Mechanical & Manufacturing Eng (Scholarly Publications)
http://hdl.handle.net/2262/208
Mechanical & Manufacturing Eng (Scholarly Publications)20151126T17:49:29ZInvestigation on parametrically excited motions of point absorbers in regular waves.
http://hdl.handle.net/2262/74878
Investigation on parametrically excited motions of point absorbers in regular waves.
MESKELL, CRAIG
Free
floating objects such as a self

reacting wave energy converter (WEC), may experience a
condition known as parametric resonance. In this situation, at least two degrees of freedom
become coupl
ed when the incident wave has a frequency approximately twice the pitch or
roll natural frequency. This can result in very large amplitude motion in pitch and/or roll.
While classic linear theory has proven sufficient for describing small motions due to sm
all
amplitude waves, a point absorber WEC is often designed to operate in resonant conditions,
and therefore, exhibits significant nonlinear responses. In this paper, a time

domain
nonlinear numerical model is presented for describing the dynamic stability
of point
absorbers. The pressure of the incident wave is integrated over the instantaneous wetted
surface to obtain the nonlinear Froude

Krylov excitation force and the nonlinear hydrostatic
restoring forces, while first order diffraction

radiation forces
are computed by a linear
potential flow formulation.
A numerical benchmark study for the simulation of parametr
ic
resonance of a specific WEC

the Wavebob

has been implemented and validated against
experimental results. The implemented model has shown
good accuracy in reproducing
both the onset and steady state response of parametric resonance. Limits of stability were
numerically computed showing the instability regions in the roll and pitch modes
PUBLISHED
20160101T00:00:00ZThe Influence of the Magnitude of Gravitational Acceleration on the Marangoni Convection about an Isolated Bubble under a Heated Wall
http://hdl.handle.net/2262/74812
The Influence of the Magnitude of Gravitational Acceleration on the Marangoni Convection about an Isolated Bubble under a Heated Wall
ROBINSON, ANTHONY; O'SHAUGHNESSY, SEAMUS
Thermocapillary or Marangoni convection is the liquid motion caused by surface tension variation in the presence of
a temperature gradient along a gas–liquid or vapor–liquid interface. This work numerically investigates the effect of the
magnitude of gravitational acceleration on the flow and temperature fields resulting from the presence of a hemispherical
air bubble of constant radius of 1.0 mm, situated on a heated wall immersed in a liquid silicone oil layer of constant depth of
5.0 mm. The model is oriented such that the Marangoni and gravitational forces act to oppose one another. To elucidate the
effect of gravity on Marangoni flow and heat transfer, the simulations were carried out for a silicone oil of Prandtl number
83, at a Marangoni number of 915. The gravity levels tested were 0
g
, 0.01
g
, 0.1
g
, 0.25
g
, 0.5
g
, 0.75
g
, and 1
g
,where
g
represents the earth gravitational acceleration of 9.81 m/s. The influence of the magnitude of gravitational acceleration on
the velocity profile along the bubble interface and on the location of maximum velocity was analyzed. It was found that the
gravity level affects the velocity profile by influencing the interfacial temperature gradient, but that the location of maximum
velocity was almost independent of gravity level. The increase in heat flux on the wall to which the bubble is attached was
calculated and it has been determined that local heat transfer enhancement of up to nearly 1.7 times that of the conduction
only case can be achieved for the parameter range tested. Furthermore, local enhancement was observed to occur up to a
distance of seven bubble radii for the zerogravity case, but increased gravity levels cause a reduction in the effective radius
of enhancement. The influence of the Marangoni flow on the heat transfer for the opposite wall has also been analyzed
PUBLISHED
20090101T00:00:00ZNumerical investigation of bubbleinduced marangoni convection
http://hdl.handle.net/2262/74811
Numerical investigation of bubbleinduced marangoni convection
O'SHAUGHNESSY, SEAMUS
The liquid motion induced by surface tension variation, termed the thermocapillary
or Marangoni effect, and its contribution to boiling heat transfer has long been a very
controversial issue. In the past this convection was not the subject of much attention
because, under terrestrial conditions, it is superimposed by the strong buoyancy convec
tion, which makes it difficult to obtain quantitative experimental results. The scenario
under consideration in this paper may be applicable to the analysis of boiling heat
transfer, specifically the bubble waiting period and, possibly, the bubble growth period.
To elucidate the influence of Marangoni convection on local heat transfer, this work
numerically investigates the presence of a hemispherical bubble of constant radius,
R
b
=
1.0 mm, situated on a heated wall immersed in a liquid silicone oil (
Pr
=
82.5)
layer of constant depth
H
=
5.0 mm. A comprehensive description of the flow driven by
surface tension gradients along the liquid–vapor interface required the solution of the
nonlinear equations of freesurface hydrodynamics. For this problem, the procedure in
volved solution of the coupled equations of fluid mechanics and heat transfer using the
finitedifference numerical technique. Simulations were carried out under zerogravity
conditions for temperatures of 50, 40, 30, 20, 10, and 1 K, corresponding to Marangoni
numbers of 915, 732, 550, 366, 183, and 18.3, respectively. The predicted thermal and flow
fields have been used to describe the enhancement of the heat transfer as a result of
thermocapillary convection around a stationary bubble maintained on a heated surface.
It was found that the heat transfer enhancement, as quantified by both the radius of
enhancement and the ratio of Marangoni heat transfer to that of pure molecular dif
fusion, increases asymptotically with increasing Marangoni number. For the range of
Marangoni numbers tested, a 1.18fold improvement in the heat transfer was predicted
within the region of
R
b
≤
r
≤
7
R
b
PUBLISHED
20090101T00:00:00ZCharacterising the machining of biomedical grade polymers
http://hdl.handle.net/2262/74780
Characterising the machining of biomedical grade polymers
ALDWELL, BARRY
PUBLISHED
20140101T00:00:00Z