Comparison between different approaches for the evaluation of the hot spot structural stress in welded pressure vessel components

Fatigue cracks in welds often occur at the toe of a weld where stresses are difficult to calculate at the design stage. To circumvent this problem the ASME Boiler and PV code Section VIII Division 2 Part 5 [1] uses the structural stress normal to the expected crack to predict fatigue life using elastic analysis and as welded fatigue curves. The European Unfired Pressure Vessel Code [2] uses a similar approach. The structural stress excludes the notch stress at the weld toe itself. The predicted fatigue life has a strong dependency on the calculated value of structural stress. This emphasizes the importance of having a unique and robust way of extracting the structural stress from elastic finite element results. Different methods are available for the computation of the structural hotspotstress at welded joints. These are based on the extrapolation of surface stresses close to the weld toe, on the linearisation of stresses in the through-thickness direction or on the equilibrium of nodal forces. This paper takes a critical view on the various methods and investigates the effects of the mesh quality on the value of the structural stress. T-shaped welded plates under bending are considered as a means for illustration

In European public health we trust?

It is now 3 months since the British people voted narrowly to leave the European Union (EU). The absence of any agreement on what the alternative is, or a coherent plan to achieve it means that this may not actually happen. However, the resulting uncertainty creates major challenges, not only for the UK, which has suffered immediate economic damage, but also for the rest of Europe.peer-reviewe

A generalised method for ratchet analysis of structures undergoing arbitrary thermo-mechanical load histories

A novel approach is presented based upon the Linear Matching Method framework in order to directly calculate the ratchet limit of structures subjected to arbitrary thermo-mechanical load histories. Traditionally, ratchet analysis methods have been based upon the fundamental premise of decomposing the cyclic load history into cyclic and constant components respectively, in order to assess the magnitude of additional constant loading a structure may accommodate before ratcheting occurs. The method proposed in this paper, for the first time, accurately and efficiently calculates the ratchet limit with respect to a proportional variation between the cyclic primary and secondary loads, as opposed to an additional primary load only. The method is a strain based approach and utilises a novel convergence scheme in order to calculate an approximate ratchet boundary based upon a predefined target magnitude of ratchet strain per cycle. The ratcheting failure mechanism evaluated by the method leads to less conservative ratchet boundaries compared to the traditional Bree solution. The method yields the total and plastic strain ranges as well as the ratchet strains for various levels of loading between the ratchet and limit load boundaries. Two example problems have been utilised in order to verify the proposed methodology

Creep fatigue analysis of DEMO divertor components following the RCC-MRx design code

In the DEMO fusion reactor, in-vessel components will be subjected to very high thermo mechanical steady and cyclic loads. A design check that is required by the RCC-MRx code used for nuclear installations and fusion reactors is a creep-fatigue check. The fatigue damage is caused by the pulsed operation of the fusion reactor while creep damage occurs during the hold time of loads at elevated temperatures. The temperature of the main divertor components is kept below that which causes creep by using cooling fluid that flows through channels fabricated within the components themselves. Other components such as the shielding liner and reflector plate supports on the divertor cassette cannot be cooled as such and so their temperature can rise high enough so that they sustain creep damage. In the presence of creep, the fatigue life of a component is reduced. In this work, a creep fatigue assessment of a representative simple geometry is carried out. The representative geometry is that of a thick cylinder under the action of steady and fluctuating loads similar to those seen by DEMO in-vessel components while in service. The cylinder example creep fatigue results are used as a benchmark and compared with those obtained using the creep fatigue assessment (CFA) tool developed at KIT (Karlsruhe Institute of Technology). Methodologies used for creep fatigue assessments within RCC-MRx are presented and explained and results discussed. The work should provide a contribution towards any necessary creep fatigue assessments of DEMO divertor components currently being developed.peer-reviewe

Political analysis in public health: middle-range concepts to make sense of the politics of health

