scholarly journals SHOALING PROPERTIES OF BOUNDED LONG WAVES

1984 ◽  
Vol 1 (19) ◽  
pp. 54 ◽  
Author(s):  
E.P.D. Mansard ◽  
V. Barthel
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Second Order ◽  
Long Waves ◽  
Experimental Results ◽  
Wave Groups ◽  
Good Insight ◽  
Set Up ◽  
Theoretical Considerations ◽  
Insight Into

Group bounded long waves which appear as a set-down under a group of high waves and a set-up in between groups are well described for constant water depth. However, their propagation into shallow water and their interaction with the constituent wave groups are not well understood and theoretically described yet. Therefore, model investigations were carried out to study shoaling properties of these second order waves in terms of amplitudes and phases. The tests give a good insight into the phenomenon and suggest distinct shoaling properties. Moreover, experimental results provide a valuable basis for future theoretical considerations.

The Set-Down and Set-Up of Directionally Spread and Crossing Surface Gravity Wave Groups in Severe North Sea Storms

2018 ◽  
Author(s):  
Mark L. McAllister ◽  
Thomas A. A. Adcock ◽  
Ton S. van den Bremer ◽  
Paul H. Taylor
Keyword(s):  
Free Surface ◽  
North Sea ◽  
Water Depth ◽  
Order Theory ◽  
Relative Magnitude ◽  
Second Order ◽  
Experimental Results ◽  
Surface Gravity Wave ◽  
Wave Groups ◽  
Set Up

Recent work by McAllister et al. (2018) [1] has experimentally confirmed that the set-down of the wave-averaged free surface, first described by Longuet-Higgins and Stewart (1962) [2], can turn into a set-up when wave groups are sufficiently spread or cross at large angles. Experimental results were shown to agree well with second-order theory, including frequency-sum and frequency-difference terms, where the latter are responsible for the wave-averaged free surface. In this paper, we review these experimental results and examine theoretically the magnitude of the wave-averaged free surface in realistic extreme North Sea conditions. Specifically, we examine the role of the shape of the spectrum, water depth, and the relative magnitude of the peak frequencies of the two crossing groups. We find that having a realistic spectrum (JONSWAP vs. Gaussian) considerably enhances the magnitude of the second-order contribution, the total second-order signal increases with decreasing depth and can display a maximum provided the water depth is shallow enough for small to moderate degrees of spreading or crossing angles and is larger for spectral peaks that are further apart.

The propagule method as a tool to study assemblage dynamics in benthic foraminifera: An example with pH variations

2021 ◽  
Author(s):  
Anna E. Weinmann ◽  
Susan T. Goldstein ◽  
Maria V. Triantaphyllou ◽  
Martin R. Langer
Keyword(s):  
Shallow Water ◽  
Benthic Foraminifera ◽  
Environmental Changes ◽  
Ph Gradients ◽  
Local Conditions ◽  
Recovery Mechanisms ◽  
Decreasing Ph ◽  
Set Up ◽  
Ph Variations ◽  
Insight Into

<p>Benthic foraminifera are important indicators for ecological studies. The assemblage composition of local communities can be used to analyze influences of environmental variables such as temperature, salinity, pH, and others. In recent years, the experimental propagule method has emerged as an effective tool to evaluate the influence of these variables on assemblage dynamics of benthic foraminifera. Propagules (tiny juveniles) of benthic foraminifera are widespread and can survive outside of a species’ natural distribution range. Their ability to become dormant and be re-activated once local conditions become suitable, is an important driver behind the capacity of foraminiferal assemblages to react quickly to environmental changes. In the laboratory, the propagules are first separated from the coarser fractions by sieving and then cultured under different conditions.</p><p>In the present study, we analyzed the effect of ocean pH on the composition of shallow-water assemblages from Corfu Island (Greece). Like other calcifying organisms, assemblages of foraminifera are susceptible to pH variations and have revealed compositional shifts along natural or experimental pH gradients. Our experimental set-up included four pH treatments between 6.5 and 8.5 at constant temperature and salinity (22°C and 38 ppt) for 5 weeks.</p><p>At the conclusion of the cultivation experiment, we found high numbers of grown specimens (825–1564 per replicate) and a high survivability rate throughout all treatments (78–87%). Higher pH (7.8 and 8.5) resulted in assemblages that were dominated by monothalamous and porcelaneous species, whereas lower pH (6.5 and 7.2) lead to a reduction in porcelaneous and an increase in agglutinated species. Several taxa showed significant positive or negative correlations with decreasing pH values.</p><p>Our results are congruent with previous findings that reported compositional shifts from calcareous to agglutinated taxa with decreasing pH (both from culture and field observations). Our study also indicates that the activation of propagules is an important mechanism behind assemblage dynamics in shallow-water foraminifera. As such, it offers an improved insight into potential resilience and recovery mechanisms of foraminiferal assemblages with regard to local or seasonal pH variations as well as ongoing ocean acidification.</p>

