OpenFAST Tutorial (1/4) - First simulation

Summary

Highlights

• OpenFAST is a multiphysics tool designed for offshore wind turbine simulation 🌬️.
• Developed by NREL, it's renowned for its efficiency and versatility ⚙️.
• Handles complex physical phenomena such as wind, vibration, and buoyancy forces 🌪️.
• Uses modular architecture, with Eloine as the main module for structural dynamics 🏗️.
• Setup involves downloading executables and configuring through input files from GitHub 💾.
• Explains mode shape reduction to simplify structural dynamics modeling 🔍.
• Guides through a simple simulation of a non-operational turbine to illustrate setup ⚡.
• Outputs simulation data for structural dynamics analysis 📊.

Key Takeaways

• OpenFAST is a versatile tool for simulating offshore wind turbines efficiently 🚀.
• The tool uses a modular structure to handle complex physical interactions 🌊.
• Eloine, a core module, focuses on structural dynamics and reducing computational load through mode shape reduction 🔧.
• Setting up involves downloading executables and configuring input files from GitHub 🔍.
• Simulations can be initially basic but illustrate key concepts in wind turbine modeling 🎓.

Overview

Chapters

• 00:00 - 00:30: Introduction and Overview of OpenFAST In this introductory chapter, Maximia Andre from Lal Central introduces the OpenFAST series, aiming to educate users on how to start using OpenFAST. OpenFAST is described as a multiphysics simulation tool crafted to simulate offshore wind turbines. It's praised for its efficiency and versatility, particularly its speed, which is attributed to its use of numerous assumptions. This chapter sets the stage for users to understand what OpenFAST is and why it might be a preferred tool for simulating offshore wind turbines.
• 00:30 - 01:00: Purpose and Necessity of OpenFAST The chapter discusses the development of OpenFAST by the National Renewable Energy Laboratory as a critical tool for wind turbines. It highlights the necessity of OpenFAST in modeling wind turbines, especially floating ones, due to the complexity involved in accounting for various loads and physical phenomena that impact the turbine. It specifically points out the challenges posed by different wind conditions.
• 01:00 - 01:30: Challenges in Wind Turbine Modeling The chapter 'Challenges in Wind Turbine Modeling' discusses various dynamic forces and factors affecting wind turbine systems. It highlights complex interactions such as turbulence, rotor rotation, and gravitational forces impacting the tower, blades, and platform. The platform experiences additional forces due to its movement, vibrations in the blades and structure, and external influences like waves and current forces. This intricate balance of forces presents unique modeling challenges in understanding and predicting wind turbine behavior.
• 01:30 - 02:00: Modular Structure of OpenFAST The chapter discusses the modular structure of OpenFAST, which is designed to model complex systems involving marine forces such as waves and currents. OpenFAST uses a modular structure where each module is responsible for different aspects of the physical processes involved. This modular approach allows it to handle the challenges of modeling components like mooring lines, CED turbines, and cables, which may be affected by marine growth. The emphasis is on the ability of OpenFAST to integrate these different factors within its simulation code.
• 02:00 - 02:30: Description of Modules in OpenFAST The chapter titled 'Description of Modules in OpenFAST' explains the integration of various modules within the OpenFAST framework using a 'gluc code.' It details specific modules such as Eloine, which models structural aspects like displacements and vibrations of platforms, towers, and blades. Additionally, there is a description of the Hine module, responsible for wave currents and aerodynamic loads, and the aerodine and inflow module. Each module plays a crucial role in the simulation and modeling process in OpenFAST.
• 02:30 - 03:00: Focus on ElastoDyn Module The chapter focuses on the ElastoDyn module within the context of a wind turbine system, part of a broader tutorial covering OpenFAST modules. ElastoDyn is highlighted as potentially the main module, essential for understanding the structural dynamics involved in wind energy systems. The tutorial aims to guide learners through using this module, among others, for simulating and analyzing wind and aerodynamic loads, power generation, and control systems in wind turbines.
