The effect of cubic damping on a base excited isolator: an experimental study for harmonic excitation

An experimental study has been conducted to validate theoretical solutions for the response of a base excited single degree-of-freedom isolation system possessing pure cubic damping. The cubic damping characteristic was implemented using an electromagnetic shaker with a simple non-linear velocity feedback control. The rig and practical implementation of the active damping are described. The base excitation was harmonic at a set of discrete frequencies with constant displacement amplitude. Consistent with theoretical predictions, the isolation performance at high excitation frequencies is shown to be worse than either the undamped or linear viscously damped isolation system with the displacement transmissibility tending to unity. This is contrary to the case of force excitation reported in the literature where cubic damping offers improved performance. The physical causes of the distinct behaviours and the consequences for isolator design are discusse

Travel choices in Scotland - the effect of local accessibility on non-work travel

Accessibility features prominently in the developing transport policies of both the United Kingdom Government and the devolved Scottish Executive which aim to promote social inclusion in particular and the integration of transport and land use planning more generally. It follows that a detailed understanding of the relationship between accessibility, personal mobility and travel behaviour is critical to the successful implementation of these policies. This paper presents the results of a disaggregate, multi-variate analysis of the Scottish Household Survey (SHS) dataset and attempts to unravel the complex relationship between socio-economical circumstance, geographical access to local services and public transport and revealed non-work travel choices. The socio-economical and geographical diversity of Scotland offers an excellent opportunity to undertake an analysis of this nature. The SHS is a continuous, cross-sectional survey funded by the Scottish Executive and undertaken by face-to-face interview based on a sample of the general population in private residences in Scotland. It seeks to provide information on the composition, characteristics and behaviour of Scottish households. The survey collects information in two parts - firstly the highest income householder provides household level data including household composition and income, key attributes of household members, transport resources available to the household including access to public transport; secondly a randomly selected adult from the household provides information on inter alia personal travel (including the completion of a one-day travel diary on the previous day) and personal views on transport, the neighbourhood and local services. The dataset analysed in this paper was collected between 1999 and 2003 and contains over 75,000 surveyed households and over 49,000 completed travel diaries. Two other variables were matched with the residential location of SHS respondents and added to the dataset; namely, an index representing proximity to local services at electoral ward level derived in the Scottish Indices of Deprivation 2003 study and a locational classification for each respondent which captures settlement size and wider regional accessibility. The primary focus of the analysis presented in this paper is an examination of the extent to which the quality of local access to services affects distance travelled for non-work purposes. Within this analysis individual and household socio-economical circumstance, available transport resources (both car ownership and local access to public transport) and the wider regional geographical context are also taken into account. It is hypothesised that good local access is negatively associated with distance travelled and that there also exists the possibility of significant interaction between local access and socio-economical circumstance and available transport resources. Regression models are developed for non-work travel which test the statistical significance of these explanatory variables. The results of the analysis reported here will add to the existing evidence base on the relationship between accessibility and travel choice. Its conclusions are expected to inform the development of strategies to enhance social inclusion and reduce overall travel which are tailored to socio-economical and geographical circumstance

Mean stress effects on random fatigue of nonlinear structures

Random fatigue analysis techniques have concentrated on linear structures that exhibit symmetric stress range probability density functions (PDF). In narrowband response and broadband random response it is assumed that the bending stress range PDF is symmetric and has zero mean stress. Structures that can exhibit geometrical nonlinearity, under large deflections, typically introduce membrane effects, which are additional positive tensile stresses that tend to skew the stress range PDF. This paper investigates fatigue analysis approaches that include mean stress effects and show how they can be applied to nonlinear random vibration problems

The effect of stocking density and bin feeder space on performance in pigs

(South African J of Animal Science, 2000, 30, Supplement 1: 70-71

Protein and lipid deposition rates in growing pigs following a period of excess fattening