Laboratory Wave Modelling for Floating Structures in Shallow Water

2006 ◽  
Author(s):  
Carl Trygve Stansberg
Keyword(s):  
Shallow Water ◽  
Low Frequency ◽  
Second Order ◽  
Wave Groups ◽  
Large Wave ◽  
Frequency Wave ◽  
Wave Modelling ◽  
Floating Structures ◽  
Wave Basin ◽  
Wave Drift Forces

The analysis of moored floating vessels in shallow water requires special attention, when compared to similar problems in deep water. In particular, low-frequency wave drift forces need to be studied. Model testing is essential in validation of numerical prediction tools for these problems. Wave-group induced low-frequency wave components is an important part of the problem. Their reproduction in laboratories needs special attention. In general, two types of low-frequency waves are present: “bound” waves following the wave groups, and “free” waves propagating with their own speed. The former is included in second-order numerical codes for floater is included in second-order numerical codes for floaters, while the latter is normally not. Therefore, identification and possible reduction of the free components is of interest. A practical way to do this in a large wave basin is described in this paper. Results from generation of bi-chromatic waves without and with correction are presented. Corrected results show a clear reduction of the free wave component.

scholarly journals CORRECT REPRODUCTION OF GROUP-INDUCED LONG WAVES

1980 ◽  
Vol 1 (17) ◽  
pp. 47
Author(s):  
N.E. Ottesen Hansen ◽  
Stig E. Sand ◽  
H. Lundgren ◽  
Torben Sorensen ◽  
H. Gravesen
Keyword(s):  
Second Order ◽  
Long Waves ◽  
Wave Problem ◽  
Wave Groups ◽  
Storm Waves ◽  
Slow Drift ◽  
Short Period ◽  
Harbour Resonance ◽  
The Waves ◽  
Wave Phenomena

In nature short period storm waves generate longer waves with periods corresponding to the wave group periods. The long waves are generally referred to as the wave set-down of water level. The set-down term is of second order in the height of the short waves. With first order reproduction of natural storm waves in the laboratory, the setdown bound to the wave groups is not reproduced. As a result, various free waves are generated, propagate towards the model and reflect from the boundaries. These so-called parasitic waves cause an exaggeration of long wave phenomena, such as harbour resonance and slow drift oscillations of moored ships. The parasitic waves can be eliminated by means of compensating free waves imposed on the system by second-order paddle motion reproducing the natural set-down. The control signal for this motion has been calculated and checked by testing. The agreement between calculated and measured results is found to be good. Further, an alternative method for reducing the parasitic wave problem is presented. Utilizing the shoaling properties of the various waves, the influence of parasitic waves can be diminished by generating the waves in somewhat deeper water before they propagate into the shallower model area.

Harbour excitations by incident wave groups

1990 ◽  
Vol 217 ◽  
pp. 595-613 ◽  
Author(s):  
Jiang-Kang Wu ◽  
Philip L.-F. Liu
Keyword(s):  
Incident Wave ◽  
Multiple Scales ◽  
Low Frequency ◽  
Second Order ◽  
Long Waves ◽  
Wave Groups ◽  
Order Of Magnitude ◽  
Harbour Resonance ◽  
Analytical Expressions ◽  
Multiple Scales Perturbation Method

By using the multiple-scales perturbation method, analytical solutions are obtained for the second-order low-frequency oscillations inside a rectangular harbour excited by incident wave groups. The water depth is a constant. The width of the harbour entrance is of the same order of magnitude as the wavelength of incident carrier (short) waves, but small in comparison with the wavelength of the wave envelope. Because of the modulations in the wave envelope, a second-order long wave is locked in with the wave envelope and propagates with the speed of the group velocity. Outside the harbour, locked long waves also exist in the reflected wave groups, but not in the radiated wave groups. Inside the harbour, the analytical expressions for the locked long waves are obtained. Owing to the discontinuity of the locked long waves across the harbour mouth, second-order free long waves are generated. The free long waves propagate with a speed of (gh)½ inside and outside the harbour. The free long waves inside the harbour may be resonated in a low-frequency range which is relevant to the harbour resonance.