• 03:00 - 03:30: Representation of Wind Turbines in ElastoDyn The chapter discusses the representation of wind turbines in the ElastoDyn module. The author emphasizes understanding how ElastoDyn perceives the turbine, which is comprised of limited but distinct components: the platform, tower, nacelle, drivetrain, hub, and blades. These components are interconnected to represent the complete turbine structure.
• 03:30 - 04:00: Flexible Bodies and Mode Shape Reduction The chapter discusses the representation of turbines in a systematic way. Initially, the platform of the turbine is described as a rigid body with six degrees of freedom. However, the tower is treated as a flexible body, specifically modeled using mode shapes. This method of representation allows for a more nuanced understanding of how different parts of the turbine can move and flex. The chapter also briefly mentions that certain components, like the H and Nel, are considered rigid bodies. Additionally, the drivetrain's flexibility is limited to bending in rotation, highlighting the specific constraints and flexibilities within the overall turbine structure.
• 04:00 - 05:00: Mode Shape Reduction Theory The chapter introduces the concept of mode shape reduction, particularly in the context of flexible bodies like blades that can deform and are represented as beams capable of bending. It highlights the computational efficiency advantages of using mode shape reduction. This method is utilized to simplify the analysis by focusing on the most significant deformation modes, thus avoiding the computational complexity of factoring in all potential deformations. This is especially relevant in systems where a rigid body (like the H-frame mentioned) interacts with these flexible elements.
• 05:00 - 05:30: Running the First Simulation Example This chapter discusses the process of representing a beam using the finite element method. It involves discretizing the beam into smaller sections and computing the interactions of these parts with each other, resulting in numerous degrees of freedom to be calculated at each time step. The chapter also points out that, upon closer inspection, the movement of structures like a tower is not random but follows specific patterns.
• 05:30 - 06:30: Setting Up OpenFAST The chapter discusses the concept of mode shapes in relation to the first and second bending modes of a tower in the context of setting up OpenFAST. It emphasizes the importance of understanding these modes as they contribute significantly to the overall motion of the tower. The summary suggests that assessing and understanding these modes beforehand is crucial for accurately characterizing the tower's behavior using OpenFAST.
• 06:30 - 11:30: Configuring ElastoDyn Input File The chapter discusses the ElastoDyn input file configuration, focusing on simulating the motion of a tower with reduced computational effort through mode decomposition. By limiting the degrees of freedom to only the first two modes of displacement, computational time is significantly reduced. However, a pre-computation of these modes is necessary before executing the simulation. The speaker indicates an intention to run a demonstration with the ElastoDyn model, emphasizing its efficiency and pre-computation requirements.
• 11:30 - 12:30: Configuring OpenFAST Glue Code The chapter introduces a basic example of configuring the OpenFAST glue code. The initial setup involves a fixed wind turbine model placed on the ground. In this controlled environment, there is no wind and the turbine isn't rotating, thus aerodynamic forces are not considered at this stage. To ensure there is activity within the simulation, an initial displacement has been introduced to the turbine, despite the seemingly static setup. This foundational example serves to familiarize users with the operation of OpenFAST.
• 12:30 - 16:30: Running the Simulation The simulation involves a tower that will be bent 10 cm in the downwind direction to observe its movement. Instead of building a new model from scratch, a reference model from NRL is being used. This reference is a 5 megawatt turbine developed at a place referred to as 'n' and has been widely used in the Wind Community. The initial step involves setting up the simulation using this existing model.
• 16:30 - 18:00: Output Files and Initial Observations In this chapter, the focus is on installing the OpenFAST executable software. The process begins by navigating to the OpenFAST GitHub repository. Within this repository, users are directed to access the 'releases' section under the 'OpenFAST' subfolder. The tutorial specifies the installation of version 3.2.1, indicating that the instructions are tailored for this particular version.

