Applying a two degree of freedom model for drive-by identification
Bayer, Jan
2024 - English
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving spring-mass the second DOF. The response of the moving spring-mass is simulated on a bridge model using different road profiles and compared to parameters of the corresponding two DOF system. The focus is the spectral shift that can be observed on the moving spring-mass during its passage along the bridge and could possibly be applied for drive-by identification. The accuracy mainly depends on the relation of the moving spring-mass to the bridge mass and the relation between the natural frequency of the spring-mass and those of the bridge. The simulations showed that road profile can significantly reduce the accuracy of identified results, which imposes limits on practical applications.
Keywords:
drive-by identification; structural health monitoring; finite element analysis; road roughness; two DOF system
Available in digital repository of the ASCR
Applying a two degree of freedom model for drive-by identification
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving ...
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Fischer, Cyril; Náprstek, Jiří
2024 - English
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type nonlinear model. Determining the response probability density function involves solving the Fokker-Planck equation, which is generally a challenging task. Hence, semi-analytical and numerical methods come into play. This contribution reviews several possible techniques and spotlights the exponential-polynomial-closure method. The shown results are limited, as the paper reflects an early stage of the relevant research direction.
Keywords:
Fokker-Planck equation; stochastic averaging; numerical solution; Galerkin approximation; van der Pol-type oscillator; partial amplitudes; exponential-polynomial-closure method
Available in digital repository of the ASCR
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type ...
Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav; Macháček, Michael
2024 - English
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by polyethylene, and used for low-voltage power lines. The susceptibility to loss of stability is analyzed for cable without and with simulated icing observed on similar real conductors. In the first case, the proneness to galloping was excluded based on the results of CFD simulation and the Den Hartog criterion. In latter case, the possible occurrence of galloping was confirmed. The critical wind velocity for the ice-covered cable was calculated utilizing quasi-steady theory. Finally, the amplitudes of limit cycle oscillation for supercritical wind speeds were estimated based on simplified numerical analysis.
Keywords:
aerial bundled cable; wind effects; galloping; limit cycle oscillation
Available in digital repository of the ASCR
Galloping of insulated bundled overhead line simplified analysis
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by ...
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2024 - English
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The rectangle object was exposed to the airflow having a given velocity at different angles of the wind attack in the wind tunnel with the aim to obtain the curves of the aerodynamic coefficients and Strouhal number depending on the impact angle. The comparative numerical 3D simulations of the wind tunnel testing were performed using COMSOL Multiphysics and OpenFoam both incorporating the Large Eddy Simulation (LES) method.
Keywords:
rectangle 2:1; wind tunnel; LES simulation; aerodynamic characteristics
Available in digital repository of the ASCR
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The ...
Studijní zkoušky pevnosti malty v omítce severního průčelí st. zámku Litomyšl
Drdácký, Miloš; Urushadze, Shota; Vála, Ondřej
2024 - Czech
Available at various institutes of the ASCR
Studijní zkoušky pevnosti malty v omítce severního průčelí st. zámku Litomyšl
Posouzení stavu a měření mechanických vlastností dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic, rejstř. číslo kult. památky: 18278/6‐619
Kloiber, Michal; Drdácký, Miloš
2024 - Czech
Průzkum popisovaný v této zprávě obsahuje vyhodnocení fyzikálních a mechanických vlastností vybraných nosných trámů dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic (obr. 1.1). Podnětem k sepsání zprávy byla objednávka od Projekčního ateliéru pro dokumentaci, průzkum a obnovu historických staveb, spol. s.r.o., se sídlem Nerudova 1139, 544 01 Dvůr Králové nad Labem. Objednávka obsahovala požadavek na posouzení stavu vybraných dřevěných prvků pomocí přístroje Resistograph a především měření mechanických vlastností, které mohou přispět ke statickému posouzení a návrhu šetrné obnovy unikátní konstrukce krovu a stropu. The survey described in this report contains the assessment of physical and mechanical properties of selected beams within timber structures of the truss and 1st floor ceiling in the state-owned castle called Hrádek u Nechanic (Fig. 1.1). The report has been elaborated based on an order placed by Projekční ateliér pro dokumentaci, průzkum a obnovu historických staveb, spol. s.r.o., headquartered Nerudova 1139, 544 01 Dvůr Králové nad Labem. The order included the demand to assess the condition of selected timber elements by Resistograph, and mainly to measure the mechanical properties that can contribute to static assessment and a design of non-intrusive renewal of the unique structures of both the truss and the ceiling.
Keywords:
timber structures; truss; ceiling; state-owned castle; timber mechanical properties
Available at various institutes of the ASCR
Posouzení stavu a měření mechanických vlastností dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic, rejstř. číslo kult. památky: 18278/6‐619
Průzkum popisovaný v této zprávě obsahuje vyhodnocení fyzikálních a mechanických vlastností vybraných nosných trámů dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic (obr. ...
