Ilie R.,Technical University of Civil Engineering Bucharest |
Chiroiu V.,Institute of Solid Mechanics |
Ioan R.,Spiru Haret University
UPB Scientific Bulletin, Series A: Applied Mathematics and Physics | Year: 2017
A 2D acoustic cloak surrounding an object to make it acoustically "invisible" when the sound is incident from any direction and passes through and around the cloak, is discussed in this paper. The key for "invisibility" is the coordinate transformation which design the metamaterial required for a given application. The acoustic cloaking is based on the property of the Helmholtz equation to be invariant under the coordinate transformations, i.e. a specific compression is equivalent to a variation of the material parameters in the original space. The theory is simple and consists in transformation of an original domain with a given shape filled with a known material into a final domain, by applying a specific coordinate transformation. The final domain will have a desired shape and will be filled with a new desired material, strongly inhomogeneous and anisotropic. This new metamaterial must be engineered at the subwavelength scale in order to imitate the exotic properties provided by the wave equations. In this paper, we show that it is possible to design an acoustic cloak surrounding a noisy machine in order to control the noise. The cloak is characterized by a rank 4 material tensor that define the properties of new metamaterial. These properties are ideal and complex, being real challenges to experimentalists, but not impossible to be achieved.
Wang X.,Beihang University |
Wang X.,Institute of Solid Mechanics |
Yang H.,Beihang University |
Qiu Z.,Beihang University
AIAA Journal | Year: 2010
Based on the availability of measured natural frequencies of structures, the interval analysis technique was proposed for structural damage identification. Influences of uncertainties in the measurements and modeling errors on the identification were investigated. Because of the lack of information on measurement uncertainties, the interval description was adopted for the measured natural frequencies in this paper. Via the first-order Taylor series expansion, the interval bounds of the elemental stiffness parameters of both undamaged and damaged structures were derived by using the model updating based on the initial analytical finite element model. The damage can be identified by comparing the differences between the two models, where the quantitative measure of the possibility of damage existence in the elements is introduced. A larger value of possibility of damage existence implied a higher possibility of damage occurrence. The damage identifications for a steel cantilever beam and a steel cantilever plate were performed by the presented method, which is validated by Monte Carlo simulation. Moreover, the case of the multidamage identification, the number of the used natural frequencies, and the effects of damage level and uncertainty level on the damage detection were studied as well. The numerical results proved the validity and applicability of the presented interval analysis method.
Sharifimajd B.,Institute of Solid Mechanics |
Olvander J.,Linköping University |
Stalhand J.,Linköping University
International Journal for Numerical Methods in Biomedical Engineering | Year: 2016
There are limited experimental data to characterize the mechanical response of human myometrium. A method is presented in this work to identify mechanical parameters describing the active response of human myometrium from the in vivo intrauterine pressure measurements. The human uterine contraction during labor is simulated by implementing a coupled model in a finite element scheme, and the intrauterine pressure is evaluated as the outcome. A meta-model is developed to approximate the finite element simulation response with a lower computational cost and used to identify model parameters through fitting its prediction to the in vivo measurements. © 2016 John Wiley & Sons, Ltd.
Picu M.,University of Galati |
Sireteanu T.,Institute of Solid Mechanics
Proceedings of the Romanian Academy Series A - Mathematics Physics Technical Sciences Information Science | Year: 2016
After an exposure to vibrations, the sensitivity of the mechanoreceptors in fingers is temporary altered and that the subjects suffer from paresthesia and numbness. So far it is not known how significant these temporary changes are, what is the frequency dependence or their likely repercussions on employment security. The subjects (10 men aged 20 to 25 years, perfectly healthy) were irradiated with vibrations with 1.2; 2.8; 5.8 şi 10.5 m/s2, for 10 and 20 min; frequencies were: 4; 16; 31.5; 63; 125; 250 şi 500 Hz. Subsequent, the subjects were tested with the Semmes-Weinstein test and Purdue Pegboard test. It is found that the results almost coincide for the two tests. This means that a prolonged irradiation with accelerations exceeding 2.8m/s2, subjects lose control of the fingers. If we compare the variation of the weighting factors based on the acceleration for these two tests with the variation of the weighting factors based on ISO 5349-1: 2001 we can see a total discrepancy. It can therefore be concluded that, as far as the vibration perception threshold is concerned, and therefore the sensitivity of the mechanoreceptors and the development of temporary neurological impairment, the ISO frequency weighting has no value.
