An Experimental Investigation of the Structural Wave Scattering Due to Impedance Discontinuities on a Cylindrical Structure

Experimental, numerical, and analytical work has shown that the response of a shell to a distributed force wave possesses unique characteristics which are dependent on the nature of structure attached to the shell. Specific characteristics which influence the response are the distribution of the discontinuities around the circumference (periodic/aperiodic), the impedance of the discontinuities relative to that of the shell, and the type of impedance (mass or stiffness). Traditional shell theory predicts low frequency, radial-dominated structural mode shapes of a shell with a sinusoidal distribution of displacement amplitudes. Due to the orthogonal nature of these mode shapes, the response of the structure to a traveling radial force wave with sinusoidal content at a given harmonic is due solely to the response of the mode shape with harmonic content of the same order. Introduction of impedance discontinuities to a shell yield complex mode shapes, which may be characterized by the summation of several harmonic components. These modes are no longer orthogonal in the presence of discontinuities, yielding harmonic content across various modal orders. As a result, a purely sinusoidal forcing function can excite several modes of the structure. Structural scattering as discussed in this paper refers to the phenomena in which a force wave at a given harmonic scatters into the response of modes with different harmonics. An experimental investigation into the harmonic scattering behavior of a shell due to mass discontinuities is presented in this paper. Knowledge of the key structural characteristics which influence scattering and their behavior will allow for a diagnostic tool when assessing the structural response of more complex cylindrical structures. Experimentally obtained data presented in this paper demonstrates some expected scattering characteristics of a cylindrical shell in the presence of periodically and aperiodically distributed masses. Some unique characteristics of the response of a shell in the presence of periodically distributed masses are discussed. Additionally, the data demonstrates that scattering characteristics may exist in even the simplest cylindrical structures due to non-idealities in the structure or its boundary conditions

An Experimental Investigation of the Structural Wave Scattering Due to Impedance Discontinuities on a Cylindrical Structure

Experimental, numerical, and analytical work has shown that the response of a shell to a distributed force wave possesses unique characteristics which are dependent on the nature of structure attached to the shell. Specific characteristics which influence the response are the distribution of the discontinuities around the circumference (periodic/aperiodic), the impedance of the discontinuities relative to that of the shell, and the type of impedance (mass or stiffness). Traditional shell theory predicts low frequency, radial-dominated structural mode shapes of a shell with a sinusoidal distribution of displacement amplitudes. Due to the orthogonal nature of these mode shapes, the response of the structure to a traveling radial force wave with sinusoidal content at a given harmonic is due solely to the response of the mode shape with harmonic content of the same order. Introduction of impedance discontinuities to a shell yield complex mode shapes, which may be characterized by the summation of several harmonic components. These modes are no longer orthogonal in the presence of discontinuities, yielding harmonic content across various modal orders. As a result, a purely sinusoidal forcing function can excite several modes of the structure. Structural scattering as discussed in this paper refers to the phenomena in which a force wave at a given harmonic scatters into the response of modes with different harmonics. An experimental investigation into the harmonic scattering behavior of a shell due to mass discontinuities is presented in this paper. Knowledge of the key structural characteristics which influence scattering and their behavior will allow for a diagnostic tool when assessing the structural response of more complex cylindrical structures. Experimentally obtained data presented in this paper demonstrates some expected scattering characteristics of a cylindrical shell in the presence of periodically and aperiodically distributed masses. Some unique characteristics of the response of a shell in the presence of periodically distributed masses are discussed. Additionally, the data demonstrates that scattering characteristics may exist in even the simplest cylindrical structures due to non-idealities in the structure or its boundary conditions

Marine invasion genomics: Revealing ecological and evolutionary consequences of biological invasions

Genomic approaches are increasingly being used to study biological invasions. Here, we first analyse how high-throughput sequencing has aided our understanding of the mechanisms associated with biological invasions. These include the transport of propagules to pre-invaded areas, an exploration of the consequences of hybridisation during range expansions, and the pre- and post- invasion adaptation of colonising populations. We then explore how contemporary genomic methods have been used to probe and monitor the spread of non-indigenous species. More specifically, we focus on the detection of species richness from environmental samples, measures of quantitative traits that may promote invasive- ness, analysis of rapid adaptation, and the study of phenotypic plasticity. Finally, we look to the future, exploring how genomic approaches will assist future biodiversity conservationists in their efforts to mitigate the spread and effects of biological invasions. Ultimately, although the use of genomic tools to study non-indigenous species has so far been rather limited, studies to date indicate that genomic tools offer unparalleled research opportunities to continually improve our understanding of marine biological invasion