Aktives Auswuchten elastischer Rotoren für industrielle Anwendung

In der vorliegenden Dissertation wird die Eliminierung von Unwucht erregten Schwingungen von gyroskopischen Rotoren mittels aktiver piezoelektrischer Lager untersucht. Hierzu wird zunächst ein Rotorprüfstand mittels FEM modelliert und anschließend die Ergebnisse experimentell abgeglichen. Bei der Modellierung wird die neue Rotorkoordinate der relativen Auslenkung eingeführt, welche die Differenz zwischen der Rotorauslenkung und einer linearen Interpolation der freien Auslenkung der Piezoaktoren ist. Weiterhin wird ein neuer Ansatz für ein modales Modell für gyroskopische Rotoren präsentiert, welcher zur Black Box Identifikation verwendet werden kann. Nach der Modellierung wird der Least Mean Squares (LMS) Algorithmus in Kombination mit Integral Force Feedback (IFF) zur Regelung des Systems zunächst analytisch untersucht und anschließend experimentell validiert. Durch die kombinierte Minimierung der Lagerkräfte und Auslenkungen der Scheibe können alle Resonanzen des Systems eliminiert werden. Basierend auf der Literatur zum LMS-Algorithmus wird ein rotormodellfreier Regelungsansatz abgeleitet, welcher die Lagerkräfte im aktiven Lager minimiert und für die Implementierung nur die Totzeit des Systems benötigt. Der Ansatz ist hierbei eine Kombination aus LMS und IFF. Weiterhin wird der LMS um einen Transform Domain (TDLMS) Ansatz erweitert, welcher die Schwingungsamplituden als Regelgröße verwendet. Zur Berechnung der Schwingungsamplituden wird die diskrete Fourier-Transformation über eine volle Rotorumdrehung verwendet. Hierdurch werden die Amplituden über eine Umdrehung gemittelt. Zur Kompensation dieses Zeitverzugs wird ein neuer, auf einem Polynom basierender Algorithmus vorgestellt. Die Funktionsfähigkeit der rotormodellfreien Regelung wird in Experimenten nachgewiesen. Der Regelungsansatz wird anschließend verwendet, um ein Modell des Rotors zu schätzen. Hierzu werden zwei Rotorausläufe durchgeführt, bei dem einmal nur IFF verwendet wird und beim anderen IFF in Kombination mit dem TDLMS-Algorithmus. Abschließend wird ein neues Design für ein aktives Piezolager vorgestellt, bei dem die Aktoren auf dem Innenring eines Wälzlagers montiert werden und somit mit dem Rotor mitrotieren. Dies ermöglicht eine modellfreie Implementierung des TDLMS und das Ausnutzen von Oversampling. Weiterhin werden die Systemkosten deutlich und der Leistungsbedarf um über 99% gesenkt. Die Aktorspannungen werden durch eine steuerbare Boost Converter Schaltung erzeugt. Die Funktionsfähigkeit des Lagers wird mit einer manuellen Steuerung an einem Rotorprüfstand experimentell nachgewiesen. Jedoch treten am Rotor nun starke Schwingungen der dritten Rotorordnung auf, welche mittels eines vereinfachten phänomenologischen Ansatzes auf die mechanische Hysterese der Aktoren und die Gewichtskraft zurückgeführt werden

Besondere Freiheit, besondere Verantwortung? Eine empirische Studie zur deutschen Politikwissenschaft in der Politikberatung

