SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday, December 31, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Combustion of Methane Hydrates

Dr. Tali Bar-Kohany

NRCN

Gas-hydrates are ice-like crystalline solids, consisting of non-stoichiometric compounds of water cavities and guest gas molecules. At high pressures and low temperatures, different gases fill the cavities within the ice preventing hydrogen-bond strain and breakage.

Deep-ocean gas-hydrates, mainly methane, occur naturally along the edge of continental shelves, represent an enormous and tempting repository of fuel which might compare with or exceed the available energy from more conventional fossil fuels. Moreover, methane hydrates, is free of hazardous pollutants such as sulfur that may be found at conventional fossil fuels. Thus, utilizing this kind of energy is tempting, especially, if this could be done, in-situ. For example, if burning these gas-hydrates in high-pressure, following by sequestering the carbon-dioxide in the deep-ocean environment, could be done.

In the present seminar, a solution for the transient vaporization and quasi-steady combustion of methane-hydrate in a diffusion-controlled spherically symmetric, three-phase particle will be presented. A single, isolated particle is an ideal representation of the physical processes that the particle undergoes in a dilute region of a spray or any bulk.

Short Bio

Tali Bar-Kohany received her mechanical engineering degrees from the University of Ben-Gurion (Ph.D. 2004, A study of the mechanism of sprays formation by bi-component liquid flashing). She won the WOLF award for outstanding Master achievements in 2000 and the Kazir scholarship by the ministry of defense in 2004, and since then she is employed at the nuclear research center of the Negev. In 2010 she received an honorary fellowship from the Australian institute of high energetic materials. During 2013-2014 she spent a Sabbatical at the University of California, Irvine, working with Professors W.A. Sirignano and D.Dunn-Rankin on the subject of combustion of methane-hydrates, which will be the topic of her talk.

School of Mechanical Engineering Seminar
Wednesday, December 31, 2014 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Semi-Active Shape Control of a Hydraulic Micro Catheter

using Electrostatic Actuators

Meytal Gershkovich

MSc Student of Dr. Gabor Kosa and Prof. Slava Krylov

There is a significant interest in developing small, at the scale of several microns up to several millimeters, flexible catheter-type actuators able to perform complex spatial motions in a controllable way. This interest is motivated primarily by medical applications such as endoscopy, minimally invasive surgery and micro robotics. Existing tools are mechanically actuated by cables and are characterized by small number of degrees of freedom while an ability of their further miniaturization probably reached its limit.  Although several devices were reported based on shape memory alloys or electroactive polymers, actuation remains probably the main challenge in these types of systems mainly due to small forces developed by micro actuators which are typically not sufficient for direct shape control of the tool. Hydraulic/pneumatic actuation distinguished by relatively high forces represents an attractive alternative. However, shape control of hydraulic actuators is difficult and requires multiple pressure channels to be delivered to the tool.

In this seminar we present the new operational principle, modeling and design of a simple large stroke high force hydraulic actuator, which is able to perform complex spatial motions while operated by only one pressure channel. The approach is based on the active changing of the structure’s bending stiffness by varying the effective properties of the catheter’s section. The device is built as a flexible tube with a pressurized internal volume. Flexible cantilever-type electrodes made of a material much stiffer than that of the tube are located on the outer surface of the tube. The electrodes can be in two digital states ON and OFF. In an initial unactuated OFF state the electrodes are detached from the tube and do not contribute to its effective bending stiffness.  By means of electrostatic actuation the cantilevers are selectively attached to the tube’s surface resulting in an increase of its effective bending stiffness in a desired non-symmetric way.  The combination of the mentioned effect with the inner pressure inside the tube creates the bending of the actuator. By strategically actuating the electrodes at different locations on the tube, complex three dimensional curves of the catheter can be achieved. We present the electromechanical model of the devices, demonstrate its functionality using the model and evaluate possible design parameters and expected performance of the tool.  We find the possible combinations of the electrodes which should be actuated to provide a required shape of the catheter. Finally we demonstrate how the actuator can follow a path of an arbitrary function.