I have a few positions (funded by NSF, AFRL, and/or ARO) for MS or PhD (preferred) students at the University of Tennessee Space Institute (UTSI) and University of Tennessee Knoxville (UTK) in the following two topics:
1. Elastodynamic metamaterials: Characterization of dispersive constitutive equations and simulation of the material with overall properties in the time domain (TD), analysis of the effect of disorder and material nonlinearities (e.g. fracture) in their performance, etc.
2. Radiative Transfer Equation (RTE) of radiative heat and electromagnetic wave propagation: Adaptive and parallel space-angle Discontinuous Galerkin formulations for the RTE.
The interested applicants should have a strong background in some or ideally all the following areas:
A) Mathematics, specifically partial differential equations (PDEs).
B) Numerical methods (e.g. finite element and discontinuous Galerkin methods)
C) Programming (Matlab, etc., and ideally C++)
D) Elastodynamics or experience with any other transient PDE (mainly for topic 1)
E) Fracture Mechanics (topic 1)
F) Parallel computing (topic 2)
G) h-, p-, or hp-adaptive methods (topic 2)
Please send me an email at rabedi@utk.edu with the following information:
- Topic you are interested in (1 or 2 above)
- The earliest you can start your studies with the program you are interested in (MS vs. PhD)
- Your CV or resume
- Ideally a short explanation why you are a good fit for this position, particularly addressing your experience on items A to G above (no more than 2 lines for each one, A-E for topic 1 and A-C, F, G for topic 2).
Thanks
Applications are sought for a research assistantship in the field of wave propagation modeling. The position is supported by a monthly stipend and tuition and fees towards a PhD degree for up to four years (subject to satisfactory progress). The start date is flexible (January 2021 preferred). The student will be based in the Department of Engineering Science and Mechanics (www.esm.psu.edu) at Penn State University in Pennsylvania, USA (www.psu.edu). To qualify for this position, you must satisfy the PhD admission requirements set by the department and university.
The work will be to study the effects of microstructural modifications in ice composites on wave propagation and scattering through multiscale modeling, as part of a project funded by the National Science Foundation (NSF). The long-term goal of the project is to introduce a new material specifically designed to couple ultrasonic signals with the bulk of geometrically complex components. The material will be a new form of ice loaded with solid particles to yield tunable rigidity and mass density which are critical for the effectiveness of ultrasonic testing. The proposed work will create a new mathematical framework to model wave propagation in particle reinforced composites that lies at the convergence of physics-based analytical approaches and numerical unit cell methods. By merging analytical and data-driven strategies, this work uncovers innovative multiscale approaches to the study of wave propagation in media with complex microstructures. You will focus on the analytical framework of the problem, which is based on homogenization methods that seek to establish the macroscopic wave displacement by ensemble averaging the microscale behavior. Throughout the project, you will work in close collaboration with a PhD student developing the numerical framework (position filled).
If you are interested in this position, please send your full CV and a cover letter describing your expertise, goals and why you are interested in pursuing this PhD position to the project principal investigator, Prof. Andrea P. Arguelles at arguelles@psu.edu. Please include CRYOULTRASOUND as the first word in the subject of your email. Qualifying applicants will be contacted for a follow-up videoconference interview over Zoom.
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Hello all,
I am working on the simulation of 1-D nonlinear elastic waves using Iteration contrast source technique. In which, I have some questions on a correct definition for spatial frequency and wavenumber. The spatial differential operator in the nonlinear force term (dx^2 and dx) will become (-k^2 and -j*k) in the frequency domain (j-imaginary number). I understand that wrong definition of k vector has a huge impact on the results because of the multiplication of square terms (-k^2) to u (displacement). I have shown my code which has different definitions of k (where M-spatial sample points). Also, whether the spatial frequency of a longitudinal wave (k_x) and shear wave (k_y and k_z) are same or different? Please share your knowledge. Many thanks in advance.
%% Spatial frequency
% dk=1/(dx); % Wavenumber increment
% kp=([(0:M/2-1) (-M/2:-1)]./M) * (dk); % == k_x %with/without 2*pi
% ks=([(0:M/2-1) (-M/2:-1)]./M) * (dk); % == k_x
% kp=(0:M-1)*(dk);
% ks=(0:M-1)*(dk);
% Zero padded
% dk=1/(dx); % Wavenumber increment
% kp=([(0:(2*M)/2-1) (-(2*M)/2:-1)]./(M)) * (dk); % == k_x%with/without 2*pi
% ks=([(0:(2*M)/2-1) (-(2*M)/2:-1)]./(M)) * (dk); % == k_x%with/without 2*pi
In this paper, we study the dynamic flexural behaviour of a long bridge, modelled as an infinite periodic structure. The analysis is applied to the ‘Brabau’ bridge across the river Tirso in Italy. The approach reduces to a spectral problem leading to the analytical expression of the dispersion relation, which provides the ranges of frequencies for which waves do and do not propagate. The contributions of the bridge structural elements on the dispersive properties of the structure are investigated in detail. The direct link between frequency intervals determined by the proposed approach and distribution of eigenfrequencies of the full three-dimensional structure is demonstrated. The analysis of the unit cell allows to avoid the tedious computations required when using a finite element code, at least at a preliminary stage of the design. Finally, we demonstrate that a more precise prediction of the eigenfrequency ranges of the bridge can be obtained by studying a single repetitive cell numerically and imposing Floquet-Bloch conditions at its ends. The proposed approach can be implemented as a simple procedure to design structures with repetitive units, with the advantage of simplifying numerical simulations and reducing the computational cost.
http://www.sciencedirect.com/science/article/pii/S0141029617303103
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For the first time, a design of a “deflecting elastic prism” is proposed and implemented for waves in a chiral medium. A novel model of an elastic lattice connected to a non-uniform system of gyroscopic spinners is designed to create a unidirectional wave pattern, which can be diverted by modifying the arrangement of the spinners within the medium. This important feature of the gyro-system is exploited to send a wave from a point of the lattice to any other point in the lattice plane, in such a way that the wave amplitude is not significantly reduced along the path. We envisage that the proposed model could be very useful in physical and engineering applications related to directional control of elastic waves.
