Investigation of approximate mode shape and transition velocity of pipe conveying fluid in failure analysis

Structures dynamic characteristics and their responses can change due to variations in system parameters. With modal characteristics of the structures, their dynamic responses can be identified. Mode shape remains vital in dynamic analysis of the structures. It can be utilized in failure analysis, and the dynamic interaction between structures and their supports to circumvent abrupt failure. Conversely, unlike empty pipes, the mode shapes for pipes conveying fluid are tough to obtain due to the intricacy of the eigenvectors. Unfortunately, fluid pipes can be found in practice in various engineering applications. Thus, due to their global functions, their dynamic and failure analyses are necessary for monitoring their reliability to avert catastrophic failures. In this work, three techniques for obtaining approximate mode shapes (AMSs) of composite pipes conveying fluid, their transition velocity and relevance in failure analysis were investigated. Hamilton’s principle was employed to model the pipe and discretized using the wavelet-based finite element method. The complex modal characteristics of the composite pipe conveying fluid were obtained by solving the generalized eigenvalue problem and the mode shapes needed for failure analysis were computed. The proposed methods were validated, applied to failure analysis, and some vital results were presented to highlight their effectiveness.

The influence of stacking technologies on structural dynamic properties of electric motors iron cores

Purpose It is essential to understand the structural dynamic behavior of electrical machines to predict their acoustic and vibrational behavior. Stacking technology, which is used to manufacture soft magnetic cores, has a strong influence on the material properties. The purpose of this paper is therefore to research the influence of the stacking technologies welding and bonding with bake varnish on the modal properties of iron cores. Design/methodology/approach A finite element simulation model is developed based on homogenization of the stator core. Eigenfrequencies, modeshapes and modal damping ratios are extracted from measurements and are used to validate the simulation model. Findings Modal characteristics depend on the participation of certain material layers at a certain mode. Higher amount of shear deformation results in higher modal damping. Bonded stacks exhibit lower shear stiffness and higher damping ratios. Originality/value This research paper provides insights to the modal characteristics of iron cores used in electric machine and compares the influence of stacking technologies.

Seismic Damage Assessment of Reinforced Concrete Grain Silos

This paper deals with seismic performance and damage assessment of concrete grain silos. An existing large silo is taken as a case study to conduct the numerical analyses. A global damage index based on target displacement is proposed to quantify numerically different damage states of the structure. To this aim, the classical N2 method is extended to adaptive multimodal to evaluate seismic performance of the structure for increasing pic ground acceleration levels with taking into account degradation of stiffness and modification of modal characteristics. The seismic capacity of the silo is evaluated, as an averaged curve, by conducting pushover and several incremental dynamic analyses using artificial and recorded accelerograms. The seismic demand is derived from the design spectrum of the Algerian seismic code (RPA 2003). The target displacement is determined by taking into account both the participation of the dominant modes, and the degradation of the structure’s modal characteristics. The nonlinear behavior of the structure’s walls is modeled by using nonlinear multilayered shell elements. The effect of the stored granular material is included through distributed equivalent masses. It is found that when the structure modal characteristics are updated as its stiffness is degraded, the target displacement is correctly computed. Whereas, it wrongly grows indefinitely, with increasing PGA, when constant modal characteristics of the intact structure are assumed, as usually done. The proposed global damage index is compared to three existing reliable indices. It better reflects the different damage states of studied silo.

Millimeter-Wave-to-Terahertz Superconducting Plasmonic Waveguides for Integrated Nanophotonics at Cryogenic Temperatures

Plasmonics, as a rapidly growing research field, provides new pathways to guide and modulate highly confined light in the microwave-to-optical range of frequencies. We demonstrated a plasmonic slot waveguide, at the nanometer scale, based on the high-transition-temperature (Tc) superconductor Bi2Sr2CaCu2O8+δ (BSCCO), to facilitate the manifestation of chip-scale millimeter wave (mm-wave)-to-terahertz (THz) integrated circuitry operating at cryogenic temperatures. We investigated the effect of geometrical parameters on the modal characteristics of the BSCCO plasmonic slot waveguide between 100 and 800 GHz. In addition, we investigated the thermal sensing of the modal characteristics of the nanoscale superconducting slot waveguide and showed that, at a lower frequency, the fundamental mode of the waveguide had a larger propagation length, a lower effective refractive index, and a strongly localized modal energy. Moreover, we found that our device offered a larger SPP propagation length and higher field confinement than the gold plasmonic waveguides at broad temperature ranges below BSCCO’s Tc. The proposed device can provide a new route toward realizing cryogenic low-loss photonic integrated circuitry at the nanoscale.