Institute of Theoretical and Applied Mechanics of the CAS

There are more possibilities how to control flow rate in a pipeline system. When the flow is provided by pump, it is very economic to use frequency converter to change the pump speed which leads to flow rate change. Another possibility is to change number of running pumps, when pump station contains more than one unit. Control valve is used in systems without pump regulation especially, when the initial costs has to be low. The paper is focused on measurement of control ability of a ball valve. Generally, ball valves are not suitable to fulfil flow control function, but in an emergency case, when the control valve is damaged and the system has to be operated, there is no other possibility, but to use the ball valve.

The paper focuses on assessment and utilization of strain-based criterion obtained using the digital image correlation in characterization of fracture behavior of Norway spruce wood. The study employed a single-edge notched beam loaded in three-point bending (SEN-TPB) to examine mode I at three anatomical directions of crack propagation (radial, tangential, tangential-radial - R, T and TR). The criterion is evaluated at the maximal load (F max ), where the compliance-based beam method (CBBM) provides critical strain energy (G c ), which ensures the proper criteria representing equivalent crack length growth is described. The novel approach also enables one to determine the fracture process zone (FPZ) length using an algorithm which finds the onset of the nonlinear region. Uniqueness of the approach lies in processing a big set of optical data and simultaneous tracking of crack length on both sides of medium-size specimens. Results indicate that crack length is dependent on the anatomical direction, for instance in T direction the criterion ε 1crit is 2.5e-3 producing crack length equal to a c =23.9 mm, whilst in R direction, the ε 1crit is least and equals 1.3e-3 producing crack length of 22.1 mm. The highest ε 1crit is attained in TR (on average ε 1crit = 3.4e-3) and distance from the place where the crack started is 19.4 mm. Size of the non-linear region here attributed to FPZ length reaches the value of 38.4 mm in T, 30.1 mm in R and 36.3 mm in TR directions, respectively. The study presents a novel approach in characterization of fracture properties by coupling optical and energetical data and may find its usage in evaluation of other fracture modes.

The Southern Corridor of bishopric district was uncovered in early 1920s as the first Romanesque remains in the 3rd Courtyard of the Prague Castle. Based on historical context it likely originates from 11th − 12th century. To benchmark this estimate, radiocarbon dating of charcoals found in its mortars was performed. The results support the previous age estimate and suggest an ongoing building activity on site such as raising cascade walls at least till 14th − 16th century.

Article presents the results of a complex traceological research of the famous statue of the „prince”of Glauberg, found in an Early La Tène funeral complex in Glauberg (Hesse). Research focused also on two other fragments of related sandstone sculptures, found together with the Glauberger prince. The sandstone „prince”of Glauberg was already in the past a subject of many archaeological studies. Nevertheless, all or absolute majority of them were focused on aspects of art historian nature or on the question of the origin, role and function of such sculptures in the Early Iron Age Central Europe. On the contrary, the aim of our research is oriented exclusively on the questions related to the manufacture of this sculpture, identification of used sculptor´s tools and applied working techniques. Our research was realised by means of digital documentation followed by the aplication of traceological methods. The character of the survived working traces on the sculpture´s surfaces was studied by mechanoscopy, while the material of used tools was determined by X-ray fluorescence. The reconstructions of used tools were compared with the existing tools as represented by the Iron Age archaeological finds. This comparison was oriented on the most relevant regions of developed La Tène culture, particularly on South Western Germany and Bohemia. However, also other relevant area, significant as the possible source of inspiration of Celtic sculptors for the creation of the monumental sculpture–Apennine peninsula, was taken into consideration. Our research revealed individual steps and phases during the sculpture´s manufacture, enabled the reconstrucion of used tools and confirmed real existence of such tools in mentioned regions. Finally it has brought first indices of the necessity of the distinguishing between ideological and technological aspects of related Celtic sculpture, when considering possible influence of Apennine peninsula on transalpine Central Europe.

Effects of gaps (rectangular surface cavities) on boundary-layer transition are investigated using a combination of linear stability theory and experiments, for boundary layers where the smooth-surface transition results from Tollmien–Schlichting (TS) instability. Results are presented for a wide range of gap characteristics, with the associated transition locations ranging from the smooth-surface location all the way forward to the gap location. The transition movement is well described by a variable N -factor, which links the gap characteristics to the level of instability amplification $e^N$ leading to transition. The gap effects on TS-wave transition are characterized by two limiting behaviours. For shallow gaps $d/w , the reduction in$N$-factor is a function of the gap depth$d$and is independent of the gap width$w$. For deep gaps$d/w > 0.028$, the reduction in$N$-factor is a function of the gap width and is independent of the gap depth. When both the gap width and depth are sufficiently large relative to the displacement thickness$\delta ^*$, the TS-wave transition is bypassed, resulting in transition at the gap location. These behaviours are mapped out in terms of ($w/ \delta ^* , d/ \delta ^*$ ), providing a predictive model for gap effects on transition.

