Johns Hopkins Whiting School of Engineering 1996 Annual Report [text version]

Whiting School of Engineering 1996 Annual Report

Mechanical Engineering
A Cold, Dark, and Dangerous Task? Send a Robot!
The Power of Pressure
Department Facts

A Cold, Dark, and Dangerous Task? Send a Robot!
Four miles down into the ocean it is pitch dark, the water temperature hovers just above freezing, and the ambient pressure of 9,000 PSI (pounds per square inch) is fatal to humans. Plus, some of the hydrothermal vents on the sea-floor are radioactive. “It’s a perfect environment for robots,” observes Assistant Professor Louis Whitcomb, who develops underwater robots for oceanographic research. Specifically, Whitcomb designs the hardware and algorithms that comprise the “brains” of these robots. The high-tech computer control systems enable scientists to remain in the safety and comfort of their surface ship while operating robots remotely on the sea floor.

Not surprisingly, scientists know more about the surface of the moon than about the Earth’s deep-ocean floors. Until recently, oceanographers could directly examine the ocean floor only as passengers in one of a few specially designed deep-ocean submarines. These expensive watercraft are tiny and can only carry a crew of two or three within their titanium pressure hulls. In addition, these vessels can operate only for approximately 12 hours under battery power and require a specially designed “mother ship” for surface support. These manned submersibles (such as the U.S. Alvin and Japanese Shinkai 6500) are considered national assets, and scientific demand far exceeds their availability.

An underwater robot like JASON, in contrast, can be deployed from any available surface ship and can operate indefinitely on the ocean floor. Prior to coming to Johns Hopkins, Whitcomb directed the control systems development for the underwater robots JASON and ARGO II at the Deep Submergence Laboratory of the Woods Hole Oceanographic Institution (WHOI). JASON links to the mother ship with a specially designed “umbilical” cable through which it receives both power and data. The cable up-links video images from JASON’s cameras in real-time to a control room on the mother ship, where they are viewed by a pilot who “flies” the vehicle remotely under joystick control. The commands from the remote pilot’s joysticks are down-linked in real-time over the cable to direct JASON’s position. Robotics researchers hope that the newest generation of underwater robots will enable unprecedented study of the world’s oceans. “We are developing robots for scientific applications to complement and extend, but not replace, the existing capabilities we have with manned submersibles,” Louis comments.

In 1994, Whitcomb oversaw the control systems during ARGO II’s first field-trial—a month-long oceanographic voyage that took the WHOI team to the Mid-Atlantic Ridge aboard the 2,000-ton mother ship R.V. Knorr. At 26’N 44’W, the team lowered ARGO II over two miles beneath the Knorr to investigate an active hydrothermal vent field on the ocean floor. Using cameras, sonars, and a variety of other scientific instruments, ARGO II snapped over 30,000 high-resolution computer-photographic images of an active hydrothermal vent field. Geologists are now using the data to unravel the mysteries of hydrothermal vent formation.

This past July, one of Whitcomb’s graduate students, Ralf Bachmayer, joined the WHOI team in another month-long voyage to the Mid-Atlantic Ridge. There the oceanographic team deployed both JASON and ARGO II on a single cruise.

While underwater robots hold potential for many applications in oceanographic research, any mention of these marvelous machines would be incomplete without acknowledging their unique ability to help clear the mists from historical events. Recently, JASON acted as eyes and hands for a team headed by explorer and scientist Dr. Robert Ballard that investigated the wreck of the Lusitania. The findings of Ballard and his group were chronicled by the National Geographic, which subsequently produced a videotape that dramatically demonstrated JASON’s capabilities in an extreme environment.

The Power of Pressure
We are all familiar with liquids. Water, blood, oils—all these impress upon our minds an essential fluidity, a tendency to flow rather than resist the application of a force. Yet, there are times when the liquids of our everyday experience can seem very tough indeed, as every beginning diver learns (the hard way!).

What determines the strength of liquids? This simple question is important because liquids literally grease the wheels of our mechanized civilization. The very common conditions of lubrication and wear constrain most of the cutting-edge technologies of today, from turbine engines to automobiles to the hard-disk spinning inside your desktop computer. And the strength of liquids is important in some areas that you may find surprising: in the working of knee joints, in the blood pumping through arteries, and in the formation of Arctic sea ice.

In a project funded by the National Science Foundation, Associate Professor K.T. Ramesh and graduate student Yongwei Zhang have been pushing liquids to extremes. They have studied the strength of liquids subjected to extremes of pressure and extremes of shear rate, such as one might find in a sliding fault several miles below the earth’s surface or between the gear teeth in a car’s transmission. The research team generates very high pressures, on the order of 100,000 atmospheres, by using a plate-impact experiment in the department’s Laboratory for Impact Dynamics and Rheology. In their investigation, Ramesh and Zhang measure the liquid strength by using laser interferometry during the impact, with a time resolution of one billionth of a second possibly the largest ratio of setup time to measurement duration in the engineering sciences. Because the experimental time is so short, tremendous pressures can be generated without the safety concerns that would normally accompany the storage of such large amounts of energy.

The results demonstrate that the strength of simple oils is a strong function of pressure. One material, which has the consistency of thin shampoo under normal conditions, has been shown to be stronger than pure aluminum at a pressure of 50,000 atmospheres! In addition, substantial changes to volume occur at these pressures. Zhang has shown that the observed compressibility of these liquids can be predicted using the known molecular structure. In future work, the researchers will study the influence of molecular shape on the strength and compressibility of simple liquids.

Established 1919
Mechanical engineering was one of the original disciplines taught in engineering, was renamed to mechanics, then included materials science. The department took its present name in 1985.

Phone 410-516-7132

Email mech_eng@jhu.edu

WWW http://www.jhu.edu/~mech/

Students
1995-96 Academic Year
Graduate: 58
Undergraduate: 85

Faculty and Researchers
William N. Sharpe, Jr., Chair
Gang Bao
Gregory S. Chirikjian
Andrew Conn
Andrew S. Douglas
Edwin R. Fitzgerald
Don P. Giddens
Kevin J. Hemker
Cila Herman
Joseph Katz
Omar M. Knio
Charles V. Meneveau
Hasan Ogüz
Andrea Prosperetti
K.T. Ramesh
Louis L. Whitcomb

Research Areas
Fluid Mechanics and Heat Transfer
Mechanics and Materials
Robotics and Electro-Mechanical Systems

Mechanical Engineering A Cold, Dark, and Dangerous Task? Send a Robot! The Power of Pressure Department Facts

Mechanical Engineering
A Cold, Dark, and Dangerous Task? Send a Robot!
The Power of Pressure
Department Facts