Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Image wavelet transforms implemented by discrete wavelet chips

Abstract: Both discrete wavelet transform (DWT) and inverse DWT are implemented using the lossless quadrature mirror filter (QMF) bank The image passing through the finite impulse response QMF filtering becomes blurred and thus requires fewer number of pixels Such a decimation amounts to the critical sampling that leads to the complexity O ( N ) for N data The data compression comes from the permissible bits per pixel dynamic range compression of those filtered images having fewer details The image reconstruction at a telereceiving station is accomplished by means of the inverse DWT Thus, a complete biorthogonal basis of QMF is implemented by a fast wavelet transform chip designed with Verilog HDL and the image processing is demonstrated numerically Adaptive DWT is sketched

Local Damage Detection with the Global Fitting Method Using Mode Shape Data in Notched Beams

Abstract: Damage in a structure alters its dynamic characteristics such as frequency response functions and modal parameters. The present study extends the ‘gapped smoothing method’ for identifying the location of structural damage in a beam by introducing the ‘global fitting method.’ The procedure uses only the mode shape data obtained from a damaged structure with an assumption that the undamaged structure is homogeneous and uniform and the damage size is small. The sensitivity of damage detection algorithm is evaluated using a finite element analysis (FEA) of a few beams having a notch. Structural irregularity index (SSI) was used to identify the locations and size of damage. The ability to detect damage was enhanced by averaging SSI over a few modes. A statistical procedure was applied to identify damage with respect to background noise. A methodology and quantitative criteria was developed to select the optimum excitation grid spacing. Numerical results showed that the present method can detect both narrow (13 mm width) and wide damage (126 mm width) associated with less than 3% local thickness reductions. Experimental results validated the numerical results and detected the depth to thickness ratio about 41% and 35% for the wide and narrow notch beams, respectively. The present method showed improved resolution on detecting the location and size of damage in a beam over the previous methods using mode shape data reported in literature.