comparisons are shown in terms of measured wave energies, primary waves, bounded waves and unwanted second order free waves elevations. In this report 0.8m of water depth is considered. In most of the cases it is observed from the results that the shallower the wave the better the wave quality after the floor work.

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National Research Council Conseil national de recherches Canada Canada Ocean, Coastal and River Génie océanique, côtier et fluvial Engineering

Second order waves before and after the floor work in the OEB in

2010: Part B

Technical Report UNCLASSIFIED

OCRE-TR-2013-004

Hasanat Zaman and Shane McKay

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ABSTRACT

This is a continuation of the work reported in OCRE-TR-2013-003 (Second order waves before and after the floor work in the OEB in 2010: Part-A). In summer 2010, the south-west side trenches (width 0.4m and depth 0.3m) under and in front of the wave makers in the OEB have been permanently filled-up to provide a homogeneous bottom and uniform water depth all over the basin. This work is to understand the improvement of the wave quality after the floor work. In this work two sets of experimental data comprised of mono- and bi-chromatic waves before and after the floor work are used to identify the impact of the development work on the generation of unwanted second order free waves in the OEB. The first set of wave data (called before from now on) was obtained from the experimental work before the trenches were filled-up and the second set of data (called after from now on) was obtained from the experiment after the trenches were filled up. In the experiments both mono- and bi-chromatic wave are considered for 0.8m water depths. Results for 0.8m water depth are reported in this report (Part-B). Results for 0.4m, 0.5m and 0.6m water depth were reported in Part-A. Comparisons of the data were done for identical wave conditions.

Please refer to report “Second order waves before and after the floor work in the OEB

in 2010: Part-A” for description of the experiments, experimental setup, data acquisition

etc..

1. INCIDENT WAVE CONDITIONS

In the experiments both mono- and bi-chromatic waves of different wave periods, wave heights and water depths are used. See Zaman and Mak (2007) and Zaman et al (2010) for several cases of mono- and bi-chromatic waves before the floor work and Zaman et al (2011) and Zaman et al (2013) after the floor work. Tables 2a and 2b show different incident wave conditions that we used in the experiments. In the tables below T1

and T2 are wave periods, H1 and H2 are the wave heights, h is the water depth, L is the

wave length and h/L is the relative water depth.

Table 2a Mono-chromatic incident wave parameters (h=0.8m) T1 (s) H1 (m) h(m) h/L

M8-1 2.370 0.06 0.8 0.133 M8-2 3.035 0.08 0.8 0.100 M8-3 4.105 0.06 0.8 0.071 Table 2b Bi-chromatic incident wave parameters (h=0.8m) T1 (s) h(m) H1 (m) T2 (s) H2 (m) h/L

B8-1 1.00 0.8 0.06 0.90 0.06 0.516 B8-2 1.55 0.8 0.02 1.45 0.02 0.236 B8-3 1.55 0.8 0.08 1.45 0.08 0.236 B8-4 2.12 0.8 0.08 2.02 0.08 0.153

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The bottom of the basin was flat and the blanking plates were deployed to cover the north beach.

2. DATA ANALYSES

We have analyzed two sets of data, one for before the floor work and the other one is

after the floor work. Different wave conditions and water depths are considered as shown in Tables 2a and 2b. All the data are compared and the results are shown in terms of surface elevations and wave energies across the wave tank at probes 5-4-3-6-7 (Probe-5, Probe-4, Probe-3, Probe-6 and Probe-7) and along the tank at probes 1-2-3-8-9 (Probe-1, Probe-2, Probe-3, Probe-8 and Probe-9), see Fig. 1. Data at Probes 10, 11, 12, 13 and 14 are not available for 0.8m water depth.

2.1 COMPARISONS - 1: Monochromatic waves

Tables 2a and 2b respectively, show the incident wave conditions for mono-chromatic waves, respectively over 0.8m (M8) water depths. All the above cases are run with and without trenches condition in front of the south and west wave makers of the OEB. Comparisons of the results are made between both cases, with and without trenches. Results are compared in terms of measured surface elevation data, wave energies and isolated wave components including second order waves across and along the wave tank. Figs. 2a to 7j show the energy distribution, measured surface elevation, isolated primary wave, bounded and second order unwanted free wave components at different probe locations in the basin for the mono-chromatic waves of 0.8m water depth mentioned in Table 2a. Measured water surface elevations, wave energies and isolated primary, bounded and unwanted free waves at across-tank probes 5-4-3-6-7 and at the along-tank probes 1-2-3-8-9 are plotted together to show the differences in the amplitudes after and before the floor work. Unwanted free waves are reproduced due to the mismatch of the boundary conditions at the wave paddle and due to the displacement of the wave paddle from its zero position.

It is observed from the results that the smaller the relative water depth h L_(i.e.

shallower the wave) the better the wave quality after the floor work. For shallower wave it is also noted that the shallower the wave the better the wave energies distributions across the tank for measured, primary, bounded and free waves for after cases. It is perceived that the second order wave components are reduced for shallow waves after the floor work.

2.2 COMPARISONS - 2: Bichromatic waves

Table 2b show the incident wave conditions for bi-chromatic waves over 0.8m (B8) water depths. The above cases are run for: with and without trenches conditions in front of the south and west wave makers of the OEB. Results are again compared between both

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elevation data, wave energies and isolated wave components including second order waves across the wave tank.

Figs. 8a to 19j show the energy distribution, measured surface elevation, isolated primary wave, bounded and second order unwanted free wave components at different probe locations in the basin for the bi-chromatic waves of 0.8m water depth for different incident wave conditions shown in Table 2b. Obtained water surface elevations, wave energies and isolated primary, bounded and unwanted free waves at across-tank probes 5-4-3-6-7 and at the along-tank probes 1-2-3-8-9 are plotted together to show the differences in the component amplitudes after and before the floor work.

