Cavitation erosion through water hammer and column separation is a major concern in hydraulic applications such as percussive rock drilling. Cavitation aspects must be considered both in early and late design stages, which require deep knowledge and tools for prediction. In this study, an oil-hydraulic test equipment for water hammer assessment was designed using state-of-the-art simulation tools. Several tests were performed, with and without column separation, showing good repeatability on measured pressures. At higher flow rates, column separation was the dominating feature and several high-pressure peaks with subsequent time delay reduction could be observed. These patterns were affected by the oil temperature, with most substantial changes at lower temperature ranges (<32 °C). Standard transmission line simulations managed to predict the water hammer, but as expected not the column separation, which is the theme of future work using this setup.
Dizziness is commonly associated with anxiety, and is often caused by a dysfunction of the balance system. While a link between dizziness and both anxiety disorders and depression has been established, less is known about information processing in dizziness. In the first experiment we tested whether 15 patients with dizziness would display an emotional Stroop effect for panic-related words. Also included was a control group of 15 persons. The Stroop task was preceded by ratings of personal relevance of the Stroop words and followed by a surprise free recall of the words. Results showed a Stroop effect for panic-related words in the dizziness group, but the interaction did not reach significance (p = 0.08). Separate analysis of dizziness-related panic words however resulted in a significant group x condition interaction. In the free recall of Stroop words a main effect of word category was found, with more panic-related words being recalled. The second experiment investigated autobiographical memories in 14 patients with dizziness and 14 matched controls. Results showed a group x condition interaction with less specific memories being recalled following positive cue-words in the dizziness group. The overall pattern of results suggests that dizziness is related to deficits in information processing, which could be targeted in treatment.
Cavitation erosion is one of the main concerns in hydraulic rock drills and can reduce both performance as well as life span. Current simulation tools can detect a potential risk of cavitation, however, the equations do not include cavitation physics and therefore cannot estimate the severity nor erosion locations. In order to evaluate the cavitation damage, long term tests are performed which are both costly and time consuming. With better computational capacity and more accurate numerical flow models, the possibilities to simulate the course of cavitation have increased. So far, most numerical studies on cavitation focus on steady-state problems while studies on hydraulic transients and water hammer effects have received less attention. This paper is a step towards simulation of water hammer induced cavitation and cavitation erosion in pipe flow using Computational Fluid Dynamics (CFD). In order to validate the results, experimental measurements are performed with a test equipment that creates hydraulic transients in a pipe and records these using piezoelectric pressure sensors. The results from CFD are compared to both the experimental data and to numerical results from a software called Hopsan, a one-dimensional multi-domain system simulation tool that uses wave characteristics to calculate pressures and flows. For smaller transients where no cavitation occur, all results show good agreement. For larger transients with cavitation, the results from Hopsan do not longer agree with the measurements, while the CFD model still performs well and is able to predict both formation and collapse of cavitation.
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