School of Mechanical Engineering Seminar
Monday, January 16, 2017at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Various aspects of coastal dynamics embedded in the observations of high-frequency radar-derived surface currents

Prof. Sung Yung Kim

                                    Department of Mechanical Engineering at Korea  

Abstract: The nearly completed U.S. West Coast (USWC) high-frequency radar (HFR) network provides an unprecedented capability to monitor and understand coastal ocean dynamics and phenomenology through hourly surface current measurements at up to 1 km resolution. The dynamics of the surface currents off the USWC are governed by tides, winds, Coriolis force, low-frequency pressure gradients (less than 0.4 cycles per day (cpd)), and nonlinear interactions of those forces. Alongshore surface currents show poleward propagating signals with phase speeds of O(10) and O(100 to 300) km/day and time scales of 2 to 3 weeks. The signals with slow phase speed are only observed in southern California. It is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of Point Conception. The seasonal transition of alongshore surface circulation forced by upwelling-favorable winds and their relaxation is captured in fine detail. Submesoscale eddies, identified using flow geometry, have Rossby numbers of 0.1 to 3, diameters in the range of 10 to 60 km, and persistence for 2 to 12 days. The HFR surface currents resolve coastal surface ocean variability continuously across scales from submesoscale to mesoscale (O(1) km to O(1000) km). Their spectra decay with k-2 at high wave number (less than 100 km) in agreement with theoretical submesoscale spectra below the observational limits of present-day satellite ealtimeters.

Bio: Sung Yong Kim is an Assistant Professor in the Department of Mechanical Engineering at Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea and the director of the Environmental Fluid Mechanics Laboratory at KAIST. He received B.S. degree in Naval Architecture and Ocean Engineering from Seoul National University, Seoul, Republic of Korea, in 1999 and Ph.D. degree in Applied Ocean Science from Scripps Institution of Oceanography, La Jolla, USA, in 2009. His present research interests are in the areas of coastal circulation, sub-mesoscale processes, statistical and dynamical data analysis, environmental parameterization, and operational coastal ocean observing system. He has served as a member of Technical Committee (MONITOR) in the North Pacific Marine Science Organization (PICES) since 2014. He is the recipient of the Young Frontier Research Scientists Award in the Korean Academy of Science and Technology in 2013, the Young Scientist Award in the Korean Society of Oceanography in 2014, the Young Scientist Award to brighten Korea for next 30 years (selected as one of 30 persons in Natural Sciences) in 2016.
 

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School of Mechanical Engineering Seminar
Wednesday, November 30, 2016 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

“MODELING ISSUES FOR SUBSEA GAS TRANSPORT PIPELINES”

Prof. Ytrehus

Professor Emeritus Tor Ytrehus

Department of Energy and Process Technology

Norwegian University of Science and Technology

The seminar will focus on fluid mechanics issues for subsea transport of gas in long export pipelines, with specific reference to the GASSCO¹⁾-operated infrastructure between the coast of Norway and continental Europe and UK. Turbulent pipe-flow at high Reynolds numbers of the order of 10⁷, and with pressure differences from 300 –to 20bar will be considered for pipelines of length up to 1000km. Computed results will be compared to “real life” situations for steady and transient flow events. Some attention to basic fluid mechanics elements, like details of the dissipation function in turbulent pipe flow, and consistent use of classical correlations for heat transfer, will be given along with some remarks on state equations for real gases.        

1) State owned operator of Norwegian gas transport infrastructure

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SCHOOL OF MECHANICAL ENGINEERING SEMINAR

Wednesday, November 16, 2016 at 15:00 Wolfson Building of Mechanical Engineering, Room 206

Dynamic Mechanical Analysis of Tubular Composite Joints: Rate Effects and Failure Prediction

Breiman Uri
MSc Student of Prof. Rami Haj-Ali

Bolted and welded connections are two common methods to join metallic parts. However, these are not viable or acceptable methods for parts made from composite materials. Bolted or riveted composites, for example, allow for local damage and delamination leading to reduced strength to weight ratio. One alternative, is to use thin adhesive layer between the joined composite parts. The mechanical behavior of such composite lap joints is strongly influenced by the adhesive layer and its elastic and strength properties as it becomes the weakest link. This dependency is pronounced in the case where joints are subjected to dynamic loading effects, especially when the polymeric layer is rate dependent.
The overall research goal was to analyze the dynamic rate behavior of polymeric materials used in composite structures. Specific goals were to investigate experimentally and computationally the polymeric mechanical behavior influence on tubular composite joints. Towards these goals, computational finite-element (FE) method was used to generate FE models at the structural level. The high fidelity generalized method of cells (HFGMC) was also employed to generate the effective linear response of the layered composite adherents. Experimental tests of the polymeric and composite material systems were also performed using digital image correlation (DIC), as well as strain gage (SG) measurement. A new rate-dependent constitutive failure model was also calibrated for the dynamic mechanical behavior of the epoxy material. Finally, the proposed rate-dependent material model along with the global FE tubular composite joint models are compared with uniaxial dynamic tensile tests.

School of Mechanical Engineering SeminarSchool of Mechanical Engineering Seminar

Wednesday, Nov 16, 2016 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Advanced Controlled Cryogenic Ablation Using Ultrasonic Sensing System

Assaf Sharon

MSc. Student of Dr. Gabor Kosa

Cryoablation process is one of the methods for treating various tissue abnormities. Cryoablation devices are mostly minimally invasive and are used in open loop control, monitored by additional imaging devices. In this study, we monitor the growth of the ablated area by using a miniature ultrasonic transducer that is collocated with the tip of the cryogenic device. The 10-20 MHz ultrasonic sensor is capable of measuring the size of the ice sphere that is created in front of the needle. The measurement is done within the ice sphere. In addition to real time monitoring of the ablation process, the ultrasonic sensor will be able to determine the local thickness of the tissue prior to the treatment (thus enabling the setting of the power of the ablation treatment). The combined device will shorten the ablation treatment and will eliminate the need for additional ablation treatments or monitoring devices. The proof of concept was done in water, ultrasonic gel and breast tissue. In the experiments we found that, in the frequency domain one can identify at 10-12 MHz frequency range, the increase of the intensity of the returned echo in the ice and the decrease of the signal after the ice-tissue boundary. The intensity represents the overall power returning to the sensor from the medium in front of it. One can correlate the increase of the intensity with the growth of the ice sphere. We created a software, calibrated by our initial experiments, which receives as an input the requested ice ball size to reach and returns a ‘stop’ pop up message in real time when the requested ice ball size is reached with 0.3 mm accuracy.