10 research outputs found
Generation and propagation of ship waves in inland and near-shore waters
Die Untersuchung von Schiffswellen hat zwei Beweggründe. Zum einen nimmt der Anteil des Wellenwiderstands am Gesamtwiderstand eines Schiffs mit zunehmender Geschwindigkeit zu, so dass bei den heutzutage eingesetzten schnellen Schiffen eine Reduzierung des Wellenwiderstands durch entsprechende Formgebung besonders wichtig ist. Zum anderen können die vom Schiff erzeugten Wellen – auch in großer Entfernung – passierenden Verkehr gefährden oder am Ufer Schäden anrichten.
Neben der Modellversuchstechnik wurden zahlreiche numerische Verfahren (CFD – Computational Fluid Dynamics) entwickelt, mit denen die Schiffsumströmung und auch die Verformung der freien Wasseroberfläche, d.h. das Wellenfeld, berechnet werden können. Von den verschiedenen eingesetzten mathematischen Modellen, eigenen sich Flachwassergleichungen besonders zur Berechnung der Wellenausbreitung in großen Gebieten. Durch eine analytische Behandlung der vertikalen Geschwindigkeitsverteilung kann das numerische Problem um eine Dimension vereinfacht werden. Im Gegensatz zu anderen CFD-Verfahren ist die Wasseroberflächenverformung in den Gleichungen implizit enthalten und muss nicht als Randbedingung iterativ erfüllt werden.
Im Rahmen der vorliegenden Arbeit wurde zuerst ein effizientes, aber trotzdem allgemein gehaltenes numerisches Verfahren entwickelt, mit dem die Wellenausbreitung von Schiffswellen in Wasser begrenzter Tiefe berechnet werden kann. Dieses Verfahren basiert auf Flachwassergleichungen vom Boussinesq-Typ; es kann aber auch für andere Gleichungstypen verwendet werden. Die Verdrängungswirkung des Schiffs wird mittels der Schlankkörpertheorie modelliert. Damit wird auch die Berechnung der dynamischen Schwimmlage (Trimm und Absenkung, Squat) möglich. Außerdem ist das Verfahren in der Lage, mit anderen Berechnungsverfahren (Panel- oder RANSE-Verfahren), mit denen eine detailliertere Berechnung der schiffsnahen Strömung möglich ist, gekoppelt zu werden, so dass die Vorteile verschiedener Verfahren genutzt werden können.
Im zweiten Schritt wurde die Anwendbarkeit des Verfahren für verschiedene schiff- und wasserbauliche Problemstellungen untersucht. Die Untersuchungen gehen von einfachen Test- und Validierungsfällen hin zu komplexen Untersuchungen der Wechselwirkung des Schiffswellensystems und der dynamischen Schwimmlage mit der Bodentopographie, der Bodenreibung und der Grundströmung. Zum Schluss wird die Wechselwirkung zweier passierender Schiffe untersucht.There are two reasons for the investigation of ship waves. First, the relative contribution of wave resistance to the total resistance of a ship increases with the speed]. Thus it becomes important with regard to the fast modern ships to reduce wave resistance by an appropriate hull shape. Secondly, the wash waves generated by fast ships are weakly damped and can travel long distances endangering other vessels or damaging shores and river banks.
In addition to model tests various numerical methods (CFD) have been developed to calculate the flow around a ship including the waves generated by the ship itself. The most suitable mathematical model to describe and calculate the wave propagation in large domains is the shallow water approximation. With an analytical treatment of the vertical velocity distribution the numerical problem can be reduced by one dimension. In contrast to other CFD-methods the wave elevation implicitly is part of the equations and does not need to be solved iteratively as a marginal condition.
In this study both an efficient and generally usable numerical method has been developed to calculate the propagation of ship waves in waters with limited depth. The method is based on Boussinesq-type shallow water equations, but it can also be easily used to solve other hyperbolic differential equations. The displacement effect of the ship is modeled by the slender body theory. Thus the calculation of the dynamic trim and sinkage (squat) has been made possible. Moreover, the method can be coupled with other CFD-methods of calculating the near-ship flow field more detailed, so that it is possible to benefit from both methods.
In a second step the applicability to different problems of naval architecture and hydraulic engineering has been investigated. The investigations start with simple test and validation cases and lead to close scrutinies on the interaction of ship waves, dynamic trim, bottom topography, bottom friction and the effect of currents. Finally the interaction of two passing ships has been analyzed
New records of neonatal and juvenile whale sharks (Rhincodon typus) from the Indian Ocean.
BACKGROUND: The probability of reimbursement is a key factor in determining whether to proceed with or abandon a product during its development. The purpose of this article is to illustrate how the methods of iterative Bayesian economic evaluation proposed in the literature can be incorporated into the development process of new medical devices, adapting them to face the relative scarcity of data and time that characterizes the process. METHODS: A 3-stage economic evaluation was applied: an early phase in which simple methods allow for a quick prioritization of competing products; a mid-stage in which developers synthesize the data into a decision model, identify the parameters for which more information is most valuable, and explore uncertainty; and a late stage, in which all relevant information is synthesized. A retrospective analysis was conducted of the case study of absorbable pins, compared with metallic fixation, in osteotomy to treat hallux valgus. RESULTS: The results from the early analysis suggest absorbable pins to be cost-effective under the beliefs and assumptions applied. The outputs from the models at the mid-stage analyses show the device to be cost-effective with a high probability. Late-stage analysis synthesizes evidence from a randomized controlled trial and informative priors, which are based on previous evidence. It also suggests that absorbable pins are the most cost-effective strategy, although the uncertainty in the model output increased considerably. CONCLUSIONS: This example illustrates how the method proposed allows decisions in the product development cycle to be based on the best knowledge that is available at each stage.15 page(s
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Sleeping tight or hiding in fright? The welfare implications of different subtypes of inactivity in mink
Effects of sub-optimal housing on inactivity vary across species and experiments, probably because inactivity is heterogeneous, reflecting both positive states (e.g. relaxation) and negative ones (e.g. fear). We therefore aimed to identify specific subtypes of inactivity that could indicate poor welfare in mink, by comparing their behaviour in enriched and non-enriched conditions (the former having been previously demonstrated to be highly preferred by mink and to enhance their welfare). We assessed this in three groups of subjects, as well as after housing conditions were reversed for the last group. During live scans, inactive animals were scored for posture, location, and whether awake or apparently asleep. Data on temperament and physiological stress indicators were also collected for one group; these confirmed that non-enriched housing increased faecal cortisol metabolites (FCM; P = 0.040). Non-enriched housing also increased locomotor stereotypy in females (sex × housing: P = 0.004). Inactivity in the nest-box (vs. in the open cage) was higher among females in non-enriched housing (housing × sex: P 0.05). This suggests that lying awake is not fear-related (e.g. not reflecting enhanced vigilance) but instead reflects some other negative state. Effects on inactivity subtypes as defined by posture were less consistent. For example, time spent lying belly down tended to decrease in mink moved from non-enriched to enriched cages (P = 0.054), but enriched mink spent significantly less time belly down (in one of the three groups; P = 0.002). Overall, two subtypes of inactivity, lying in the nest-box and lying awake seem likely to be valid indicators of housing-induced poor welfare in this species, being consistently increased by non-enriched cages. Lying in the nest-box may indicate fear or anxiety, and lying awake, a boredom-like state