Project logistics

Optimized project and risk management is a key competence for the successful and cost efficient planning, construction and operation of offshore wind farms. In order to achieve this, Fraunhofer IWES develops and utilizes modern and tailor-made methods using comprehensive wind energy system competences. Project management plans, validates, steers and controls the implementation of schedules, costs and quality of projects. This comprises, for example, time scheduling (incl. weather dependency) and cost efficiency models (incl. Life Cycle Costs). Concept, project and process uncertainties are recorded, analysed and optimized through risk management pursuant to ISO 31000:2009

The construction of offshore wind farms is associated with very high costs and risks. One essential factor are high deployment costs of offshore equipment (e.g. vessels or cranes). Thus a realistic forecast, including weather dependencies, of activity and project durations decreases the costs and risks of offshore works. To achieve this, the Fraunhofer IWES developed and applies the WaTTS – Weather Time Series Simulation – Method, a concept mapping and evaluating activities into weather time series. The analysis further considers Marine Operation rules, e.g. DNV-OS-H101, and weather forecast uncertainties. We also offer weather window statistics.

The installation of offshore wind farms involves large investments. High deployment costs of the offshore equipment (e.g. ships, crane) represent a major factor. A realistic prediction of the installation duration is therefore an essential part in the optimization of the project costs and risk profile.

Offshore equipment and operations are subject to technically conditioned, pre-defined weather constraints. An exceedance of these affects the safe execution of activities. The limits are defined by various weather parameters such as significant wave height, wind speed or current speed and are associated with different activities (e.g. crane works or jacking-up).

Weather conditions have therefore a great impact on offshore installation durations. The execution of activities requires proper weather windows. These represent time frames where relevant weather restrictions are continuously fulfilled throughout the full length of the window. A realistic prediction of installation durations is, inter alia, essential for the following problems:

• Installation duration
• Charter times for offshore equipment (e.g. ships, platforms)
• Number of possible turbine installations
• Impact of delays
• Time of commissioning / beginning of operation
• Comparison of cost/benefit for different equipment concepts
• Interaction between subprojects (e.g. installation of foundations, wind turbine, inter-array cables, substation, etc.)

WaTSS Method
Currently, weather impact on project schedules is considered by adding contingencies using weather window statistics. The latter are generated from long time series. Information about the temporal sequence is inevitably lost in the process. Consideration of operations with different weather constraints is thus limited. Fraunhofer IWES has developed an alternative to weather window statistics called “WaTSS” (“Weather Time Series Scheduling”). In this method the project schedule is mapped with its entire complexity and an arbitrary level of detail onto weather data.

When performed on weather time series of multiple years with a particular start date, the simulation gives predictions of the installation and project duration including probabilities of occurrence. The simulation allows an arbitrary combination and number of weather constraints to be defined per activity.

Moreover, an evaluation of various events, at which a vessel travels back to base harbor or to a temporary shelter respectively
due to adverse weather conditions such as “call-to-port” and “seek-for-shelter” is possible. Installation schedules can be optimized by means of sensitivity analyses with respect to weather risk. The prediction of installation duration can facilitate decisions leading to a cost and risk optimal installation strategy.

Primary and secondary weather risks during project realization

User interface of the COAST software

Distribution of project durations depending on weather data

To make the weather a calculable factor already during the planning phase, Fraunhofer IWES has developed a new software tool named COAST (Comprehensive Offshore Analysis and Simulation Tool), which is designed to simplify the weather data-based planning, validation and assessment of offshore work processes in the installation and operation phases. Incorporation of the analyses into the day-to-day work flows is quick and easy thanks to compatibility with MSProject and an intuitive user interface.

The issues and own-interests associated with the management of offshore activities are many and varied for all parties involved: Planners review their timetables in advance for practical viability. Logistics and installation specialists optimize the deployment of their vehicles / vessels. Operators improve their maintenance tasks and component replacement strategies. Investors and banks validate their financial models. Insurers design customized cover concepts for weather risks or cover amounts. Lawyers and economists devise sophisticated payment plans,
contractual penalties and concepts for spreading the weather risks.

If delays have occurred in the implementation of a project, the COAST software enables project acceleration measures to be realistically estimated. On completion of the construction phase, the influence of weather risks can be validated, compensation claims asserted or rejected, and lessons learned for the future.

WaTSS – Weather Time Series Scheduling method
The WaTSS method is designed to simulate the work flows involved in offshore activities with all their weather restrictions. The system uses weather time series going back many years in order to realistically take account of weather-induced delays. Subsequently, the simulation results are statistically evaluated. The processes are defined through timetables in MS-Project XML format and can therefore be drafted using planning tools such as Asta Powerproject, Primavera and MS-Project. The local conditions and weather boundaries, on the other hand, are described using time series that may cover over 50 years.

 

As a result, not only measured or model data time series such as wind, wave heights or wave periods can be taken into account in the analysis, but also any other time restrictions, e.g. day/night, lock opening times, tidal windows or water levels. User-friendly and ideal in everyday application. To identify project durations and their distribution, simulation results are statistically
evaluated. All results and the distribution of the project durations can be exported to MS-Excel or CSV format. The individual simulations can be graphically displayed and exported as a plan. Weather data can also be read from MS-Excel. Incorporation of the “DNV-OS-H101 Marine Operations” (2012) guideline in the analyses is another possibility.

The COAST software makes it possible to compare between different work flow planning concepts and variants in terms of the weather risks. Project plans can be optimized using sensitivity and scenario analyses. The results render weaknesses and bottlenecks in specific phases / activities clearly visible. The WaTSS method offers more in-depth analysis of the weather and other related conditions than the frequently used weather window statistics.

Data sheet

The influence of the weather on a process depends in general on three parameters: the restriction of the operation with respect to one or several weather parameters (e.g. significant wave height), the required time for the execution of the operation, hence the length of the required weather window, and the seasonal point in time the activities are to be performed.

A weather window is defined as a time frame in which certain weather conditions are continuously fulfilled. Simple statistics of weather data, which do not consider weather window length and a point in time at which the operation is to be executed are not sufficient for the prediction of operation/ project durations or the accessibility of a wind farm. Conversely, weather window statistics state the percentage of usable time in a month. A particularly useful application is the evaluation of a sequence of operations.

The execution of operations is often restricted simultaneously by more than one weather parameter. In such cases Fraunhofer IWES can deliver 2-parameter statistics, or in other words, combined weather windows statistics.

The data input for the generation of statistics is of vital importance for their quality. Data sets are frequently inconsistent, inhomogeneous
and/or fragmentary. This can cause erroneous results. Thus, Fraunhofer IWES verifies and, if necessary, corrects the input data. Evaluation can be based on historical measured data as well as hindcast data for a specific location. A comparison of different data is also possible.

Fraunhofer IWES has a long standing experience and an extensive know-how in the field of weather analysis and verification. This represents a substantial prerequisite for high-quality weather window statistics. Fraunhofer IWES has provided weather window statistics for both already completed offshore projects and for projects which are currently in the planning phase.

• Generation of 1-and 2-parameter weather windows statistics based on measured and/or modeled data
• Provision, verification and correction of data used for the calculation of weather window statistics
• Evaluation of project schedules by means of weather window statistics