ABAQUS simple case 1: reservoir filled with pressurized liquid

If we read ABAQUS manuals, we can find a lot of case studies and instruction explaining how to analysis a model. Beam and truss analysis are the most popular examples used in university because of its easiness and simplicity. If you are not familiar with ABAQUS features, please read it first on internet. However, ABAQUS manual does not provide the step-by-step instruction for pieces with complex shape and interaction. This is the reason I write this blog. I just want what I have learned in my class.

Please keep in mind that ABAQUS is a general Advance Finite Element (FE) tools to solve wide variety and complex problems. It is just a “tool” which helps up to solve the problem but we are the one who are responsible for defining the problem. The validity of our result strongly depends on how we understand and define the physical model. It is differed from SAP2000 or other “specialized” FE software in civil engineering. As consequence, it needs special care and little bit imagination. The most powerful feature in ABAQUS is its calculation capacity to address linear or non linear physical behavior, not in design like other CAD softwares such as AutoCAD, Catia, Solidwork, etc. So, try to simplify the design if it is possible.

Suppose that we have a simple 3D reservoir having wall thickness 5 mm, encastred on its neck, weight applied and under pressure from liquid which fill all spaces. It is made of cast iron which is a brittle virtually non-maleable metal that is considered generally inflexible. The mechanical properties are shown below :

E = 210.E9  Pa                         ν = 0.3                            ρ = 7100 kg/m³

Calculate and find the position where stress concentration is maximum?

model of simple reservoir filled with pressurized liquid

The following description are step by step processing using ABAQUS student version 6-12.2. In this tutorial, I will not go into details, please read manual instruction of ABAQUS for further details.

1. Create Model (part, material property). The model was created by revolving 3D, deformable shell. Please see “getting started with Abaqus”

2. Define step, load and boundaries condition. The inital state of our reservoir is empty. Before fluid filling, there is only gravity force applied on the body. When we inject the fluid, uniform pressure applied on the body. So there are three main steps as seen on the above schema. Apply pressure in the load module and encastrement on the neck as seen on the following schema.

define pressure for liquid and internal faceencastred1

3. Create Seed, mesh and mesh verification. The result accuracy depends on the mesh quality such as density, uniformity, shape ratio, angle variations, etc. In this model, we used seed edge and swept meshing.

There is no fixed rules of meshing according to manual instruction of ABAQUS but the regions which might have large deformation should have high mesh density. It is recommended to use hexagonal, quadratic elements (all element ends with “4” such as CPE4, CPE4T, DC2D4) instead of trilingual element (all element ends with “3” such as CPS3, CPE3T, DC2D3) to ensure convergence value. The element selection depends strongly on the physical  phenomena works in the model. The element we use for heat transfer or thermo-mechanical problems will be different for contact or stress analysis. Please see manuals for further details of the choice of elements. Since the wall thickness is thin enough compared to the whole size, we assume that plane stress is applied, thus CPS4 element is used.

Distorted element will lead to non-convergence value and it can be very frustrating, so please use mesh verification, edit and control if it is necessary.

before mesh improvement - swept meshing after mesh improvement - swept meshing

 mesh improvement of neck-front surface using swept mesh

before mesh improvement - mesh control using face curvature after mesh improvement - mesh control using face curvature

mesh improvement using face curvature control

4. Define F-output, job submission and view result.

view result along path

If we want to view stress value along the certain point or path, we can use edit note list path from visualization Module

result1

Von Mises distribution representing the location of stress concentration

view deformed section

Deformed part and stress concentration

Hope you learn something, the next post will be in “contact” cases  :)

PS :  This model is made using ABAQUS student version which has very limited nodes (maximum 1000 nodes). If you want to use complex shape, try to use other version. The more nodes you use, the more accurate is the result.

Download link :

http://filesmy.com/file/0TY8Q

3 thoughts on “ABAQUS simple case 1: reservoir filled with pressurized liquid

  1. excellent post thanks for making us understand so nicely. i have similar problem. plz explain how i should do analysis. i am doing a analysis of o-ring of pneumatic hydraulic shock absorber. the fluid is introduced from top in pressurized condition. the rod moves up an dowm from bottom. the alternating motion creates friction on o-ring. the fluid act as a damper and also lubricates the o-ring. i want to know the contact pressure and fluid leakage.

    • sorry for late reply as I did not receive notifications frequently from wordpress, i’ll modify my notification parameters.
      From my understanding, you concern about pressure applied to O-ring. It is more complicated than my case. At least there are 3 parts in your model which are ring, rod and cylinder. By defining reference point of rod and displacement movement on U2 [means only in y-axes], it moves up-down. Then put constraint “rigid” or “tie” between O-ring and rod, depends on the attachment behavior of your ring-rod. Fluid pressure is already applied at the initial step so when the rod moves it will increase the internal pressure incrementally and it creates contact pressure to your O-ring. As the fluid acts as lubricant, you can assume it as “frictionless” on the interaction properties between ring-cylinder.
      For the leakage, I have no idea because i assume that O-ring is not deformable/rigid part. Otherwise you make it as deformable after thousand cycles, which is quite complicated for me. Let me know what you think?

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