Numerical investigation of an influence of square cylinder crossovers on twin bare hulls in close proximity

This paper investigates the influence of two crossovers on twin bare spheroids in close proximity. Firstly, to examine the impact of the crossovers to the flow behaviour and overall drag coefficient of spheroids. Secondly, to compare the drag coefficient for various speeds. The CFD RANS-SST with a commercial code ANSYS CFX simulation is performed for the fully submerged twin spheroids with transverse separation (S/D) of 1.02; where S is the distance between centreline to centreline and D is the maximum diameter of a spheroid. The Reynolds Numbers used are 2 × 106, 3 × 106, and 4 × 106. The results show that each spheroids experience an additional 20% drag which is dominated by crossovers. The drag coefficient of small volume crossovers between spheroids is 10 times higher than the drag of each spheroids, consequently, the total drag of system is increased by 11 times compares to twin bare spheroids system. Increasing speed results in the drag reduction. At the Reynolds Number 2 × 106 shows the highest drag coefficient of twin hulls for both cases (with or without crossovers). The result suggests the use of twin bare hulls without crossovers in the fleet, an application; for example, a fleet of small autonomous underwater vehicles

An improved support vector regression and its modelling of manoeuvring performance in multidisciplinary ship design optimization

In this paper, the combination of the Laplace loss function and Support Vector Regression (SVR) are presented for the estimation of manoeuvring performance in multidisciplinary ship design optimization, and a new SVR algorithm was proposed, which has only one parameter to control the errors and automatically minimized with v, and adds b2/2 b to the item of confidence interval. It is shown that the proposed SVR algorithm in conjunction with the Laplace loss function can estimate the ship manoeuvring performance appropriately compared to the simulation results with Napa software and other approximation methods such as Artificial Neural Network (ANN) and classic SVR. In this article, we also gather enough ship information about the offshore support vessel; the Latin Hypercube Design is employed to explore the design space. Instead of requiring the evaluation of expensive simulation codes, we establish the metamedels of ship manoeuvring performance; all the numerical results show the effectiveness and practicability of the new approximation algorithms

Filamentary Accretion Flows in the Embedded Serpens South Protocluster

One puzzle in understanding how stars form in clusters is the source of mass -- is all of the mass in place before the first stars are born, or is there an extended period when the cluster accretes material which can continuously fuel the star formation process? We use a multi-line spectral survey of the southern filament associated with the Serpens South embedded cluster-forming region in order to determine if mass is accreting from the filament onto the cluster, and whether the accretion rate is significant. Our analysis suggests that material is flowing along the filament's long axis at a rate of ~30Msol/Myr (inferred from the N2H+ velocity gradient along the filament), and radially contracting onto the filament at ~130Msol/Myr (inferred from HNC self-absorption). These accretion rates are sufficient to supply mass to the central cluster at a similar rate to the current star formation rate in the cluster. Filamentary accretion flows may therefore be very important in the ongoing evolution of this cluster.Comment: 19 pages, 8 figures, 2 tables; accepted for publication in Ap

Numerical simulation of an ultrasonic vibratory cavitation device

Cavitation erosion prediction is one of the most important tasks in the ship propeller design. While predominantly qualitative methods are used such as paint tests or high speed video image analyses, there have been efforts to quantify such risks especially in the field of computational fluid dynamics (CFD).As an experimental quantitative method to assess erosion risk, the acoustic emission (AE) technique has been employed, for example, by Lloyds Register for more than a decade now to complement their borescopic cavitation observation at the ship scale. Boorsma and Fitzsimmons (2009) reported (see Fig. 1,) its correlation with borescope observed cavitation events appeared very positive and the location of cavitation impingement on the rudder (shown in the left image of Fig. 1) coincided with the estimated location by multiple synchronous measurements of AE at different locations. If it is possible to decipher how the AE connected with the pressure waves emitted from any given cavitation event, predicting the pressure waves we may be able to predict AE and eventually where and what intensity of cavitation events occur on any given propeller or ship structures. The transfer function can be useful for establishing quantitative correlations between CFD, full-scale trial data and with model test data.As the first step in being able to model this process and gain greater understanding in links between acoustic signal and type/location of cavitation, an open source Computational Fluid Dynamics programme openFOAM (version. 3.0.1) has been used to simulate ultrasonic cavitation on a sonotrode and hence to predict cavitation phenomena and pressure impact loads on a test specimen under the ultrasonic horn. The aim of the work is to evaluate the physical realism required and the limitations of current cavitation models

