150,445 research outputs found
Porous Titanium surfaces to control bacteria growth: mechanical properties and sulfonated polyetheretherketone coating as antibiofounling approaches
Here, titanium porous substrates were fabricated by a space holder technique. The relationship between microstructural characteristics (pore equivalent diameter, mean free-path between pores, roughness and contact surface), mechanical properties (Young’s modulus, yield strength and dynamic micro-hardness) and bacterial behavior are discussed. The bacterial strains evaluated are often found on dental implants: Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. The colony-forming units increased with the size of the spacer for both types of studied strains. An antibiofouling synthetic coating based on a sulfonated polyetheretherketone polymer revealed an effective chemical surface modification for inhibiting MRSA adhesion and growth. These findings collectively suggest that porous titanium implants designed with a pore size of 100–200 µm can be considered most suitable, assuring the best biomechanical and bifunctional anti-bacterial properties.University of Seville VI Plan Propio de Investigación y Transferencia—US 2018, I.3A
A survey of partial differential equations in geometric design
YesComputer aided geometric design is an area
where the improvement of surface generation techniques
is an everlasting demand since faster and more accurate
geometric models are required. Traditional methods
for generating surfaces were initially mainly based
upon interpolation algorithms. Recently, partial differential
equations (PDE) were introduced as a valuable
tool for geometric modelling since they offer a number
of features from which these areas can benefit. This work
summarises the uses given to PDE surfaces as a surface
generation technique togethe
Automatic polishing process of plastic injection molds on a 5-axis milling center
The plastic injection mold manufacturing process includes polishing
operations when surface roughness is critical or mirror effect is required to
produce transparent parts. This polishing operation is mainly carried out
manually by skilled workers of subcontractor companies. In this paper, we
propose an automatic polishing technique on a 5-axis milling center in order to
use the same means of production from machining to polishing and reduce the
costs. We develop special algorithms to compute 5-axis cutter locations on
free-form cavities in order to imitate the skills of the workers. These are
based on both filling curves and trochoidal curves. The polishing force is
ensured by the compliance of the passive tool itself and set-up by calibration
between displacement and force based on a force sensor. The compliance of the
tool helps to avoid kinematical error effects on the part during 5-axis tool
movements. The effectiveness of the method in terms of the surface roughness
quality and the simplicity of implementation is shown through experiments on a
5-axis machining center with a rotary and tilt table
Multifunction tests of a frequency domain based flutter suppression system
The process is described of analysis, design, digital implementation, and subsonic testing of an active control flutter suppression system for a full span, free-to-roll wind tunnel model of an advanced fighter concept. The design technique uses a frequency domain representation of the plant and used optimization techniques to generate a robust multi input/multi output controller. During testing in a fixed-in-roll configuration, simultaneous suppression of both symmetric and antisymmetric flutter was successfully shown. For a free-to-roll configuration, symmetric flutter was suppressed to the limit of the tunnel test envelope. During aggressive rolling maneuvers above the open-loop flutter boundary, simultaneous flutter suppression and maneuver load control were demonstrated. Finally, the flutter damping controller was reoptimized overnight during the test using combined experimental and analytical frequency domain data, resulting in improved stability robustness
Air Entrainment in Dynamic Wetting: Knudsen Effects and the Influence of Ambient Air Pressure
Recent experiments on coating flows and liquid drop impact both demonstrate
that wetting failures caused by air entrainment can be suppressed by reducing
the ambient gas pressure. Here, it is shown that non-equilibrium effects in the
gas can account for this behaviour, with ambient pressure reductions increasing
the gas' mean free path and hence the Knudsen number . These effects first
manifest themselves through Maxwell slip at the gas' boundaries so that for
sufficiently small they can be incorporated into a continuum model for
dynamic wetting flows. The resulting mathematical model contains flow
structures on the nano-, micro- and milli-metre scales and is implemented into
a computational platform developed specifically for such multiscale phenomena.
The coating flow geometry is used to show that for a fixed gas-liquid-solid
system (a) the increased Maxwell slip at reduced pressures can substantially
delay air entrainment, i.e. increase the `maximum speed of wetting', (b)
unbounded maximum speeds are obtained as the pressure is reduced only when slip
at the gas-liquid interface is allowed for and (c) the observed behaviour can
be rationalised by studying the dynamics of the gas film in front of the moving
contact line. A direct comparison to experimental results obtained in the
dip-coating process shows that the model recovers most trends but does not
accurately predict some of the high viscosity data at reduced pressures. This
discrepancy occurs because the gas flow enters the `transition regime', so that
more complex descriptions of its non-equilibrium nature are required. Finally,
by collapsing onto a master curve experimental data obtained for drop impact in
a reduced pressure gas, it is shown that the same physical mechanisms are also
likely to govern splash suppression phenomena.Comment: Accepted for publication in the Journal of Fluid Mechanic
Key Challenges and Opportunities in Hull Form Design Optimisation for Marine and Offshore Applications
New environmental regulations and volatile fuel
prices have resulted in an ever-increasing need for reduction
in carbon emission and fuel consumption. Designs of marine
and offshore vessels are more demanding with complex
operating requirements and oil and gas exploration
venturing into deeper waters and hasher environments.
Combinations of these factors have led to the need to
optimise the design of the hull for the marine and offshore
industry. The contribution of this paper is threefold. Firstly,
the paper provides a comprehensive review of the state-ofthe-
art techniques in hull form design. Specifically, it
analyses geometry modelling, shape transformation,
optimisation and performance evaluation. Strengths and
weaknesses of existing solutions are also discussed.
Secondly, key challenges of hull form optimisation specific
to the design of marine and offshore vessels are identified
and analysed. Thirdly, future trends in performing hull
form design optimisation are investigated and possible
solutions proposed. A case study on the design optimisation
of bulbous bow for passenger ferry vessel to reduce wavemaking
resistance is presented using NAPA software.
Lastly, main issues and challenges are discussed to stimulate
further ideas on future developments in this area, including
the use of parallel computing and machine intelligence
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