A mechanical system is often modeled as a set of particles and rigid bodies, some of which are constrained in one way or another. A concise method is proposed for identifying a set of constraint forces needed to ensure the restrictions are met. Identification consists of determining the direction of each constraint force and the point at which it must be applied, as well as the direction of the torque of each constraint force couple, together with the body on which the couple acts. This important information can be determined simply by inspecting constraint equations written in vector form. For the kinds of constraints commonly encountered, the constraint equations are expressed in terms of dot products involving velocities of the affected points or particles and angular velocities of the bodies concerned. The technique of expressing constraint equations in vector form and identifying constraint forces by inspection is useful when one is deriving explicit, analytical equations of motion by hand or with the aid of symbolic algebra software, as demonstrated with several examples.
Identifying Sets of Constraint Forces by Inspection
Contributed by the Applied Mechanics Division of ASME for publication in the Journal of Applied Mechanics. Manuscript received February 7, 2012; final manuscript received August 29, 2012; accepted manuscript posted September 10, 2012; published online January 25, 2013. Assoc. Editor: Alexander F. Vakakis.
This material is declared a work of the US Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.
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Roithmayr, C. M., and Hodges, D. H. (January 25, 2013). "Identifying Sets of Constraint Forces by Inspection." ASME. J. Appl. Mech. March 2013; 80(2): 021019. https://doi.org/10.1115/1.4007577
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