The Characterisation and Numerical Modelling of Viscoelastic Polyurethane Foams for Use in Custom Wheelchair Seating

Viscoelastic polyurethane foam is widely used in wheelchair cushions as it offers good pressure relieving capabilities. However, the behaviour of this material is largely un-quantified, by comparison with conventional elastomeric materials.Consequently, in many cases, inadequate cushioning is provided to wheelchairusers with complex seating requirements. This thesis characterises andnumerically models viscoelastic polyurethane foam.Temperature-dependent static compression and simple shear test procedures are conducted on a range of viscoelastic polyurethane foams and selected results are utilised to identify Ogden Hyperfoam material model parameters. Time-dependent creep and stress relaxation test procedures are conducted and test results are used in conjunction with Time-Temperature-Superposition (TTS), William-Landel- Ferry (WLF) and Arrhenius theories to generate long-term predictions of material behaviour. Appropriate spring-dashpot models are utilised to model predicted long-term viscoelastic performance. Thermal conductivity parameters are obtained using Glicksman’s theoretical model. The accuracy of predictions obtained using TTS and WLF theories has been proven. Validation has also been achieved for the temperature-dependent Hyperfoam, long-term viscoelastic and thermal conductivity parameters.The range of fully validated material model parameters were utilised to simulatethe in-service seating behaviour of polyurethane foam. Simulation results wererelatively compared and analysed with respect to relevant pressure ulcer riskfactors. From analyses of the FE simulations, results lend support to findings from clinical trials particularly with respect to the relationship between shear and direct pressure in wheelchair seating. Other FE results disagree with accepted seat prescription timings used in current clinical practises

The Characterisation and Numerical Modelling of Viscoelastic Polyurethane Foams for use in Custom Wheelchair Seating.

Viscoelastic polyurethane foam is widely used in wheelchair cushions as it offers good pressure relieving capabilities. However, the behaviour of this material is largely un-quantified, by comparison with conventional elastomeric materials. Consequently, in many cases, inadequate cushioning is provided to wheelchair users with complex seating requirements. This thesis characterises and numerically models viscoelastic polyurethane foam. Temperature-dependent static compression and simple shear test procedures are conducted on a range of viscoelastic polyurethane foams and selected results are utilised to identify Ogden Hyperfoam material model parameters. Time-dependent creep and stress relaxation test procedures are conducted and test results are used in conjunction with Time-Temperature-Superposition (TTS), William-Landel- Ferry (WLF) and Arrhenius theories to generate long-term predictions of material behaviour. Appropriate spring-dashpot models are utilised to model predicted long-term viscoelastic performance. Thermal conductivity parameters are obtained using Glicksman’s theoretical model. The accuracy of predictions obtained using TTS and WLF theories has been proven. Validation has also been achieved for the temperature-dependent Hyperfoam, long-term viscoelastic and thermal conductivity parameters. The range of fully validated material model parameters were utilised to simulate the in-service seating behaviour of polyurethane foam. Simulation results were relatively compared and analysed with respect to relevant pressure ulcer risk factors. From analyses of the FE simulations, results lend support to findings from clinical trials particularly with respect to the relationship between shear and direct pressure in wheelchair seating. Other FE results disagree with accepted seat prescription timings used in current clinical practises

The Irish Folklore Commission 1935-1970: History, ideology, methodology

"Between 1935 and 1970 the Irish Folklore Commission (Coimisiún Béaloideasa Éireann), under-funded and at great personal cost to its staff, assembled one of the world’s largest folklore collections. This study draws on the extensive government files on the Commission in the National Archives of Ireland and on a wide variety of other primary and secondary sources, in order to recount and assess the work and achievement of this world-famous institute. The cultural, linguistic, political and ideological factors that had a bearing on the establishment and making permanent of the Commission and that impinged on many aspects of its work are here elucidated. The genesis of the Commission is traced and the vision and mission of its Honorary Director, Séamus Ó Duilearga (James Hamilton Delargy), is outlined. The negotiations that preceded the setting up of the Commission in 1935 as well as protracted efforts from 1940 to 1970 to place it on a permanent foundation are recounted and examined at length. All the various collecting programmes and other activities of the Commission are described in detail and many aspects of its work are assessed and, in some cases, reassessed. This study also deals with the working methods and conditions of employment of the Commission’s field and Head Office staff as well with Séamus Ó Duilearga’s direction of the Commission. This is the first major study of the Irish Folklore Commission, which has been praised in passing in numerous publications, but here for the first time its work and achievement is detailed comprehensively and subjected to scholarly scrutiny. This work should be of interest not only to students of Irish oral tradition but to folklorists everywhere. The history of the Irish Folklore Commission is a part of a wider history, that of the history of folkloristics in Europe and North America in particular. Moreover, the Irish Folklore Commission maintained contacts with scholars on all five continents, and this work has relevance for many areas of the developing world today, where conditions are not dissimilar to those that pertained in Ireland in the 1930's when this great salvage operation was funded by the young, independent Irish state.

