Numerical modelling of unsteady turbulent flow in smooth-walled pipes

An efficient numerical model for turbulent friction has been developed for smooth-walled pipe flow. The aim was to develop a new approach to the numerical modelling, eliminating some important approximations and sources of error, such that the method can be applied reliably under a wide range of conditions. A simple two-region model of effective viscosity is used. For short timescales, the turbulence level and effective viscosity distribution are ‘frozen’ in time. The velocity profile is determined numerically for a range of frequencies and viscosity distributions, and this is used to determine the frequency-dependent friction. This is then approximated using simple weighing functions. This turbulence model can be implemented readily in several types of numerical model for pipe flow, including simple lumped parameter models, finite difference/finite element methods, and the method of characteristics. </jats:p

Condition Monitoring of Aircraft Fuel Pumps using Pressure Ripple Measurements

Gear pumps are used for delivery of high-pressure fuel to aircraft engines. These pumps can suffer from erosion due to cavitation, which eventually causes an increase in leakage and reduced performance. An early warning of excessive wear is desirable, before the performance becomes unacceptable so that replacement can be scheduled conveniently without disrupting the operation of the aircraft. Pressure ripple and flow ripple measurements were performed on a range of fuel pumps with bearing conditions ranging from good to badly worn. The flow ripple was determined indirectly by analysis of pressure ripple measurements. Results suggest that there is a clear and fairly consistent increase in the pressure ripple and flow ripple measured at the high-pressure outlet port when the bearing is in a worn condition. This increase seems to occur at a wear condition that is not sufficiently bad to worsen the pump performance significantly. This measurement could provide a clear and simple indication of pump wear, at an opportune point in the wear cycle. However whilst these results look promising they are not conclusive, as other differences between the pumps may have affected the results.</p

Condition monitoring and fault diagnosis for vane pumps using flow ripple measurement

Vane pumps are simple in principle and can be mass produced inexpensively, making them well suited to the automotive industry. They also have many other applications, such as in the chemical industry and food industry. A common type of damage to a vane pump is cavitation erosion on the side plates. If this damage is not detected in time, it could cause failure of the pump, which depending on the type of system may have safety implications, and in some cases a high cost from lost production whilst the system is shut down. This kind of damage is common on other types of pumps such as gear pumps and piston pumps. So a practical method for fault diagnosis of hydraulic pumps is required which does not necessitate removal of a pump from the working system. This paper presents a method of detecting and identifying cavitation damage on pump side plates via pump flow ripple. Power steering vane pumps are used for this study, although the principles may also be applicable to other types of vane pump, and indeed to piston and gear pumps. The investigation has been done through measurement and simulation. A numerical model of a vane pump is described, and simulated cavitation damage is introduced into the model. This damage is shown to have a clear effect on the simulated flow ripple. The pump flow ripple has also been measured experimentally using the Secondary Source Method, and artificial damage has been introduced into the pump. The damage is shown to have a clear effect on the measured flow ripple, consistent with the simulation results. Whilst the secondary source enables the measurement of flow ripple in laboratory conditions, it is generally impracticable for in-situ measurement for condition monitoring. A simplified method for calculation of pump flow ripple from in-situ pump pressure ripple measurements and system impedance is discussed

Flow ripple reduction in power steering hydraulic pumps

Noise in hydraulic power steering systems is mainly generated by the hydraulic pump due to the cyclic pumping mechanism that creates pulsating flow transmitted by the fluid. This flow ripple and pressure ripple, propagating through the hydraulic circuit, interacts in a complex way with the other parts of the vehicle, generating audible noise inside the vehicle. The present work shows two ways to reduce the flow ripple amplitude generated by a vane pump through the redesigning of the pump rotating group. First, a nine-vane rotor pump is proposed and, secondly, a pump with three discharge ports is proposed. To check their results, a MatLab/Simulink based pump model was created according to the new geometrical characteristics and the results are compared with the regular pump ones. Also, a flow ripple experimental test was run using the Secondary Source Method to validate the numerical model results of the regular pump. The new designs simulation results show large flow ripple amplitude reduction (from 6dB to 16dB per harmonic) as well as frequency displacement in the discharge flow ripple spectra in both designs. Also, the simulations show perpendicular force on the pump shaft generated by the non-balanced conditions created by the new designs

Feeding the Worlth Healthily: the Challenge of Measuring the effects of Agriculture on Health

Agricultural production, food systems and population health are intimately linked. While there is a strong evidence base to inform our knowledge of what constitutes a healthy human diet, we know little about actual food production or consumption in many populations and how developments in the food and agricultural system will affect dietary intake patterns and health. The paucity of information on food production and consumption is arguably most acute in low- and middle-income countries, where it is most urgently needed to monitor levels of under-nutrition, the health impacts of rapid dietary transition and the increasing ‘double burden’ of nutrition-related disease. Food availability statistics based on food commodity production data are currently widely used as a proxy measure of national-level food consumption, but using data from the UK and Mexico we highlight the potential pitfalls of this approach. Despite limited resources for data collection, better systems of measurement are possible. Important drivers to improve collection systems may include efforts to meet international development goals and partnership with the private sector. A clearer understanding of the links between the agriculture and food system and population health will ensure that health becomes a critical driver of agricultural change

Security: Collective good or commodity?

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2008 Sage.The state monopoly on the legitimate use of violence in Europe and North America has been central to the development of security as a collective good. Not only has it institutionalized the state as the prime national and international security provider, it has helped to reduce the threat from other actors by either prohibiting or limiting their use of violence. The recent growth of the private security industry appears to undermine this view. Not only are private security firms proliferating at the national level; private military companies are also taking over an increasing range of military functions in both national defence and international interventions. This article seeks to provide an examination of the theoretical and practical implications of the shift from states to markets in the provision of security. Specifically, it discusses how the conceptualization of security as a commodity rather than a collective good affects the meaning and implementation of security in Western democracies.ESR

Explaining clinical behaviors using multiple theoretical models

PMID: 23075284 [PubMed - indexed for MEDLINE] PMCID: PMC3500222 Free PMC ArticlePeer reviewedPublisher PD