84 research outputs found
Cavitation Cloud Translation in Focused Ultrasound
No full textCavitation mediated effects in liquids exposed to ultrasound, play pivotal roles in a number of industrial arenas, including precision acoustic cleaning (megasonics) and sonochemistry. The spontaneous occurrence of cavitation, and the subsequent interaction with the liquid and the acoustic field, is however poorly understood, which prevents optimization for any given application. In this paper we report on observations made of single isolated cavitation-bubble clouds, exposed to a well characterized burst of propagating focused ultrasound, and the resulting translational motion of the clouds under the action of the primary acoustic radiation force. As may be expected, larger clouds develop under higher intensity insonations, which translate away from the ultrasound source more rapidly, although a larger associated drag force somewhat tempers the effect. Critically, however, a resonant condition is identified whereby small clouds at lower intensities translate much more rapidly than might otherwise be expected. A model is derived from first principles, adapted to the experimental conditions and demonstrates good agreement with the observations, including the frequency resonance. We anticipate the results will have significance for any application in which understanding and predicting a dynamic cavitating liquid is important, particularly under non-standing wave conditions
Structural Optimization Of A Vertical Axis Wind Turbine With Aeroelastic Analysis
No full textCurrently, the price per kW of offshore wind energy is 55% larger than onshore [38, 52]. Of this price, the rotor corresponds to 22%. To reduce the price of wind energy, it is necessary to investigate wind turbine concepts with scales above 10 MW. The commonly known Horizontal Axis Wind Turbine (HAWT) requires offshore a large support structure. If the turbine is designed to be floating, a deep floater is needed to limit the tilt angle. A possible concept to meet this challenges is the lift-driven Vertical Axis Wind Turbine (VAWT). This thesis aims to optimize the structural design of a VAWT rotor blade and to decrease the mass to area ratio by varying blade shape and structural layout. The choice of mass to rotor area ratio as an optimization function follows from the fact that this area is directly proportional to the energy output while mass drives production and installation costs. The VAWT is defined by an axis perpendicular to the unperturbed flow direction. The rotor geometry is described through a Troposkein shape. It is assumed that the blades carry their own weight leading to a reinforced root region. During operation the blades experience aerodynamic and inertia forces, which are deflecting the blades outwards, leading to an alternation of the aerodynamic loads.The interplay of load alternation and blade deflection could lead to a diverging flutter motion. After a fitting design is obtained, the blade motion has to be inspected for a safe use during operation. The rotor is designed with an adjusted optimizer, originally written by M. Schelbergen [62]. The optimizer uses the Matlab optimization toolbox in combination with Nastran. The modification allows a smooth transition of the thickness of skin, shear web and girder. The airfoil section is varied along the blade. The optimization is based on load cases such as a parked rotor and the maximum up- and downwind forces. These loads are simplified and assumed to vary neither by the motion nor the deflections of the blade. In addition, an aeroelastic model is required to observe the blades’ motion. Through out thisthesis two aeroelastic codes were used. The VAWT AeroElastic Multibody Panel Solver (VÆMPS) was created by coupling Sandia National Laboratories OWENS and the near wake panel solver UMPM. However, its computational performance was not satisfying and it was decided to use HAWC2 coupled with an actuator cylinder model to determine the induction.European Wind Energy Masters (EWEM
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Designing Video-Based Interactive Instructions
No full textWhen attempting to accomplish unfamiliar tasks, people often look for tutorials to follow instructions. While it is easy to access online instructions shared by domain experts, navigating step-by-step guidance using existing tools remains inefficient. In addition, producing high-quality instructions that are easy to follow requires authoring expertise and a significant time investment in editing. This dissertation introduces video-based recording, editing, and playback tools optimized for creating and consuming tutorials from author demonstrations. Our interactive systems capture videos and high-level events that are important to a learner. Using video and audio analysis techniques, we develop algorithms that automatically produce high-quality instructions, which dramatically reduce the effort required for amateur creators. By introducing novel tutorial formats combined with video content, these designs in turn improve viewers’ learning experience.We present a series of authoring tools that enable amateur authors to create effective tutorials: 1) MixT is a system that automatically generates step-by-step mixed media tutorials from software demonstrations. 2) DemoWiz is a tool that provides an increased awareness of upcoming events in a software demonstration video. 3) DemoCut is a semi-automatic video editing tool for physical tasks. 4) Kinectograph is a recording device that automatically follows an instructor for filming a physical demonstration. 5) DemoDraw is a multi-modal system to generate step-by-step motion illustrations from author’s body movements. Current authoring practices from professionals are encoded into automatic algorithms and interactive techniques. These systems are evaluated through a series of studies, which demonstrate that users can efficiently create and follow concise instructions using our tools
Robot-assisted Ultrasound-guided Tracking of Anatomical Structures for the Application of Focused Ultrasound
