An experimental verification of a damage detection process using novel optimization techniques such as modified real coded genetic algorithms and swarm-based algorithms is presented. Here, the objective function is defined as the sum of differences of the modal frequencies between intact and stiffness damaged state, which has to be minimized to identify the damage location and its severity in the process of model updating. In addition to the structural or damage variables such as the mass or stiffness of the numerical model, the profiles of modal frequency shifts are also damage-sensitive features. The iterative process that uses the proposed population-based optimization algorithms successfully identifies the local mass change of a test structure by updating the damage variables to fit the modal data of test structures such as a cantilevered beam and multibay truss frame.

SUMMARY This study adopts the Isomap algorithm that uses the variation of modal frequencies caused by stiffness damage to classify damage locations in a structure. The Isomap algorithm belongs to a nonlinear generalization of classical multidimensional scaling, which makes a new coordinate system for high‐dimensional data. And this coordinate system provides good observations for the extraction of the data pattern and for the classification of their nonlinear characteristics. Thus, the Isomap can easily find globally meaningful coordinates and identify the nonlinear structure of complex data sets for many cases, whereas neither the principal component analysis (PCA) nor multidimensional scaling has been successful. This study compares the performances of the PCA and the Isomap algorithm in classifying damage locations in terms of modal frequency changes. The article also investigates the benefits of incorporating the concept of sensitivity enhancing control in the Isomap‐based damage classification to improve the level of resolution of a modal frequency shift. It is demonstrated that the Isomap algorithm successfully enhances the quality of patterns and classifications related to damage locations through simulation examples. Copyright © 2013 John Wiley & Sons, Ltd.

This paper provides experimental results from an investigation to assess the compressive strength of ice-powder pellets for potential use as a solid form of gas hydrate. The mechanical strength of the pellets is one of the key parameters in designing a cost effective storage system, as well as transportation carrier ships and re-gasification processes, because the amount of BOG (boil off gas) is directly related to the size of the storage tank, the pellet size, and the shape and permeability of the pellets. Ice powder, being a convenient substitute for hydrate powder, can be fabricated into cylindrical and capsule-type shaped pellets, and the resulting mechanical strength, in terms of the stackable height, has been measured for different press forces. A procedural verification of producing and testing the ice pellets suggests some useful insights for deciding the porosity, size and shape of the pellet designs for realizing a portable media for natural gas hydrates.

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