Dynamic vehicle–bridge interaction (VBI) plays a crucial role in the train-induced vibrations of a railway bridge for its coupling effects may reduce the bridge response and down-shift the resonant speed. The commonly used nominal theoretical resonant speed (=fbD) of a typical railway bridge, however, is only related to the bridge frequency (fb) and car length (D), but it neglects the VBI effects of the moving trains. Such a shifted resonance phenomenon would become significant for a bridge under two trains passing by each other. This study develops a method using an equivalent modal mass to be added onto the bridge to account for the frequency shift due to the presence of multiple train cars for estimation of the shifted resonant speed. The numerical study demonstrates that the proposed method can predict the shifted resonant speed and explain the shifted-resonance phenomenon of railway bridges under train passages.

The presented study investigates the dynamic resistance of cement-based large-format elements with various types of reinforcement and retrofitting. Both inner and outer reinforcement has been assessed. The effect of matrix type (low, high, and ultra-high-strength), amount of steel fibres, and ribbed reinforcing steel on impact toughness has been evaluated. The influence of an additional polymer-based layer to increase impact resistance level has also been investigated. The effectiveness of each reinforcing method has been compared. An large-scale impact hammer device KYV-I-2020 (up to 1100 J) has been used to determine the impact toughness. The results show that ribbed reinforcing steel increases the impact toughness more effectively than the fibre reinforcement, steel mesh and additional polymer layer. However, fibers significantly reduce fragmentation, especially at a higher concentration of 2.5 vol%, contributing to the overall higher impact resistance of the elements and their safety in practical use. The test results also show a significant effect of the matrix type, with the most increased impact toughness achieved when using a high strength matrix. The addition of an antifragmentation polymer layer then provides a further increase in impact toughness. The results also indicate that similar resistance capacity can be achieved using different reinforcement combinations, which is crucial for designing the material composition with the optimal performance/cost ratio. The presented research is a part of the development process of the restraint systems for stopping trucks. The data obtained has been used to create the elements with suitable composition; their effectiveness has been successfully verified by numerical simulations and real tests.

Analytical study of ball vibration absorber behavior is presented in the paper. The dynamics of trajectories of a heavy ball moving without slipping inside a spherical cavity are analyzed. Following our previous work, where a similar system was investigated through various numerical simulations, research of the dynamic properties of a sphere moving in a spherical cavity was carried out by methods of analytical dynamics. The strategy of analytical investigation enabled definition of a set of special and limit cases which designate individual domains of regular trajectories. In order to avoid any mutual interaction between the domains along a particular trajectory movement, energy dissipation at the contact of the ball and the cavity has been ignored, as has any kinematic excitation due to cavity movement. A governing system was derived using the Lagrangian formalism and complemented by appropriate non-holonomic constraints of the Pfaff type. The three first integrals are defined, enabling the evaluation of trajectory types with respect to system parameters, the initial amount of total energy, the angular momentum of the ball and its initial spin velocity. The neighborhoods of the limit trajectories and their dynamic stability are assessed. Limit and transition special cases are investigated along with their individual elements. The analytical means of investigation enabled the performance of broad parametric studies. Good agreement was found when comparing the results achieved by the analytical procedures in this paper with those obtained by means of numerical simulations, as they followed from the Lagrangian approach and the Appell–Gibbs function presented in previous papers.

In this article, an adjustable frequency device based on curved beam theory is designed to control vertical stiffness of an instrumented vehicle that it can detect dynamic data when moving on a test beam for frequency measurement. The adjustable frequency device consists of a set of two-layer cantilever semi-circular thin-beams to support a lumped mass for vibrations, in which a rotatable U-frame is used to change its subtended angle for adjustment of the supporting stiffness and corresponding vertical frequencies of the vehicle. Based on curved beam theory, an analytical frequency equation of the single-degree-of-freedom test vehicle was derived and applied to mobile frequency measurement of a simple beam. To determine the sectional rigidity of the semi-circular thin-beams, both theoretical and experimental studies were be carried out in the ITAM laboratory of the Academy of Science in Czech. The analytical and experimental results indicated that the present semi-circular beam model with guided ends is applicable to prediction of natural frequencies of the test vehicle considering different supporting stiffness

