A two step viscothermal acoustic FE method

Previously, the authors presented a finite element for viscothermal acoustics. This element has the velocity vector, the temperature and the pressure as degrees of freedom. It can be used, for example, to model sound propagation in miniature acoustical transducers. Unfortunately, the large number of coupled degrees of freedom can make the models big and time consuming to solve. A method with reduced calculation time has been developed. It is possible to partially decouple the temperature degree of freedom, as result of the differences in the characteristic length scales of acoustics and heat conduction. This leads to a method that uses two sequential steps. In the first step, a scalar field containing information about the thermal effects is calculated (not the temperature). This is a relatively small FE calculation. In the second step, the actual viscothermal acoustical equations are solved. This calculation uses the field calculated in the first step and has the velocity vector and the pressure as the degrees of freedom. The temperature is not a degree of freedom anymore, but it can be easily calculated in a post processing step. The required computational effort is reduced significantly, while the difference in the results, compared to the fully coupled method, is negligible. Along with the theoretical basis for the method, a specific FE calculation is presented to illustrate its accuracy and improvement in calculation time

A flexible rotor on flexible supports: modeling & experiments

In this study, a flexible rotor with variable support stiffness has been analyzed. Simple support models consisting of mass, spring systems are extracted from modal analysis of the isolated support and by applying static loads to the finite element model of the supports. The derived equivalent models of the supports are then implemented in the finite element based structural model which predicts the dynamic behavior of the rotor. Finally experimental modal analysis of the rotor is performed with different support stiffnesses. The experimental and theoretical results have been compared and different support modeling approaches have been examined

Thermal modeling of a mini rotor-stator system

In this study the temperature increase and heat dissipation in the air gap of a cylindrical mini rotor stator system has been analyzed. A simple thermal model based on lumped parameter thermal networks has been developed. With this model the temperature dependent air properties for the fluid-rotor interaction models have been calculated. Next the complete system has also been modeled by using computational fluid dynamics (CFD) with Ansys-CFX and Ansys. The results have been compared and the capability of the thermal networks method to calculate the temperature of the air between the rotor and stator of a high speed micro rotor has been discussed

The Pattern of Correlated X-ray Timing and Spectral Behavior in GRS 1915+105

From data obtained from the PCA in the 2-11 keV and 11-30.5 keV energy range, GRS 1915+105 is seen during RXTE observations between 1996 May and October on two separate branches in a hardness intensity diagram. On the hard branch, GRS 1915+105 exhibits narrow quasi-periodic oscillations ranging from 0.5 to 6 Hz with ${\Delta \nu \over \nu} \sim 0.2$. The QPOs are observed over intensities ranging from about 6,000 to 20,000 counts s$^{-1}$ in the 2 - 12.5 keV energy band, indicating a strong dependence on source intensity. Strong harmonics are seen, especially, at lower frequencies. As the QPO frequency increases, the harmonic feature weakens and disappears. On the soft branch, narrow QPOs are absent and the low frequency component of the power density spectrum is approximated by a power-law, with index $\sim -1.25$ for low count rates and $\sim -1.5$ for high count rates (\gta 18000 cts/s). Occasionally, a broad peaked feature in the 1-6 Hz frequency range is also observed on this branch. The source was probably in the very high state similar to those of other black hole candidates. Thermal-viscous instabilities in accretion disk models do not predict the correlation of the narrow QPO frequency and luminosity unless the fraction of luminosity from the disk decreases with the total luminosity.Comment: ApJ Lett accepte

Neglected Achilles tendon rupture with central insertional plantaris tendon hypertrophy: two cases

A neglected Achilles tendon rupture is often characterized by muscle weakness and an overlengthened repair by scar tissue. Reconstructive surgery is usually performed taking into account the patient’s required level of function. Two surgical cases of neglected Achilles tendon rupture are presented in this article. In both instances it was expected that central fibrosis, possibly after neglected tendon rupture, would be found. However, after longitudinal opening of the tendons, a thickened plantaris tendon was evident at the insertion on the calcaneus in both cases. This hypertrophic tendon occupied most of the diameter of the Achilles tendon. Due to partial or complete rupture of the Achilles tendon, there was notable weakening and tendon transfer-augmentation was performed. A thickened plantaris tendon as a reaction to a neglected rupture of the Achilles tendon is a rare presentation. It can be detected preoperatively by MRI and subsequently preoperative planning can be optimized