|
|
Finite element modal analysis of a silicone vocal fold filled with fluid
Hájek, P. ; Radolf, Vojtěch ; Horáček, Jaromír ; Švec, J. G.
A three dimensional (3D) finite element (FE) model of a silicone vocal fold (VF) filled with fluid is presented here. The silicone part of the model is based on partial differential equations of the continuum mechanics and consider large deformations. The fluid domain encapsulated in the silicone VF is defined semianalytically as a lumped-element model describing the fluid in hydrostatic conditions. The elongated and pressurized silicone VF was subjected to perturbed modal analysis. Results showed that the choice of the fluid inside the VF substantially influences the natural frequencies. Namely, the water-filling lowers the natural frequencies approximately by half over the air-filling. Besides, the procedure of reverse engineering for obtaining the geometry of the VF from already 3D-printed mold is introduced.
|
|
|
Dynamics of a cantilever beam with piezoelectric sensor: Parameter identification
Cimrman, Robert ; Kolman, Radek ; Musil, Ladislav ; Kotek, Vojtěch ; Kylar, Jaromír
The piezoelectric materials are electroactive materials often applied for real-time sensing or structural health monitoring, both important research topics in dynamics. Mathematical models of such structures have to allow also for the external electrical circuits and contain several material parameters that need to be identified from experiments. We present a model of a simple experiment involving dynamics of a cantilever beam with an attached piezoelectric sensor excited by a suddenly removed weight. The external circuit can be taken into account as having either a finite or infinite resistance. We also outline the parameter identification procedure based on automatic differentiation and present the experimental and numerical results.
|
|
|
Porušování jemnozrnného cementového kompozitu v blízkosti rozhraní plniva a matrice
Vyhlídal, Michal ; Kabele,, Petr (referee) ; Profant, Tomáš (referee) ; Keršner, Zbyněk (advisor)
The Interfacial Transition Zone (ITZ) between the aggregate grain/reinforcement bar and the matrix is considered to be the weakest element in cementitious composites and is, according to some authors, directly responsible for the nonlinear (more precisely, quasi-brittle) behavior of the composites. The aim of this work is verification of the generally accepted paradigm of the weakest element by means of fracture experiments and corresponding numerical simulations. In the experimental part, in addition to traditional fracture tests, modern methods of 3D scanning, scanning electron microscopy, chemical analysis using an electron microprobe and nanoindentation were used. In the numerical part, models based on generalized linear elastic fracture mechanics as well as modern models intended for the simulation of cement composites, namely crack band model with smeared cracks and the Microplane model, were used. Based on the results, the numerical part was complemented by the Cohesive Zone Material model simulating the behavior of the interface. All results are discussed and put into context with already published work. The main conclusion of the work is that the properties of the ITZ do not have such an influence on the behavior of cement composites as the adhesion between the inclusion and the ITZ, i.e. the matrix.
|
|
| |
|
|
Comparison of machine learning training sampling schemes for induction machine modeling
Bílek, Vladimír
The aim of the paper is to demonstrate the modelingof an induction machine using a chosen machine learningtechnique, followed by a comparison of the training samplingschemes for this technique. A simple 3-phase induction machinewith an axially slitted solid rotor has been selected for the casestudy, where FEM-based program Ansys Electronics Desktophas been used for its calculation. A total of 3 training schemeswere considered and compared with each other for the machinelearning technique. Some of the comparison results are given anddiscussed at the end of this paper. The described methodologycan be used to accelerate the design and optimization of any typeof electrical machine.
