The average shape of large waves in the coastal zone

The ability of the NewWave focused wave group (the scaled auto-correlation function) to represent the average shape in time of large waves in a random sea state makes it a useful tool for the design of offshore structures. However, the profile has only been validated against field data for waves on deep and intermediate water depths. A similar validation is advisable when applying NewWave to shallow water problems,where waves are less dispersive and more nonlinear. For this purpose, data recorded by two Channel Coastal Observatory (CCO) wave buoys during two large storms in January 2014 are analysed to assess the ability of NewWave to replicate the average shape of large waves in shallow water. A linear NewWave profile is shown to successfully capture the average shape of the largest waves from the Perranporth and Porthleven wave buoys during these large storm events. The differences between the measurements obtained by a surface-following buoy and a fixed sensor become important when considering the ability of a second-order corrected NewWave profile to capture weakly nonlinear features of the measured data. A general expression for this effect is presented for weakly nonlinear waves on intermediate water depths, leading to Lagrangian second-order sum corrections to the linear NewWave profile. A second-order corrected NewWave profile performs reasonably well in capturing the average features of large waves recorded during the January storms. These findings demonstrate that the NewWave profile is valid in relatively shallow water (kpD values less than 0.5), and so may have potential for use as a design wave in coastal engineering applications

Lagrangian modelling of nonlinear viscous waves generated by moving seabed deformation

A Lagrangian flow model is used to investigate highly nonlinear, dispersive waves generated by moving seabed deformation (MSD) of an otherwise horizontal seabed. Applications include free surface wave responses to horizontal co-seismic displacements and to novel bed-driven wave making systems used in surfing competitions. This paper considers gravity waves in viscous liquid, without restrictions on wave steepness, dispersion coefficient, and flow regime. Numerical computations are carried out using a Moving Particle Explicit method, which provides a Lagrangian flow description with far fewer particles than existing meshless methods. We show that the MSD speed has different effects in shallow and intermediate water depths. In shallow water, raising the MSD speed to a transcritical value promotes generation of leading solitary waves as expected. In supercritical flow, the highly nonlinear dynamics promotes breaking of the precursor soliton. In intermediate depth, wave dynamics is dominated by nonlinearity and dispersion, which act concurrently to generate a large leading wave that travels faster than predicted by linear theory, followed by a train of dispersive, short, steep waves. These waves break, even at subcritical values of MSD speed. We show that strongly nonlinear viscous dynamics occurs in the presence of a steep seabed deformation. This triggers flow separation, linked to strong amplification of wave steepness. Finally, we show that an oscillating MSD is capable of generating higher harmonics by means of nonlinear wave–wave interactions. The model is validated and verified by comparison to previously published experimental data and approximate analytical solutions

Weakly nonlinear theory for dispersive waves generated by moving seabed deformation

We present a weakly nonlinear theory for the evolution of dispersive transient waves generated by moving seabed deformation. Using a perturbation expansion up to second order, we show that higher-order components affect mostly the leading wave and the region close to the deforming seabed. In particular, the leading wave in the nonlinear regime has higher crests and deeper troughs than the known linear solution, while the trough that propagates together with the moving seabed exhibits pulsating behaviour and has larger depth. We also validate the analytical model with experimental data and obtain good agreement between both approaches. Our results suggest a need to extend existing models that neglect the effects of wave dispersion and higher-order components, especially in view of practical applications in engineering and oceanography.</jats:p

Survivability assessment of fastnet lighthouse

Historic rock lighthouses are unusual structures that are situated in hostile marine environments to provide warning to mariners. Even in an era of satellite navigation their role continues to be an important one, but their survivability into the future is not assured. Out of concern for their ongoing service, the multidisciplinary STORMLAMP project is assessing their survivability under wave loading. This paper presents the various stages of investigations into the structural integrity and stability assessment of the Fastnet lighthouse, situated just off the coast of Ireland. The paper describes: Extreme Bayesian analysis to quantify waves of particular return periods resulting in a 1 in 250 year return period wave with H 0.1% of 17.6 m and an associated maximum force of 20,765 kN; logistically challenging field modal tests revealing the key modal parameters, like the modal masses of 1822 t and 1 675 t for 4.8 Hz and 5.0 Hz modes respectively, the cantilevered nature of the overall lighthouse and the directional effects due to the asymmetric contact with the granite rock; and details of a discontinuous finite element model that is used to determine the stability of the tower under the 1 in 250 year return period breaking wave condition, which is well within stability and material strength limits, causing maximum horizontal displacements in the order of 1 mm at the top of the tower. The overall assessment is that the sheer mass of the lighthouse and its interconnected joints are able to withstand the worst of the Atlantic storms. Coastal Engineerin

