I Penesis

Phase Averaged Flow Analysis in an Oscillating Water Column Wave Energy Converter

The paper presents the application of phase averaging to experimental data obtained during scale model testing of a forward facing bent duct oscillating water column (OWC). Phase averaging is applied to both wave probe data and a two-dimensional velocity field at the centerline plane of the OWC model obtained using particle imaging velocimetry (PIV). Results are presented for one monochromatic wave condition. The influence of varied wave frequency is briefly discussed.

Phase averaging of the velocity fields in an oscillating water column using splines

The principal objective of this paper is to present a phase averaging method by curve fitting using B-splines. The method was designed specifically to process phase-clumped and discontinuous periodic data. Phase averaging by ensemble averaging of data clumped in phase will cause phase bias error if the mean phase of the clumped data does not equal the desired phase. The curve-fitting method presented here avoids phase bias error. The performance of the curve-fitting method was compared favourably with the ensemble averaging method when processing phase-clumped experimental data. Generally, the curve-fitting method exceeded the performance of the ensemble averaging method when the data were clumped in phase and matched the performance of the ensemble averaging method when the data were randomly distributed in phase. Experimentally obtained phase-clumped two-dimensional velocity fields at the centre-line of a forward-facing bent-duct oscillating water column were processed using the curve-fitting method. The phase-averaged velocity fields were combined for visualization purposes in the form of animated graphics interchange format (GIF) images to show the velocity fields over a wave cycle. The GIF images correspond to the four separate monochromatic wave frequencies tested and accompany the online version of this paper. The GIF images reveal the two-dimensional phase-averaged flow characteristics at the centre-line of the model with phenomena including oscillating flow, water column heave and slosh, front-wall swash and down wash, an outflow jet and vortices. It was concluded that phase averaging using splines finds a niche for the phase averaging of data which are dispersed (or clumped) in phase.

Sensitivity of vessel responses to environmental contours of extreme sea states

A comparative study of two methods for the generation of the environmental contours is presented investigating the sensitivity of the predicted extreme vessel responses to the type of the contour lines. Two approaches for the generation of environmental contours of the significant wave height and peak period are compared: the Inverse First Order Reliability Method (IFORM) and Constant Probability Density (CPD) approach. Case studies include several global responses of a ship-shaped weather-vaning vessel and a semisubmersible platform. The case studies reveal that the differences between the IFORM and CPD contours are more pronounced in the range of long wave periods. Vessel responses which are less sensitive to long wave periods exhibit less difference (less than 1.0%) in their maximum values between the two types of contours. In contrast, responses which are sensitive to long wave periods show significantly larger differences of up to 7.0%. Uncertainties also exist in the predicted extreme responses where the environmental contour and the response isoline behave tangentially. Differences between the extreme responses produced by the two contours generally decrease with an increase in return period; however exceptions exist due to the tangential behaviour. It is advised that these sensitivities should be taken into consideration when the environmental contours are used in the design.

Wetdeck slamming loads on a developed catamaran hullform – experimental investigation

ABSTRACT Catamaran wetdeck slamming has been experimentally investigated using a servo hydraulic slam testing system. A series of controlled-speed water impacts was undertaken on a rigid catamaran bow section with two interchangeable centrebows. Entry into the body of water was at two fixed trim angles: 0° and 5°. The vertical velocity was varied from 3 to 5 m/s in 0.5 m/s increments. This study presents a new dataset of pressure distributions and slam forces on the arched wetdeck structure of catamaran vessels. The relationships between the peak force magnitudes, relative impact angle and vertical velocity are observed, with a small reduction in slam force for an amended centrebow. Limited pressure measurements along the archway were not found to be representative of wetdeck slamming loads.

Computational fluid dynamics re-mesh method to generating hydrodynamic models for maneuvering simulation of two submerged bodies in relative motion

An Autonomous Underwater Vehicle (AUV) operating closer to a larger vessel experiences significant hydrodynamic forces requiring an adaptive control mechanism to maintain acceptable trajectory. It is therefore important that the designer understands the hydrodynamic characteristics of the vehicle in this scenario in order to develop appropriate control algorithms to deal with its dynamic behaviour. This requires developing simulations of the vehicles behaviour close to the larger vessel, the control algorithms, and the dynamic interface between the two. This paper presents a method to generate a complete hydrodynamic model of underwater vehicles using the Computational Fluid Dynamics (CFD) code ANSYS CFX, which can then be interfaced with the vehicles control algorithms within a simulation environment. The essential aspect of the method is the re-mesh approach, where the mesh deforms locally around the bodies using an Arbitrary Lagrangian-Eulerian form of the governing fluid equations and re-meshes when the deformation significantly compromises the quality of the mesh. This overcomes the motion limitations imposed by a pure deforming mesh approach. Preliminary work to validate the method is based on two smooth spheres moving relative to each other. It shows that this method is able to adequately simulate the fluid behaviour around the bodies. The paper also describes the future work focused on a 6 degrees-of-freedom (6-DOF) AUV modelled in CFD to obtain its hydrodynamic behaviour to be interfaced to the control system within MATLAB.

Reskilling the manufacturing workforce and developing capabilities for the future

Abstract Australia needs a stronger workforce over the next three to five years with more qualified engineers and associated professionals with the high-level skills capable of delivering the needs of the advanced manufacturing and maritime industries. Australia’s graduation rates in science, technology, engineering and mathematics fields are low by international comparison, providing challenges in meeting qualified workforce needs. With a focus on Tasmania, this paper identified the mismatch between current skills and future needs from a literature review, and through semi-structured interviews with companies in these industries, qualitative data on future skills were determined. The results clearly indicate that there is a need for Vocational Education and Training and Higher Education to be flexible in their course offerings, work with industry to ensure that it is delivering consistent and quality learning outcomes, thus creating a culture of communication and collaboration underpinned by mutual understanding of industry and education and training sector needs, possibilities and constraints.

