Company description

We at Vattenfall are committed to making fossil-free living possible. To succeed, as one of Europe's largest energy companies, we must first become completely fossil-free ourselves. But that is not enough. To contribute to a fossil-free society, we need to do more than just focus on sustainable energy production.

Join us on the road to fossil-free living.

About the role

Power Climate Smarter living - that's our purpose. We are looking for talented students to help us on our journey towards fossil-free living. Writing a thesis at Vattenfall gives you a unique opportunity to contribute to our purpose. All we ask is that you unleash your superpowers and share your energy with us.

Background

Hydro power has a relatively small climate impact and accounts for almost half of Sweden's electricity production. Vattenfall owns and operates about 125 large-scale hydropower units, of which about half of these units are of the kaplan turbine type. In these units, the blade angle of the runner can be regulated to achieve high efficiency at varying water flow and head. The internal mechanism that regulates the blade angle is subjected to a cyclic load that can lead to fatigue if it is incorrectly designed.

One of Vattenfall's major focus areas in hydropower is to increase the reliability of kaplan turbines. To achieve this for a new runner, a relevant set of requirements is required as input to the work of verifying the strength of the intended design. An understanding of the loading of the Kaplan turbine control mechanism is crucial in order to formulate these design requirements and thereby achieve a sufficiently low probability of failure over the technical lifetime of the runner.

The standard approach to assess the fatigue life of the kaplan runner control mechanism is via accepted stress-based fatigue analysis. The stress variation in critical areas is calculated by FEM analysis with a model of the impeller that is idealized in various ways compared to reality. The model is used to calculate a nominal load level in the impeller, and the introduced simplifications and uncertainties are then taken into account by applying safety factors to the calculated load level before the theoretical fatigue life is evaluated.

Objective

The objective of this thesis is to investigate commonly used simplifications and to quantify the effect of their introduction. The work can be used as a basis for validating the reasonableness of applied safety factors used today. Examples of commonly used simplifications are

• Bearing games: All bearings are described with nominal bearing games. In reality, the bearing clearances will vary (within defined tolerance intervals), which causes load imbalances between the components of the control mechanism.
• Friction: The friction properties are described by the same principle for all bearings. In reality, some variation between the properties of the bearings can be expected, which in turn gives rise to an uncertainty in the assessed friction losses and thus the load levels. This aspect can also contribute to possible load imbalances between the components of the control mechanism.
• Inertia effects: The analyses are normally performed with quasi-static analyses where inertia effects associated with acceleration of the system are neglected. The components of the control mechanism are very large and associated with very high mass inertias, which can affect the estimated load in some situations.
• Hydraulic water load: The hydraulic load from the water is considered to be known but is always associated with a certain degree of uncertainty. The water load contributes to very high load levels on the bearings supporting the running wheel blades. These bearing loads, together with the frictional properties of the bearings, determine the main frictional losses in the impeller and thus indirectly influence the load on the internal control mechanism. In other words, an uncertainty in the water load in turn implies an uncertainty in the estimated load on the control mechanism.

Suggested work steps

• Literature study with focus on:
• Design, function and operation of Kaplan turbines
• Load on the internal control mechanism of the Kaplan turbine
• Methodology for fatigue life assessment
• Mechanical properties of commonly used bearing materials
• Systematic experimental design, regression analysis and analysis of variance
• Management of uncertainties in input data for fatigue assessment
• Discussions (e.g. interviews) with Vattenfall's experts in the field. This with the aim of understanding uncertainties in input parameters
• Analyze the effect of commonly used simplifications and assumptions based on FEM analyses in ANSYS Workbench and/or proprietary code.
• Evaluate the overall effect of the simplifications and derive required safety factors
• Report writing

Requirement specification

We are looking for student(s) who want to work towards fossil free and who will soon graduate from your academic studies. You are also someone who identifies with our principles: Active, Open, Positive and Safety

• Education - Master's degree in Mechanical Engineering or similar with a focus on engineering calculations and strength.
• Very good knowledge of Swedish and English

Additional information

• The assignment starts: 2025-01-13 or by agreement
• Location: Vattenfall's offices in Älvkarleby or Solna.
• Application - a file with your CV and a copy of your grades.
• Last day to apply is 2024-12-08
• Contact person and supervisor at Vattenfall is Erik Isaksson, erik.isaksson@vattenfall.com, 070 388 10 67

Diversity and inclusion - in everything we do

We are convinced that heterogeneous teams can outperform homogeneous teams. But we can only unleash and use the power of diversity when everyone feels included.