Investigation of wave impacts on porous structures for coastal defences

There is great scientific interest in further understanding the underlying wave impact dynamics on solid and/or permeable structures for coastal defences. The accurate and validated simulation of the dynamics of the flow at microsecond temporal scale prior to, at, and after impact is an outstanding and challenging numerical problem in CFD. More advanced numerical models of free surface flow processes which include entrapment of large air pockets is required. These models will yield more insight into the trends of pulse-like forces involved at impact with solid and/or porous material and will enable the understanding of the mechanical stability and integrity of defence structures. Furthermore, the development of advanced numerical models for solving such problems will need to be made accessible as information systems to a wider community of civil engineers in order to achieve integrated design of structural defences (coastal, offshore oil and gas, hydraulic dams etc.). This research is on the development of free surface flow simulations, flow visualisation, analyses of forces of impact, and analyses of the integrity of offshore structures in an information system environment. A large dataset of compressible (and incompressible) numerical models have been generated to simulate waves impacting at solid and porous structures. Initial studies focus on the behaviour of wave impacts with a solid structure in a 2 dimensional domain. The simulations data are verified through a grid independence study. Numerical results are validated against two sets of experimental data. Air bubble entrapment and consequential multi-modal oscillatory pressure response trends are observed in the compressible simulations during wave impact. Frequency domain analyses of the oscillatory impact pressure responses are undertaken. The numerical model data sets are compared with results generated from analytic methods and experimental data with good agreement. These initial findings confirm the robustness of our numerical model predictions concerning the simulated air bubble formations when compared with theories on air bubbles at impact and their resonance frequency modes. The compressible numerical model is extended to a 3 dimensional simulation. A range of porous structure morphologies are incorporated into the domain to replace solid wall impact interface. A brief overview of previous research on the subject of fluid flow in porous media is presented. The characterisation of the porous model morphologies is examined. Various permeability flow models are discussed in detail. The methods for the generation of the various porous structures and their integration into the CFD model are described. The results from a soliton wave impact at the porous structure morphologies both with and without air entrainment effects at the free surface is investigated in detail.Finally future work to develop an experimentation specification for the analysis of fluid flow thorough a porous structure is discussed. It is envisioned that this experimental work with have dual outcomes. Firstly it will serve to validate the numerical models created over the course of this study and secondly the potential for clean, renewable energy harvesting from oscillatory pressures through the incorporation of smart sensor hardware within the porous structure will be investigated

Analysis of fluid flow impact oscillatory pressures with air entrapment at structures

Hydrodynamic wave loading at coastal structures is a complex phenomenon to quantify. The chaotic nature of the fluid flow field as waves break against such structures has presented many challenges to Scientists and Engineers for the design of coastal defences. The provision of installations such as breakwaters to resist wave loading and protect coastal areas has evolved predominantly through empirical and experimental observations. This is due to the challenging understanding and quantification of wave impact energy transfer processes with air entrainment at these structures. This paper presents a numerical investigation on wave loading at porous formations including the effects of air entrapment. Porous morphologies generated from cubic packed spheres with varying characteristics representing a breakwater structure are incorporated into the numerical model at the impact interface and the effect on the pressure field is investigated as the wave breaks. We focus on analysing the impulse impact pressure as a surging flow front impacts a porous wall. Thereafter we investigate the multi-modal oscillatory wave impact pressure signals which result from a transient plunging breaker wave impinging upon a modelled porous coastal protective structure. The high frequency oscillatory pressure effects resulting from air entrapment are clearly observed in the simulations. A frequency domain analysis of the impact pressure responses is undertaken. We show that the structural morphology of the porous assembly influences the pressure response signal recorded during the impact event. The findings provide good confidence on the robustness of our numerical model particularly for investigating the air bubbles formation and their mechanics at impact with porous wall

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline

Initial invasive or conservative strategy for stable coronary disease

BACKGROUND Among patients with stable coronary disease and moderate or severe ischemia, whether clinical outcomes are better in those who receive an invasive intervention plus medical therapy than in those who receive medical therapy alone is uncertain. METHODS We randomly assigned 5179 patients with moderate or severe ischemia to an initial invasive strategy (angiography and revascularization when feasible) and medical therapy or to an initial conservative strategy of medical therapy alone and angiography if medical therapy failed. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, or hospitalization for unstable angina, heart failure, or resuscitated cardiac arrest. A key secondary outcome was death from cardiovascular causes or myocardial infarction. RESULTS Over a median of 3.2 years, 318 primary outcome events occurred in the invasive-strategy group and 352 occurred in the conservative-strategy group. At 6 months, the cumulative event rate was 5.3% in the invasive-strategy group and 3.4% in the conservative-strategy group (difference, 1.9 percentage points; 95% confidence interval [CI], 0.8 to 3.0); at 5 years, the cumulative event rate was 16.4% and 18.2%, respectively (difference, 121.8 percentage points; 95% CI, 124.7 to 1.0). Results were similar with respect to the key secondary outcome. The incidence of the primary outcome was sensitive to the definition of myocardial infarction; a secondary analysis yielded more procedural myocardial infarctions of uncertain clinical importance. There were 145 deaths in the invasive-strategy group and 144 deaths in the conservative-strategy group (hazard ratio, 1.05; 95% CI, 0.83 to 1.32). CONCLUSIONS Among patients with stable coronary disease and moderate or severe ischemia, we did not find evidence that an initial invasive strategy, as compared with an initial conservative strategy, reduced the risk of ischemic cardiovascular events or death from any cause over a median of 3.2 years. The trial findings were sensitive to the definition of myocardial infarction that was used