Effects of helical strakes on the vortex-induced vibration over a thermowell in a pipe flow
A thermowell is a device to protect a thermometer used for measuring temperature in many industrial application. The thermowell is exposed to vortex-induced vibration when the flow speed in a pipe is large so that shedding frequency due to Karman vortex streets downstream of the thermowell corresponds with its natural frequency. The vortex-induced vibration can cause fracture of the thermowell structure by cyclic loading. This phenomenon has long been a research topic in the field of marine engineering. Now, it can be a concern in metrology area. The present study investigates the suppressing effect of the vortex-induced vibrations of the thermowell by means of helical strakes. Flow visualizations can show that the helical strakes can suppress the vortex-induced vibration by generating three-dimensional shedding vortices with short spanwise length. The three-dimensional shedding vortices does not give resonance to the thermowell effectively because the vortices generate asynchronous forces along the thermowell. In this study, flow visualizations of the thermowell vibrations and resonant frequency measurements were attempted to investigate the suppressing effect of the helical strakes for safely using the thermowell in operating conditions with high flow speeds.
Computational study on aerodynamic mitigation of wind-induced, large-amplitude vibrations of stay cables with strakes
Abstract Modifications of circular cylinder surfaces, such as strakes and helical wires, effectively mitigate Karman vortex-induced vibrations normal to flow and have been applied to the reduction of large-amplitude vibrations of stay cables in bridges, which occur under wind oblique to a cable with or without rainfall. This aerodynamic control method cannot be fully effective without understanding the behavior of the flow around and the associated forces on oblique cables. To address this issue, flow around a yawed cylinder with various strake patterns was studied using three-dimensional detached eddy simulation (DES) at Reynolds number of 1.4×10 5 . Results demonstrated that strake patterns strongly influence the development of flow structures around a yawed cylinder and therefore the associated forces on the cylinder. The results suggest that particular strake patterns can mitigate large-amplitude and low-frequency vibrations of stay cables induced by oblique wind.
The Soviet Home Front, 1941-1945: A Social and Economic History of the USSR in World War II
List of tables and maps Preface Acknowledgements Abbreviations and technical terms Part 1: On the Eve 1. Building Socialism 2. The Great Patriotic War 3. The State in Wartime Part 2: Soviet Society at War 4. Mobilisation 5. Subsistence and Survival 6. The Social Order Part 3: The Productive Effort 7. Fortress of the Rear 8. Labour: The 'Ultimate Bottleneck' 9. 'In Labour as in Combat' 10. Production: The Power of Victory 11. Planning: 'The Military-Economic Staff' Epilogue Tables Important dates References Maps Index