OpenFAST Tutorial (1/4) - First simulation Transcription

• 00:00 - 00:30 welcome everyone my name is maximia Andre and I'm working at Lal Central the N I am making this series of video in order to teach you about how to start using open fast so first what is open fast you may ask well open fast is a multiphysics simulation tool designed to simulate offshore wind turbines it is efficient and versatile it's really fast compared to other codes because it uses a lot of assumptions it
• 00:30 - 01:00 is developed by Nel so it's a national renewable energy Laboratory um and it's a really efficient tool so why do we need such tool for win turbines well it's because modeling win turband and especially floating win turband can be really difficult because uh there are many different loads and physical phenomenon that that can affect the turbine so first we have the wind the wind can be um
• 01:00 - 01:30 uh of different form and usually it's a turbulance uh we have the rotation of the rotor uh we have the the gravity which is pulling on the tower the blades and the platform um the platform is moving uh we can have some vibration in the blades and in the structure uh the platform itself is undergoing the bcy force it can have forces from the waves uh forces from the current uh the platform is m and the
• 01:30 - 02:00 Ming lines can have um also forces from the waves and current and they are they are anchored the CED turbine and the cables can be subject to Marine growth so it's really hard to model everything um in one code and but this is what open fast does and to do to do this uh it uses a modular structure uh which means that each module will be in charge of some aspect of the phys pH involved and the model
• 02:00 - 02:30 the modules are coupled together by what is called a gluc code so to give you an example of the modules we have eloine which is the module for the structure so this is what models the the displacements of the platform and the tower and blades and also the vibration and the loads that they are undergoing we have the Hine module for the wave currents and the aerodynamic loads we have the aerodine and inflow module for
• 02:30 - 03:00 the wind and the aerodynamic loads we have the moing with several modules that can be used we have sodine which is a module for um uh the power generation and the control system of the turbine and the goal of this tutorial is to guide you through each of the module one by one and we will start with the eloine module so it's the first module and maybe the main module of open fast so today we
• 03:00 - 03:30 will only use this module for our first example so first um you have to understand that eloine will see the turbine in a particular way um here we have only a very limited number of uh different objects that represent the turbine in fact the turbine is only composed of the platform the tower the Nel and the drivetrain the up and the blades and all these objects linked
• 03:30 - 04:00 together um are how Eline represents the turbine now the platform is a rigid body so it can only have six degrees of freedom the tower is a flexible body but um it's represented in a particular way uh using the mode shapes and we will talk about that in a few minutes uh the H is a rigid the Nel is a rigid body the dri train can only Bend IN rotational
• 04:00 - 04:30 Direction you can have torsional moments the H is a rigid body and the blades are flexible body that can deform so it's quite simple um all the flexible bodies are represented as beams that can bend uh but uh in order to avoid having too much computation open fast uses the mode shape reduction so what is this uh Theory well basically if you wanted to
• 04:30 - 05:00 represent a beam via a finite element method you would discretize the beam in several smaller parts and then you have to compute the interaction of each part with one another so you have many um degrees of freedom you can have hundreds and hundreds of degrees of freedom that you need to compute at each time step but if you look closer you can see that the motion of the tower for example it's not arbitrary motion but it's
• 05:00 - 05:30 usually a combination of the first bending mode of the Tower so here we have the first bending mode and here we have the second bending mode and if you summarize the motion to only these two modes we just have uh we can see that the the motion of the tower is roughly a sum of the two modes so what we need to do is just know the modes of the tower beforehand and then uh we need to to know um how much
• 05:30 - 06:00 uh of each mode composes the final motion and we get the motion of the Tower with just two degrees of freedom which are the displacements in the first two modes so we gain a lot of computational time by using this um method uh and this is what theine uses the only drawback is that you need to pre-compute the modes before running the simulation so now to illustrate what we said to illustrate um eloine we will run
• 06:00 - 06:30 a first example so it will also be the opportunity to see how open fast is run so for this first example we will have a fixed wind turbine so you can see it here it's fixed on the ground there is no wind uh because we don't want to look at the aerodynamic forces for now um and the turbine is not rotating so it's can be pretty boring so we added some initial displacement to make sure that something happens in the simulation so
• 06:30 - 07:00 the tower will be bent 10 cm in the downwind direction and we will see how it moves for our examples we are not building a model from scratch but instead we are using a reference model from um NRL so this reference is the 5 megawatt uh turbine that was developed at n and that has been widely used in the um Wind Community since okay so the first thing that we going to do is that we are going to
• 07:00 - 07:30 install the open fast executable uh so the software in itself to do this we will navigate to the open fast GitHub folder you have the address here and we will open the open fast sub folder in this sub folder we will navigate to the releases section with the latest versions and then we will go to the version 3.2.1 because this tutorial was designed with
• 07:30 - 08:00 this version but um you can also start using it from another version but maybe the files won't work the input files won't work for the version that you are using so if you want to run the tutorial I recommend you go to the version 3.2.1 um for uh Mac and Linux users you need to compile it yourself but don't worry it's quite easy to do and for Windows user we can just download the
• 08:00 - 08:30 executable file so it's this one and and then you can uh you can you're ready to to run open fast so once your download is complete you can put the open fast executable in um the home folder of the quick start and then we will navigate to the first example and we will have a look at the input files for open fast okay so to run the open fast simulation I need two things I need the executable file that that I just