Develop a District-Wide Discipline Policiy for Exceptional Misconduct

Cascade School District in North Central Washington was developed a district-wide discipline program to improve student citizenship. A study of selected school districts in the North Central Washington School Districts identified connnon elements in previous discipline plans. The comparison study resulted in the development of a consistent discipline policy within Cascade School District. Cascade School District staff and connnunity members developed a comprehensive school board policy providing for a discipline sanction range from kindergarten through grade twelve

Preparing for your preceptorship midwife interview: a student's guide

This is a very busy and exciting time in the academic year as third year students come to the end of their programme of study and start to apply for preceptorship posts. Whilst there remains a shortage of midwives (Royal College of Midwives (RCM, 2015), applications for posts are still very competitive and so candidates need to ensure they are as well prepared as possible to ensure they perform at their very best on the day. This article revisits what constitutes ‘a good midwife’ (Power, 2015) and then goes on to look at the recruitment process from the perspectives of the interviewer and the interviewee. Paula Briody, Matron for Intrapartum Care (Northampton General Hospital NHS Trust) is actively involved in the recruitment process for her Trust and outlines the key characteristics she looks for in candidates. The article also shares the experiences of third year students who have recently been interviewed for their first midwifery posts. It is hoped that hearing about the process from both perspectives might be useful for all third year students currently applying for their first jobs as they get one step nearer to realising their dreams of becoming a qualified midwife

Characterisation, Modelling and Simulation of Flexible Polyurethane Foam

Flexible polyurethane foam is an open-celled polymeric material that exhibits strain rate and temperature effects. It has found various applications in areas including the packaging, medical, sports, aerospace and aeronautical industries. Polyurethane foam is ubiquitous in seating applications and finds particular use in specialised wheelchair seating where customised seating solutions are required which can provide proper comfort and support without the risk of developing pressure ulcers. Proper seating design is critical for users if this problem is to be avoided, but a lack of quantitative knowledge of this material’s behaviour has limited its effectiveness. The objectives of the work presented here are twofold. Firstly to characterise the behaviour of the materials and secondly to develop a validated numerical model which can be used to increase understanding of in-service behaviour. Three commonly used foams having different densities and viscoelastic properties were subjected to compression in a uni-axial test machine fitted with a custom-built temperature chamber. The results of these tests were analysed and are presented to aid in the characterisation of these materials. The effects on the stiffness of foam of different additives, densities, strain rates and temperatures were noted. A material model was developed to simulate indentation, in which compression and shear were the predominant modes of deformation. The results from the uni-axial characterisation tests were employed to determine material constants for Ogden’s constitutive model for compressible materials. Simple shear tests were also conducted with a custom-built dual lap shear tester and material constants were then determined for this mode of deformation. A curve-fit was developed which was a compromise between both modes of deformation to provide increased material model robustness. To validate the accuracy of the developed model, uni-axial indentation of standard polyurethane seating foam was then modelled using Finite Element (FE) code. Results show a high degree of accuracy

Working at the Speed of Innovation: Impedance Mismatch in Rapid and Innovation Projects

In this paper we report on the results of an ethnographic study of a rapid design innovation (RDI) experiment in NASA Aeronautics. This work is based on the study of the Aeronautics Autonomy Testbed Capability (AATC) team in the Convergent Aeronautics Solutions (CAS) project. This paper focuses on and summarizes one of the key over-arching findings from the study: there is a significant mismatch in the organizational culture in the rest of the organization compared with that required for RDI. And, if this organizational cultural mismatch is not addressed, the likelihood of any organization being able to advance a new and different type of work (such as RDI) will be jeopardized. We delineate several aspects of the two different cultures identified in order to enable leaders and practitioners to better understand what contributes to the cultural dissonance and the implications of the differences in the cultures. As well, we identify ways in which those differences can be addressed. Research from organization and other social sciences are incorporated to highlight the differences. The implications of the research suggest that the significant cultural differences trigger a strong and resistive response from the dominant culture that may negate leaderships strategy to build the new capacity for RDI. While the research results noted the pervasive nature of innovation throughout the workplace, the type of innovation envisioned in RDI is a rare type of innovation that requires significantly new methods, work processes, tools, and skills such that approaches used in the dominate culture cannot be adopted by expediting the existing approaches. Examples include: innovation teaming and leadership; the need for adaptive leadership that changes the relationship of a research leader to the other researchers; and, an interdisciplinary teaming approach which shapes team relationships and activities. Each of these aspects requires new teaming, tools, and skills in order to succeed. Thus, when introducing RDI activities where there is a different dominant culture, teams need to be: well trained; protected; recognized and rewarded. And, team leaders must also be trained in the unique types of teaming and innovation tools used in RDI. Both RDI teaming and team leadership must be sanctioned, supported, and rewarded by leadership. Because of the cultural mismatch, in some organizations looking to add RDI to their existing and established organizations, sep to avoid or mitigate the negative impact of the culture mismatch