Oils, e.g. linseed oil, has been used as mortar admixtures or components of lime-oil mastic since ancient times. The reason was either to increase the mortar durability and/or to prolong the mortar/mastic workability. Historic mortars are conventionally analyzed by means of X-ray diffraction and thermal analysis, but these methods are not able to detect the organic compounds directly. The goal of the present research was to evaluate the applicability of thermal analysis, infra-red spectroscopy, solid state NMR spectroscopy and gas chromatography for detection and possible quantification of linseed oil in prepared mortar containing, beyond the oil, just lime and calcite. Both applied spectroscopies were able not only detect the presence of oil but may be used also for study of the oil chemical transformation in the alkaline environment of the lime mortar. Thermal analysis is not able to identify kind of organic admixture, but when it is known that it is e.g. linseed oil, its quantification by help of Evolved Gas Analysis is very good. The results of gas chromatography of mortar’s extract are affected by the polymerization of oil in mortar. The total organic content analysis is providing good information about the total amount of organics in mortar. There in not any single method, which could provide all information about the oil admixture in mortar (kind of oil, content of oil, fate of oil after mortar’s mixing) by itself; the combination of techniques must be used.

Historic concrete buildings are at risk. Limited knowledge of concrete technology until the 1960s led to more sensitive buildings than modern concrete buildings. In addition, the lack of sensibility regarding their heritage value and insufficient protection is leading to remorseless demolition. Still, concrete has proved to be a resilient material that can last over a century with proper care. There is not yet an estimation of the status of historic concrete buildings in Europe. Until now, a few attempts have been done to secondarily, and subjectively, gauge their conservation status. This paper is the result of a joint investigation studying forty-eight historic concrete buildings distributed in four countries. They were surveyed by expert teams according to a predefined methodology. The study aims to identify recurrent damages and parameters affecting the conservation state. It also aims to serve as the first trial for an objective and measurable methodology, to apply it with a statistically significant number of cases. Damages related to the corrosion of reinforcement and moisture-related processes were the most recurrent. The use of plasters, flat roofs, and structural façade walls show a positive effect in protecting the concrete. The state of conservation has a great variability across countries.

An optimal control algorithm using a virtual tuned mass damper called virtual TMD to control the levitation force of a magnetic system is developed for resonance suppression of a maglev vehicle moving on multi-span guideway girders. Since the optimal dynamic parameters of a TMD in vibration control are well developed, the optimal tuning gains required to control the magnetic oscillations of the maglev bogie can be directly used and fed back to the maglev control system. To address the dynamic interaction analysis from the maglev vehicle to the guideway girders and vice versa, the entire coupling system is decomposed into two subsystems, one is the moving vehicle subsystem and another the stationary guideway subsystem. Then, an incremental–iterative procedure associated with the Newmark method is presented to solve the two sets of subsystem equations. Finally, the control effectiveness and parametric studies of the optimal virtual TMD scheme on resonance reduction of the moving maglev vehicle are demonstrated.

The aim of the paper is to outline some important attributes of non-holonomic systems, which appear in dynamics of deformable systems interacting with neighborhood. The paper is oriented to theoretical way of investigation. Its core consists in characterization of basic and generalized non-holonomic systems inspired by civil and mechanical engineering, but coming also frequently from other disciplines. Definition of a dynamic system consists of specification of the system itself and relevant constraints representing links with surrounding environment. The governing differential system itself is deduced from a definition based on the Hamiltonian principle. A new form of the generalized Lagrange equation system is derived assuming higher time derivatives of displacement components in the kinetic energy definition, as they emerge due to interaction of mechanical and other physical fields. Linear and nonlinear definitions of non-holonomic constraints including arbitrary time derivative order, which originate from interaction of mechanical and other physical fields are discussed. Consequently, the constraints can be of a very general character; they include many variants from a simple geometric coupling with fixed points and interaction with the movement trajectory to a soft relation to surrounding area via complicated time-dependent constraints of deterministic or random types. Lagrangian multiplier techniques are employed incorporating the non-holonomic constraints of simple or higher order into the complete mathematical model. Comparison with corresponding equation systems obtained by means of the virtual works principle is done. Several particular mathematical models deduced by this conventional way including classical Lagrangian equation system are cited and interpreted in view of the new model following from the Hamiltonian principle. Strengths and shortcomings of both procedures are evaluated and domains of the new approach preference are outlined. Four illustrating examples are included to demonstrate the large variety of dynamic systems. Relation to some branches beyond classical definition of dynamics are mentioned in order to demonstrate the general character of the theoretical background discussed and its applicability in domains apparently far from mechanical or civil engineering.

