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Mesh design is mostly about finding just enough mesh elements to accurately represent the geometry of interest. Minimizing the number of mesh elements reduces the time and computing power required for the simulation, but not having enough increases the error of the results. A quick metric to use is the total number of elements. This number gives a rough idea of the mesh resolution and can help predict how long a simulation will take, or if SimScale can even complete the simulation. What I mean by this is that after about 12-14M elements, SimScale will run out of memory when using 16 cores. For reference, we mostly used 10-12M elements during the development of MSXIV.
First, the region that will be simulated must be determined. This is known as the Background Mesh Box (Also commonly called the bounding box or domain). Typical guidelines are to use 2-8 times the car’s dimensions. Less space is needed on the sides, moderate space is needed in front of the car, and the majority of space should be behind the car. So for MSXIV (Approximately 5 m long, 2 m wide, 1 m tall), the domain should extend about 15 m (= 5 m * 3) in front of the car, 35 m (= 5 m * 7) behind the car, and 5 m above and on either side. Now, it is important to note that there is a plane of symmetry running down the center of the car. This means that we only need to simulate half of the car. The resulting drag (and other forces) can be doubled when post-processing, since each half of the car should have identical drags. This can drastically reduce the number of elements in your mesh, without sacrificing resolution, and is something that was not taken advantage of for the design of MSXIV. For example, the 12M element meshes we used could have been recreated to the same resolution by using a 6M element “half-mesh”. Or, more importantly, the accuracy of the simulation could be improved by using a half-mesh with 7-9M elements (equivalent to 14-18M elements of a full mesh) and SimScale will still have enough memory even on 16 cores. The end result is a domain that is still 50 m long and 5 m tall, but only 5 m wide offset to one side of the car.
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