Taming the Quake’s Shakes
Using Magnetorheological Fluids for
Structural Support of Seismic Mitigation

Kyle Downum

Magnetorheological fluids, or MR fluids, are liquids that harden or change shape when subjected to a magnetic field. MR fluids are currently used in shock absorbers of racecars and other sports cars. Although this is their only current commercial use, research is continuing on other applications from stabilizing rocket launches to stabilizing washing machines. These fluids might also be used in stabilizing building structures during extreme conditions such as hurricanes and earthquakes. The purpose of this experiment is to determine if magnetorheological fluids can be used to help stabilize buildings during simulated earthquake activity. It is hypothesized that the properties of MR fluid will improve stability of structures during such simulation. The procedures were as follows: MR fluids were manufactured and placed in an electromagnetic damper. The dampers were attached to the base of the structure with a water container on top. The structure was placed on a waterbed to simulate seismic activity. A weight was dropped from a height of 30 cm. The height of the water splash in the water container was measured immediately indicating the amount of vibration. The process was repeated with 1, 2, 3, and 4 dampers activated. The average height the water splashed when no dampers were used was 31 mm, with one damper, the splash reached 18 mm; with two dampers, 15 mm; three dampers, 13.6 mm; and all four dampers, 10.5 mm. The addition of a single damper significantly decreased the amount of vibration at each trial. It has been concluded that the attachment of active MR dampers increased the stability of the structure. As the number of dampers used increased, the mean height of the splash decreased as did the standard deviation. Future studies would include perfecting the damper model. A better technical design for the dampers should further increase the stability of the structure.

Racecar drivers know the value of a well-tuned set of shock absorbers. Rally car drivers, for instance, leave their shocks soft so all their tires will be on the road at all times, no matter how bad the bumps and potholes get. Formula-one drivers, on the other hand, like to keep their shocks tight, allowing their chassis to stay just a few millimeters off the pavement without ever touching. Wouldn’t it be nice if a driver could just change the shocks while on the go, making them soft and mushy for country roads and tight for city driving? Thanks to an extremely unusual fluid, it already can be done. These fluids are called magnetorheological fluids – or MR fluids for short.
MR fluids are liquids that harden or change shape when subjected to a magnetic field and behave like any fine motor oil when left alone. MR fluids are easily made by simply combining a fine oil, such as cooking or motor oil, with some powdered iron filing. In the presence of a magnetic field, all of the iron particles within the MR fluid line up and get organized. That makes the fluid increasingly stiff. Under a strong enough magnetic field, it can achieve the same consistency as cold peanut butter (1).
Today the only commercialized use of MR fluids are in shock absorbers. The Lord Corporation, the only current commercialized manufacturer of MR fluids, built shock absorbers that are utilized in the new 2002 Corvette. Systems with MR fluids can respond instantly and controllably to varying levels of vibration, shock or motion, says Lord Corporation (2). By analyzing the signals from motion sensors, the computer in the Corvette can decide instantly how firm the shock absorbers should be (3).
Although MR fluids only have the one commercial use, space engineers sometimes use the updated shock absorbers to suppress vibrations during rocket launches. Astronauts are also studying MR fluids because they might one day “flow in the veins of robots, making the robot’s joints as nimble as any human’s (4).” Some future planes for interplanetary exploration for this fluid are, controlling the movement of remote controlled space suits, smoothing bumps of space station docking, preventing the buckling of delicate solar arrays when probe or satellite emerges from an eclipse, regulating oxygen flow within space stations, reducing stress caused by responding satellites, and creating molds that can be reconfigured to manufacture different machine parts in a pinch (5).
These fluids are remarkably versatile. “Altering the attraction by increasing or decreasing the strength of the applied field, permits continual control of the rheological properties of the MR Fluid (6).” MR Fluids are not highly sensitive to moisture or other contaminates that might be encountered during manufacture and use, which makes them perfect for shock absorbers and dampers because there is little chance of failure.
Another possible application of the MR fluid absorbers lies in the design of buildings and structures in areas threatened by earthquakes or high winds. Civil engineers in the construction industry are incorporating Lord’s MR technology into the structural engineering of buildings and bridges. The system is relatively inexpensive, needs little maintenance and requires very little power to operate. A damping system utilizing MR fluid dampers works similarly to an automotive shock absorber. “Engineers hope these high tech shocks may save buildings from getting damaged by major earthquakes and hurricane strength winds (7).”
The purpose of this experiment is to determine if magenetorheological fluids can be used to help stabilize buildings during simulated earthquake activity. It is hypothesized that the properties of MR fluid will improve stability of structures during such simulation.