Public health is about policy, power, and the public and as such might be thought necessarily political. That does not mean, however, that the place of political analysis and engagement in public health is uncontroversial, and there have been longstanding arguments that to discuss politics sullies the scientific nature of public health. This article, introducing a special issue on political science in public health, argues that rigorous use of middle-range theory can inform our analysis of public health problems and avoid the risks of politicization, excessive abstraction or excessive concreteness. It summarizes key political science concepts discussed in the papers: epistemic communities, interest groups, advocacy coalitions, political parties, institutions, legalism, discourse and the political economy of labour. We hope that the series will provide the public health community with some tools and methods for how to integrate public health knowledge into the sphere of decision making in an appropriate way

An underwater towed vehicle to monitor the Sicily-Malta channel

The problem of monitoring pollution coming from oil spills assumes wide importance for the highly congested Sicily-Malta channel. Hydrocarbons, as well as other polluting substances, have a huge influence on the health status of the sea. In this paper we present the preliminary design of an underwater towed vehicle (UTV) to monitor the Sicily-Malta channel. The design of this towfish incorporates ideas for a camera, lens system and stroboscope illumination system that can be used to take images of phytoplankton and zooplankton having a size range of 100 microns up to 1 centimeter. The underwater platform includes a high definition (HD) camera for monitoring jellyfish population at different sea depths. Unlike the autonomous underwater vehicles (AUVs), an UTV is not independent and must be towed by a surface boat. This disadvantage is balanced by having a simpler design and control system and an increased payload for instruments, sensors and cameras due to the absence of heavy battery systems. In order to increase maneuverability, stability and depth control, actuated hydroplanes are used to vary the angle of attack and to change the total downward force exerted on the moving towfish. The depth of dive of the towfish is automatically controlled to a set value. Automatic control is preferred so as to reduce the work and human concentration necessary during a monitoring mission. The hydroplanes are used to control rolling and pitching of the towfish. This kind of corrective action and a means of knowing the inclination of the towfish are deemed to be necessary because of the effect that underwater currents may have on the dynamics of the towfish. In addition to active control against the rolling action, the main hydroplanes (wings) of the towfish are at a small anhedral angle in order to create a passive anti roll action by creating a corrective moment acting about the main longitudinal axis of the towfish. The stern of the towfish also carries a rudder. The rudder would mainly be used when turning and to steer the towfish away from the surface boat wake when taking surface or close to surface measurements. The towfish is towed via an umbilical cord which carries all the power supply and signal lines necessary for towfish control and data acquisition. The umbilical cord is mechanically strong enough in order to tow the underwater towfish which is subjected to hydrodynamic drag. For proper logging and mapping of pollutants and camera images it is required to know the exact position and positional depth of the towfish during a mission. The positional depth of the towfish is recorded by means of a depth sensor. The position of the towfish is found by having a Global Positioning System (GPS) on the surface boat coupled with a commercially available sonar based instrument that can be used to calculate the relative position between the surface boat and the towfish.peer-reviewe

Charge separation: From the topology of molecular electronic transitions to the dye/semiconductor interfacial energetics and kinetics

Charge separation properties, that is the ability of a chromophore, or a chromophore/semiconductor interface, to separate charges upon light absorption, are crucial characteristics for an efficient photovoltaic device. Starting from this concept, we devote the first part of this book chapter to the topological analysis of molecular electronic transitions induced by photon capture. Such analysis can be either qualitative or quantitative, and is presented here in the framework of the reduced density matrix theory applied to single-reference, multiconfigurational excited states. The qualitative strategies are separated into density-based and wave function-based approaches, while the quantitative methods reported here for analysing the photoinduced charge transfer nature are either fragment-based, global or statistical. In the second part of this chapter we extend the analysis to dye-sensitized metal oxide surface models, discussing interfacial charge separation, energetics and electron injection kinetics from the dye excited state to the semiconductor conduction band states

Challenges in developing a solar powered stirling engine for domestic electricity generation

This paper investigates the challenges in developing a solar powered Stirling engine for domestic electricity generation. All the system components, the parabolic troughs, heat transfer fluid and the Stirling engine are individually analysed. The analysis includes a market survey and performance assessments of such components. A mathematical analysis for the Stirling engine is carried out in order to understand the affect of varies parameters with the work output per cycle and the engine efficiency. Such parameters are the phase angle between pistons, the diameter ratio of the power and displacer piston, and change in temperature.peer-reviewe