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| Carta et al. (2017) - Scientific Reports.pdf | 3.59 MB |
A funded PhD position is open for summer or fall 2017 in the Mechanics and Dynamics Laboratory in the Department of Aerospace Engineering at Wichita State University. The research program will focus on the design and development of mechanical metamaterials, their application towards aerospace structures, and will involve a combination of analytical, numerical, and experimental methods. The candidate must have a MS in Aerospace or Mechanical Engineering and a strong background in structural mechanics and dynamics. Familiarity with CAD and FEM software packages (preferably Comsol) is expected. Candidates with a background in vibrations and elastic wave propagation are highly encouraged to apply. You can learn more about our research at www.madlab-wsu.com.
Interested applicants should email a cover letter summarizing their background and research interests, their CV (including list of related courses, projects, and any publications), and GRE/TOEFL scores (if available) to bhisham.sharma@wichita.edu. Please put PhD applicant in the subject of your email.
Review of the applicants will begin immediately until the position is filled.
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| PhD position - Fall 2017.pdf | 186.88 KB |
The paper presents a novel analysis of localisation and transmission properties of randomly-perturbed flexural systems. Attention is given to the study of propagation regimes and the connection with localised resonance modes in the context of Anderson's localisation. The analytical study is complemented with numerical simulations relevant to the design of efficient vibration isolation systems.
Eigenvalues, reflected and transmitted energy, localisation factors for the examined bi-coupled random system:
http://s725.photobucket.com/user/giorgio_carta/media/Figure_zpsumei02ss....
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| Preprint.pdf | 17.42 MB |
Recently we published a paper in Physical Review Applied. It can be downloaded from the link
http://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.3.064014
Abstract of the article is below:
The acoustic diode (AD) can provide brighter and clearer ultrasound images by eliminating acoustic disturbances caused by sound waves traveling in two directions at the same time and interfering with each other. Such an AD could give designers new flexibility in making ultrasonic sources like those used in medical imaging or nondestructive testing. However, current AD designs, based on nonlinear effects, only partially fill this role by converting sound to a new frequency and blocking any backward flow of the original frequency. In this work, an AD model that preserves the frequencies of acoustic waves and has a relatively high forward-power-transmission rate is proposed. Theoretical analysis indicates that the proposed AD has forward, reverse, and breakdown characteristics very similar to electrical diodes. The significant rectifying effect of the proposed AD is verified numerically through a one-dimensional example. Possible schemes for experimental realization of this model as well as more complex and efficient AD designs are also discussed.
Comments and feedback are welcome.
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| Frequency-Preserved Acoustic Diode Model with High Forward-Power-Transmission Rate.pdf | 741.26 KB |
Politecnico di Milano
Department of Civil and Environmental Engineering
Postdoc position in Solid/Computational Mechanics
Fixed term position for up to 18 months
Salary: 25,000 Euro per annum
A Postdoc position will be soon opened at the Department of Civil and Environmental Engineering of Politecnico di Milano, to work within the Safer Helmets project. This project will be conducted in collaboration with the University of Pavia, the Chemistry Materials and Chemical Engineering Department and the Mechanical Engineering Department of Politecnico di Milano, and the Centro Internazionale Disordini Apprendimento Attenzione ed Iperattività. The aim of the project is to enhance the performance of bike and ski helmets through microstructured polymeric composite materials, by decreasing in amplitude the acceleration peaks (already recognized by international standards to cause injuries) and also shifting them toward frequencies less dangerous for the human brain.
The goals of the work to be carried out are: provide an effective (homogenized) constitutive law for the polymeric materials; model the effects of high strain rates, typically experienced during an impact event; define a suitable distribution of materials density (gradation), compatible with standard production processes, so as to reduce peak values of local accelerations at the helmet/head interface; model damage/cracking in the above defined functionally graded materials; model the global response of the helmet.
Applicants should hold a PhD (or equivalent) in Civil Engineering, Mechanical Engineering, Computational Physics or Applied Mathematics. They should have experience in continuum and multi-scale modelling of solid materials. Preference will be given to applicants with a proven research record and publications in relevant areas. Applicants as also expected to be fluent in spoken and written English.
For additional information, please contact Stefano Mariani ( stefano.mariani@polimi.it ).
Hi everybody, I'm so interested in analysis of wave propagation in solid medias. and I've started by studying some books like "Ultrasonic wave propagation in solid media"(Rose). My question is about the importance of this analysis (propagation of high frequency elastic waves) in the structures. I know that the major application is in the field of Nondestructive Testing(NDT). but I don't know if it is usefull in vibrational analysis of mechanical structures (elastic waves with frequencies around KHz or MHz). is this study important in "dynamic response analysis" of mechanical structures in some special kind of loading like impact? I'd be gratefull if you could introduce me some examples.