• 08:30 - 09:00 downloaded and I need some input files these input files I didn't develop them myself I took them from NL NL GitHub page and these are input files for the 5 megawatt wind turbine so because we are using the eloine module we first need to set the configuration file for eloine so let's open it so this is what uh typical fast input
• 09:00 - 09:30 file look like um you have several section in each section you have some key for the parameters and some value and you also have some comments to describe uh what the parameter is you have more information on the documentation that you can find online but uh it's already helpful to have these comments so in the first section of eloine we need to set the degrees of freedom that we want for the simulation so for example the first
• 09:30 - 10:00 degree of freedom is do you want to allow the blade to move in the flapwise direction and in the first mode so for will be true because we want to see some vibration in the structure so we set it to through and you can set all of the degrees of freedom like you want here because we have a fixed wind turbine uh all the platform degrees of freedom are disabled because we want the base to be static so we don't have a surge sway Eve and rotational degrees of
• 10:00 - 10:30 freedom but later we will allow these degrees as well then we can move to the initial conditions so here everything is um at the zero position at the beginning of the simulation except for the tow toop displacement because uh as we said we want a bit of motion in the simulation so we set it to .1 M so 10 cm and then next section is dedicated to
• 10:30 - 11:00 turbine configuration um this is what was prepared by NRL so this is the 5 Mega 5 megawatt wind turbine if you want to look at the documentation for this you can check that all these values are the right one but as long as we don't change the turbine we don't need to change these parameters the same for the mass and inertial parameters and then we will look at the blade so the blade can be pretty uh t used to describe so instead of having
• 11:00 - 11:30 all the parameters here we will resort to another file in which the blade is described so we we just need to specify where to look for the blade information and because we have the same blade we use the same file for the three different uh Blades of the turbine so let's have a look at this file it is here so this blade file um describes the
• 11:30 - 12:00 blade as a function of its length so we have the First Column which is the blade fraction and it goes from zero to one and as we move through the blade we can have different parameter so we have the pitching axis The Twist the mass density the the flapwise stiffness and the edge wise stiffness so all of these are used to describe the blade as a beam
• 12:00 - 12:30 so this this describes only the mechanical properties of the blade and not its aerodynamic properties and then we need to to specify the modes of deformation of the blade as we said to use model shape reduction we need to have the modes so the modes are provided in the form of polinomial here we don't have zero or first order term because um the blade is R rigidly fixed to the H but we have the other terms
• 12:30 - 13:00 so here the blade the mechanical properties of the blade of the blade are described uh then we have the teer but we are not using it um we have the drivet train information but it's not really important for now for the tower as same as the blade we have a file which will describe the mechanical properties of the Tower and then we move to the last part the output part where we specify um what we want to Output from eloine eloine
• 13:00 - 13:30 will compute a lot of of information during its process and by default it will will not output everything because it will be too much so instead we have to specify what we want to see in the output file so here we say we want to see the outof plane deflection of the first Blade the inplane deflection of the first blade and the tower toop displ displacement in the four after direction if you want to look look at some output
• 13:30 - 14:00 data uh you can have you can access this uh Excel file which is available on open fast documentation and all the available parameters are listed in this file so for example here I'm in the eloine sheet and you can see that for the first blade out of place out of displacement you have the description and you also have the um reference reference which this um displacement is given so
• 14:00 - 14:30 this F is really large and you have all the information that can ask from open fast so now we are done our eloine configuration file is complete but we need another config file is the configuration file for the gluc code so for the main open fast software and it's this one it's the file with the FST extension so we will open it and we will see what it does so in this main f file have some s control parameters and here is what I want to show you it's where you choose
• 14:30 - 15:00 to uh turn on or off the different modules so today we only want to use eloine so we set one to the eloine value and zero to the rest so we are telling open fast only use eloine for now we have other things that we can specify and here we will tell open fast where to look for the for the configuration file for each module so for for eloine we want to look into this
• 15:00 - 15:30 configuration file config eloine and uh this pass is relative to the main. FST file location so because in the same folder we don't need to have a complicated pass and then you have other SIM okay so we are ready to launch the simulation to do that we will open a terminal window
• 15:30 - 16:00 in this terminal window I will call for my open fast executable and then I will call for the FST file and then I just have to press enter and the simulation will start so because I'm recording at the same time it's a bit long but if you do
• 16:00 - 16:30 it on your computer uh it will be really fast and we done the simulation is over so where are the outputs of the simulation well if you like look in this this folder we have two uh new files so one file is the uh outb so out binary file and the other one is uh just a plain text uh output file so the one that we are going to open
• 16:30 - 17:00 okay so we have data in different columns and we can see that we have the time it's it's always the first column and then we have the three channels that we asked open fast to Output so the out of plan deflection inl deflection and a toop displacement as you can see the initial toop displacement is 10 cm and then the tower starts oscillating because I don't want to make the first video too long we will not um
• 17:00 - 17:30 look too much into the data but in the next video we will see how to open the data with python