Krejci P.,Institute of Solid mechanics |
Bradac M.,Institute of Solid mechanics
Mechatronics: Recent Technological and Scientific Advances | Year: 2011
The paper deals with using LabVIEW graphical programming language for design and prototyping of mechatronic system controller. The paper describes possibility of using LabVIEW Real-Time and LabVIEW ARM module for control of electronic automotive throttle valve and its controller development. The advantage of this approach is using high-level graphical design tools for programming of RISC processors instead of using low level programming techniques. This allows to engineers quick transitions from hardware and software development to deployment.
Bol M.,Institute of Solid Mechanics |
Ehret A.E.,Institute of Solid Mechanics |
Bolea Albero A.,Institute of Solid Mechanics |
Hellriegel J.,TU Braunschweig |
Krull R.,TU Braunschweig
Critical Reviews in Biotechnology | Year: 2013
In recent years, the advances in microbiology show that biofilms are structurally complex, dynamic and adaptable systems including attributes of multicellular organisms and miscellaneous ecosystems. One may distinguish between beneficial and harmful biofilms appearing in daily life as well as various industrial processes. In order to advance the growth of the former or prevent the latter type of biofilm, a detailed understanding of its properties is indispensable. Besides microbiological aspects, this concerns the determination of mechanical characteristics, which provides the basis for material modelling. In the present paper the existing experimental methods that have been proposed since the 1980s are reviewed and critically discussed with respect to their usefulness and applicability to develop numerical modelling approaches. © 2013 Informa Healthcare USA, Inc.
Baldovin D.,Institute of Solid Mechanics |
Baldovin S.,Polytechnic University of Bucharest
Romanian Journal of Acoustics and Vibration | Year: 2012
Conventional railway vehicle systems exhibit lateral instability phenomenon doe to self-induced oscillations of the rigid axle wheelsets, which increases component wear and imposes operating speed limits. To improve the stability performances, without increasing the rail-wheel interaction forces above safety limits, elastic joints and dissipative devices are used to connect the wheelset to the bogie frame. Using the linear elastic and damping model, this paper derives the governing differential equations of motion for a bogie with independently rotating wheelsets. The bogie is modeled by a 6 degree-of-freedom (DOF) system which considers the lateral displacement and yaw angle of each wheelset and the lateral displacement and yaw angle of the truck frame. The equations of motion of the mechanical model, were proceeding in a Matlab-Simulink program. In this paper is presented the influence of the damping coefficients of the model on the hunting motion stability of the considered bogie by numerical simulations.
Lu Z.,Institute of Solid Mechanics |
Chen M.,Institute of Solid Mechanics |
Yang Z.,Institute of Solid Mechanics
Polymer Composites | Year: 2014
The procedure of pulling a carbon nanotube/nanofiber (CNT/CNF) with interfacial defect out from a polymer matrix is studied in this article. By ignoring the fiber-matrix interaction and the stress concentration in the zone of interfacial defect, an analytical model is proposed to describe the pull-out behavior of the CNT/CNF. The accuracy and rationality of the model is validated by comparing to the pull-out experiment and the finite element simulation. The results from the parametric study indicate that the geometric parameters of the interfacial defect have pronounced influences on the pull-out behavior of the CNT/CNF. The influence of the defect on the strength and toughness of the composites is discussed in detail. © 2014 Society of Plastics Engineers.
Fuis V.,Czech Institute of Thermomechanics |
Koukal M.,Institute of Solid Mechanics |
Florian Z.,Institute of Solid Mechanics
Mechatronics: Recent Technological and Scientific Advances | Year: 2011
One type of total hip replacement function loss is acetabular cup loosening from the pelvic bone. This article examines manufacture deviations as one of the possible reasons for this kind of failure. Both dimensions and geometry manufacturing deviations of ceramic head and polyethylene cup were analyzed. We find that deviations in the variables analysed here affect considered values of contact pressure and frictional moment. Furthermore, contact pressure and frictional moment are quantities affecting replacement success and durability.
PubMed | Institute of Solid Mechanics
Type: Journal Article | Journal: Critical reviews in biotechnology | Year: 2013
In recent years, the advances in microbiology show that biofilms are structurally complex, dynamic and adaptable systems including attributes of multicellular organisms and miscellaneous ecosystems. One may distinguish between beneficial and harmful biofilms appearing in daily life as well as various industrial processes. In order to advance the growth of the former or prevent the latter type of biofilm, a detailed understanding of its properties is indispensable. Besides microbiological aspects, this concerns the determination of mechanical characteristics, which provides the basis for material modelling. In the present paper the existing experimental methods that have been proposed since the 1980s are reviewed and critically discussed with respect to their usefulness and applicability to develop numerical modelling approaches.