|
|
|
2D Physical Modelling of Semiconductor Equations for Verification of 1D Lumped-Charge Model of Bipolar Power Devices
Mikláš, Jan ; Procházka, Petr
The paper demonstrates a finite-element method(FEM) simulation model of semiconductor devices operation.Classical semiconductor equations employing drift, diffusionand generation-recombination transport of charge carriers areestablished and variational forms for FEM assembly are derivedin detail, including a basic voltage and current boundary conditions.Mathematically, a system of mutually coupled nonlinearequations need to be solved, which requires extensive use ofnonlinear iteration solver. The derived model was coded inPython by strict use of open source tools, mainly grouped aroundFEniCSx project. Graphic output figures and characteristics forbasic semiconductor structures are presented to demonstrate thefunctionality of model.An ultimate goal of presented effort is derivation and verificationof simplified semi-analytical model of Insulated-gate bipolartransistor (IGBT), including precise transient behavior.This kind of model should be calibrated by use ofmeasurement-obtained data, so the qualitative behavior of devicephysics at reasonable computational cost is of primary interestof presented FEM model as opposed to commercial devicedevelopment tools aiming at precise quantitative outputs; whichneed to be experimentally calibrated even so.As an additional step to simplified one-dimensional modelusability verification, results of unusual way of experimentalestimation of minority-carrier excess charge within power bipolartransistor collector and base during on-state is presented andcompared to simulation result.
|
|
|
Automated Python-Controlled Thermal Analysis of Rotor of Line-Start Permanent Magnet Synchronous Machine
Súkeník, Jakub
This paper deals with the thermal analysis of the rotorof the line-start permanent magnet synchronous machine(LSPMSM). First, a concept of a fully controlled parametricgeometry creation using the Python programming languageis introduced. The geometry is created using the FreeCADsoftware. Afterwards, the geometry is used to perform a thermalanalysis using the finite element method (FEM) in the AnsysWorkbench Software. This analysis is also controlled by Python.A thermal model of the analyzed rotor was also created usinglumped parameter thermal network (LPTN). Finally, the resultingtemperatures from the FEM-based analysis are used to verifythe functionality of the lumped-parameter thermal network.
|
|
|
Computational modelling of isovolumic contraction of left ventricle
Kubík, Matej ; Burša, Jiří (referee) ; Vaverka, Jiří (advisor)
This diploma thesis deals with computational modelling of isovolumic contraction of the left heart ventricle by using finite element method. Part of the thesis includes research on the anatomy and physiology of the heart, where the structure of the heart muscle is analyzed in more detail. The passive mechanical response of the model reflects this very structure. It is included in the computational model by using a reduced Holzapfel & Ogden hyperelastic model. The active tension of muscle fibers, which is a consequence of electrical stimulation, is included in the model by the so-called active stress approach. A main goal of thesis is the implementation and testing of this approach in ANSYS program with the help of subroutine Usermat.
|
|
|
Influence of annular seal on rotor dynamics
Kurková, Michaela ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
The thesis deals with the problem of annular seals and their influence on rotor dynamics. In the first part the derivation of the basic analytical solution is presented. Subsequently, a FEM model of the rotor with the influence of annular seal is constructed. The model is used to analyze the effect of the seal on the rotor dynamics. The last part of the paper is devoted to the conceptual design of the experiment and its basic dynamic analysis.
|
|
|
Comparative analysis of the effect of nonlinearities on the lumbar segment stress/strain of the spine after correction of spondylolisthesis
Holá, Lucia ; Ščerba, Bořek (referee) ; Vosynek, Petr (advisor)
This final thesis focuses on the stress-strain analysis of the physiological, postoperative and degenerative state of the lumbar spine segment. The aim of this thesis is to implement nonlinear material characteristics into previously made computational models and to compare these two models. The solution is performed by computational modeling using the finite element method. The geometry model was made by modification of the previous model of geometry. The group of degenerative state models comprises of three different levels of spondylolisthesis, according to Myereding’s classification. Based on the performed analysis, it was found that the increasing severity of spondylolisthesis, as well as the change in material definition plays a huge role in the stress development in the intervertebral discs and in the vertebrae. The total deformation of the spine segment increases with the use of nonlinear material characteristics, as well as with the increasing variability from the physiological state. However, the stress distribution in the intervertebral disc decreases with the use of nonlinear material characteristics and in case of the vertebral stress distribution increases, unlike in the linear material models. The biggest similarity with the physiological state of the lumbar spine segment was found in the postoperative state using the spinal implants.
|
guest ::