3. LWAVE utilization

A NRC-IOT computer code LWAVE that can split a measured surface elevation data set into its component waves is used for the analysis. This code is utilized to isolate the primary waves, bounded second order waves and unwanted free waves from the raw measured data at every probe location.

4. RESULTS

In this experiment 0.8m water depths (h= 0.8m) was used. The incident wave parameters are shown in Table 2a for mono- and Table 2b for bi-chromatic waves.

Results are compared between the measured wave data, before and after the floor work in OEB.

Appendix-I compares energy distribution and second order wave components for mono-chromatic wave over 0.8m water depth at different probe locations.

Appendix-II compares energy distribution and second order wave components for bi-chromatic wave over 0.8m water depth at different probe locations.

5. CONCLUSIONS

Comparisons of the results for surface elevations and energy propagations between the measured data before and after the floor work are shown. Deep water wave (h Lt0.5₎

will not be affected by the floor and the wave starts to feel the bottom when the relative water depth (h L_{) is less than 0.5. So the smaller the value of}h L_{means more the}

effects of the bottom on the propagating waves. From the data it is observed that after the floor work, the wave quality in the tank improved for the shallow water where the floor effect is essentially an important issue. For intermediate and deep water case this change or improvement is insignificant.

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John’s.

Zaman, M. H., Baddour, E. and Mckay, S. (2011): Wave propagation before and after the floor work in the OEB in 2010, TR-2011-16, March, National Research Council Canada, Institute for Ocean Technology.

Zaman, M. H., Peng, H., Baddour, E., Spencer, D. and Mckay, S. (2010): Identifications of spurious waves in the wave tank with shallow water, 29th Int. Conf. on offshore Mech. and Arctic Eng. (OMAE-2010), American Society of Mechanical Engineers (ASME), Shanghai, China, on CD-ROM.

Zaman, M. H. and L. Mak (2007): Second order wave generation technique in the laboratory, 26th Int. Conf. on offshore Mech. and Arctic Eng. (OMAE-2007), American Society of Mechanical Engineers (ASME), San Diego, USA, on CD-ROM.

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Appendix – I

Energy distribution and second order wave components for monochromatic wave over 0.8m water depth

Probes array: Probes: 1-2-3-8-9 Probes: 5-4-3-6-7

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Fig. 2a: Comparisons between primary and low frequency wave energy Probes: 1-2-3-8-9

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Fig. 2b: Comparisons between high frequency wave energy Probes: 1-2-3-8-9

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Fig. 2c: Comparisons between primary and low frequency wave energy Probes: 5-4-3-6-7

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Fig. 2d: Comparisons between high frequency wave energy Probes: 5-4-3-6-7

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Fig. 3a: Isolated wave components from measured wave data at Probe-1 M8-1 : REGP8_H0P06_T2P370

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Fig. 3c: Isolated wave components from measured wave data at Probe-3 M8-1 : REGP8_H0P06_T2P370

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Fig. 3e: Isolated wave components from measured wave data at Probe-5 M8-1 : REGP8_H0P06_T2P370

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Fig. 3g: Isolated wave components from measured wave data at Probe-7 M8-1 : REGP8_H0P06_T2P370

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Fig. 3i: Isolated wave components from measured wave data at Probe-9 M8-1 : REGP8_H0P06_T2P370

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Fig. 5a: Isolated wave components from measured wave data at Probe-1 B8-2 : REGP8_H0P08_T3P035

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Fig. 5c: Isolated wave components from measured wave data at Probe-3 B8-2 : REGP8_H0P08_T3P035

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Fig. 5e: Isolated wave components from measured wave data at Probe-5 B8-2 : REGP8_H0P08_T3P035

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Fig. 5g: Isolated wave components from measured wave data at Probe-7 B8-2 : REGP8_H0P08_T3P035

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Fig. 5i: Isolated wave components from measured wave data at Probe-9 B8-2 : REGP8_H0P08_T3P035

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Fig. 7a: Isolated wave components from measured wave data at Probe-1 B8-3 : REGP8_H0P08_T4P105

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Fig. 7c: Isolated wave components from measured wave data at Probe-3 B8-3 : REGP8_H0P08_T4P105

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Fig. 7e: Isolated wave components from measured wave data at Probe-5 B8-3 : REGP8_H0P08_T4P105

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Fig. 7g: Isolated wave components from measured wave data at Probe-7 B8-3 : REGP8_H0P08_T4P105

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Fig. 7i: Isolated wave components from measured wave data at Probe-9 B8-3 : REGP8_H0P08_T4P105

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Appendix – II

Energy distribution and second order wave components for bichromatic wave over 0.8m water depth

Probes array: Probes: 1-2-3-8-9 Probes: 5-4-3-6-7

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Fig. 9b: Isolated wave components from measured wave data at Probe-2 B8-1 : BIP8_H0P06_T1P0_T0P9

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Fig. 9d: Isolated wave components from measured wave data at Probe-4 B8-1 : BIP8_H0P06_T1P0_T0P9

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Fig. 9f: Isolated wave components from measured wave data at Probe-6 B8-1 : BIP8_H0P06_T1P0_T0P9

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Fig. 9h: Isolated wave components from measured wave data at Probe-8 B8-1 : BIP8_H0P06_T1P0_T0P9

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Fig. 9j: Isolated wave components from measured wave data at Probe-10 B8-1 : BIP8_H0P06_T1P0_T0P9

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