uri kushnir

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Papers by uri kushnir

Fracture Electromagnetic Radiation Induced by a Seismic Active Zone (in the Vicinity of Eilat City, Southern Israel)

This paper deals with the quantitative analysis of measured fracture-induced electromagnetic radi... more This paper deals with the quantitative analysis of measured fracture-induced electromagnetic radiation (FEMR) in the vicinity of the Dead Sea Transform using the Angel-M1 instrument, which enables the recording of FEMR signals in a 3D manner. Results show both the possibility of estimating the sizes of micro-fractures that are the sources of the radiation, and of assessing the direction of their location to the measuring device and the range of magnitude Mw of the impending "events" (EQ's) associated with the present FEMR measurements. Moreover, the relation between the measured FEMR activity (the number of FEMR hits per unit time) and the FEMR event magnitudes shows consistency with the Gutenberg-Richter relationship for the region. Such measurements could therefore constitute a preliminary 'field reinforcement' towards an EMR valid method for a real earthquake forecast, which would provide much earlier warnings than the seismic ones. Obviously, the present ob...

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Spectrum-Based Logistic Regression Modeling for the Sea Bottom Soil Categorization

The paper deals with applying Artificial Intelligence techniques to examine CHIRP-recorded data i... more The paper deals with applying Artificial Intelligence techniques to examine CHIRP-recorded data in sand and sandstone sea-bottom sites. The provided analysis of the state of the art portrays that actual time series or spectrum backscattered data from a point on the sea bottom were rarely used as the features for machine learning models. The results of the examination indicate that types of sea bottom can be quantitatively characterized by applying logistic regression models to either the backscatter time series of a frequency-modulated signal or the spectrum of that backscatter. The examination accuracy reached 90% for the time series and 94% for the spectra. The application of spectral data as features for more advanced machine learning algorithms, and the advantages of its combination with other types of data have great potential for future research and the enhancement of remote marine soil classification.

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Spectral Acoustic Fingerprints of Sand and Sandstone Sea Bottoms

Journal of Marine Science and Engineering

Modern studies which dealt with the frequency domain analysis showed that a frequency-domain appr... more Modern studies which dealt with the frequency domain analysis showed that a frequency-domain approach has an essential advantage and mentioned an inner qualitative relationship between the subsurface structure and its frequency spectra. This paper deals with the acoustic spectral response of sand and sandstone sediments at the sea bottom. An acoustic data collection campaign was conducted over two sand sites and two sandstone sites. The analysis of the results shows that reflections of acoustic signals from sand and sandstone sea bottom are characterized by various spectral features in the 2.75–6.75 kHz range. The differences in acoustic response of sand and sandstone can be quantified by examining the maximal normalized reflected power, the mean frequency, and the number of crossings at different power levels. The statistical value distribution of these potential classifiers was calculated and analyzed. These classifiers, and especially the roughness of the spectrum quantified by t...

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Nonlinear ferro-electro-elastic beam theory

International Journal of Solids and Structures, 2009

Motivated by the uniqueness and potential of the nonlinear range of piezoelectric and ferroelectr... more Motivated by the uniqueness and potential of the nonlinear range of piezoelectric and ferroelectric smart materials and structures, a static physically nonlinear ferro-electro-elastic beam theory which takes the effect of domain switching into account is developed. The kinematic assumptions adopt the geometrically linear Bernoulli-Euler form for the mechanical components and a first-order theory for the electrical potential, and lay the basis for further augmentation to higher order theories. The beam theory includes the field equations that correspond to the static case, the boundary conditions and the constitutive equations of ferro-electro-elasticity. The general 3-D constitutive equations are reduced to comply with the beam theory and formulated as ordinary differential equations by means of a set of generalized electro-mechanical stiffnesses. A micromechanical constitutive model that accounts for the loading history and for the domain switching phenomenon is adopted and an iterative solution procedure that incorporates the micromechanical approach is suggested. A numerical example that demonstrates the impact of the domain switching on the nonlinear electromechanical static response of a ferro-electro-elastic beam is presented and discussed. The quantitative assessment of this behavior takes a step towards new structural applications that cope with or even take advantage of the nonlinear ferro-electro-elastic range.