Materials

Powdered iron
Cooking oil
9v battery
Alligator clips
Copper wiring
Foam board
Balsa wood
Waterbed
200g weight
Cooking oil
Powdered iron
Gloves
Eye protection
Tubing
Water
Graduated cylinder
Food coloring
Black permanent marker
Hot Glue
Meter stick
Rubber stopper
Velcro
Newsprint paper strips


Procedures

1. Make MR fluid (1ml oil / 6.8g of iron filling).
   

1. Pour 10 ml of oil into plastic container.
   

1. Mix in 68 g of iron powder.
   

1. Stir.
   

1. Apply a strong magnet to the outside of container.
   

1. Drain off excess fluids.
   

1. Construct electromagnet and MR damper.
   

1. Wrap insulated copper wire tightly and evenly around plastic tubing.
   
2. Fill tube with MR fluid and add stoppers to each end. Attach alligator clips to each end of electromagnet. To activate, attach the other ends to a 9-volt battery.
   

1. Construct building structure, 60 cm x 14 cm x 14 cm.
   

1. Building should have four levels equally spaced to model a four-story structure.
   
2. The sides of structure are made 2 strips of balsa wood and the floors are 14 cm x 14 cm foam board.
   

1. Attach dampers with “twisty ties” to balsa strips at the corners of the bottom story of structure. Dampers should fit snugly under the “first floor”.
   

1. Attach with Velcro a graduated cylinder filled with 20 mL of colored water to the top of the structure to measure splash height during simulation.
   

1. Stand a strip of newsprint paper inside the graduated cylinder to record the height of the splash. Secure with a strip of tape across the top.
   

1. Drop weight from a height of 30 cm 10 times with no MR dampers activated.
   

1. After motion has stopped, immediately remove newsprint and measure how high the water was absorbed. Record data.
   

1. Repeat steps 6-8 with 1, 2, 3, and 4 MR dampers activated.
   

Table 1. Vibration Levels with Varying Numbers of Active Dampers

Table 2. Statistical Analysis Comparing the Mean Splash Height for Different Numbers of Active Dampers

Results

The data clearly shows that the attachment of running MR dampers increased the stability of the structure (see Table 1 and Graph 1). As the number of dampers activated increased, the height of the splash decreased. The height of the splash was reduced by almost half with the simple activation of one MR damper. The mean height fell from 31.5 mm with no active dampers to 10.5 mm with four active dampers. The activation of additional dampers also decreased the variability of the splash. The standard deviation decreased from 7.13 with no dampers activated to 1.96 with all four dampers activated. This data supports the hypothesis of this experiment. The decrease in mean height and variability of the splash that were used to measure the vibration level indicate that the MR dampers were absorbing the simulated seismic activity.

Conclusion and Discussion

With the statistical analysis, the means of the different data sets were compared to assess the evidence that any differences are not due to chance. A p-value of less than 0.05 would offer extremely strong evidence that the first mean is greater than the second. In terms of this experiment, the activation of each damper resulted in a reduction of structural vibration as indicated by a decrease in splash height. The mean height decreased significantly with the activation of each new damper as the results of two-sample t-tests indicate. The extremely small p-values resulting when comparing the mean splash height after activating additional MR dampers give strong statistical evidence that the properties of the MR fluids do aid in adding structural support to the building during seismic simulation.
Future studies would include perfecting the damper model. A better technical design for the dampers following the design of a shock absorber might further increase the stability of the structure. The MR fluid constructed for this experiment was also lacking a third, patented ingredient. The omission of this third ingredient is minor for this experiment because the ingredient does not allow the iron particles to be affected by gravity. Without the third ingredient the MR fluid (if allowed to set) would eventually separate out between the oil and iron.

1. Carlson, D. (2002). Magnetorheological Fluid Damping. Retrieved 9/24/02, from News: http://www.sensorsmag.com/articles/
   

1. (2002). Applications, seismic and wind mitigations. Retrieved 9/24/02 from, Dampers: http://www.rheonet.com/seismic_mitigtion.htm
   

1. (2002). MR technology at UNR. Retrieved 9/23/02 from Education Coe web: http://coeweb.engr.unr.edu/ciml/mt2.html
   

1. (2002). MR Fluid. Retrieved 9/23/02 from MR Fluids:
   

1. (2002). Magneto rheological fluid. Retrieved 9/23/02 from amazing Fluids: http//personal.Redestb.es/mascum/mrhtml
   

1. (2002). Full-scale 20 ton seismimagnetoreological damper. Retrieved 9/23/02, from University of Notre Dame: http://wwww.nd.edu/~quake/ facilities/mrdamper.html
   

1. (2002). Golden Anniversary Edition Corvette sports lord corporate Rheonetic R MR fluid. Retrieved 9/20/02 from Lord corp. http://www/rheonetic.com.
   

Acknowledgements

I would like to thank the following people for help or support in completing this science fair project.

Pam Benne
Mom
Pam Chaney
Teri Rogers
Mrs. Benne's Physics Class