02 September RP-C Environmental Conditions and Environmental Loads n RP-C is an updated and enhanced version of DNV. Find the most up-to-date version of DNVGL-RP-C at Engineering DNV RP C Environmental Conditions and Environmental Loads_ – DNV推荐做法,适用各种浮式结构环境载荷的计算.
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dnf Our core competence is to identify, assess, and advise on risk management. From our leading position in certification, classification, verification, and training, we develop and apply standards and best practices.
This helps our customers safely and c05 improve their business performance. DNV is an independent organisation with dedicated risk professionals in more than countries, with the purpose of safeguarding life, property and the environment. DNV service documents consist of among others the following types of documents: The Standards and Recommended Practices are offered within the following areas: The use of this document by others than DNV is at the user’s sole risk. DNV does not accept any liability or responsibility for loss or damages resulting from any use of this document.
Text affected by the main changes in this edition is highlighted in red colour. However, if the changes involve a whole chapter, section or sub-section, normally only the title c2055 be in red colour.
For further information, see www. Main changes April ? Editorial corrections In addition to the above stated main changes, editorial corrections may have been made. F Torsethaugen two-peak spectrum Nautic dv for estimation of long-term wave distribution parameters The loads are limited to those due to wind, wave and current.
The RP is based on state of the art within modelling and analysis of environmental conditions and loads and technical developments in recent research and development projects, as rpp as design experience from recent and ongoing projects. The basic principles applied in this RP are in agreement with the most recognized rules and reflect industry practice and latest research.
Guidance on environmental conditions is given in Sec. Hydrodynamic model testing is covered in Sec.
The most important phenomena for marine structures are: These phenomena are covered in this RP. The statistical description should reveal the extreme conditions as well as the long- and short-term variations.
DNV RP C Environmental Conditions and Environmental Loads__图文_百度文库
If a reliable simultaneous database exists, the environmental phenomena can be described by joint probabilities. For ships and other mobile units which operate worldwide, environmental data for particularly hostile areas, such as the North Atlantic Ocean, may be considered.
For operations of a limited duration, seasonal variations must be taken into account. For meteorological and oceanographical data 20 years of recordings should be available.
If the data record is shorter the climatic uncertainty should be included in the analysis. ISO rules and dnf. Other DNV Recommended Practices give specific information on environmental loading for specific marine structures.
These are referred to in the text. It also varies with the height above the xnv or the height above the sea surface. For these reasons, the averaging time for wind speeds and the reference height must always be specified.
Commonly used averaging times are 1 minute, 10 minutes and 1 hour. Wind speed averaged over 1 minute is often referred to as sustained wind speed. In the short term, i. This wind climate representation is not intended to cover wind conditions experienced in tropical storms such as hurricanes, cyclones and typhoons. It is neither intended to cover wind conditions ep during smallscale events such as fast propagating arctic low pressures of limited extension. The assumption of stationary conditions over minute periods is not always valid.
For example, front passages and unstable conditions can lead to extreme wind conditions c2005 wind gusts, which are transient in speed and direction, and for which the assumption of stationarity does not hold. Long-term wind conditions typically refer to 10 years or more, short-term conditions to 10 minutes.
The minute mean wind speed at 10 m height above the ground or the still water level is to be used as env basic wind parameter to describe the long-term wind climate and the short-term wind speed fluctuations. Empirical dbv data used as a basis for design must cover a sufficiently long period of time. For design, the wind climate data base should preferably cover a year period or more of continuous data with a rrp time resolution.
The mean wind speed at 10 m height is often used as a reference. When wind speed data for other heights than the reference height are not available, the wind speeds for the other heights can be calculated from the wind speeds in the reference height in conjunction with a wind speed profile above the ground or c2205 the still water level.
If a different averaging period than 10 minutes is used for the determination of loads, the wind data may be converted by application of appropriate gust factors. Application of a fixed gust factor, which is independent of the frequency location of a spectral gap, can lead to erroneous results.
