A design for the fail-safe mechanism of a guide vane in a Francis-type hydro turbine is proposed and analyzed. The mechanism that is based on a shear pin as a sacrificial component was designed to remain simple. Unlike the requirements of... more
A design for the fail-safe mechanism of a guide vane in a Francis-type hydro turbine is proposed and analyzed. The mechanism that is based on a shear pin as a sacrificial component was designed to remain simple. Unlike the requirements of conventional designs, a shear pin must be able to withstand static and dynamic loads but must fail under a certain overload that could damage a guide vane. An accurate load determination and selection of the shear pin material were demonstrated. The static load for various opening angles of the guide vane were calculated using the computational fluid dynamics Fluent and finite element method Ansys programs. Furthermore, simulations for overload and dynamic load due to the waterhammer phenomenon were also conducted. The results of load calculations were used to select an appropriate shear pin material. Quasi-static shear tests were performed for two shear pins of aluminum alloy Al2024 subjected to different aging treatments (i.e. artificial and natural aging). The test results indicated that the Al2024 treated by natural aging is an appropriate material for a shear pin designed to function as a fail-safe mechanism for the guide vanes of a Francis-type hydro turbine.
The main issue in controlling safety-critical systems such as nuclear power reactors or railway interlocking systems is to provide high safety and reliability where the risk ratio is at the highest level because small errors might result... more
The main issue in controlling safety-critical systems such as nuclear power reactors or railway interlocking systems is to provide high safety and reliability where the risk ratio is at the highest level because small errors might result in hazardous accidents (e.g., death or injury of many people). The N-version programming technique, where N-different modules run in parallel, can be used to improve the reliability and safety of such systems at the desired safety level. Decisions of N-different modules are then evaluated by another component, usually known as the voter, using different voting strategies. In the current study a bitwise voting strategy to evaluate module decisions that are based on safe-states of variables is proposed and possible synchronization problems between the modules are determined. Sequence diagrams and solutions for synchronization problems are also explained.
Policies have been widely used to govern the action of a system. With the increasing availability of sensitive data on-line, privacy becomes one of the most important aspects to be considered in e.g. health, financial and genetic... more
Policies have been widely used to govern the action of a system. With the increasing availability of sensitive data on-line, privacy becomes one of the most important aspects to be considered in e.g. health, financial and genetic information areas. However, when deployed in real systems, many different types of system failures are likely to occur due to software malfunction, human error, contradiction of internal policies with the legislation, etc. This can result in a privacy breach. In this paper we introduce a Privacy Policy Fail-Safe device which is based on the Fail-Safe concept to mitigate the effect of system failures to be in the safe state.