In den letzten Jahren wurde in der deutschen Politikwissenschaft (und darüber hinaus) eine intensive Debatte über die gesellschaftliche und politische Relevanz der Disziplin geführt. Dabei blieb allerdings die faktische politikberatende Rolle mindestens genauso umstritten wie die normative Seite dieser Tätigkeit; und auch innerhalb der vergleichenden Forschung zu Politikberatung wurde der Politikwissenschaft keine gezielte Aufmerksamkeit geschenkt. Dieser Artikel untersucht, wie, für wen und wie häufig Politikwissenschaftler*innen in Deutschland ihre Expertise für die Politik bereitstellen. Die Analyse basiert auf den deutschen Ergebnissen (n=376) einer Umfrage, die 2018 in mehr als 30 europäischen Ländern durchgeführt wurde. Neben ersten empirischen Einblicken in ein bislang wenig untersuchtes Phänomen ist es Ziel des Beitrags, deutsche Politikwissenschaftler*innen in einer Typologie von Beratungsrollen zu verorten. Die Analyse zeigt durchaus umfangreiche und diverse, im Ländervergleich allerdings unterdurchschnittliche politikberatende Tätigkeiten. Der zentrale Unterschied für Art und Ausmaß der Politikberatung scheint zwischen Politikwissenschaftler*innen auf befristeten und unbefristeten Stellen zu bestehen.Recent years have seen intensive debates in German political science (and beyond) on the discipline's societal and political relevance. Yet within this debate, the actual policy-advisory role has been at least as disputed as its normative foundation. Moreover, political science has not been at the focus of policy-advisory research. This article studies how, for whom, and how often political scientists provide expertise for policy-making. The analysis is based on the German responses (n=376) in a survey of political scientists carried out in more than 30 European countries in 2018. Next to empirical insights into a so-far understudied phenomenon, the aim is to locate German political scientists in a typology of policy-advisory roles. The analysis highlights that German political scientists are rather active in a diverse set of policy-advisory activities, though less active than colleagues in other European countries. A key result is that political scientists are more active in policy advice if they are on permanent positions

Strategic advisory boards - the emergence of shadow governance in universities?

Numerous universities throughout the world have established top-level advisory boards – informal bodies and councils that the institutional leadership may consult on issues perceived as important. Through a series of qualitative interviews with members of such entities as well as representatives of the institutions appointing them, the article sheds light on how strategic advisory bodies function, and how these entities frame and interact with the institutional leadership. We observe that strategic advisory boards represent a hybrid form of governance installing mutual dependencies between representatives of the boards and the institutional leadership – what we label as a kind of controlled collegiality. While university leadership acts as a gatekeeper controlling access to these boards, once members are nominated the power relations between the actors, become more equal. The study highlights the importance of strategic advisory boards as new elements in higher education governance – working in the shadow of more formal governance arrangements. Here, we argue that the establishment of these boards can be interpreted as a re-introduction of a collegial element in universities exposed to a number of reforms resulting in more streamlined and managerial governance structures

Legitimacy, Stratification, and Internationalization in Global Higher Education: The Case of the International Association of Universities

Abstract The International Association of Universities (IAU) is the only inclusive global university association, its membership barriers are low, yet few universities are members despite considerable benefits. What determines membership in this long-standing international university alliance? Reviewing recent trends toward a more networked, stratified and internationalized global higher education field, we argue that universities with a greater need for legitimation and those ‘born’ into a global era are more likely to become members of an inclusive international network like the IAU. Thus, we expect lower status and younger universities to be more likely to join. We apply regression models to test hypotheses implied by these arguments. Our findings are consistent with these hypotheses, even after controlling for other factors. We discuss these findings using neo-institutional arguments about legitimacy and imprinted logics and suggest potential analytical avenues for further research

Controller parameterization and bias current reduction of active magnetic bearings for a flexible and gyroscopic spindle

A magnetically levitated spindle was designed for fatigue testing of cylinders made of fiber reinforced plastic. In these fatigue tests, the speed of the cylinders is varied cyclically between 15,000 and 30,000 rpm until their mechanical failure occurs. Several eigenfrequencies have to be passed to reach the operational speed range. During long‐term operation, the rotor of the spindle is prone to overheating due to various losses. One way of reducing the rotor temperature is to decrease the bias current of the radial active magnetic bearings. Since the bias current influences the dynamic behavior of the system, the control of the bearings has to be adapted as well. This article describes a controller design for the system with different bias currents to determine the smallest usable bias current. A detailed model of the plant is developed, which is then used to optimize the parameters of the utilized controller with a predefined structure using the weighted ℋ∞ norm as the objective function. Since the rotor is highly gyroscopic, its eigenfrequencies change with the rotational speed. To ensure that the system meets certain robustness criteria at all rotational speeds, the parameters of the controller are simultaneously optimized for the plant model at different speeds. This approach leads to a controller which can be used in the entire speed range without the need for gain scheduling. The functionality of the controller and the influence of the bias current on the rotor temperature are investigated through measurements