The tight regulation of cytoskeleton dynamics is required for a number of cellular processes, including migration, division and differentiation. YAP-TEAD respond to cell-cell interaction and to substrate mechanics and, among their downstream effects, prompt focal adhesion (FA) gene transcription, thus contributing to FA-cytoskeleton stability. This activity is key to the definition of adult cell mechanical properties and function. Its regulation and role in pluripotent stem cells are poorly understood. Human PSCs display a sustained basal YAP-driven transcriptional activity despite they grow in very dense colonies, indicating these cells are insensitive to contact inhibition. PSC inability to perceive cell-cell interactions can be restored by tampering with Tankyrase enzyme, thus favouring AMOT inhibition of YAP function. YAP-TEAD complex is promptly inactivated when germ layers are specified, and this event is needed to adjust PSC mechanical properties in response to physiological substrate stiffness. By providing evidence that YAP-TEAD1 complex targets key genes encoding for proteins involved in cytoskeleton dynamics, we suggest that substrate mechanics can direct PSC specification by influencing cytoskeleton arrangement and intracellular tension. We propose an aberrant activation of YAP-TEAD1 axis alters PSC potency by inhibiting cytoskeleton dynamics, thus paralyzing the changes in shape requested for the acquisition of the given phenotype.

Metakaolinite was obtained by thermal treatment of natural kaolinite. Both of them, kaolinite with structurally bonded water and metakaolinite without it, were, after sieving to acceptable size fraction, plasma sprayed. The coatings were rather lightweight and composed predominantly of amorphous material. Stainless steel was used for producing self standing deposits, whereas other materials like carbon steel or ceramic tiles formed a permanent substrate-coating system. Metakaolinite coating was less porous, harder and its thermal behavior was simpler compared to kaolinite. Crystallization and formation of secondary phases was monitored after annealing with and without dust particles known in the barrier coatings field as CMAS.

The contribution deals with the architecture of a virtual collection of cuneiform tablets, conceived as a complex system combining and integrating several domains of information obtained from various types of analyses. The collection, containing some 400 Old Assyrian tablets from the excavations of Bedřich Hrozný in Kültepe (Turkey, ancient Kanesh) and originating in a narrow chronological window (ca. 20th–19th century BCE), is a special type of pottery with additional layer of textual information in cuneiform script. The digitization of the collection includes the digital models of the artifacts (3D models, stereometric and standard photographs, Structure-from-Motion), but also additional data on individual objects (physical properties, such as dimensions, colour, shapes, composition). The textual part is made available via standard methods of corpus linguistics and philological data is grouped together for some important attributes (persons, goods, links). The data stemming from the collection is connected with external data, placing the database in the context of cultural and historical development.

The contribution regards a mathematical single-degree-of-freedom model of a slender structure vibrating in an air flow. Based on an experimental investigation, movement of such structures can be expressed by van der PolDuffing-type equations. Several particular configuration parameter settings for a white and non-white Gaussian random excitation together with deterministic harmonic forcing are considered and numerically analysed. The results support recently published analytic formulas.

The aim of the study is to demonstrate a couple of special states which can be encountered at the system of a ball moving in a spherical cavity working as a passive tuned mass damper (TMD) of slender engineering structures. The system includes six degrees of freedom with three non-holonomic constraints being under horizontal additive kinematic excitation. The Appell–Gibbs approach is used to deduce the governing differential system. Uniaxial and biaxial types of kinematic excitation are considered. Among biaxial, a special attention is paid to circular setting. Influence of the rolling and spinning damping in contact of the ball with cavity is discussed. Under uniaxial excitation is the system auto-parametric and posses multiple solutions. The individual response branches can be identified when the excitation frequency is swept up or down with respect to setting up of initial conditions. Among stable branches reveal those with very low and sometimes zero approaching stability level. Although the accessibility of relevant trajectories is often very subtle due to effect of the dynamic stability, these post-critical phenomena accumulate a lot of energy. Hence, they can be very dangerous for TMD and other important engineering systems. Some general recommendations for practice are formulated.

The growing volumes of particularly heavy truck traffic with high road pavement loading values and, in many cases, poor quality and uneven road pavement surfaces intensify the effects technical seismicity on buildings situated in the vicinity of traffic routes.