The Proceedings Fifth International Conference on Numerical Ship Hydrodynamics (1990) / Chapter Skim
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Development of a New Velocity Measurement System by Using Computerized Flow Visualization and Numerical Method
Development of a New Velocity Measurement System by Using Computerized Flow Visualization and Numerical Method
Pages 481-492
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From page 481... ...
More and S Ninom~ya Hiroshima University Hiroshima, Japan Abstract A hybrid method is developed to measure 3-dimensional flows where the image processing method and numerical computational method are complementarily used; the 3-dimensional flow field is reproduced by the numerical calculations by making use of several scanned plane flows which have been obtained by the flow visualization and image processing.
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From page 482... ...
A laser light sheet is used to scan a plane flow field which is traversed in z direction whose velocity component w is presumed the smallest among the three components. A 25 mW He-Ne laser beam and a circular cylindrical lens are used to realize a light sheet in the present experiment.
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From page 483... ...
As shown in Fig.3, the thinned line Ci is determined as the centerline of the segment Ai-Bi. 2.3 Calculation of plane velocity As shown in Fig.4, the plane veloAIA A2 He'd / B3 _ ~/~ 1—-I// 1—4/ B2 BE ~3,— / BE Fig.3 Thinning process of images t, ~2 _ ~ ~ (d ' ' ." <)
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From page 484... ...
The nominal accuracy of the image analysis is given in terms of the density of the pixels of COD camera and the sampling interval time. The resolving power of the image processing, denoted by d, is given by d = L_ (3)
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From page 485... ...
4. Reproductionof the 3Dimensional Flow Field 4.1 Invoked equations and the scheme The reproduction of the 3-dimensional flows from the scanned plane velocity fields is achieved numerically by a variational method to satisfy the continuity equation [5]
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From page 486... ...
The coordinates and the analyzed region is shown in Fig.8. The plane flows are provided on twenty horizontal planes by the potential flow calculation.
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From page 487... ...
In the present experiment, the model is traversed vertically for the plane flows to be scanned. Cathode / CCD Camera _ ~ r- it ~ Fig.10 to the Pulse Generator \\\ Arrangement for the meas to the Image Processi ng ~ urements of the wake of Wigley model Sys ted ~ 487
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From page 488... ...
This means that the determined velocity field is the mean velocity for 6 seconds. 5.2 Results of the plane flows Fig.12 shows one example of tracer images on z=0 plane, the reflecting plane; (a)
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From page 489... ...
Although the results do not always agree quantitatively with those by conventional method, the third velocity components are well reproduced. The computation was stable and robust as expected even if the measured plane flows contain some errors.
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From page 490... ...
"Development of a Method to Measure Flow Field by Flow Visualization and Image Processing Techniques", J of the Society of Naval Architects of Japan, Vol.162, pp.81-89 (1987)
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From page 491... ...
The laser sheet in Fig.2 shows us a cross section, x-y plane, of the hydrogen bubble sheet, so that you can get the velocity components u and v independently on w in this paper. However, the hydrogen bubble sheets are inclining their vertical plane, even if the platinum wire is kept vertically, after the sheet streams down along the streamlines near the ship stern (see Fig.Al)
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