Vibrations of streamlined perforated plate

Object and purpose of research. A study of inception conditions for hydroelastic self-induced vibrations of perfo-rated plate in slip flow. Materials and methods. Vibration spectra measurements of plate in flow. Analysis of physical nature of vibration fre-quency spectra maximums. Main results. Inception conditions for hydroelastic self-induced vibrations of perforated plate in slip flow were determined. Conclusion. Proposals for prevention the inception of hydroelastic self-induced vibrations in ship structures including per-forated plates in water slip flow were formulated.

Investigation of grease lubricated deep groove ball bearing with multi-defected outer race using vibration signature analysis

Failure of any rotary machine is mainly due to bearing failure being the key element. Defect frequency is the function of speed, ball diameter, and pitch circle diameter of bearing. The number of defects does not affect the excitation frequency, but increase in the level of vibrations is observed in total. The inner race is mounted on the rotary shaft, and the outer race is fixed in the housing. Hence, a defect on the outer race does not rotate with the shaft. This article highlights the study of the multi-crack detection technique at a comparatively higher speed. Amplitudes of vibrations increase with speed, but with load, they almost remain the same. The experiment has been performed at the range from 1000 to 5000 r/min with 5 kg load on the test bearing. The location and size of the defect affect the level of vibrations with noticeable increase. However, the presence of a second defect with respect to the load zone plays an important role. As the defect is at the peak position in the load zone, outer race defect frequency excites more in the vibration spectra. The location and size of the second defect are varied, and acceleration amplitude parameters like RMS, peak, and peak to peak are compared. The current work emphasizes the effect of location and severity of the second defect on the vibration spectra and amplitude parameters of the vibrations.

Analyzing Raman spectral data without separabiliy assumption

Raman spectroscopy is a well established tool for the analysis of vibration spectra, which then allow for the determination of individual substances in a chemical sample, or for their phase transitions. In the time-resolved-Raman-sprectroscopy the vibration spectra of a chemical sample are recorded sequentially over a time interval, such that conclusions for intermediate products (transients) can be drawn within a chemical process. The observed data-matrix M from a Raman spectroscopy can be regarded as a matrix product of two unknown matrices W and H, where the first is representing the contribution of the spectra and the latter represents the chemical spectra. One approach for obtaining W and H is the non-negative matrix factorization. We propose a novel approach, which does not need the commonly used separability assumption. The performance of this approach is shown on a real world chemical example.

Toward the design of dynamically similar artificial insect wings

Flapping wing deformation influences the aerodynamics of insect flight. This deformation is dictated by the dynamical properties of the insect wing, particularly its vibration spectra and mode shapes. However, researchers have not yet developed artificial insect wings with vibration spectra and mode shapes that are identical to their biological counterparts. The goal of the present work is to develop artificial insect wings that are both isospectral and isomodal with respect to real insect wings. To do so, we characterized hawkmoth Manduca sexta wings using experimental modal analyses. From these results, we created artificial wings using additive manufacturing and heat molding. Between artificial and real wings, the first two natural frequencies differ by 7% and 16% respectively, with differences of 16% and 131% in gains evaluated at those natural frequencies. Vibration modes are similar as well. This work provides a foundation for more advanced wing design moving forward.

Spectroscopic and thermal studies of cyano bridged hetero-metallic polymeric complexes derived from ligands containing N and S donor atoms

The new cyano bridged hetero-metallic polymeric complexes [Cu(dmtu)2Pd(CN)4]∙H2O and [Cu(H2O)2(detu)2Pd(CN)4]∙2H2O (dmtu = N,N'-dimethylthiourea, detu = N,N'-diethylthiourea; abbreviated henceforth as Cu–Pd–dmtu and Cu–Pd–detu) have been synthesized for the first time in powder form and their structures have been determined by vibrational (FT-IR and Raman) spectroscopy, thermal and elemental analysis techniques. Using vibration spectra of the complexes, it has been discussed whether the ligands are bound to metal atoms or not. According to the results obtained from the spectra of the complexes, the palladium atom is four coordinated with four cyano groups in a square planar geometry whereas the copper(II) atom of Cu–Pd–detu is six coordinated with two bridging cyano groups, two aqua and two detu ligands (four bridging cyano groups and two dmtu ligands for Cu–Pd–dmtu) in a distorted octahedral geometry. In addition, complex Cu–Pd–dmtu is similar to structure of the Hofmann type complexes and its structure consists of polymeric layers of |Cu–Pd(CN)4|∞ with the dmtu ligand bounded to the copper(II) atom. Thermal stabilities and decomposition products of the complexes were also investigated in the range of 30–1000 ºC in the static air atmosphere using TG, DTG and DTA techniques. KEY WORDS: Tetracyanopalladate(II), N,N'-dimethylthiourea, N,N'-diethylthiourea, Cyano-bridged complex, Vibration spectra Bull. Chem. Soc. Ethiop. 2020, 34(2), 365-376 DOI: https://dx.doi.org/10.4314/bcse.v34i2.13

Vibration Data Processing for Bedload Monitoring in Underwater Environments

This paper proposes a novel data processing framework dedicated to bedload monitoring in underwater environments. After calibration, by integration the of total energy in the nominal bandwidth, the proposed experimental set-up is able to accurately measure the mass of individual sediments hitting the steel plate. This requires a priori knowledge of the vibration transients in order to match a predefined dictionary. Based on unsupervised hierarchical agglomeration of complex vibration spectra, the proposed algorithms allow accurate localization of the transients corresponding to the shocks created by sediment impacts on a steel plate.