Multi-directional focused wave group interactions with a plane beach

Numerical simulations and laboratory measurements are presented of multi-directional focused wave groups interacting with a plane beach. The numerical model is a two-dimensional-horizontal (2DH) hybrid flow solver, governed by a Boussinesq equation set with enhanced dispersion characteristics pre-breaking, and the nonlinear shallow water equations post-breaking. Waves are introduced into the model via an in-built multi-element piston wavemaker, allowing for complete reproduction of laboratory experiments. A wetting and drying algorithm models shoreline movement in both cross-shore and longshore directions. Predicted free surface motions of the multi-directional focused wave groups are in good agreement with wave gauge data from laboratory experiments previously carried out at the UK Coastal Research Facility (UKCRF) using a linear paddle wave generator. Both phase decomposition into Stokes-like harmonic components and wavelets provide insight into nonlinear interactions as the wave groups propagate up the beach. Free second-order error waves in a multi-directional wave group are smaller than for the corresponding uni-directional case, and spread laterally around the incoming wave group. Of the free error waves generated by linear paddle signals, only the low-frequency second-order error wave affects extreme run-up on the beach. By applying a second-order correction to the paddle signals used to generate a multi-directional wave group, it is shown that, whereas the long error wave causes a significant increase in the maximum run-up, the impact is not as severe as for the uni-directional analogue. Shoaling and run-up of the bound long waves in a spread sea are studied. Examination of the transverse structure of these subharmonic components reveals that sideways spreading in the inner surf zone contributes to reduced run-up in directionally spread groups

CD62L (L-selectin) shedding for assessment of perioperative immune sensitivity in patients undergoing cardiac surgery with cardiopulmonary bypass

OBJECTIVE: To investigate the suitability of blood granulocyte and monocyte sensitivity, as measured by the quantity of different agonists required to induce CD62L shedding, for assessment of perioperative immune changes in patients undergoing cardiac surgery with cardiopulmonary bypass. METHODS: Patients scheduled for aortocoronary bypass grafting or for valve surgery were included in this prospective observational study. Blood samples were drawn before anesthesia induction, directly after surgery and 48 hours after anesthesia induction. We determined the concentration of two different inflammatory stimuli--lipoteichoic acid (LTA) and tumor necrosis factor alpha (TNF)--required to induce shedding of 50% of surface CD62L from blood granulocytes and monocytes. In parallel monocyte surface human leukocyte antigen (HLA)-DR, and plasma interleukin (IL)-8, soluble (s)CD62L, soluble (s)Toll-like receptor (TLR)-2 and ADAM17 quantification were used to illustrate perioperative immunomodulation. RESULTS: 25 patients were enrolled. Blood granulocytes and monocytes showed decreased sensitivity to the TLR 2/6 agonist Staphylococcus aureus LTA immediately after surgery (p = 0.001 and p = 0.004 respectively). In contrast, granulocytes (p = 0.01), but not monocytes (p = 0.057) displayed a decreased postoperative sensitivity to TNF. We confirmed the presence of a systemic inflammatory response and a decreased immune sensitivity in the post-surgical period by measuring significant increases in the perioperative plasma concentration of IL-8 (p </= 0.001) and sTLR (p = 0.004), and decreases in monocyte HLA-DR (p<0.001), plasma sCD62L (p </= 0.001). In contrast, ADAM17 plasma levels did not show significant differences over the observation period (p = 0.401). CONCLUSIONS: Monitoring granulocyte and monocyte sensitivity using the "CD62L shedding assay" in the perioperative period in cardiac surgical patients treated with the use of cardiopulmonary bypass reveals common changes in sensitivity to TLR2/6 ligands and to TNF stimulus. Further long-term follow-up studies will address the predictive value of these observations for clinical purposes

Risk Factors Associated with Positive QuantiFERON-TB Gold In-Tube and Tuberculin Skin Tests Results in Zambia and South Africa

INTRODUCTION: The utility of T-cell based interferon-gamma release assays for the diagnosis of latent tuberculosis infection remains unclear in settings with a high burden of tuberculosis. OBJECTIVES: To determine risk factors associated with positive QuantiFERON-TB Gold In-Tube (QFT-GIT) and tuberculin skin test (TST) results and the level of agreement between the tests; to explore the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST. METHODS: Adult household contacts of tuberculosis patients were invited to participate in a cross-sectional study across 24 communities in Zambia and South Africa. HIV, QFT-GIT and TST tests were done. A questionnaire was used to assess risk factors. RESULTS: A total of 2,220 contacts were seen. 1,803 individuals had interpretable results for both tests, 1,147 (63.6%) were QFT-GIT positive while 725 (40.2%) were TST positive. Agreement between the tests was low (kappa = 0.24). QFT-GIT and TST results were associated with increasing age (adjusted OR [aOR] for each 10 year increase for QFT-GIT 1.15; 95% CI: 1.06-1.25, and for TST aOR: 1.10; 95% CI 1.01-1.20). HIV positivity was less common among those with positive results on QFT-GIT (aOR: 0.51; 95% CI: 0.39-0.67) and TST (aOR: 0.61; 95% CI: 0.46-0.82). Smear positivity of the index case was associated with QFT-GIT (aOR: 1.25; 95% CI: 0.90-1.74) and TST (aOR: 1.39; 95% CI: 0.98-1.98) results. We found little evidence in our data to support our hypotheses. CONCLUSION: QFT-GIT may not be more sensitive than the TST to detect risk factors associated with tuberculous infection. We found little evidence to support the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST