The Rwenzori Mountains, a Paleoproterzoic crustal shear belt crossing the Albertine rift system

This contribution discusses the development of the Paleoproterozoic Buganda-Toro belt in the Rwenzori mountains and its influence on the western part of the East African Rift System in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal scale nappe whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle inverse faulting. The Paleoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running rift system exactly at the node where the highest peaks of the Rwenzori mountains are situated and where the lake George rift terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced rift propagation and brittle fault development within the Rwenzori mountain and that this stiff belt may form part of the reason why the Rwenzori mountains are relatively high within the rift. Keywords: East African Rift, Basement, Buganda Toro, Inverse Metamorphic Gradient, Microtectonics, Rwenzori mountain

Shear localisation in anisotropic, non-linear viscous materials that develop a CPO: A numerical study

Localisation of ductile deformation in rocks is commonly found at all scales from crustal shear zones down to grain scale shear bands. Of the various mechanisms for localisation, mechanical anisotropy has received relatively little attention, especially in numerical modelling. Mechanical anisotropy can be due to dislocation creep of minerals (e.g. ice or mica) and/or layering in rocks (e.g. bedding, cleavage). We simulated simple-shear deformation of a locally anisotropic, single-phase power-law rheology material up to shear strain of five. Localisation of shear rate in narrow shear bands occurs, depending on the magnitude of anisotropy and the stress exponent. At high anisotropy values, strain-rate frequency distributions become approximately log-normal with heavy, exponential tails. Localisation due to anisotropy is scale-independent and thus provides a single mechanism for a self-organised hierarchy of shear bands and zones from mm-to km-scales. The numerical simulations are compared with the natural example of the Northern Shear Belt at Cap de Creus, NE Spain

Directive versus empowering leadership: A field experiment comparing impacts on task proficiency and proactivity

Using a field experiment in the United Arab Emirates, we compared the impacts of directive and empowering leadership on customer-rated core task proficiency and proactive behaviors. Results of tests for main effects demonstrated that both directive and empowering leadership increased work unit core task proficiency, but only empowering leadership increased proactive behaviors. Examination of boundary conditions revealed that directive leadership enhanced proactive behaviors for work units that were highly satisfied with their leaders, whereas empowering leadership had stronger effects on both core task proficiency and proactive behaviors for work units that were less satisfied with their leaders. We discuss implications for both theory and practice. © Academy of Management Journal

The transition from single layer to foliation boudinage: A dynamic modelling approach

Foliation boudinage is a deflection of foliation in the vicinity of a central discontinuity in foliated rocks, mostly filled with vein material. It shows evidence for brittle deformation and void-opening during ductile flow. We used a two-dimensional visco-elastic spring model based on a discrete element approach to study the dynamic development of foliation boudinage and the behaviour of anisotropic visco-elastic material deformed under pure shear conditions. The anisotropies are set by defining rheological heterogeneities in the models with (1) a single layer in a weaker matrix; (2) multi-layers with different elastic properties and (3) random-distributed “micas”, rows of horizontally aligned elements with the same elastic properties. The models show the nucleation and propagation of fractures during ductile deformation and flow perturbation and localization in the vicinity of fractures. Voids localize along extension fractures, at intersections of conjugate shear fractures and in small pull-apart structures along shear fractures, which look identical to boudin necks in isolated stiff layers. Results show that strain localization is strong in models with lower elastic constants and anisotropy whereas it is distributed in the models with higher elastic constants and anisotropy in which asymmetric and complex geometries develop. The models successfully show the development of and transitions between a single layer, multi-layer and foliation boudinage that are common structures in high strain z

