Computational Study of Scattering Elastic Waves Due to a Teredo Marine Borer-Like Cylindrical Defect Embedded in an Isotropic Solid Cylinder

This paper showcases a quantitative investigation of scattering of ultrasonic waves experiences when impinging on a cylindrical defect inside a solid cylinder. Such cylindrical bores reduce the structural capacity of the cylinder, these defects constitute an even greater risk as they cannot be observed from the surface. The focal point investigated herein is to develop a better understanding of the wave’s scattering when interacting with defects of cylindrical bore, mimicking the Teredo marine borer, within the solid cylinder. Two-dimensional Finite Element simulations are carried out using ABAQUS software. A 200 kHz 5.5 cycle Hann windowed excitation on an isotropic cylinder is simulated a point source excitation at the circumference of the cylinder is used. The scattering wave fields from a range of defect diameters through the solid cylinder are presented. Using Two-Dimensional Fast Fourier Transform, the wave mode and velocity of the scattered wavefield along various directions was identified in cylindrical coordinates, to decouple the wave modes. Computational results are presented for the scattering pattern as a function of cylindrical bore diameter size relative to wavelength. This study serves as an efficient approach when choosing an input for ultrasonic imaging, with the aim to obtain high fidelity imaging resolution for structural health monitoring applications.

Performance Studies of Powder-Lubricated Journal Bearing Having Different Pocket Shapes at Cylindrical Bore Surface

It becomes impossible to use conventional fluid film journal bearings in the hot working environments (500–800 °C) due to rapid thermal degradation of lubricating oils. Under this situation, powder lubricants prove beneficial in spite of high friction values associated with them in comparison to lubricating oils. Thus, reduction of friction in powder-lubricated journal bearings is an essential task for making the operation energy efficient. Hence, the objective of this paper is to explore the reduction of coefficient of friction in a powder-lubricated journal bearing employing different pocket shapes (elliptical, parabolic, rectangular, and trapezoidal) placed on bore surface. Based on the investigations reported herein, it is found that the journal bearing having rectangular pocket yields least coefficient of friction among all the cases.

Numerical Investigation of Knurled Shaft-Hub Connections and Especially of the Joining Process

Faced with increasing cost pressures, manufacturers need to find new solutions for shaft-hub connections. One example is the knurled interference fit, where a shaft with knurls and interference is pressed in a soft hub with a cylindrical bore. At present the potential of the knurled interference fit is not fully used, because there are no general standards available for the design and for the joining process. But the joining process in particular has an important impact on the join strength. A predominantly forming joining process offers some advantages compared to cutting. Forming allows a clearly higher contact pressure over the groove because of the displacement of the hub material, which leads to greater axial reliability. Also, the natural material structure is preserved by the forming, and this, in combination with the hardening of the hub, should allow a higher transmittable torque. The Finite Element Method is used for detailed investigation of the joining process and the transmission behavior in the axial direction. With this method, the local loads, for example the hardening of the hub over the groove due to the formed join, are investigated as well as further parameter variations (e.g., chamfer angle, interference). Hence, an analytical approach for the determination of the necessary joining force was derived.

Heat and Fluid Flow Around a Sphere With Cylindrical Bore

This work is devoted to the numerical investigation of heat and fluid flow past a sphere with a centric, cylindrical bore. Such spherical rings are of interest in many technological processes. In chemical reactors, for example, spherical rings are used as a catalyst with an increased reacting surface. Motivated by this fact, we considered spherical rings with different bores and different orientations in flow regimes corresponding to Reynolds numbers from 10 up to 300. The results show a significant influence of the bore diameter on the symmetry and hence the steadiness of the flow field. The Nusselt number can be increased, which leads to a moderate rise in the drag coefficient. Thereby, the effect of the borehole depends on the Reynolds number, the bore diameter, and the angle of attack. For that reason, drag forces and total heat transfers do not simply follow the heat exchanging surface area. Based on the presented results, new correlations are given for both the drag coefficient and the Nusselt number; correlations which incorporate the bore geometry and the bore orientation in the flow field.

EFFECT OF THE ROTATION ON WAVE MOTION THROUGH CYLINDRICAL BORE IN A MICROPOLAR POROUS MEDIUM

In the present paper, we have studied the propagation of axial symmetric cylindrical surface waves through rotating cylindrical bore in a micropolar porous medium of infinite extent possessing cubic symmetry. The frequency equation for surface wave propagation in the micropolar porous medium has been derived and liquid filled bore are derived. The effect of the rotation on phase velocity of surface wave has been studied in detail. Radius of bore and other material parameters for empty and liquid filled bore are derived. A particular case of interest has been deduced. Numerical results have been obtained and illustrated graphically to understand the behavior of phase velocity versus wave number of a wave. The results have indicated that the effect of rotation on phase velocity is highly pronounced. Comparisons are made in the absence of rotation.

Comparison of the Steady-State and Dynamic Performance of Two Fixed-Geometry Journal Bearings

This paper evaluates two different journal bearings: a cylindrical bore plain journal bearing and a tri-lobe taper land bearing. Each bearing has the same nominal diameter (89mm) and aspect ratio (L/D = 0.7). The shaft rotational speed ranged from 6krpm to 14krpm and the bearing specific load from 700kPa to 2800kPa. The bearings’ steady-state performance is evaluated according to relative bearing and shaft displacement, bearing operating temperature and power loss. A frequency-domain analysis is used to determine bearing rotordynamic coefficients — it treats the bearing as a mass-spring-damper system. Excitation frequencies range between 20Hz and 350Hz. Ultimately, the tri-lobe taper land bearing offers better stability whereas the cylindrical bore plain journal bearing has a lower eccentricity and runs cooler for a given operating condition. The dynamic properties of the two bearings are found to be similar, although the higher stability of the tri-lobe taper land bearing is also reflected in the dynamic coefficients.