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Weather Window
A weather window occurs when weather forecasts indicate that a given set of marine operations or offshore construction activities can be performed within their maximum limits for wave height, wind speeds etc. Critical elements for offshore operations are use of time and expected weather. Planning of marine operations should be based on an operation's reference period defined as: Operation reference period (TR) = Estimated time of operation + Estimated unforeseen time If unforeseen time has not been identified, the operation reference period is normally set at twice the estimated operation time. Marine operations with a reference period less than 72 hours can be defined as weather-limited operations. These operations can be planned independently of statistical data and based only on weather forecasts. For weather-limited operations, critical factors such as forces, movements and acceleration shall be calculated in a rather worse weather condition (design criterion) than the wea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weather Forecasting
Weather forecasting is the application of science and technology forecasting, to predict the conditions of the Earth's atmosphere, atmosphere for a given location and time. People have attempted to predict the weather informally for millennia and formally since the 19th century. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere, land, and ocean and using meteorology to project how the atmosphere will change at a given place. Once calculated manually based mainly upon changes in atmospheric pressure, barometric pressure, current weather conditions, and sky condition or cloud cover, weather forecasting now relies on numerical weather prediction, computer-based models that take many atmospheric factors into account. Human input is still required to pick the best possible forecast model to base the forecast upon, which involves pattern recognition skills, teleconnections, knowledge of model performance, and knowledge of model biases ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Offshore Construction
Offshore construction is the installation of structures and facilities in a marine environment, usually for the production and transmission of electricity, oil, gas and other resources. It is also called maritime engineering. Construction and pre-commissioning is typically performed as much as possible onshore. To optimize the costs and risks of installing large offshore platforms, different construction strategies have been developed. One strategy is to fully construct the offshore facility onshore, and tow the installation to site floating on its own buoyancy. Bottom founded structure are lowered to the seabed by de-ballasting (see for instance Condeep or Cranefree), whilst floating structures are held in position with substantial mooring systems. The size of offshore lifts can be reduced by making the construction modular, with each module being constructed onshore and then lifted using a crane vessel into place onto the platform. A number of very large crane vessels w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wave Height
In fluid dynamics, the wave height of a surface wave is the difference between the elevations of a crest and a neighboring trough. ''Wave height'' is a term used by mariners, as well as in coastal, ocean and naval engineering. At sea, the term ''significant wave height'' is used as a means to introduce a well-defined and standardized statistic to denote the characteristic height of the random waves in a ''sea state'', including wind sea and swell. It is defined in such a way that it more or less corresponds to what a mariner observes when estimating visually the average wave height. Definitions Depending on context, wave height may be defined in different ways: *For a sine wave, the wave height ''H'' is twice the amplitude (i.e., the '' peak-to-peak amplitude''): H = 2a. *For a periodic wave, it is simply the difference between the maximum and minimum of the surface elevation : H = \max\left\ - \min\left\, with ''c''p the phase speed (or propagation speed) of the wave. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wind Speed
In meteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer. Wind speed affects weather forecasting, aviation and maritime operations, construction projects, growth and metabolism rate of many plant species, and has countless other implications. Note that wind direction is usually almost parallel to isobars (and not perpendicular, as one might expect), due to Earth's rotation. Units Metres per second (m/s) is the SI unit for velocity and the unit recommended by the World Meteorological Organization for reporting wind speeds, and is amongst others used in weather forecasts in the Nordic countries. Since 2010 the International Civil Aviation Organization (ICAO) also recommends meters per second for reporting wind speed when approaching runways, replacing their former recommendation of using kilometres per h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Significant Wave Height
In physical oceanography, the significant wave height (SWH, HTSGW or ''H''s) is defined traditionally as the mean ''wave height'' (trough to crest) of the highest third of the waves (''H''1/3). Nowadays it is usually defined as four times the standard deviation of the surface elevation – or equivalently as four times the square root of the zeroth-order moment (area) of the ''wave spectrum''. The symbol ''H''m0 is usually used for that latter definition. The significant wave height (Hs) may thus refer to ''H''m0 or ''H''1/3; the difference in magnitude between the two definitions is only a few percent. SWH is used to characterize ''sea state'', including winds and swell. Origin and definition The original definition resulted from work by the oceanographer Walter Munk during World War II. The significant wave height was intended to mathematically express the height estimated by a "trained observer". It is commonly used as a measure of the height of ocean waves. Time domain def ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Det Norske Veritas
DNV (formerly DNV GL) is an international accredited registrar and classification society headquartered in Høvik, Norway. The company currently has about 12,000 employees and 350 offices operating in more than 100 countries, and provides services for several industries including maritime, oil and gas, renewable energy, electrification, food and beverage and healthcare. DNV GL was created in 2013 as a result of a merger between two leading organizations in the field — (Norway) and (Germany). In 2021, DNV GL changed its name to DNV, while retaining its post-merger structure. DNV is the world's largest classification society, providing services for 13,175 vessels and mobile offshore units (MOUs) amounting to 265.4 million gross tonnes, which represents a global market share of 21%. It is also the largest technical consultancy and supervisory to the global renewable energy (particularly wind, wave, tidal and solar) and oil and gas industry — 65% of the world's of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
