There is detailed tutorial on COMSOL website for learners/education along with the model file and presentation. You may use the those resources Ramasastry D.V.A.
Thank you very much for your valuable inputs to both of you
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Dr.O.P. Gupta - Sir, very thankful to you answer/ reply. But, we are working to simulate weldment flow - liquidifying and then cooling to solidify and to study for any possible defects and the causes.