What is in this Article?

1. Introduction

2. Before We start

3. Implementation

Terminologies

1. Introduction

What is the stiffener?

Stiffeners are secondary plates or sections attached to the primary structure to stiffen them against out-of-plane deformations. Below is an example of a stiffener plate with several types of stiffener cross-sections:

Figure 1. Stiffeners in a real structure

Why is 1D stiffener used in the FOWT simulation model?

In the simulation, the stiffened can be modeled by 1D, 2D, and 3D elements based on the use case and required in the standard. 

In FOWT, we usually use 1D & 2D stiffeners for modeling. The 2D/3D stiffener will return more accurate results but it requires more effort on the modeling stage. The 1D stiffener can be used in the early design stage where the designer can easily change the 1D cross-section property and from that find the best model design, also 1D stiffener takes less effort in the modeling.

Figure 2. Akselos FOWT model modeled with 2D stiffener (left) and 1D stiffener (right)

1D stiffener in Akselos

Akselos Modeler well supports creating and setting up 1D cross-sections for 1D stiffener inside the FOWT model. In Akselos, we support a lot of cross-section types from general types: Rectangular, Circular, circular tube, L, I, T, …

In this tutorial, we will mainly focus on working with rectangular cross-sections, other cross-section types can work in the same way. This tutorial will guide you on how to set up a 1D stiffener in the prepared component:

What you will learn with this tutorial:

• Creating & defining cross-section profiles.

• Assigning Cross-section to 1D stiffener subdomain.

• Rotating and offsetting 1D cross-section. 

2. Before We start

To follow the instructions below, please contact our support team at [email protected] for :

• Akselos Modeler – our simulation software used in this tutorial.

• A sample collection has been prepared for you to use as a reference. Access the sample DCW 5MW tutorial 1 on Akselos Dashboard.

Follow the steps below to import the DCW 5MW tutorial 1 collection into Akselos Modeler:

• In Akselos Modeler, click on the Cloud tab on Ribbons → Authentication → Enter your username and (password or token) → Click on the Check button and wait for Authentication status to turn green and show Authentication successful.

Figure 3. Checking authentication

• On the File tab, click on Import Collection… → On the Import Collection window, find and select DCW 5MW tutorial 1  collection → Double-click on it or click on the Import button to pull the collection into your computer. You will receive a success message when the collection is successfully imported. 

Figure 4. Importing collection - DCW_5MW_tutorial_1 

3. Implementation

This part will guide users to create and set-up the Cross Section which will be used to assign to  subdomains of 1D stiffeners.

STEP 1: Create a new cross-section

Akselos modeler supports a Cross-section group in that the user can define several types of cross-sections and can reuse many places within the collection. 

In this step, we will guide you on creating and defining a cross-section

• This collection already has a Cross-section group located in the Collection named CrossSectionGroup_1. Now, you have to create a new Cross-section by right-clicking in the group → Add Property → Crosssectiongroupitem. Each item has an ID number on the right, it starts from 1 with the default item. The ID number is used to assign the cross-section to the model.

Figure 5. Adding a new Cross-section

When you complete this step above, you will see that a new Cross-section named CrossSection 2 with ID = 2 is added to the group.

• Rename cross-section: Click on CrossSection 2 then see the Property Tree → Right-click on CrossSection 2 → Rename → Input new named Rectangular_800_50_new.

Figure 6. Renaming Cross-section item

Define cross-section: Select RectangularCrossSection in cross_section then input the parameters (height = 0.8*m, width = 0.05*m). The graphic window will show the cross-section.

Figure 7. Setting up Cross-section parameters

Save change: After you complete all the steps above, right-click on the collection name in the Collection → Save Changes.

Figure 8. Saving the component changes in the collection

STEP 2: Assign cross-section to 1D stiffener

• Add the prepared component to the graphic window. Click Add → Components(s) → Select components/5MW_MC_Middle_newly_import → Click on the Add button.

Figure 9. Adding a new component to the model

• After finishing the steps above, a new component will be added to the Components in the Structure Tree and Graphic Window.

Figure 10. Newly added component in Graphic Window

• Reset component to origin: right-click on the component name in the structure tree → Reset to the original position

Figure 11. Resetting the component to the origin position

• To assign a newly created Cross-section from step 2 to the 1D stiffener, Select subdomains MC_OuterShell_LongStiff_ &  MC_OuterShell_RingStiff_ in the Subdomains. In the Property tree, input the Cross-section ID = 2 to the cross_section_id box.
  

Figure 12. Assigning Cross-section ID to stiffener subdomains 

Once you complete defining and assigning cross-section to 1D subdomains, you can visualize it in the Graphic Window by enabling Show Beam Cross-section in the Configure view settings.

Figure 13. Showing beam cross-section

STEP 3: Rotate Cross Section

In this step, we will guide you on how to rotate the cross-section in 2 ways:

• Inputting the angle in the Property Tree.
• Using the Orient Beam tool.

Using Property tree:

• Select subdomain MC_OuterShell_RingStiff_ in the Subdomains → In the Property tree, input 90 in angle (degree).

Figure 14. Input angle for rotating beam cross-section

You now see all ring stiffeners are rotated perpendicular to the outer shell.

Using the Orient Beam tool:

In Akselos Modeler, we have the Edit Beams tool to create and other features such as split/merge, orient, etc. This tool is located on the right panel.

Figure 15. Edit Beams tool 

• In the Edit Beams tool, to tab Orient → Select t2 in the Axis field and Center of Subdomain in the Options field → Click on the Orient button then select MC_OuterShell_LongStiff_ in the Graphic Window

Figure 16. Using the Orient tool for rotating Cross-section

You now can see that all longitudinal stiffeners are rotated perpendicular to the outer shell.

STEP 4: Offset Stiffeners

In this step, we will guide you on how to offset stiffeners by using the Property tree. In Akselos, we define vectors t1 and t2 for offsetting the cross-sections. You can visualize it in the Graphic Window by enabling Show Beam Axis in the Configure view settings:

Figure 17. Show Beam Axis

• Select MC_OuterShell_RingStiff_ → In the Property tree, input -0.4 in offset_t2. Select MC_OuterShell_LongStiff_  → In the Property tree, input 0.4 in offset_t2.

Figure 18. Input offset values

After completing the step above, you will see all stiffeners now completely rotate and offset to perpendicular with the outer shell.

Figure 19. Component completed offset and rotating

You can double-check with a reference component 5MW_MC_Middle_rotate_offset prepared in the component library:

Figure 20. Component 5MW_MC_Middel_rotate_offset for comparison

• After completing all the steps above. You have to save all you change within this component by right-clicking on 5MW_MC_Middle_newly_import → Save Changes

Figure 21. Save change component

Want to know more about related articles?

• Floating Offshore Wind Turbine - DeepCwind