Forces on cylinders and plates in an oscillating fluid

The inertia and drag coeffi cien ts o f cylinders and plates in simple sinusoidal c urrents are investigated. The midsection of a rectangu lar basin wi t h standing wa ves s urg ing ill it is selected as t he locale of curren ts. The cyl inde rs and plates are fi xed hori zontally a nd below t h e water surface. The average values of t he inertia and d rag coefficients over a wave cycle sh ow variations wh e n the intensity of t he current and t he s ize of th e cylinders or plates a re ch anged. These variation s, h owever, can be correlated wi t h t h e p eriod parameter Um TI D, where U m is th e maximum intensity of t he sinusoidal c urrent, T is the p eriod of t he wave a nd D is t he di am eter of t he cylinder or t he width of the plate. For t he cylinders UmTI D eq ua ling 15 is a c ri tical rond ition y ielding t he lowest va lu e of t he inertia coefficient a nd th e largest valu e of t he drag coe ffic ie11t. For t he plates t he higher values of t he drag coefficie nt are assoc iated with t he small er va. lu es of Um TI D a nd t he higher valu es of t he mass coe ffici e nt wi t h t he larger valu es of Um TI D . The variatio n of th e coefficients with t he phase of t h e wa ve is examin ed a nd the bearing of t hi s o n t he formul a for the fo rces is disc ussed. The flow patterns aro und t he cylinde rs a nd plates a re examined photographically, a nd a s uggestion is advan ced as to t he physical m eaning of the parameter Um TI D.