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Piezoelectric-Ferroelectric Actuator Device

Advanced piezoelectric–ferroelectric stack actuator

Sensors and Actuators A: Physical, 2009

A conceptual design and an operational algorithm for an advanced piezoelectric–ferroelectric stac... more A conceptual design and an operational algorithm for an advanced piezoelectric–ferroelectric stack actuator are developed. The actuator takes advantage of the large strains due to the domain-switching phenomenon and utilizes the nonlinear range of response of the ferroelectric material. As a result, the proposed conceptual design allows for deformations that are considerably larger than the ones obtained using conventional piezoelectric actuators and contributes to overcoming the travel range and performance limitations of standard actuators. The shape control algorithm is based on a discrete optimization of the domain state of the active layers and it allows the operation and the shape control of the advanced actuator in spite of the nonlinear and hysteretic material response. The conceptual design of the advanced actuator and the capabilities of the shape control algorithm are demonstrated through numerical examples. The results demonstrate the contribution of the approach to extending the operational range of the actuator through a continuous and controllable response. A summary, conclusions, and directions of future research towards realization of the concept close the paper.

Non-linear Piezoelectric and Ferroelectric Actuators — Analysis and Potential Advantages

Journal of Intelligent Material Systems and Structures, 2008

The ability to enhance and to improve the efficiency of piezoelectric actuators through extending... more The ability to enhance and to improve the efficiency of piezoelectric actuators through extending their operational range into the non-linear regime is analytically investigated. Motivated by the limited strain actuation capabilities of the existing piezoelectric actuators, it is proposed to take advantage of the non-linear ferroelectric regime, which involves large remanent strains. In order to examine this hypothesis, an analytical model for the one-dimensional electro mechanical behavior of a ferroelectric structure operated in the non-linear range is developed. The model is applicable to rod actuators, to an active layer in a stack actuator, or to an active fiber in a Micro-Fiber-Composite actuator. The governing equations and the boundary conditions, the non-linear, hysteretic, and history-dependent constitutive relations, and the solution procedure are developed and discussed. Illustrative examples that examine an active layer operating against a dead load, against a linear sp...

Grain Orientation Scattering in Nonlinear Constitutive Modeling of Piezoelectric-ferroelectric Materials

Journal of Intelligent Material Systems and Structures, 2007

The ability to enhance and to improve the efficiency of micromechanical models for the coupled el... more The ability to enhance and to improve the efficiency of micromechanical models for the coupled electromechanical constitutive behavior of piezoelectric materials in the nonlinear regime is investigated. Motivated by the limited strain actuation capabilities of the existing piezoelectric materials and structures, it is recognized that the nonlinear regime has to be explored. However, due to the complex, strongly coupled, and hysteretic behavior of the material, the quantitative prediction of its nonlinear response requires complex and time-consuming algorithms. In this study, the ability to improve the efficiency of the micromechanical algorithm by using a deterministic set of directions as a representative of the scattering of grain's orientation within the piezoelectric polycrystal is investigated. Various types of deterministic grain sets that include an equal area, a spiral, and Fekete grain sets are examined. The constitutive micromechanical model for the piezoelectric mater...

A Multiscale Approach to Nonlinearity in Piezoelectric-Ferroelectric Smart Structures: From Micromechanics to Engineering

International Journal for Multiscale Computational Engineering, 2008

Electrical body forces and electrical tractions in the nonlinear response of ferroelectric actuators

European Journal of Mechanics - A/Solids, 2011

ABSTRACT The influence of the electrical body forces and electrical tractions on the nonlinear re... more ABSTRACT The influence of the electrical body forces and electrical tractions on the nonlinear response of ferroelectric stack actuators is analytically investigated. While the role of the electrical body forces and tractions in the response of piezoelectric actuators is well documented (and in many cases is not significant), the questions of their effect on ferroelectric active materials is still of interest. To examine this influence, the analytical model for the electro-mechanical behavior of a ferroelectric stack actuator is augmented to account for the electrical body forces along the actuator and the electrical tractions at the material–electrode interfaces. Focusing on the effect of the electrical forces and tractions on the ferroelectric domain switching phenomenon, the model is used for the numerical analysis of a ferroelectric layer and for the comparison with the case that neglects the electrical body forces and traction. The comparison theoretically designates cases in which the effect of the electrical body forces and tractions may be prominent and other cases where the classical approach that neglects these effects can be adopted.

A principle of virtual work and governing equations for nonlinear ferro-electro-elasticity

Acta Mechanica, 2008

The variational principle of virtual work, the governing equations, and the boundary conditions f... more The variational principle of virtual work, the governing equations, and the boundary conditions for nonlinear ferroelectric structures are developed. The variational principle takes into account the presence of electrical body forces and body moment as well as the physical nonlinearity that results from the dissipative domain switching effect. The switching phenomenon also involves large strains. Hence, the geometrical nonlinearity is also taken into account and the electro-mechanical principle of virtual work is formulated in an Eulerian and Lagrangian type of description. The variational principle is used for the derivation of the generalized equilibrium equations (field equations) and the generalized boundary conditions. The governing equations for the ferroelectric structure are derived taking into account the nonlinear constitutive equations, the large deformations, and the spatial variation of the material tensors associated with the domain switching phenomenon. O. Rabinovitch was supported by the Taub Foundation.