Scandinavian Higher Education Governance – Pursuing Similar Goals through Different Organizational Arrangements

Under embargo until: 2022-02-03The differences and similarities among the three Scandinavian countries, Denmark, Norway, and Sweden have been discussed by social scientists on several occasions. Focusing on higher education (HE) governance systems, this paper raises three questions. (1) What are the differences and similarities among the three countries? (2) How can the similarities and differences be explained? (3) Are the similarities strong enough to justify the common label of a Scandinavian model of HE governance? The three HE governance systems are briefly described and compared. They are then analyzed as, respectively, outcomes of partisan politics or politico-administrative regimes. The paper argues that similarities such as publicness, massive investments, and emphasis on access are best explained in terms of partisan politics, while the variation in governance arrangements can best be explained by path dependencies following choices made at critical junctures within similar politicoadministrative regimes.acceptedVersio

The Swiss Approach - feasibility of a national low-dose CT lung cancer screening program

BACKGROUND Lung cancer is the leading cause of cancer-related deaths in Switzerland. Despite this, there is no lung cancer screening program in the country. In the United States, low-dose computed tomography (LDCT) lung cancer screening is partially established and endorsed by guidelines. Moreover, evidence is growing that screening reduces lung cancer-related mortality and this was recently shown in a large European randomized controlled trial. Implementation of a lung cancer screening program, however, is challenging and depends on many country-specific factors. The goal of this article is to outline a potential Swiss lung cancer screening program. FRAMEWORK An exhaustive literature review on international screening models as well as interviews and site visits with international experts were initiated. Furthermore, workshops and interviews with national experts and stakeholders were conducted to share experiences and to establish the basis for a national Swiss lung cancer screening program. SCREENING APPROACH General practitioners, pulmonologists and the media should be part of the recruitment process. Decentralisation of the screening might lead to a higher adherence rate. To reduce stigmatisation, the screening should be integrated in a "lung health check". Standardisation and a common quality level are mandatory. The PLCOm2012 risk calculation model with a threshold of 1.5% risk for developing cancer in the next six years should be used in addition to established inclusion criteria. Biennial screening is preferred. LUNG RADS and NELSON+ are applied as classification models for lung nodules. CONCLUSION Based on data from recent studies, literature research, a health technology assessment, the information gained from this project and a pilot study the Swiss Interest Group for lung cancer screening (CH-LSIG) recommends the timely introduction of a systematic lung cancer screening program in Switzerland. The final decision is for the Swiss Cancer Screening Committee to make

The Swiss Approach - feasibility of a national low-dose CT lung cancer screening program.

BACKGROUND Lung cancer is the leading cause of cancer-related deaths in Switzerland. Despite this, there is no lung cancer screening program in the country. In the United States, low-dose computed tomography (LDCT) lung cancer screening is partially established and endorsed by guidelines. Moreover, evidence is growing that screening reduces lung cancer-related mortality and this was recently shown in a large European randomized controlled trial. Implementation of a lung cancer screening program, however, is challenging and depends on many country-specific factors. The goal of this article is to outline a potential Swiss lung cancer screening program. FRAMEWORK An exhaustive literature review on international screening models as well as interviews and site visits with international experts were initiated. Furthermore, workshops and interviews with national experts and stakeholders were conducted to share experiences and to establish the basis for a national Swiss lung cancer screening program. SCREENING APPROACH General practitioners, pulmonologists and the media should be part of the recruitment process. Decentralisation of the screening might lead to a higher adherence rate. To reduce stigmatisation, the screening should be integrated in a "lung health check". Standardisation and a common quality level are mandatory. The PLCOm2012 risk calculation model with a threshold of 1.5% risk for developing cancer in the next six years should be used in addition to established inclusion criteria. Biennial screening is preferred. LUNG RADS and NELSON+ are applied as classification models for lung nodules. CONCLUSION Based on data from recent studies, literature research, a health technology assessment, the information gained from this project and a pilot study the Swiss Interest Group for lung cancer screening (CH-LSIG) recommends the timely introduction of a systematic lung cancer screening program in Switzerland. The final decision is for the Swiss Cancer Screening Committee to make