Software for load and fatigue analysis enables 90% savings during development

Unscheduled downtimes of up to 300 hours – a horrendous scenario for the operators of wind energy plants, which can only be avoided by the perfect interaction between turbine component design, optimally scheduled maintenance intervals and the consideration of material fatigue under different load scenarios.

But how can reliable statements be made about the availability of a wind turbine, for example, in 20 years? Only special software for fatigue and load analysis can support designers in their work to improve robustness and cost-efficiency.

The demand for wind energy is constantly increasing. In Germany alone, 25,000 megawatt is planned from wind energy plants in offshore farms by the year 2030. But this renewable energy is also forging ahead in numerous other countries as well. This can be clearly seen in the USA: The energy produced from wind plants rose in 2007 by 45% in comparison to the year before. And China announced massive expansion in wind energy in August 2009: the country intends to produce 100,000 megawatt from such plants by 2020.

Unscheduled downtimes of up to 300 hours

It is obvious that this new energy policy also places great demands on the materials used, in particular the wind energy turbines. The unavailability of a wind turbine means high costs that can rapidly become a critical factor in an offshore system as unscheduled repair and maintenance work is extremely complex in this case. The study "Reliability of different wind turbine concepts with relevance to offshore application" issued by the European Wind Energy Conference (EWEC) in 2008 showed that, for example, problems with a turbine gear unit could cause an average downtime of around 300 hours.

Rising material requirements

The general need for improved robustness of design has been shown by newer, larger machines, producing over 2 megawatt, being more prone to unforeseen problems. This is mainly due to the increasing weight: The rotor normally weighs between 10 and 20 tons, but the weight in some newer machines can be up to 50 tons. The challenge here therefore is to save weight and, at the same time, increase structural strength and reliability.

Cumulative damage models provide conclusions about optimal design

Even possible emergency shutdowns, as defined in the standard ISO-IEC 61400, and the influences of the control system must also be taken into account. These additional burdens can exceed the permissible loads in daily operation by a significant measure.

These burdens must also be added to the damage that the plant has already undergone in normal ongoing operation. These cumulative damage models, which a plant must theoretically withstand over 20 operating years, then provide inputs to optimize the design and maintenance intervals.

Fatigue analysis on gear unit components

These conclusions cannot of course be derived from long-term tests that last 20 years. The solution here is specialized software for fatigue and load analyses with which the right decisions can be made during development. This is why Hansen Transmissions, a global leader in the manufacture of gear units for wind turbines, is using the software nCode DesignLife™ from HBM, to perform fatigue analyses on the gear unit components in order to meet the high requirements imposed on the service life of the turbines.

Improved cost-efficiency

With their decision to use DesignLife, Hansen Transmissions were immediately able to optimize their fatigue and load analyses. The software supports the engineers in calculating and evaluating more design variants in a shorter period, in significantly reducing development and test cycles and therefore drastically reducing costs. In addition, this software works without problems with the ANSYS® software used for FEM analysis.

Complex load scenarios

Before Hansen Transmissions decided to use DesignLife, numerous software solutions were subjected to a thorough performance comparison. Dr. W. Meeusen, head of Product Technology at Hansen Transmissions said: "We selected DesignLife because it combines an intuitive interface, the analysis functionality we needed for rotating machinery, as well as the ability to use complex load cases. nCode engineers worked with us during the evaluation process, ensuring that the DesignLife solution meets our needs."

Optimally suited to the application

Jon Aldred, product manager for nCode DesignLife at HBM: "Wind energy is a rapidly growing market for nCode products because durability is a key design issue  in wind turbines and related systems. Downtimes due to fatigue are extremely cost-intensive both in terms of repairs and lost production. That Hansen Transmissions has decided to use DesignLife in order to optimally design their main components during product development shows how DesignLife is well suited for such applications.”

Software solutions from HBM can increase efficiency and decrease costs. An overview of these products include:

nCode DesignLife – Service life analyses during development

nCode DesignLife is the software for service life analysis. nCode DesignLife uses FEM results and structural durability tests for service life estimation – during product development itself. Numerous loading scenarios can be taken into account here, for instance, different wind strengths or one-off/rare events such as emergency shutdowns - and all this for the complete 20 years of permanent operation. And because of the streamlined analysis process, customers report time savings of up to 90% by using DesignLife in their development process.

nCode DesignLife is certified by GL Renewables Certification (GL RC) which assures customers that their component designs, such as wind turbine hubs and main shafts, can be analyzed in conformity with GL Renewables Certification’s Guideline for the Certification of Wind Turbines (2010) by choosing the right settings in the software. This includes fatigue analysis under complex real world loading conditions specified in GL RC’s guidelines or IEC 61400-1 international standard.

nCode GlyphWorks® – Test data analysis

nCode GlyphWorks is the leading software for test data analysis. GlyphWorks processes large data quantities and offers a graphical, process-oriented user interface.

nCode Automation – Monitoring

nCode Automation provides a web-based system for analyzing and sharing measured data. Monitored loads can be automatically uploaded and processed: This can help identify trends and helps quantify real_world loading, The collected data can then also be easily accessed by design teams and taken into account in new developments.

Function tests on wind systems with torque flanges

The installation of a torque flange is recommended if the efficiency of power transmission from the motor to the gear unit needs to be checked and the ongoing operation monitored. This principle is followed by Siemens Ltd. China in their function tests on turbine gear units for wind energy plants. A T10FM flange is used here for the measurement of torques up to 50 KNm, in order to evidence the loss-free transfer of power from the motor to the gear unit with corresponding measurement data. The T10FM is installed directly between the motor and gear unit, made possible by the high reliable lateral forces. The signals are then forwarded by the MP60DP single-channel amplifier for incremental encoder via Profibus without losses to a PC which is equipped with the appropriate data processing software.

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