Fluid Forces on a Bridge - Homework


An object submerged in a fluid flow is subjected to forces due to the relative motions between the fluid and the object. Such fluid forces are known as the aerodynamic or hydrodynamic forces, depending on whether the fluid is a gas (usually air) or a liquid (usually water). Civil engineers must take the impact of these fluid forces into account when designing a new structure, such as a bridge. Neglecting them can be damaging or even catastrophic. A classic example is the collapse of the old Tacoma Narrows Bridge in 1940, which is believed to have been caused by the strong resonant vibrations induced by the wind’s aerodynamic forces. Another example is damage to bridges caused by the abnormally high hydrodynamic forces of a devastating flood. This simulation example compares the drag forces on a bridge sector caused by air and water flows at the same Reynolds number.


In this simulation example, you will learn how to simulate flows of air and water over a bridge section and calculate drag forces and corresponding non-dimensional drag coefficients for different fluid types.


Download the Mesh file needed for setting up the simulation and the associated Case & Data files here. Follow the instructions below to set up this simulation in Ansys Fluent starting with a Mesh file. In case you face any issues setting up or running the simulation, then please refer to the corresponding initial and final Case and Data files.

Alternate video link.

Results and Discussion

Let us now analyze the simulation results and understand the physics of fluid forces on a bridge sector.