Využití termografie v průzkumech památek
Valach, Jaroslav; Eisler, Marek
2024 - Czech
Termografie rozšiřuje portfolia metod, jimiž lze studovat vlastnosti objektů okolního světa. Ještě před deseti lety byla tato technologie kvůli potenciálním vojenským aplikacím úzkostlivě kontrolována, což omezovalo konkurenci v nabídce výrobků a výrobců a vedlo k vysokým cenám zařízení založených na těchto principech. Teprve díky uvolnění této kontroly došlo k rozmachu výroby a zpřístupnění zjednodušených výrobků masovému využití, takže si dnes může zákazník například pořídit chytrý telefon s doplňkovým termografickým modulem jen s malým navýšením ceny. Spolu s dostupností zařízení pozorujeme nárůst uplatnění termografie v mnoha oblastech, včetně průzkumů staveb a památek. Thermography expands the portfolio of methods that can be used to study the properties of objects in the surrounding world. As recently as a decade ago, the technology was frowned upon for potential military applications controlled, which limited competition in the offer of products and manufacturers and led to high prices of devices based on these principles. It was only thanks to the release of this control that it happened to expand production and make simplified products available to mass use, so get it today for example, a customer can purchase a smartphone with an additional thermographic module for only with a small price increase. Together with the availability of equipment, we observe an increase in the application of thermography in many areas, including surveys of buildings and monuments.
Keywords:
thermography; survey of historical structures
Available at various institutes of the ASCR
Využití termografie v průzkumech památek
Termografie rozšiřuje portfolia metod, jimiž lze studovat vlastnosti objektů okolního světa. Ještě před deseti lety byla tato technologie kvůli potenciálním vojenským aplikacím úzkostlivě ...
Book of Abstracts. 19th Youth symposium on experimental solid mechanics
Kytýř, Daniel; Zlámal, Petr; Pagliaro, A.; Doktor, T.
2024 - English
The YSESM symposium provides a forum for young researchers and engineers, PhD students and students dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all areas of experimental research and its application in solid and fluid mechanics. The topic will particularly concern to: Conventional and advanced experimental methods in solid and fluid mechanics - Non-destructive testing and inspection - Measurements in material science - Computer assisted testing and simulation - Engineering design simulation - Hybrid methods, experimental techniques – Numerical simulation - Optical methods and image processing - Measurements in biomechanics - Sensor techniques for micro- and nano-applications - Measurement methods for forensic engineering
Keywords:
experimental mechanics; solid mechanics; fluid mechanics
Available at various institutes of the ASCR
Book of Abstracts. 19th Youth symposium on experimental solid mechanics
The YSESM symposium provides a forum for young researchers and engineers, PhD students and students dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all ...
Galloping of insulated bundled overhead line - nonlinear numerical analysis in time domain
Macháček, Michael; Hračov, Stanislav
2024 - English
Our contribution focuses on a 3D numerical nonlinear analysis of galloping in a specific bundled overhead line with ice accretion. We studied the susceptibility to this self-excited oscillation, critical onset wind speeds, and global dynamic response of a very low-tensioned line with simulated icing observed on similar real conductors. Due to the highly nonlinear mechanical behavior of such a flexible cable, we employed the Newmark integration method combined with the iterative Newton-Raphson method. We analyzed two numerical models of the overhead line loaded by the wind: one assuming nonlinearity only in the wind load, while retaining the linearity of the mechanical system itself, and the other representing a fully nonlinear system including geometrical nonlinearity. Our analysis revealed that the determined critical wind speeds for the onset of galloping are in relatively close ranges for both models. However, numerical simulations with the fully nonlinear system indicated significantly lower amplitudes of limit cycle oscillations, especially at higher wind speeds, compared to the linear model of the line. This underscores the necessity of using fully nonlinear models during the design stage of such low-tensioned aerial conductors.
Keywords:
aerial bundled conductors; wind effects; galloping; limit cycle oscillation
Available in digital repository of the ASCR
Galloping of insulated bundled overhead line - nonlinear numerical analysis in time domain
Our contribution focuses on a 3D numerical nonlinear analysis of galloping in a specific bundled overhead line with ice accretion. We studied the susceptibility to this self-excited oscillation, ...
Průzkum spojení kamenných bloků ozdobného „klenutíʺ průhledů cimbuří Prašné brány v Praze
Válek, Jan; Kotková, Kristýna; Kozlovcev, Petr
2024 - Czech
Průzkum napojení kamenných prvků cimbuří Prašné brány v Praze pomocí zemního radaru. Cílem je ověření existence propojovacích prvků ve styčné/ložné spáře mezi kameny „zaklenutí“ průhledů cimbuří a bočními opěrami. Interpretace radargramů ukazuje na kamenické spojky. Malta obsahuje železitou příměs. Survey of the connection of the stone elements of the Powder Tower in Prague using ground penetrating radar. The aim is to verify the existence of connecting elements with the „archingʺ of the battlements and side supports. Interpretation of the radargrams points to a stonemasonry dowels. The mortar contains an iron admixture.
Keywords:
ground penetrating radar; masonry joints; NDT survey
Available at various institutes of the ASCR
Průzkum spojení kamenných bloků ozdobného „klenutíʺ průhledů cimbuří Prašné brány v Praze
Průzkum napojení kamenných prvků cimbuří Prašné brány v Praze pomocí zemního radaru. Cílem je ověření existence propojovacích prvků ve styčné/ložné spáře mezi kameny „zaklenutí“ průhledů cimbuří a ...
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