Sangarapillai Kanapathipillai

Engineering students' understanding of the role of experimentation

Resource constraints have forced engineering schools to reduce laboratory provisions in undergraduate courses. In many instances hands-on experimentation has been replaced by demonstrations or computer simulations. Many engineering educators have cautioned against replacing experiments with simulations on the basis that this will lead to a misunderstanding of the role of experimentation in engineering practice. However, little is known about how students conceptualize the role of experimentation in developing engineering understanding. This study is based on interviews with third-year mechanical engineering students. Findings are presented on their perceptions in relation to the role of experimentation in developing engineering knowledge and practice.

Stretch‐dependent changes in surface profiles of the human crystalline lens during accommodation: A finite element study

A non‐linear isotropic finite element (FE) model of a 29‐year‐old human crystalline lens was constructed to study the effects of various geometrical parameters on lens accommodation.

Effects of a porous jacket on sound radiated from a pipe

Conventional pipe laggings incorporate a porous jacket and an impervious outer cladding sheet. It has been observed during investigations of such pipe laggings that a simple porous jacket applied by itself to a pipe can actually increase the sound radiated. Reasons for this phenomenon are discussed. The effect of a rigid frame porous jacket around a pipe is examined theoretically for the breathing, bending, and ovalling modes of pipe vibration. The predicted insertion loss associated with the bending mode of pipe vibration is compared with the corresponding experimental result and some of the results of a parametric study are given.

Sound Transmission Loss of a Panel Backed by a Small Enclosure

Sound transmission loss (STL) tests of acoustic insulation panels are commonly performed in large reverberation rooms. Large size rooms are required by acoustic standards to ensure that a large number of modes can be excited in the frequency range of interest, to create a diffuse sound field. However for STL measurements in low frequency range small enclosures should be able to provide adequate homogenous sound fields, namely ‘pressure sound fields’. The expected effect of the air sealed in an enclosure backing a panel, is to increase the stiffness of the panel artificially raising the first natural frequency of the panel, which corresponds to a minimum value in the STL spectrum. In this paper the influence of the air cavitys added stiffness on the panel STL is investigated in detail. As expected the effect of the sealed air is to increase the plate stiffness and as a result to increase the frequency of its first natural mode, however the effect on the STL in this frequency region is unexpectedly insignificant which removes the need for correcting STL measurements using small enclosures in low frequency range-around their first natural frequency of the panels.

The sound of urgency : understanding noise in the emergency department

Hospital noise is a worldwide issue, with detrimental effects on health and healing. The busy emergency department (ED) typically generates excess noise. Few studies have investigated noise levels within the Australian ED. This study examines noise in this setting, in turn suggesting how noise levels may be reduced. Noise level measurements occurred in 4 locations within the ED during peak staff and patient flow times over selected 7-hour periods. These were compared to the available standards and guidelines and supplemented by regular staff surveys documenting perceived noise. Findings indicated that all 4 locations exceeded the maximum recommended levels by up to 20 dB. Staff perception surveys suggested that most noise was created by people (conversations). Reducing noise in the ED may be achieved by (1) decreasing the generation of noise and (2) reviewing building layout and introducing physical noise controls such as noise-absorbing ceiling tiles and acoustic barriers/curtains.

Submarine structural and acoustic attenuation

In this paper, the low frequency vibro-acoustic responses from a submerged hull are attenuated using passive, active, and hybrid control strategies. An analytical model representing a simplified physical model of a submarine hull is developed, including the effects of ring-stiffeners, bulkheads, and external fluid loading. At low frequencies, rotation of the propeller results in discrete tones at the blade passing frequency and its harmonics. The fluctuating forces at the propeller are transmitted through the propulsion system, resulting in excitation of the low frequency hull vibrational modes, which in turn results in a high level of structure-borne radiated noise. In this work tuned vibration absorbers, active vibration control, and hybrid vibration absorbers are used to attenuate the breathing and bending modes of the submerged hull. The control performance of a hybrid vibration absorber is compared to the attenuation achieved using a passive absorber and the control performance of a fully active system. Results show that implementation of the hybrid vibration absorber results in significant attenuation of the structural and acoustic responses of the hull. The hybrid vibration absorber also requires a control force of lower magnitude compared with a fully active control system.

Determining the optomechanical properties of accommodating gel for lens refilling surgery using finite element analysis and numerical ray-Tracing

A key step in the design of an accommodating gel to replace the natural contents of the presbyopic human crystalline lens is to find the equivalent homogeneous mechanical and material properties of the gel that yield comparable optical response as the lens with gradient properties. This process is compounded by the interplay between the mechanical and optical gradient. In order to find uniform properties of the lens both gradients need to be considered. In this paper, numerical ray-tracing and finite element method (FEM) are implemented to investigate the effects of varying the uniform elasticity and refractive index on the accommodative amplitude. Our results show that the accommodative amplitude be expressed as a function of gel refractive index and Youngs modulus of elasticity. In other words infinite sets of elasticity and refractive index exist that yield a certain amount of accommodation.

Finite element study on the effects of GRIN order on the accommodative response of the human crystalline lens

The gradient refractive-index (GRIN) inside the crystalline lens has been described using a number of functions. One of the most widely used functions for this purpose is the polynomial. Changing the order of the GRIN polynomials alters the relative refractive index profile across (radially) and along (axially) the lens. In this paper, numerical methods are used to investigate the effects of varying GRIN polynomial order on the accommodative response of the lens; in particular, accommodative amplitude. Our results suggest that the GRIN order does not have a significant influence on the accommodation amplitude.

Finite element analysis of notched bars subjected to elastic-plastic deformation

For many years engineers and scientists have speculated about the relationship between the load carrying capacity of notched bars and their stress concentration factors. However, past attempts to quantify this relationship have failed and the problem remains largely unresolved. This study strongly supports the view that this relationship exists, and that there are correlations between load carrying capacity and stress concentration for notched bars subjected to tension. The study was done with the use of computer aided technology and finite element analysis, which allowed for more rigorous testing procedures when compared with conventional tensile testing methods. Two studies were conducted: firstly, an analysis which assumed perfectly elastic conditions, and secondly, an analysis which assumed realistic elastic-plastic conditions. Variables of interest included maximum strain energy density, plastic collapse load, elastic stress concentration factor, elastic-plastic stress concentration factor, root radius and the distance between the notch surface to the maximum load. It was found that these variables correlate to one another and that most of them are dependent on material properties. Both linear and non-linear relationships were found. Linear relationships were quantifiable and were represented by equations. Equations for most of the non-linear relationships could not be substantiated, as there were not enough data points present.

Estimating the insertion losses of simple pipe laggings

A procedure for estimating the insertion losses produced by simple pipe laggings formed of either a porous jacket alone or a porous jacket covered by an impervious jacket is presented. The procedure is based on a model involving an infinitely long pipe, which is supporting various types of structural waves. It is pointed out why the bending type of structural wave is often of particular importance. Data that enables the insertion loss produced by laggings for the bending type of structural wave in the lagged pipe is given in a dimensionless form. An example of how this data can be used to predict the insertion loss produced by a typical lagging applied to a typical pipe is given.