Adaptive Rotor Blade Concepts -Direct Twist and Camber Variation-

Applying adaptronics to helicopters has a high potential to significantly suppress noise, reduce vibration and increase the overall aerodynamic efficiency. Since the interaction of non-stationary helicopter aerodynamics and elastomechanical structural characteristics of the helicopter blades causes flight envelope limitations, vibration and noise, a good comprehension of the aerodynamics is essential for the development of structural solutions to effectively influence the local airflow conditions and finally develop a structural concept. With respect to these considerations, this paper presents recent investigations on two different structural concepts: the direct twist and the camber variation concept. The direct twist concept allows to directly control the twist of the helicopter blades by smart adaptive elements and through this to positively influence the main rotor area which is the primary source for helicopter noise and vibration. The concept is based upon the actively controlled tension-torsion-coupling of the structure. For this, an actuator is integrated within a helicopter blade that is made of anisotropic fibre composite material. Driving the actuator results in a local twist of the blade tip, in such a way that the blade can be considered as a torsional actuator. Influencing the blade twist distribution finally results in a higher aerodynamic efficiency. The direct twist concept was analytically modelled using an expanded Vlassov Theory before a proof-of-principle demonstration structure was manufactured. Subsequently, a Mach-scaled Bo105 model rotor blade with an integrated piezoelectric actuator was designed and successfully tested. Next, small scale rotor tests and investigation of thermal loads are planned. The camber variation concept uses the experiences gained in the design of the direct twist concept to create a rotor blade, that will be able to change the shape of its cross-section in operation. This shape control approach uses material anisotropy (e.g. tension-torsion-coupling) to create a smooth aerodynamic surface and to avoid the airflow disturbances created by the leading or trailing edge flaps, that have already been investigated. First, a structural model was numerically investigated to identify the most influential parameters of this concept. From this model, the two-dimensional surface quality of the deformed rotor blade was extracted as a basis for aerodynamic calculations that are necessary to derive the quantity of deformation needed to successfully delay aerodynamic stall onset. As a next step, a proof-of-principle structural demonstrator is presently being designed. Both concepts were designed to be activated using a piezoelectric stack-actuator integrated at the blade tip. Since continiuously integrated piezo sheets promise a potential to increase the concepts performance, thin actuator modules are currently under investigation

Steigerung der Jahresenergieausbeute von Windkraftanlagen durch den Einsatz adaptiver Struktursysteme

Die Adaptronik als interdisziplinäres Forschungs- und Entwicklungsgebiet eröffnet völlig neuartige Möglichkeiten, Leichtbaustrukturen den jeweiligen Randbedingungen aktiv anzupassen. Dafür werden multifunktionale Materialien wie z.B. Piezoelektrika, Magnetostriktiva und Formgedächtnislegierungen als hochintegrierte Werkstoffsysteme strukturkonform in Leichtbaukomponenten integriert und mittels einer adaptiven digitalen Signalverarbeitung zu einem adaptiven Struktursystem vereint. Diese Technologie erlaubt u.a. - aktive Gestaltänderung und Positionsregelung sowie - aktive Schwingungs- und Lärmunterdrückung. Im Flugzeug- und Helikopterbau sind bereits adaptive Systeme in der Entwicklung, die durch Anpassung der Profilgeometrie eine gezielte Änderung der aerodynamischen Eigenschaften gestatten. Angewendet auf WKA erlauben diese Konzepte die Realisierung von Rotorblättern, deren Verwindung entlang der Blattachse differenziert werden kann, um so erheblich besser auf Windgeschwindigkeitsänderungen reagieren zu können, als dies bisher durch eine Pitchregelung allein möglich ist. Eine solche adaptive Verwindung ermöglicht zusammen mit einer starren Verwindung und einer Pitchregelung - die Erhöhung der abgegebenen Leistung unterhalb der Nennwindgeschwindigkeit und gleichzeitig - die Herabsetzung der Anfahrwindgeschwindigkeit. Erste überschlägige Berechnungen versprechen eine Steigerung des Jahresenergieertrages in der Größenordnung von 10%. Um dieses ehrgeiziges Ziel zu verwirklichen, muß bei vorgegebener Aerodynamik und Länge eines Rotorblattes - eine leistungsfähige Verwindungsaktuatorik in dessen Struktur integriert und zusammen mit - der vorhandenen Sensorik für Rotordrehzahl, Windgeschwindigkeit und -richtung sowie - einer der Betriebsführung unterstellten adaptiven Regelung zu einem autarken, selbstoptimierenden System vereint werden. Das Hauptaugenmerk dieser Arbeiten liegt auf der Entwicklung der Verwindungsaktuatorik, die die nötigen Verwindungsänderungen ermöglicht und dabei gleichzeitig die lasttragende Funktion übernimmt. Im Rahmen dieses Beitrages werden zunächst adaptive Struktursysteme allgemein vorgestellt. Darauf aufbauend werden der Nutzen und die Umsetzung dieser Technologie für WKA mit Schwerpunkt auf der Steigerung der Jahresenergieausbeute durch eine adaptive Verwindung dargestellt. Abschließend werden als weitere Einsatzgebiete die Entlastung der Struktur sowie die Minimierung der Lärmabstrahlung von WKA präsentiert

Adaptive Camber Variation Utilising Local Anisotropy

This paper presents an investigation of an actively controllable camber variation for rotor blades. The new structural Concept described here is based upon a 3-cell blade design using tension-torsion-coupling together with piezoelectric stack-actuators to bend the cross-section about the blade axis. A finite-element-model of an adaptive camber rotor blade is used to perform a parameter optimisation to maximise camber variation at the blade tip. Both, geometric as well as material and manufacturing parameters are evaluated. Their influence is presented