The objective of this experiment was to test the proposition that fatter pigs, when fed a high crude protein (CP) diet, would attempt to correct the effects of excess fattening on body composition by returning to a state that is consistent with pigs grown under non-limiting nutritional conditions. The experiment was divided into two phases: Phase 1 was from 15 to 30 kg in which 72 of the 96 Large White x Landrace x Duroc pigs (equal male and female) were made fatter by consuming a low CP food (LP1) (181 g/kg (as fed)). The remaining 24 pigs were fed a high CP food (HP1) (223 g/kg (as fed)) to provide the rate and composition of growth associated with unrestricted or normal growth. Phase 2 was the rehabilitation phase and was divided into two periods: 30 to 45 kg and 45 to 60 kg. Pigs that were fed LP1 were randomly allocated to one of a high CP (HP2) (204 g/kg (as fed)), low CP (LP2) (159 g/kg (as fed)) or medium CP (MP2) (181 g/kg (as fed)) food, respectively. Pigs fed HP1 in Phase 1 continued to be fed HP2 in Phase 2. During Phase 1, pigs fed HP1 consumed less food but grew at a similar rate to pigs fed LP1. Pigs fed LP1 were significantly fatter, had less body water and had a higher lipid:protein ratio (0.86±0.04 vs. 0.67±0.09 g/g, respectively) at the end of Phase 1. Between 30 and 45 kg, pigs fed HP2 and previously fed LP1, retained significantly less lipid and had the lowest lipid growth:protein growth ratio (0.38±0.05) than all other treatments. By 45 and 60 kg, there were no significant differences in the lipid content and lipid:protein ratio of pigs across all treatments. It can be concluded that nutritionally induced, fat pigs will attempt to restore their body lipid contents, to those levels in animals not previously nutritionally deprived, by reducing their rate of lipid retention when fed a higher crude protein food. South African Journal of Animal Science Vol.32(2) 2002: 97-10

Evaluation of the growth parameters of six commercial crossbred pig genotypes 2. Under ideal temperature conditions in chambers

To test whether animals grown under ideal temperature conditions would have different growth parameters to animals grown in more conventional housing, 60 Large White x Landrace male pigs from three genotypes were housed in six temperature-controlled chambers. The results were compared with data from a similar trial, with the same three genotypes, conducted in an open-sided house. Estimates of mature size (as measured by mature protein weight (Pm)), rate of maturing (B) and levels of inherent fatness (LPRm) were obtained from serial slaughtering four pigs per genotype at 30, 40, 70, 80 and 90 kg live weight. The results indicate that for commercial crossbred male pigs there were no significant differences in the growth parameters between genotypes grown under ideal temperature conditions (Controlled), nor were there any differences between similar genotypes grown in Controlled vs. commercial conditions (Uncontrolled). The rate of maturing was also similar for all three genotypes and for all components. Mean estimates of Pm, B and LPRm determined from both Controlled and Uncontrolled conditions can be combined to give values of 40.4±1.62 kg, 0.0114±0.0005 per day, and 1.67±0.153 kg/kg, respectively. Furthermore, controlling temperature had minimal effect on the allometric relationships between protein and the remaining body components for different genotypes. The determination of growth parameters for commercial crossbred pig genotypes can, therefore, be accomplished when the animals are grown individually in an open-sided house

Stress: should animals be fed to their potential requirements?

(South African J of Animal Science, 2000, 30, Supplement 1: 42-44

Energy transfer in a beam-framed structure using a modal method and a wave method at mid frequencies

A fully framed system consisting of four beams and a rectangular plate has been investigated in terms of the energy transfer between the beams and the plate when a force is applied to one of the beams. This configuration, which is a mixture of stiff and flexible elements, is a particularly important example in the industrial area, as it is widely used. A modal model based on interface basis functions is used. A wave model, which is an approximate method, has also been developed in which the plate, acting as a wave impedance, is separately attached to each beam. Experimental studies have been carried out for validation. The investigation with respect to power flow and energy shows the validity of both models in the mid-frequency region. The results show that most energy is dissipated by the flexible plate. The physical phenomena and limitations of the wave method for this particular structural configuration are discussed. Even though it is an approximate method, the wave approach can describe the dynamic characteristics of the excited beam and the plate in terms of the ratios of power and energy of each component. The comparison of the two methods shows that the plate rather than the beams plays a crucial role in transferring the energy from the excited beam to the parallel opposite beam in the beam-framed structure when these two beams have identical properties, whereas the energy transfer is reduced when the beams have dissimilar properties