No full textHigh intensity focused ultrasound is used as a surgical tool to treat completely non-invasively several diseases. Examples of clinical applications are uterine fibroids, prostate cancer, thyroid nodules, and varicose veins. Precise targeting is key for improving the treatment outcome. A method for an automated, robot-assisted tracking system was developed and evaluated. A wireless ultrasound scanner was used to acquire images of the target, in this case, a blood vessel. The active contour approach by Chan and Vese was used to segment and track while moving the scanner along the target structure with a collaborative robotic arm. The performance was assessed using a custom made Agar phantom. The mean tracking error, which is defined as the remaining distance of the lesion to the images’ centre line, was 0.27 mm ± 0.18 mm
Bifurcation of ensemble oscillations and acoustic emissions from early stage cavitation clouds in focused ultrasound
No full textThe acoustic emissions from single cavitation clouds at an early stage of development in 0.521 MHz focused ultrasound of varying intensity, are detected and directly correlated to high-speed microscopic observations, recorded at 1 × 10 frames per second. At lower intensities, a stable regime of cloud response is identified whereby bubble-ensembles exhibit oscillations at half the driving frequency, which is also detected in the acoustic emission spectra. Higher intensities generate clouds that develop more rapidly, with increased nonlinearity evidenced by a bifurcation in the frequency of ensemble response, and in the acoustic emissions. A single bubble oscillation model is subject to equivalent ultrasound conditions and fitted to features in the hydrophone and high-speed spectral data, allowing an effective quiescent radius to be inferred for the clouds that evolve at each intensity. The approach indicates that the acoustic emissions originate from the ensemble dynamics and that the cloud acts as a single bubble of equivalent radius in terms of the scattered field. Jetting from component cavities on the periphery of clouds is regularly observed at higher intensities. The results may be of relevance for monitoring and controlling cavitation in therapeutic applications of focused ultrasound, where the phenomenon has the potential to mediate drug delivery from vasculature
Major Accident Prevention - Lessons Learned and Reinforcement Initiatives Ongoing in Statoil
No full textAbstract
Statoil’s contribution to this session of the SPE HSSE Conference is to share how we have reinforced our safety culture in the way we lead and work to reduce the risk of facing high potential incidents or major accidents.
The main objective of this paper and lecture is twofold:Raise the awareness of barrier challenges that historically have caused major accidents in our industry, and still do.Present specified risk areas that Statoil have reinforced attention on based on our learning from high potential incidents and major accidents in the period of 2012-2017.
The paper is seen from an operational user perspective and founded in the author and presenter’s more than 35 years of operational experience from "sharp end" worker and management positions within offshore operations and greenfield projects.
Key risks to be covered: Plant vibrations Plant corrosion Overdue/backlog of safety critical maintenance Diffuse gas leakages Transport of risks between an onshore planning party and offshore executing party Last minute change of plans Compliance with safe work requirements Competence
A film is developed to support the lecture in plenary.</jats:p
Development of Optimized Test Planning Procedures for Stabilizing Ramp-up Processes by Means of Design Science Research
No full textAbstractUnplanned engineering changes represent a major field of disturbance during production ramp-up. They require time-consuming qualification and approval procedures for product- or process-related redesign. Numerous engineering changes during production ramp-up can be traced back to lack of product maturity, not sufficiently increased during the precedent stage of product development. By applying effective and efficient product testing processes, product maturity can be measured and enhanced at an early stage. As a consequence, unplanned engineering changes can be avoided. Nevertheless, contemporary test management procedures lack of methodological support, especially in the field of test planning. To date, the successful evaluation of testing demand and selection of necessary test specifications mainly depends on the expert knowledge of the test management team. The present paper focuses on the development of optimized test planning procedures in order to accelerate early product maturity enhancement for stabilizing production ramp-up processes. Following design science research methodology, the relevance of the problem statement in the application environment of production ramp-up will be assessed. Furthermore, approaches of the knowledge base related to test management will be analyzed in order to constitute rigor of the applied research approach. Based on the evaluation of business needs from the relevant environment as well as the investigation of application knowledge, a research framework for deriving optimized test planning procedures is presented
How much randomness is needed for statistics?
No full textIn algorithmic randomness, when one wants to define a randomness notion with respect to some non-computable measure λ, a choice needs to be made. One approach is to allow randomness tests to access the measure λ as an oracle
(which we call the \classical approach"). The other approach is the opposite one, where the randomness tests are completely effective and do not have access to the information contained in λ (we call this approach \Hippocratic"). While the Hippocratic approach is in general much more restrictive, there are cases
where the two coincide. The first author showed in 2010 that in the particular case where the notion of randomness considered is Martin-Löf randomness and the measure λ is a Bernoulli measure, classical randomness and Hippocratic randomness coincide. In this paper, we prove that this result no longer holds for
other notions of randomness, namely computable randomness and stochasticity
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