Design Statistics
Metocean design criteria have a major bearing on the cost of offshore and coastal structures. They are calculated by applying Extreme Value Analysis (EVA) to a database of Metocean variables representative of the site of the development.
OceanMetriX specialises in developing robust, high quality independent and joint probability Metocean design criteria using modern EVA methods. Our estimates are supported by meaningful confidence intervals: a true measure of uncertainty and an important input into the design process. Our procedures are more complex than traditional methods, as they incorporate recently developed EVA theory and take advantage of modern statistical techniques. The results, however, can reduce design conservatism and lead to major savings in construction costs.
The form of Metocean design criteria depends on the choice of design practice. Traditional practices require Independent design criteria, which are developed using Univariate EVA methods. Reliability based practices use joint probability or dependent criteria, which are calculated using Multivariate EVA methods.
Independent Criteria:
OceanMetriX's basic approach to Univariate EVA is to model extremes using statistically rational distributions which permit calculation of meaningful confidence intervals. We develop inferences using computer intensive methods which minimise uncertainty by exploiting all relevant data, and using the data in the most efficient manner.
In some cases we modify the basic statistical model, for example: to account for complex structure of data, such as the combination of tide and surge in sea level extremes; to pool information from neighbouring sites; or to test sensitivity of designs to climate instability or sea level rise.
Joint Probability Criteria:
Our approach to Multivariate EVA builds on to our Univariate procedures. Our proprietary software uses modern techniques to characterise dependence structures at extreme levels, and sophisticated models to replicate and extrapolate the joint tail of the distributions to design levels.
Operations Statistics
OceanMetriX specialises in using advanced statistical methods to assist operators to plan efficient marine operations and to work safely in the marine environment
Operations Weather Thresholds:
We use statistical models to develop GO/ NO GO weather thresholds for marine operations. The models define a relationship between the probability of success of an operation and a range of weather variables and associated factors. Final “working” thresholds are decided in consultation with the marine operators.
Operations Planning Statistics:
Significant cost savings can be realised by using minimum specification, fit-for-purpose equipment, or by working in the off-season. The economics will depend on weather downtime. Metocean databases are generally too short to provide accurate downtime statistics. OceanMetriX accounts for this by using simulation techniques to generate many years of sea-state realisations from relatively short data records.
We usually express the planning statistics in the form of seasonal or monthly charts, tables, or “persistence/exceedence” graphs. Where an operation is tide limited we can predict the tides and generate Tide Tables which highlight the limiting conditions.
Operations Advisories:
Graphs displaying an operation’s weather threshold and “real-time” and forecast weather variables are useful management tools. They forewarn of impending downtime and indicate the probable length of the delay.
Deep Water Current Profiles
As Oil & Gas industry activities move into deep waters they tend to become increasingly susceptible to currents. This is both a function of increased drag on subsea structures (e.g. drilling riser), and the tendency for currents to increase at the ocean-sea boundary.
OceanMetriX's oceanographers are specialists in the complex dynamics of deep-water regions.
We are able to carry out regional reviews to identify potential flow forcing mechanisms and to assess the risks of significant currents at a particular location. If there is a case for on-site currents measurements, we can specify and manage the data collection programme. We can use the measurements, together with the results of the regional review, to build statistical models of the flow processes. We can use these models to construct:
• Envelopes of "Normal" currents;
• Profiles of "Survival" currents;
• Flow regimes (for fatigue analysis); and
• Flow forecasting algorithms.