The Prince TLP Steel Catenary Risers: Design and Fatigue Challenges

2003 ◽  
Author(s):  
Basim B. Mekha ◽  
Bart Heijermans
Keyword(s):  
Fracture Mechanics ◽  
Gulf Of Mexico ◽  
Shallow Water ◽  
Fatigue Test ◽  
Water Depth ◽  
Oil And Gas ◽  
Floating Structure ◽  
Critical Flaw ◽  
Steel Catenary Risers ◽  
Insight Into

The Prince field in Ewing Bank Block 1003 in the Gulf of Mexico was developed using a “Moses” Tension Leg Platform in a water depth of 455m (1492 ft). Two 12-inch Export Steel Catenary Risers (SCRs) connected to the TLP were designed for oil and gas transportation. The Prince field water depth is the shallowest so far for SCRs connected to a floating structure. Having the SCRs in such relatively shallow water provided many challenges to the SCRs designers, as well as the TLP hull designers. The SCR design required large departure angles of 24 degrees to mitigate the touchdown area stresses and to accommodate the TLP surge (i.e. near and far) motions. The large SCR departure angles resulted in long suspended sections of the SCRs and consequently long sections were required on the seabed. Also, the SCR configuration caused high static and dynamic horizontal loads that were directed to the TLP hull. The motions of the TLP in this water depth affect the entire SCR length and thus, the fatigue and the corresponding fracture mechanics assessment became a very significant aspect of the SCR design. This paper gives a brief introduction to the Prince TLP and its two export SCRs. It also provides an insight into the challenges faced and overcome during their design. The fatigue approach and results with data from the fatigue test programs are also presented. A summary of the fracture mechanics assessment and the critical flaw sizes derived based on BS 7910 (1999) are given.

Diffraction of sea waves by a slender body. Part 2. Water of finite depth

1990 ◽  
Vol 216 ◽  
pp. 133-160 ◽  
Author(s):  
J. A. P. Aranha ◽  
C. A. Martins
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Body Part ◽  
Finite Depth ◽  
Second Order ◽  
Slender Body ◽  
Sea Waves ◽  
Finite Water Depth

A uniformly valid theory (all wavelengths and angles of incidence) for the diffraction of sea waves by a slender body, correct to second order in the slenderness parameter, has been derived for the shallow-water limit. This theory is now extended to the finite water depth case, with the same results and accuracy.

Long wave generation by the shoaling and breaking of transient wave groups on a beach

2006 ◽  
Vol 462 (2070) ◽  
pp. 1853-1876 ◽  
Author(s):  
T.E Baldock
Keyword(s):  
Shallow Water ◽  
Water Waves ◽  
Surf Zone ◽  
Laboratory Data ◽  
Short Wave ◽  
Long Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Spatial Gradients ◽  
Long Wave

This paper presents new laboratory data on the generation of long waves by the shoaling and breaking of transient-focused short-wave groups. Direct offshore radiation of long waves from the breakpoint is shown experimentally for the first time. High spatial resolution enables identification of the relationship between the spatial gradients of the short-wave envelope and the long-wave surface. This relationship is consistent with radiation stress theory even well inside the surf zone and appears as a result of the strong nonlinear forcing associated with the transient group. In shallow water, the change in depth across the group leads to asymmetry in the forcing which generates significant dynamic setup in front of the group during shoaling. Strong amplification of the incident dynamic setup occurs after short-wave breaking. The data show the radiation of a transient long wave dominated by a pulse of positive elevation, preceded and followed by weaker trailing waves with negative elevation. The instantaneous cross-shore structure of the long wave shows the mechanics of the reflection process and the formation of a transient node in the inner surf zone. The wave run-up and relative amplitude of the radiated and incident long waves suggests significant modification of the incident bound wave in the inner surf zone and the dominance of long waves generated by the breaking process. It is proposed that these conditions occur when the primary short waves and bound wave are not shallow water waves at the breakpoint. A simple criterion is given to determine these conditions, which generally occur for the important case of storm waves.

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