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2 PROJECT PARTICIPANTS
Concerning the semi-active damper, the following partners are involved in the project;
Industrial representatives:
• Maurer Soehne GmbH & Co KG as bridge equipment manufacturer
• Bilfinger + Berger AG as construction company
• Thales Underwater System as a designer / manufacturer of electronic and acoustic underwater
equipment
Universities:
• KTH Polymerteknologi, largest technical university of Sweden, for the development of MR fluids
and materials to be used in the manufacturing of the MR dampers.
• Universita di Roma 3, for the development of mathematical control algorithms, analytical and
numerical modelling of device behaviour
Private research institutions:
• ISMES, a contract research organisation, performs tests on MR devices
• ENEA, the Italian National Agency for New Technologies, Energy and Environment, is entrusted
with the development and validation of numerical models of the devices.
• ENEL, one of the world's largest utilities companies, is involved in the numerical modelling of
structures and mock-ups as well as in dynamic analysis.
3 MAGNETORHEOLOGICAL DAMPERS
Energy dissipation is a very important measure to mitigate the action of earthquakes, wind and other
vibrations on structures. However, passive devices are designed on the base of clearly defined
parameters regarding load, velocity etc. As soon as the occurring real event deviates from the designevent,
the efficiency of the installed passive devices is diminished.
Semi-active devices have the capability to modify their stiffness and/or damping characteristics and
adapt their response behaviour to the real event. That means for every single event, the energy
dissipation can be optimised and the damper can be adapted to different excitations.
The essential characteristic of controllable fluids is their ability to change within milliseconds from a
free-flowing, linear viscous fluid to a semisolid with a controllable yield strength when exposed to an
electric (ER fluids) or magnetic (MR fluids) field. From today's point of view, the use of
magnetorheological fluids has the following advantages over electrorheological fluids:
• MR fluids are not sensitive to impurities which can arise from manufacturing and usage
• MR fluids can be mixed with a wide choice of additives to enhance stability, seal life etc.
» MR fluids have a maximum yield stress of up to 100 kPa (ER fluids: 3-3,5 kPa)
» MR fluids can operate at temperatures from - 40°C to + 150°C with only slight variations in yield
stress
On the other hand, the employment of MR fluids makes it necessary to overcome the following
obstacles:
» The generation of an evenly distributed magnetic field is more complicate than the generation of an
electric field
• The occurring effects of sedimentation are much stronger in case of MR-fluids than in ER-fluids.