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Hullform Design and Standard Series   

Alion naval architects have 60 years of hullform design experience. Hullform design, modification and research products include, but not limited to, patrol boats, coast guard cutters, frigates, destroyers, cruisers, amphibious and landing ships, ocean graphic research vessels, drilling ships, catamarans and passenger ferries, high speed planning boats and high speed surface effect ships. For monohulls, Alion has the complete and digitized Taylor Series data and program in addition to other proprietery hull series. For catamarans, Alion purchased and now owns the complete INCAT hullform series, tank test data and design programs.


Hullform Performance Anlysis Using Computational Fluid Dynamics  





To aid hullform design and reduce towing tank test cost, Alion experts use the most advanced hydrodynamic CFD tools for hullform performance analysis. Methods include linear potential flow, nonlinear potential flow, boundary-layer viscous flow, RANS for tubulent flow, and a combinatioin of potential flow, boundary-layer and tubulent viscous flow. These numerical analysis can be used to assess, explore and improve a wide range of hullform performance objectives: drag reduction, Lcb location, bow shape,  bulb shape, bulb size, bulb position, stern shape,  skeg shape/size, single skeg vs. twin skegs, stern wedge and flap study optimum stern flap angle, interceptor, air bubble sweepdown, sonar placement,  measures to prevent bubble injection into sonar array, flow fence , gondola, cow catcher, air injection into propeller, propeller cavitation and prevention, wake profile in the propeller disk , catamaran and SES sidehull separation, etc.



Linear and Nonlinear Potential Flow AnalysisNorthAtlantic2


Potential flow analysis is used to evaluate not only ship's main characteristics (Cb, fore body Cp, aft body Cp, Cm, cross-section area curve, etc) but also hullform local details (bow shape, bulb shape/size/positioin, stern shape, skeg size/shape, flap, wedge, interceptor, etc). Compared with RANS viscous analysis, potential flow offers an efficient and reliable way for hullform trade-off study and exploration before tank test. Potential flow analysis results include wave making drag, pressure contours, wave profile, fluid velocity field and streamline traces which are presented in various text and graphic formats. In addition to provided guidance on hullform design and tank test, these results will also help appendage design (sonar positioning, for example) and propulsion integration.


Effective use of numerical flow analysis can greatly reduce tank test matrix and cost. Following are some examples of Alion past applications:



Potential flow analysis uses panel method which requires surface meshing on the body surface and free surface only. It is fast and offers a quick turn-around in comparison and trade-off study where many options and parameter combinations are to be explored. Panel method is generally robust and reliable if meshing quality is good.





Viscous Flow Analysis: Boudary and Turbulent Flow 


Viscous flow analysis using RANS method involves 3D meshing of the whole fluid domain, not just meshing on the surfaces. Better results usually requires finer meshes and bigger fluid domain. Fine mesh and large fluid domain easily make an application of RANS analysis prohibitively large and expensive.


However, RANS CFD analysis is sometime necessary, especailly in the aft-body and stern region, where visoucs effect cannot be ignored. To make the analysis manageable, Alion experts usually use a combination of the potential flow analysis and viscous flow analysis: do a potential flow analysis, with boudary layer and geometry details,  for the whole ship first; the results of the potential flow analysis is subsequently used as entry and free-surface boundary conditions for RANS CFD analysis. The RANS CFD analysis is usually done for the aft body only.


Following are some examples of Alion past applications:




















































Hull Form:  Mr. Steve Toby, atoby@alionscience.com, 001 703 933 6673



CFD:   Dr. Changben, cjiang@alionscience.com, 001 703 933 6612 



Manager: Mr. Russ Krull, rkrull@alionscience.com, 001 703 933 6812