These are simply circles arranges around a circle over regular intervals. Different size of circles and different intervals create different patterns.
Once you have all these circles, taking out arc segments in a regular way can create beautiful patterns. Think about how this one is done.
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Again, take out areas can create different effects.
In this one, you replace arcs by lines to create a different effect.
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This spiral design is done by taking out all arc segments of one orientation.
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