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Table 1 Buildings currently under construction employing semi-active hydraulic dampers
Name
Stones
Height (m)
# of Semi- active
Dampers
Completion Date
Chuden Gifu Building
Niigata B-prqject
Siodome M-Building
Siodome N-Building
Siodome K-Tower
Roppongi Tower
Siodome T-Building
S-Hotel
H-Building
11
31
25
28
38
54
19
30
23
56
140.5
119.9
136.6
172
241.4
98.9
104.9
100.4
42
72
38
60
88
356
27
66
28
March 2001
December 2002
January 2003
March 2003
April 2003
May 2003
May 2003
December 2004
August 2004
lable yield strength in milliseconds when exposed to an electric (for ER fluids) or magnetic (for MR fluids)
field. In the absence of an applied field, these fluids flow freely and can be modelled as Newtonian.
When the field is applied, a Bingham plastic model (Shames and Cozzarelli 1992) is often used to
describe the fluid behavior.
Although the discovery of both ER and MR fluids
Electric or Magnetic Choke
dates back to the late 1940's (Rabinow 1948; Winslow
1947, 1949), for many years, research programs
Controllable Fluid
concentrated primarily on ER fluids. Nevertheless, X Jlpssi M
some obstacles remain in the development of commercially
feasible damping devices using ER fluids.
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;••»,» -w» ** * _1
1
For example, the best ER fluids currently available
1
have a yield stress of only 3.0 to 3.5 kPa and cannot Figure 12. Schematic of controllable fluid damper
tolerate common impurities (e.g., water) that might
be introduced during manufacturing or use. In addition, safety, availability and cost of the high voltage
(e.g., -4000V) power supplies required to control the ER fluids need to be addressed.
Recently developed MR fluids appear to be an attractive alternative to ER fluids for use in controllable
fluid dampers (Carlson 1994; Carlson and Weiss 1994; Carlson et al. 1995a,b) (see also: http://
www.rheonetic.com/). MR fluids typically consist of micron-sized, magnetically polarizable particles
dispersed in a carrier medium such as mineral or silicone oil. Carlson and Weiss (1994) indicate that the
achievable yield stress of an MR fluid is an order of magnitude greater than its ER counterpart and that
MR fluids can operate at temperatures from -40 to 150°C with only modest variations in the yield
stress. Moreover, MR fluids are not sensitive to impurities such as are commonly encountered during
manufacturing and usage, and little particle/carrier fluid separation takes place in MR fluids under common
flow conditions. The size, shape and performance of a given device is determined by a combination
of T> and T^id) . The design equations for most controllable damper geometries indicate that
minimizing the ratio V t^eid) is desirable. This ratio for MR fluids ( V 1^) = 5xicr n sec/Pa) is
three orders of magnitude smaller than the corresponding ratio for today's best ER fluids. Thus, controllable
devices using MR fluids have the potential of being much smaller than ER devices with similar
capabilities. Further, the MR fluid can be readily controlled with a low power (e g. 9 less than 50 watts),
low voltage (e.g., -12-24V), current-driven power supply ourpurting only -1-2 amps. Such power lev-