Practical issues in model-based surge control for centrifugal compressors

The performance and operating range of centrifugal compressors is limited by the occurrence of an aerodynamic instability called surge. This paper deals with the technological barriers for feedback stabilization of full-scale centrifugal compression systems. A dynamic model for a single stage compressor test rig is presented and a surge control strategy is discussed. Then the critical problems of model accuracy and sensor and actuator limitations are discussed. These problems are illustrated with simulation results and experimental data. We conclude by suggesting directions for further work in order to successfully implement active surge control in full-scale applications

Stability parameter identification for a centrifugal compression system

This paper presents the application of a lumped parameter model to describe the dynamic behavior of a centrifugal compression system including surge. The response of the model is compared with experimental surge measurements from an industrial single stage compressor test rig. A parametric analysis of the model reveals the large influence of the stability parameter on the transient response. However, a good value for this parameter is not easily obtained fromsurge data. Therefore, an identification method is proposed to uniquely determine the stability parameter that is based on an approximate realization algorithm, making use of the fact that the step response of the system has the characteristics of a first order system. Simulation results show that this method canprovide an estimate for the stability parameter of a centrifugal compression system

Evidence-Based Quality Improvement: A recipe for improving medication safety and handover of care

In healthcare we strive to provide the highest possible quality of care. Even though healthcare professionals work together with the intention to provide safe care, medical errors still threaten patient safety. Patient safety has received considerable attention since the beginning of this century, resulting in quality and safety improvement initiatives worldwide. Often these initiatives are implemented without evidence of their effectiveness. This may result in changes in the system of care, but it may not always be improvements. As a consequence, the changes are not naturally embraced by healthcare professionals and it may even result in resistance, frustration and waste of valuable resources. Through the studies in this thesis we researched the requirements for evidence-based quality improvement (EBQI) of two processes with high potential for errors: the medication process and handover of care. From our studies it becomes clear that important requirements for EBQI are: • Careful research into the complex problems that underpin QI with sufficient attention for local context. • Practice based iterative design and small scale evaluation of QI interventions that build up towards rigorous research designs and long term measurement of effectiveness as well as implementation. • Information from Electronic Patient Records (EPRs) that supports high quality care through the incorporation of clinical decision support as well as performance management through use of indicators. • Further professionalization in quality improvement, through continuous education and a safety culture with adequate leadership

Analysis of the effect of fast transients in LNG process equipment

Some years ago a root cause analysis was made of a large oil spill caused by a leak in an oil offloading system. It appeared that the leak was caused by a large pressure pulse initiated by the sudden closure of the bow loading valve at the tanker, called water hammer. The magnitude of the initial pulse was largely amplified by reflections at several diameter changes. Similar phenomena can occur in (offshore) LNG transfer systems with even more serious consequences. In addition to the water hammer "column separation" may cause even larger pressure pulses. This occurs when, due to a passing water hammer wave, the pressure locally drops to the vapor pressure and the liquid starts to boil. As the LNG in a transfer system is close to its boiling conditions, this phenomenon is likely to occur. In order to evaluate to what extent water hammer and column separation can endanger the integrity of the system a computer model has been made of three generic ship-to-ship transfer systems. The peak pressures during an emergency release of the flexible transfer hose at full flow have been calculated. The sensitivity for length of the hose, closure time and wave propagation speed has been evaluated. In spite of the modeling uncertainties the results show that water hammer and column separation can cause shock loads that are an order of magnitude larger than the static loads. Therefore it is recommended to perform an analysis as part of the design and to optimize the layout of the system. It is suggested to include this as a requirement in the applicable design codes. Also it is recommended to test components such as flexible hoses on dynamic loads caused by water hammer

Introduction

This chapter introduces the field of perpetrator studies, the topic of perpetrators of mass atrocity crimes, and provides short summaries of all the remaining chapters. It first describes perpetrator studies as a newly emerging, inter-, and multi-disciplinary field of scholarly interest focusing on perpetrators of mass atrocities, in which we include genocide, crimes against humanity, war crimes, and terrorism. Secondly, it demarcates the scope of the book and discusses the subject of perpetrator studies—the perpetrator. Perpetrators of mass atrocity crimes as a category is contested and complex. We deliberately use it in a broad sense to include all individuals that are involved in one way or another in the perpetration of mass atrocities. Lastly, it explains the focus on theories, methods, and evidence, and briefly introduces all the book’s chapters