Selective lesions of the cholinergic neurons within the posterior pedunculopontine do not alter operant learning or nicotine sensitization

Cholinergic neurons within the pedunculopontine tegmental nucleus have been implicated in a range of functions, including behavioral state control, attention, and modulation of midbrain and basal ganglia systems. Previous experiments with excitotoxic lesions have found persistent learning impairment and altered response to nicotine following lesion of the posterior component of the PPTg (pPPTg). These effects have been attributed to disrupted input to midbrain dopamine systems, particularly the ventral tegmental area. The pPPTg contains a dense collection of cholinergic neurons and also large numbers of glutamatergic and GABAergic neurons. Because these interdigitated populations of neurons are all susceptible to excitotoxins, the effects of such lesions cannot be attributed to one neuronal population. We wished to assess whether the learning impairments and altered responses to nicotine in excitotoxic PPTg-lesioned rats were due to loss of cholinergic neurons within the pPPTg. Selective depletion of cholinergic pPPTg neurons is achievable with the fusion toxin Dtx-UII, which targets UII receptors expressed only by cholinergic neurons in this region. Rats bearing bilateral lesions of cholinergic pPPTg neurons (>90 % ChAT+ neuronal loss) displayed no deficits in the learning or performance of fixed and variable ratio schedules of reinforcement for pellet reward. Separate rats with the same lesions had a normal locomotor response to nicotine and furthermore sensitized to repeated administration of nicotine at the same rate as sham controls. Previously seen changes in these behaviors following excitotoxic pPPTg lesions cannot be attributed solely to loss of cholinergic neurons. These findings indicate that non-cholinergic neurons within the pPPTg are responsible for the learning deficits and altered responses to nicotine seen after excitotoxic lesions. The functions of cholinergic neurons may be related to behavioral state control and attention rather than learning

Only connect: addressing the emotional needs of Scotland's children and young people

A report on the SNAP (Scottish Needs Assessment Programme) Child and Adolescent Mental Health Phase Two survey. It describes a survey of a wide range of professionals working with children and young people in Scotland, and deals with professional perspectives on emotional, behavioural and psychological problems. Conclusions and recommendations are presented

Shifting sands: the narrative construction of early career aboriginal teachers' professional identities at the cultural interface

This study explores issues facing early career Aboriginal teachers as they construct and enact their personal, professional and situated identities when learning to teach. Narrative constructions of identity simultaneously illuminate and challenge dominant discourses about Aboriginal teachers as they take up, resist and/or reject these discourses. The role of Aboriginality is mediated by factors such as lived experience, positioning of and by the teachers and school contexts. These issues are explored through the theoretical perspectives of Foucault, Bourdieu and Nakata. Like shifting sands, identity construction and teaching work can be unstable terrain, requiring complex contextualised understandings, skills and dispositions. Participants are pre-service Aboriginal teachers in an away-from-base secondary Aboriginal Studies teacher education program at the University of Sydney. They are mature-aged with varying levels of experience of formal education and living in Aboriginal communities. Using narrative methodology, eleven in-depth conversational interviews followed by two focus groups revealed emerging storylines and themes and four participants were identified for further interviews to collaboratively construct the final narratives. This approach privileged participant voices and created spaces to articulate the tacit knowledge and understandings that contribute to the development of a professional identity drawn from personal, professional, cultural and contextual sources. Three themes emerged: discourses of Aboriginality, narratives of belonging, and conceptualising a pedagogical cultural identity. The implications of these themes bring focus to pre-service and in-service teacher professional learning based on valuing Aboriginal community engagement. When nurtured early in a teacher’s career, relationships serve a socio-cultural and political role that contribute significantly to the development of agentic and resilient identities at the cultural interface