Large Effect Size Studies of Computers in Schools: Calculus for Kids and Science - ercise

This report describes two computer-based interventions in Year 6 (age 11–12 years) classrooms. The interventions positioned sophisticated software alongside multimedia learning materials to teach topics from curriculum objectives many years ahead of these students’ chronological ages. These were transformative interventions (Fluck, 2003), changing what and how students learn when using computers. Students solved real world problems using integral calculus (Calculus for Kids) and studied both special relativity and quantum mechanics (Science-ercise). Calculus for Kids was conducted with 478 students in 26 schools from five Australian states; and Science-ercise was conducted with 187 students in five Tasmanian schools. Student learning achievement was measured using calibrated items in a post-test, with the students able to use the sophisticated software during the test. The results showed a majority of students exhibited learning achievements 4–6 years above their chronological age when using suitable computer tools. The studies bring into question the correct way to calculate effect sizes for such high impact interventions. Relying on Glass et al. (1981), we estimate this transformative use of computers in education achieved an effect size >4.0, well above Hattie’s (2007) hinge point of 0.4 for a significant innovation. This approach offers a pathway to shorten the time between knowledge generation and its incorporation in school curricula.

Variability of extreme responses due to wave frequency motions of a weather-vaning FPSO

The variability of extreme responses of a flexible riser due to wave frequency motions of weather-vaning FPSO is investigated numerically. The objective of this study is to examine such variability in isolation from that caused by the low frequency (slow drift) vessel motions and vessel offsets.Investigation of the extreme value distributions of flexible risers provides the statistical foundation for flexible riser Response Based Analysis (RBA) for use in system design; the determination of the statistical properties of extreme flexible riser responses provides a method for the prediction of extreme responses of offshore systems in cyclonic conditions.A case study conducted in OrcaFlex included an FPSO vessel with a Lazy-S configured riser system. Five riser responses were selected in critical locations including tension, heave, and curvature responses. The environmental cases included two cyclonic storms consisting of multiple half-hour intervals. For each interval, time domain simulations included 40 wave realizations in order to provide a dataset for robust fitting of the extreme value distributions in the Gumbel format.Once the short term interval distributions were established, response distributions in a storm were generated by multiplying the short term distributions and the most probable maximum (MPM) response in a storm computed. A comparison of maximum interval, storm and 3-hour MPMs is presented, which indicates to what extent the MPM response in a storm exceeds the corresponding maximum interval response. Differences between the tension and heave responses are compared with those observed in the curvature responses.This study was limited to riser excitation by waves, current and wave frequency motions of a turret moored FPSO and it is expected that further inclusion of low frequency motions would contribute to the response variability. The inclusion of such variability will ultimately enable the storm-based statistical approach to be used for the development of long-term distribution of the riser responses.Copyright

A Risk Assessment of a Novel Bulk Cargo Ship-to-Ship Transfer Operation Using the Functional Resonance Analysis Method

Risk assessments underpin a maritime operation’s safety management system. When applied to an untested concept a risk assessment can also assist with overcoming resistance to new technology. This paper proposes the functional resonance analysis method (FRAM) as a tool for developing design recommendations and fulfilling the safety management objectives of the ISM Code. The FRAM is applied to benefit the floating harbour transhipper (FHT), a novel concept for the transhipment of bulk commodities. The FHT acts as a large floating warehouse with an aft well dock that provides shelter for a feeder vessel. The FHT’s materials handling equipment transfers bulk cargo from the feeder vessel onto its own stockpile or directly to an export vessel moored alongside, or from its stockpile to the export vessel. Most risk assessment tools focus on identifying and addressing system components that can potentially fail. With the FRAM however, the scope, direction and recommendations are guided by a practical understanding of the variability of work undertaken rather than preconceived notions of potential failure modes. Adopting a method based on maximising resilience rather than minimising the causes of accidents promotes a shift from a blame culture to a safety culture. Applying the FRAM generated a deeper, broader and more transparent understanding of the FHT transfer operation than what would have been achievable using traditional risk assessment tools. This understanding was used to develop recommendations designed to improve the resilience of the FHT operation.

Safety analysis of a new and innovative transhipping concept: a comparison of two Bayesian network models

The floating harbour transhipper (FHT) is a new and innovative concept designed to improve the efficiency of bulk commodity export. As with all new and untested maritime systems, a rigorous safety analysis is essential prior to the operation’s launch. Sophisticated tools, such as Bayesian networks, are increasingly being adopted for safety analysis in the maritime industry. Bayesian networks have predominately been used to replace fault trees due to their flexibility and improved handling of uncertainty. However, when applied to complex socio-technical systems Bayesian networks, as currently used, inherit many of the same shortcomings as traditional risk-based methodologies. These limitations are not indicative of the methods potential. This paper compares the traditional approach for developing Bayesian networks with an approach based on a foundation of resilience engineering. Both models were applied to an aspect of manoeuvring during the FHT’s operation. The resilience-based approach successfully developed a representative network. The two approaches led to vastly different models, both in terms of structure and parameters. However, the descriptive approach of resilience-based model produced more proactive safety recommendations and, unlike the traditional model, serves as a knowledge base for future investigation.