אביחי רון

תלמיד המחלקה להנדסה ביו רפואית לתואר שני ירצה בנושא:

Monitoring bone mineral density (BMD) of the wrist –A parametric EIT simulation

Our goal is to validate the feasibility of monitoring wrist bone mineral density at home using a Parametric Electric Impedance Tomography (EIT) simulation.

Introduction: BMD testing is a vital component in the diagnosis and management of Osteoporosis. It is an excellent predictor for future fracture risk. Furthermore, deterioration of BMD in peripheral sites is a good predictor for fractures risk at the hip. Hip fractures are followed by an increased risk of future fractures. Approximately 20 percent of hip fracture patients require long-term nursing home care, and only 40 percent fully regain their pre-fracture level of independence.  

EIT is a Non-invasive bio-impedance measurement. The method is used for reconstructing the electrical and dielectric properties of the body. "Injected current method" uses surface electrodes array for current injection and potential measurement. By solving the backward problem by using a computerized model of the body we can then achieve a reconstruction. At high current frequencies we see a good correlation between the BMD of the bone and its electrical properties- conductivity [S/m] and Permittivity [F/m].

Methods: We solve the forward problem of the developing potential around the wrist due to current injection by using a Matlab numerical simulation of an adult human phantom (XCAT, Duke Uni.). The inverse problem is solved by building a lookup table of different bone densities which represent different disease stages.

Results: We examine the differences in potentials on the different electrodes between different stages of the disease. We found a high sensitivity for deterioration of the cortical bone, 80 percent change between a healthy stage (0.32 g\cm³ BMD) and Osteoporosis stage (0.16 g\cm³ BMD), 18 percent sensitivity for deterioration of the cancellous bone and 100 percent sensitivity for the simultaneous deterioration of both parts of the bones. The measurement is highly robust to electrical noises but the robustness to deposition of the electrode is limited to 1cm.

Conclusion: The technology may provide a simple method for evaluating changes in the BMD of the wrist.       

העבודה נעשתה בהנחיית פרופ' שמעון עבוד , המחלקה להנדסה ביו-רפואית, אוניברסיטת תל-אביב

ההרצאה תתקיים ביום ראשון 29.3.15, בשעה 14:15,

בחדר 315, הבניין הרב תחומי, אוניברסיטת תל אביב

School of Mechanical Engineering Seminar
Monday, April 20, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Liquefaction due to severe storms and pipeline floatation on the Israeli coast-

Rotem Soffer

MSc Student of Prof. Supervisor Eliezer Kit

The goal of this research is to achieve a better understanding of the wave-induced soil liquefaction phenomenon, and its impact on maritime structures and especially on buried coastal pipelines, in the view of discovered in 2006, flotation of the LNG pipeline, that supposedly can be related to soil liquefaction. 

The soil liquefaction phenomenon occurs under large cyclic wave loads, usually generated during significant storms that occur under extreme weather conditions, and in loose soils. The research was stimulated by occurrence of such an event comprised by a sequence of two extreme storms, which apparently activated soil liquefaction just after LNG pipelines have been installed at November 2004. A later survey conducted in 2006 revealed that the LNG pipelines, which in 2004 had been laid in a trench below the seabed at water depths varying from 1 to 3 m,  changed their vertical position significantly and in some segments were exposed. Another survey from 2009 displayed very similar results, only with 50 centimeters shift that might be related to a wrong benchmark in the 2006 survey since the background bathymetry obtained in this survey differs from other two, 2004 and 2009, which are in a good agreement. It is noteworthy to mention that the dredged in mid-November 2004 sand was left at the trench bank, and was supposed to naturally fill the trench. It was hypothesized that the sequence of storms, occurred in 2004, caused the liquefaction according to the following scenario: the first storm filled the trench with the dredged sand but due to the magnitude of the storm, the fill remained in a "loose" state, and didn't have time to be naturally compacted before the occurrence of the second strong storm, only 36 hours later. Hence, the second storm acted on the loose sand, thus contributing to rapid development of overburden pressure that caused the soil liquefaction and the pipeline flotation.

An algorithm to determine the probability of extreme event comprised of two independent storms in a sequence was developed, in order to assess the return period of such an event. This algorithm was extended to any sequence, given a long enough sample.  A numerical model for the pore pressure accumulation based on an analytical solution for wave-soil interaction and empirical source term was adopted and extended to irregular wave loads. Using actual wave time series during the November 2004 event, pore pressure accumulation was calculated by different methods that were developed in the time domain. The approaches included sequences of spectral steps, and construction of randomly occurring wave train groups based on Rayleigh distributions, in order to apply the irregular wave load. The different wave loads were applied to the Palmachim region section and through a "Monte Carlo" simulation was found that the liquefaction can definitely provide a plausible explanation for pipe flotation, however in order to determine more reliable results the soil parameters should be verified in experiment.

This research provides further understanding of the soil liquefaction phenomenon, especially for the Mediterranean coast of Israel, and for irregular wave loads. Additionally, the research emphasizes the importance of soil fill methods in the marine environment.