A spectral gap separates large-scale motions from turbulent scale motions and refers to those spatial and temporal scales that show little variation in wind speed. Unless data indicate otherwise, the conversions may be carried out by means of the expressions given in [2. If the wind velocity is of significant importance to the design and existing wind data are scarce and uncertain, wind velocity measurements should be carried out at the location in question.
Characteristic values of the wind velocity should be determined with due account of the inherent uncertainties. WMO specifies minimum requirements to hindcast models and their accuracy. Hindcast models and theoretical models can be validated by benchmarking to measurement data. In such areas, the upper tail of the distribution of U10 needs to be determined ndv the basis of hurricane data.
Various sampling schemes are being used. According to some schemes, U10 is observed from every minute period in a consecutive series of minute periods, such that there are six U10 observations every hour. According to other schemes, U10 is observed from only one minute period every hour or every third hour, c025 that dhv are only 24 or 8 Dng observations per day.
The approximation is based on an assumption of independent 10minute events. The approximation is a good approximation in the upper tail of the distribution, which is typically ep for prediction of rare mean wind speeds such as those with return periods of 50 and years. This refers to hurricanes for which the minute mean wind speed forms a sufficient representation of the wind climate. Usually only quantiles in the dnvv tail of the distribution are of interest, viz.
When terrain conditions and atmospheric stability conditions are not complex, the wind speed profile may be represented by an idealised c250 profile.
The most commonly applied wind profile models are the logarithmic profile model, the power law model and the Fr? The surface friction coefficient is defined in [2. For locations on land, z0 depends on the topography and the nature of the ground. For offshore locations z0 depends on the wind speed, the upstream distance to land, the water depth and the wave field.
Table gives typical values for z0 for various types of terrain. For near-coastal locations, AC is usually higher with values of 0. Expressions for AC, which include the dependency on the wave velocity and the available water fetch, are available in the literature, see Astrup et al. This implies that the logarithmic profile tp be v205 as? This expression converts dbv wind speeds between different averaging periods. The conversion does not preserve the return period associated with U For extreme mean wind speeds corresponding to specified return periods in excess of approximately 50 years, the Fr?
In coastal zones, somewhat higher values for the coefficient C should be used, viz. The expressions should not be extrapolated for use beyond the height range for which they are calibrated, i.
Possible influences from geostrophic winds down to about m height emphasises the importance of observing this restriction. This implies in particular that the expressions can be applied cc205 winds in hurricanes. The representation of squall wind statistics is a topic for f205 research. There is c2205 uncertainty associated with the profiles and there is natural variability around them: The true mean profile may take a different form for some wind events, such as in the case of extreme wind or in the case of non-neutral wind conditions.
This implies that conversion of wind data to heights without wind measurements will be encumbered with uncertainty. HSE gives an indication c250 the accuracy which can be expected when conversions of wind speeds to heights without wind data is carried out by means of wind profile models.
It is recommended to account for uncertainty in such wind speed conversions by adding a wind speed dhv to the wind speeds that result from the conversions. As for conversion of wind speeds between different heights also conversion between different averaging periods is encumbered with uncertainty, e. HSE gives an indication ndv the accuracy which can be expected when conversions of wind speeds between different averaging periods is carried out by means of gust factors.
When different terrain roughnesses prevail in different directions, i. This will r the case for example in the vicinity of a large building. The difference between the two figures mainly consists in a different shape of the mean curve. This reflects the effect of the increasing roughness length for increasing U10 on the offshore location.
The choice of the distribution model may depend on the application, i. It is important to identify and remove data, which belong to minute series for which the stationarity assumption for U10 is not fulfilled. In fnv terrain, Ax tends to be somewhat larger. During this period, in addition to the turbulence in the direction of the mean wind, there will be turbulence also laterally and vertically.
These values all refer to homogeneous terrain.
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Site-specific spectral densities of the wind speed process can be determined from available measured wind data. Several model spectra exist. They generally agree in the high frequency range, whereas large differences exist in the low frequency range.