2,294 research outputs found
Generator Power Optimisation for a More-Electric Aircraft by Use of a Virtual Iron Bird
A prodedure is developed to minimise the generator design power within the electric power system of a future more-/ all-electric aircraft. This allows to save weight on the generators and on other equipment of the electic power system. Execution of the optimisation procedure by hand demonstrates the complexity of the problem. An automation of the process shows the capabilities of integrated modelling, simulation and optimisation tools
Modelling of Elastic Gearboxes Using a Generalized Gear Contact Model
The object of this paper is to present an universal
model that describes the gear contact between two
gears in a planar environment. The model includes
elastic effects between the gear wheels. Using this
model it is possible to create arbitrary spur gear connections
as well as all kinds of epicyclic gearing
configurations by supplying the proper external constraints.
The presented model is implementated in the
Modelica language and Dymola is used for the simulations
Modelling of high temperature storage systems for latent heat
There is a huge demand for heat storages for evaporation
applications. Thermal storage systems are
used to increase the efficiency of thermal systems by
an improved adaption of energy availability and energy
demand.
In this paper a possible solution for modular storage
systems from 200-600 °C and pressures up to 100
bar is presented. The application of steam as a working
medium requires the availability of isothermal
storage if charging/discharging should take place at
almost constant pressure. The saturation temperature
range is between 200°C and 320°C. Therefore nitrate
salts are used as phase change material (PCM). The
solution developed at DLR is characterized by a
modular concept of tube register storages surrounded
by both sensible and latent heat storage material.
The focus in this paper is on modelling of the PCM
storage. A model is introduced for melting and freezing
of the PCM. To perform with an acceptable heat
transfer rate inside the PCM, fins are used to increase
the overall thermal conductivity. Instead introducing
mean storage material parameters, like thermal conductivity
or specific heat capacity, the geometry of
the finned tube is modelled by using discrete elements.
Therefore the model allows detailed studies
on heat transfer during space and time. The fin design
can be varied in order to find an optimal configuration.
A set of partial differential equations is
created and solved. When considering a stand alone
system, that means tube, fin and PCM, without a
connection to other components, investigation is
quite effective. In case of the PCM storage there is
the big advantage, compared with a sensible regenerator,
that the almost constant fluid temperature,
when evaporating or condensing, leads to a uniform
temperature distribution in fluid flow direction.
Therefore only a very rough discretisation in axial
direction is needed, what even allows bonding with
other components e.g. from the Modelica Fluid Library.
Sensible storages as they are used for preheating and
superheating have a characteristic temperature gradient
in axial direction. To describe their thermal behaviour
concentrated models, using dimensionless
numbers, are used
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