This was calculated as by Wagner, but computed with the velocity distribution along 

 the line of zero potential of the prism instead of with that of the flat plate. Unfortu- 

 nately an incorrect velocity distribution was used in [3]. Computations based on the 

 correct velocity distributions have been made by the writer as part of a study of 

 extensions of Wagner's method [4]. 



A new approach to the exact solution for normal symmetric wedge impact has 

 been given very recently by Bor? [5]. 



The authors tell how Coombs has utilized an expanding hollow wedge model 

 for the wedge impact flow, and how this is an outgrowth of work (by Chou) with 

 an expanding spherical bowl model of normal sphere impact. The direct two-dimen- 

 sional analogue of Chou's work has also been considered, that is the expanding circular- 

 arc model for the normal broadside impact of a circular cylinder [6]. 



Oblique Entry 



In some recent work at the Naval Ordnance Test Station in Pasadena, miniature 

 accelerometers inside two-inch diameter models have given data on axial and cross 

 components of impact force during oblique inpact. For a hemisphere-cylinder con- 

 figuration, the results have compared well with the predictions of Trilling's zero surface- 

 rise, ellipsoid-fitting approximation, after some necessary rederivation of the expressions 

 for the added mass of half-submerged spheroids. Reports are in preparation. 



Water-Entry Modeling 



While this facet of hydroballistics was not discussed by the authors, it seems 

 worthy of note that recent work at NOTS under Dr. Wau<?h has demonstrated accuracy 

 of the modeling technique wherein model cavitation index and Froude number are 

 made the same as for the prototype. For a family of head shapes, the pitch versus 

 penetration in diameters has been shown to be modeled accurately for at least several 

 diameters of travel. Investigation is underway of the importance of gas-density scaling 

 on transient cavities. This work is answering many of the questions raised by wartime 

 research in modeling, e.g. [7]. 



In closing, this writer would like to mention two little known reports which 

 may be of interest. The first of these, [8] by Birkhoff and Isaacs, expands in consider- 

 able detail the references to transient water entry cavities in Birkhoff's book "Hydro- 

 dynamics." The second [9] is a translation of Weible's summary of German wartime 

 work on water impact loads, including Schmieden's extension to three dimensions of 

 Wagner's approximation. 



REFERENCES 



1. Dergarabedian, P. "Compressibility Effects During Water Entry." NAVORD Report 



3523 (NOTS 1159), June 1955. 



2. DePrima, C. R. and F. E. Marble. "Impact of an Elastic Body Upon the Surface of a 



Compressible Liquid. Part I. Contributions of Previous Investigators to Solution of 

 the Elastic Problem." California Institute of Technology unpublished report. 



3. Bisplinghoff, R. L. and C. S. Doherty. "Some Studies of the Impact of Vee Wedges on 



a Water Surface." Jour. Franklin Inst., Vol. 253, No. 6, June 1952. 



4. Fabula, A. G. "Ellipse-Fitting Approximation of Two-Dimensional Normal, Symmetric 

 Impact of Rigid Bodies on Water." Proc. Fifth Midwest. Conf. Fl. Mech., Ann Arbor, 



Mich., 1-2 April 1957, Univ. of Michigan Press, 1957. 



5. Borg, S. F. "Some Contributions to the Theory of Wedge-Water Entry." Proc. IXth Int. 



Congr. Appl. Mech., Brussels, 1956. 



6. Fabula, A. G. and I. D. Ruggles. "Vertical Broadside Water Impact of Circular Cylinder: 



Growing Circular-Arc Approximation." NAVORD Report 4947 (NOTS 1268), Octo- 

 ber 1955. 



237 



