### Structural Mechanics Blog Posts

## Modeling the Hydrostatic Pressure of a Fluid in a Deformable Container

##### Walter Frei | April 9, 2014

In a previous posting, we looked at computing and controlling the volume of a cavity filled with an incompressible fluid, which solved for the static deformation of a fluid-filled rubber seal. In that example, we did not explicitly model the fluid, but added an equation to solve for the pressure, assuming incompressibility of the fluid. Here, we will extend this approach and include the hydrostatic pressure of the fluid in the deforming container.

Read more##### Supratik Datta | April 4, 2014

Previously, you saw how to compute stiffness of linear elastic structures in 0D and 1D. Today, we will expand on that and show you how to model this in 2D and 3D. We will also show you an alternate method to compute stiffness.

Read more##### Supratik Datta | April 3, 2014

Today, we will introduce the concept of structural stiffness and find out how we can compute the stiffness of a linear elastic structure subjected only to mechanical loading. In particular, we will explore how it can be computed and interpreted in different modeling space dimensions (0D and 1D) and what factors affect the stiffness of a structure.

Read more##### Alexandra Foley | March 17, 2014

When modeling computationally taxing geometries, you can save time by using cyclic symmetry to cut down on memory usage. This can be more complex for rotationally than axially symmetric geometries. However, with the Structural Mechanics Module you can easily solve a single section of an impeller model and still get accurate results.

Read more##### Henrik Sönnerlind | March 7, 2014

Buckling instability is a treacherous phenomenon in structural engineering, where a small increase in the load can lead to a sudden catastrophic failure. In this blog post, we will investigate some classes of buckling problems and how they can be analyzed.

Read more##### Gerard Hegemans | March 4, 2014

Cars come with either an automatic gearbox or a manually operated one, a stick shift. With a manual gearbox, we use the stick shifter very frequently while driving the car, yet we hardly ever think about the way the mechanism works. Here, we investigate how it works and what forces are acting on it when submitted to a very common load case — selecting first gear — with the help of a COMSOL Multibody Dynamics model of the gearshift mechanism.

Read more##### Walter Frei | February 3, 2014

There are various ways of handling interactions between fluids and solids in COMSOL. You can, for example, explicitly model the fluid using the full Navier-Stokes equations for the pressure and fluid velocity fields. Although that can be a very accurate approach, it’s much more expensive than is needed for certain types of Fluid-Structure Interaction (FSI) problems. Here, we’ll introduce a method for modeling enclosed volumes containing incompressible fluids, under the additional assumption that the momentum and energy transfer via the […]

Read more##### Mateusz Stec | January 1, 2014

Computer aided engineering (CAE) helps us understand how mechanical systems work before they are physically realized. In order to properly reflect the reality, we continuously increase the modeling complexity when we simulate, validate, or optimize our applications. A simple technique to improve a model is to increase the number of finite elements that in turn create more evaluation points. The hardware and simulation time, however, may limit the size of the model, and other solutions are necessary — such as […]

Read more##### Laura Bowen | December 20, 2013

The question of exactly how strong living bones are poses many important considerations for the medical industry. There is not currently a single-purpose device in the field to test bone strength. However, it is possible for researchers to get measurements of bone strength by modeling the entire makeup of the bone and using multiphysics simulation to perform stress and strain analyses. Simulating bone strength starts with a simple map of the external topology of the bone and then delves into […]

Read more##### Henrik Sönnerlind | November 21, 2013

In structural mechanics you will come across a plethora of stress and strain definitions. It may be a Second Piola-Kirchhoff Stress or a Logarithmic Strain. In this blog post we will investigate these quantities, discuss why there is a need for so many variations of stresses and strains, and illuminate the consequences for you as a finite element analyst. The defining tensor expressions and transformations can be found in many textbooks, as well as through some web links at the […]

Read more##### Alexandra Foley | September 26, 2013

When analyzing a bolted joint, one thing to consider for an accurate analysis is the bolt pretension. With COMSOL Multiphysics, the effects of prestressing a bolt can be easily computed using the Bolt Pre-tension feature available in the Structural Mechanics Module. After modeling prestressed bolts, a further analysis can then be conducted on an external load applied to the structure. Here, we will explore how to include prestressed bolts in a tube connection model, and then carry out a stress […]

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