OUR OPPORTUNITIES

Potential opportunities MEC owe not only to the high professional level of executors and their wide work experience, but also to the created software allowing solving the most complicated research and design problems quickly and effectively. Brief data on two development which can be applied by us at work by the forces below are resulted or offered to other organisations for independent use.

PROGRAM PACKAGE "ANCHORED STRUCTURES"

The Program package " Anchored Structures " is designed for modelling of statics and dynamics of the floating constructions having anchor systems (AS), under action of wind, current, waves and ice. In structure of a package there are also modules of calculation of loads on stationary sea structures.

The software package allows:

• To set design parameters of AS.
• To set geometric parameters of structures as well as mooring and breaking devices parameters when one or several anchored constructions (up to five) are present.
• To perform calculation of non-linear stiffness parameters (SP) of anchor lines of various types. SP are functions of AS reaction vector from moving object and are used for modelling of objects static and dynamic behaviour.
• To perform calculation of static and dynamic (regular and irregular) loads on the considered floating and stationary constructions from wind, currents, waves and ice, and waves - in view of interference of structures (when several constructions are present)
• To perform calculation of hydrodynamic parameters of constructions cases - factors of added masses and of wave resistance
• To carry out calculation of static and dynamic movement of objects, tension of anchor lines, forces in mooring and breaking devices in three-dimensional non-linear statement.
• To carry out calculation of dynamic movements in both frequency and time ranges.
• To operate the program in interactive (dialogue) mode (set the method of data collection, parameters of spectral and probabilistic analysis, environmental affects).
• To observe, with the help of the graphic support block, objects dynamic behaviour from various directions and distances (three-dimensional image) and with different time scale of display.
• To find own frequencies of fluctuations of structures and to make spectral analysis of loads, oscillations of objects and lines reactions.
• To make statistic analysis of amplitudes of objects fluctuations and lines reactions.
• To carry out probabilistic modelling of construction's behaviour for the period of its operation.

The software package can be used for analysis of freely floating, anchored or fixed offshore structures (semi-submergible and TLP - platforms, drilling vessels, pipe-layers, floating cranes, docks, stationary platforms etc.). The software package has the certificate of the Russian maritime register of shipping of computer program type approval and is used by the Russian design bureaus for design of floating anchored structures.

PROBABILISTIC MODELLING OF ICE LOADS ON THE OFFSHORE STRUCTURES

While designing the platforms for development of the largest Russian fields in the Arctic regions ice loads often appear to be determining and reliable estimation of their values, probable during the whole operation period of platforms is necessary. For this purpose the computer program is developed, allowing to carry out probabilistic modelling of ice loads on marine structures, to determine extreme loads with the given return period, and also to study frequently repeating loads which can become the reason of fatigue failures of the construction.

The program is based on the methodology of ice parameters probabilistic modelling in combination with deterministic methods of ice loads calculation, according to the codes of different countries (upon choice).

Probabilistic modelling of ice conditions is carried out for the period many times exceeding the construction's operation term in order to obtain the estimations of loads, which is reliable enough. On the basis field observation data and previously received probability distributions of ice parameters in the given water area, characteristics of ice conditions and parameters of ice, with which the construction interacts during its operation term, are modelled: presence of any ice floes at present time in the construction area, ridged ice floes, ice compaction, geometric characteristics of level or ridged ice floes, velocities of ice floes, air temperature etc.

Laws of probability distribution of various ice parameters are accepted as constants within every month of year, but the parameters modelled by the Monte Carlo method, change with different intensity. For example, the factor of ice compaction, ice rigidity parameter, air temperature are modelled once per day and are considered as constants during this time interval. The linear sizes and thickness are modelled for each ice floe. If ice at present time appear ridged - the structure of each ice floe includes ridges, the total area of which is determined by rigidity parameter, and thickness of the consolidated part, depth and width of keel are modelled by known laws of distribution for the given thickness. Speed of ice movement, corrected every 6 hours is exposed to the most intensive changes.

Thus, on the basis of laws of probability distribution of ice characteristics (changing from one month to the other) the parameters are modelled, which are necessary for the description of construction's interaction with each of ice floes during the given time interval.

The forces arising at interaction of each ice floes with construction, are calculated with the help of an author's technique, and also on the basis of the codes: СНиП2.06.04-82 (ред.1996), API (1995), CAN/CSA-S471-92.

As a result of probabilistic modelling the program allows to receive probability distributions of ice loads amplitudes, to calculate extreme forces with the given return period on their basis (or with the given probability of exceedance) and also to study fatigue effects in the structure design.