The added wave resistance of a ship computed
using the new model and compared to
experimental measurements.
Predicted sheet cavitation for a propeller
operating in an inhomogeneous wake field.
Atomistic simulations are performed to
study thermally driven nanopumps based on
carbon nanotubes. The study is performed in
collaboration with Uni. de Concepcion, Uni. Illinois
at Chicago and ETH Zurich. ACS Nano 2017, 11,
9997.
Ocean Wave 3D-Seakeeping an open source tool for wave-structure
interaction
For both economic and environmental reasons,
ships are generally sailing slower today than
they were designed to. Current trends in limiting
greenhouse gas and other emissions by
ships suggest that this trend will continue and
require new ships to be designed and optimized
for lower speeds. The energy required to move
the ship through the water is always the sum of
the calm-water resistance and the added resistance
due to wind and waves. At low-speed,
the added resistance can be as large, or even
larger than the calm-water resistance. Thus,
accurately predicting this quantity is of great
importance for ensuring safety and predicting
economic and environmental performance. The
goal of this project has been to produce an
accurate and efficient computational tool for
predicting ship response, and added resistance
in waves, using a high-order finite difference
method on overlapping grids. This open source
software is the product of Mostafa Amini
Afshar’s PhD project, followed by a two-year
post-doc project financed by the Danish Maritime
Analysis of Ship Propeller Cavitation Performance
Applied and fundamental fluid dynamics
Fund. The tool is being further developed
thanks to new funding granted jointly by the
Danish Martime Fund and the Orients Fund.
Cavitation or vaporization of water is a phase
change observed in high speed flows wherein
the local absolute pressure reaches the vicinity
of the vapor pressure at the ambient temperature.
This phenomenon is of vital importance in
ship propulsion because of the damage of metal
surfaces produced by vapor bubble collapse and
degradation of performance of lifting surfaces
with extensive cavitation. It is also a source of
vibration and high-frequency noise.The description
must fit into this box without changing the
format.
For years, the strategy by naval architects and
ship propeller designers was to avoid cavitation
as far as possible. But with the growth in ship
size and increasing demands to the performance
of the ships, the strategy has changed
into controlling the cavitation performance, i.e.
its growth and collapse over the blade when it
rotates in the wake field behind the ship. This
requires computer programs for propeller flow
analyses that combine high accuracy with high
computational speed to make it possible to
analyze the propeller in a design situation.
In this project, models for sheet and tip vortex
cavitation have been built into the propeller
panel code ESPPRO. Both partial and supercavitation
is included and successful comparisons
have been made with the results of other
methods, both experiments and numerical
methods. Both conventional propellers, including
high-skew propellers, and Kappel propellers
can be dealt with.
The work is the result of the PhD project and
later Postdoc project of Pelle Regener and the
PhD (industrial) project by Yasaman Mirsadraee.
The projects were partly supported by The Danish
Advanced Technology Foundation and by
DTU. The industrial PhD was done in cooperation
with MAN Diesel & Turbo.
A number of research projects are conducted
spanning multiple scales and discliplines to provide
insight into the complex motion of fluids.
Ongoing projects include the study of flow in
nano scale systems (see illustration), the flow
in multicellular sponges, combustion and fluid
flow in diesel engines, bluff body aerodynamics,
granular flow in sand casting processes,
multiscale simulations of flow in oil wells and
reservoirs, and the lubrication and cavitation in
journal bearings.
The projects are performed in collaboration with
Danish industry and national and international
research groups.
Contact:
Harry B. Bingham, e-mail: hbb@mek.dtu.dk
Mostafa Amini Afshar, e-mail: maaf@mek.dtu.dk
Contact:
Poul Andersen, e-mail: pa@mek.dtu.dk
Contact:
Jens Honore Walther, e-mail: jhw@mek.dtu.dk
Fluid Mechanics, coastal and maritime engineering 31