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Advanced Ferroelectric MFC Actuators: The Effect of Ferro-Elastic Domain Switching

Volume 1: Advanced Energy Systems; Advanced and Digital Manufacturing; Advanced Materials; Aerospace, 2008

Macro Fiber Composite (MFC) actuators, which are commonly integrated in modern smart structures, ... more Macro Fiber Composite (MFC) actuators, which are commonly integrated in modern smart structures, may be subjected to high levels of mechanical loads. Opposed to the electrical actuation, these loads are not always controlled or anticipated by the user. Thus, they may yield a response that is beyond the linear range due to a stress induced ferro-elastic domain switching. In this paper, the phenomenon of domain switching and mechanical depolarization in the MFC actuator and the resulting degradation of the actuation capabilities are investigated. As an illustrative numerical example, the response of MFC layers in an active beam element is analyzed. Emphasis is placed on the location of the fiber segment along the active beam with a distinction between the compressed and the tensed layers. The results highlight the range of effects associated with the potential nonlinear response of the active structure under high levels of mechanical load.Copyright © 2008 by ASME

Ch13-Sharvit

by Jacob Sharvit and uri kushnir

In Centro volume 3, 2023

The ancient harbor known as Sebastos, built by King Herod the Great at Caesarea Maritima , was on... more The ancient harbor known as Sebastos, built by King Herod the Great at Caesarea Maritima , was one of the ancient world's most ambitious engineering projects. Since serious study of the harbor began more than fifty years ago, archaeologists have speculated on possible reasons for the Herodian harbor's destruction, a problem that is inseparable from the question of how it was built.

Investigating an ancient harbor presents a variety of technical-scientific challenges that are best solved by multi-disciplinary teams and collaboration. Recent advances in marine robotics, underwater imaging, and acoustics, in particular, have given underwater archaeologists powerful new tools to map and excavate submerged port structures. Since 2014, three EU-funded projects deployed some of these new tools (autonomous surface and underwater vehicles, 3D imaging, and acoustic multibeam survey) to conduct new investigations of the sunken Herodian ruins at Caesarea. An Israel Antiquities Authority Maritime Unit-University of Rhode Island team led the accompanying archaeological survey and excavation, as well as reanalyzed the relevant ancient literary evidence.

The results of these 2014-2019 investigations are presented here. We offer a resolution to the discrepancies between the ancient historical records and Caesarea's visible archaeological remains, and new analysis and explanation of the port's history from construction to destruction.
העיר קיסריה ונמלה המלאכותי סבסטוס נבנו בימיו של הורדוס מלך יהודה (37- 4 לפסה"נ) . הנמל היה לאחד הפרויקטים השאפתניים ביותר מבחינה לוגיסטית והנדסית שך העת העתיקה, ונחשב לאחד ממפעלי הבניה המורכבים ביותר שנבנה בחופי הים התיכון. הנמל שנבנה במהלך של כ- 12

שנים (22 – 10 לפסה"נ) נועד להבטיח מקום עגינה נח ובטוח לספינות בגדלים שונים וכן לספק מגוון שירותי נמל הנדרשים לכלי השייט וצוותי האוניות. אך מה קרה לנמל הגדול והמפואר? מאז החל מחקר ארכיאולוגי שיטתי של הנמל לפני יותר מחמישים שנה, ארכיאולוגים וגיאולוגים העלו השערות שונות לסיבות ותיארוך ההרס של הנמל ההרודיאני. חקירתו של נמל עתיק מציגה בפני הארכיאולוגים מגוון אתגרים טכניים ומדעיים, שלרוב הדרך לפתרונם הוא בשיתופי פעולה רב-תחומיים. התקדמות משמעותית התרחשה בעשור האחרון בתחום הרובוטיקה הימית, הדמיה תת-ימית ואקוסטיקה וזמינות השימוש בהם למחקרים ארכיאולוגים תת ימיים מאפשרת בחינה מחודשת של הסוגייה. באמצעות כלים טכנולוגים אלו בוצע לראשונה מיפוי מדויק של הנמל. = = בבורות בדיקה נבחנו מחדש חלקים שונים בנמל אשר הובילו לתובנות חדשות המאפשרות הבנה מחודשת של שיטות הבניה, הסיבות להרס הנבל ובחינת מצבו היום.

בהרצאה זו יוצגו הממצאים החדשים מחקר הנמל בקיסריה שנערך על ידי המשלחת המשותפת של היחידה לארכיאולוגיה ימית ברשות העתיקות, אוניברסיטת רוד איילנד והמכללה האקדמית להנדסה ע"ש סמי שמעון.

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