Punctual Loads Research Articles

On the modal characteristics and stability of translating cable: Application to an overall line of cable transport systems

Moving cables are used for many applications in engineering structures such as cable-supported transport systems that involves mobile cables suspended between supports for moving attached vehicles. Advantages of such systems in terms of cost, footprint and energy efficiency make its urban integration as one of the solutions to meet the need for new mobilities. Because of the inherent cable’s flexibility and the modification of dynamic properties during the cable movement, such systems are sensitive to the effects of perturbations and self-sustaining oscillations. The methods commonly used to describe cable dynamics are restricted to small static sag case with a predominant vertical dynamics. To accurately analyse a multi-segment mobile cable, this paper proposes an hybrid analytical–numerical strategy to deal with a general mechanical elementary model of a cable in unsteady translation formulated in curvilinear abscissa derived from the formalism of continuum mechanics. An assembly procedure permits to deal with a more complex system considering a cable loop in contact with intermediary supports and punctual loads according to different boundary conditions, considering the coupling between the vertical dynamics activated at the local scale of a span and the longitudinal dynamics activated at the scale of the whole cable loop. The translation speed and acceleration gyroscopic effects on the system’s complex modes are studied and design rules are provided to guide an optimal conception avoiding strong oscillations of the system.

Towards the numerical ground-borne vibrations predictive models as a design tool for railway lines: A starting point THE

In recent decades, High-Speed Railway (HSR) lines have become one of the most extended and environmental-friendly ways to plan new mass transport networks. These systems are directly influenced by its operational speed generated dynamic effects and the areas where it runs through. This necessarily requires to predict ground-borne vibrations generated by trains passing-by populated areas and its influence zone.Trends in ground-borne measurements, prediction models, and isolation systems are usually performed for maximum operation speed. This method implies the maximum dynamic forces which are suitable for structural calculations (generally developed in time domain) but not necessary for vibration related issues (emission and/or transmission). Additionally, these studies are mainly focused on urban areas where maximum operational speed are frequently far from railways service’s top speeds.Related to frequency domain, it is known that upper frequencies are not the most disturbing ones. In fact, European structural standards usually cut frequencies off at 30 Hz, so much relevant information for vibrational prediction is ignored due to it does not influence structural issues.Moreover, current common predictive numerical models usually apply punctual loads (birth & death) that are disposed to run in certain speed conditions. This method, which is considered valid for time domain analysis, are identified to be incomplete for frequency domain components due to its discontinuous application of loads.The implementation of contact theories in the wheel-rail interface implies a continuous load application, refining the obtained results but increasing computational cost.In this study, different scenarios are compared varying inner and boundary conditions of a model, with the aim of validate results and optimize resources by obtaining a parametrical influence study that will show how different assumptions and cases could condition ground-borne vibrational studies results.

Flexural failure of fabric reinforced cementitious mortar (FRCM) plates under punctual loads: Experimental test, analytical approach and numerical simulation

Fabric-reinforced cementitious matrix (FCRMs) are composites that produce lighter and more durable strengthening solutions. In this study, carbon and basalt fabrics were used to manufactured FRCM plate specimens. These plates were subjected to a centered punctual load with different punch diameters. Flexural failure mode was observed. Experimental tests showed that carbon and basalt fabrics improved notably the load capacity and the stiffness of mortar plates compared to unreinforced ones. Moreover, failure in the reinforced plates was progressive, preventing the sudden brittle failure of the unreinforced ones. Analytical and numerical models were adjusted and validated from experimental results, and both have proved to be effective calculation tools. What is more, numerical model allowed to determine a sliding tensile stress for the carbon fabric used in this study.

Practical expressions for the design of DGUs. The BAM approach

The structural response of Double Glazing Units (DGUs), composed by two glass panes held together by structural edge seals, entrapping a gas for thermal and acoustic insulation, is governed by the load sharing between the glass elements, due to a complex interaction with the gas in the interpane space. Various methods are proposed by standards to evaluate it when DGUs are subjected to climatic loads and/or uniform pressure, but the case of line distributed and punctual load usually requires the use of FEM softwares.Very recently, a new approach -the Betti’s Analytical Method (BAM)- has been proposed for the evaluation of the load sharing in DGUs under the most various boundary and loading conditions. Here, the method is revised, providing compact formulas and synthetic tables for ease of reference and immediate applicability, for both rectangular and triangular DGUs. Furthermore, the BAM approach is validated by means of comparison with numerical results obtained with MEPLA ISO software. For DGUs made of laminated glass panels, a practical approach, based on the use of the Enhanced Effective Thickness (EET) model, is suggested, and its accuracy is validated by means of numerical comparisons.

Simulation of hyperelastic materials in real-time using deep learning.

The finite element method (FEM) is among the most commonly used numerical methods for solving engineering problems. Due to its computational cost, various ideas have been introduced to reduce computation times, such as domain decomposition, parallel computing, adaptive meshing, and model order reduction. In this paper we present U-Mesh: A data-driven method based on a U-Net architecture that approximates the non-linear relation between a contact force and the displacement field computed by a FEM algorithm. We show that deep learning, one of the latest machine learning methods based on artificial neural networks, can enhance computational mechanics through its ability to encode highly non-linear models in a compact form. Our method is applied to three benchmark examples: a cantilever beam, an L-shape and a liver model subject to moving punctual loads. A comparison between our method and proper orthogonal decomposition (POD) is done through the paper. The results show that U-Mesh can perform very fast simulations on various geometries and topologies, mesh resolutions and number of input forces with very small errors.

Desenvolvimento de um programa computacional para análise de vigas Euler-Bernoulli utilizando a linguagem Pytho

Among the many areas of Civil Engineering, there is one known as Structures. In view of the growing sophistication of the constructions, and consequently an increase in the complexity of the calculations involved, auxiliary computational software has been revolutionizing this area. Already present in the professional work of the engineer, this technological support has a direct effect on the teaching and learning process, since many computer programs, some of them difficult to understand by students, are study tools of the disciplines of the Structures area. Among the contents in which the students present more difficulty, there is Finite Element Analysis, a discipline offered on graduation and that had its practical development linked to the advent of computation. By being the method most used as a computational tool in the field of engineering these days, this knowledge is indispensable to the students of this course. The objective of this work is to construct a computational code in order to facilitate the study of linear-elastic behavior of Euler-Bernoulli beams with punctual loads using the Finite Element Analysis. For this, a numerical example was analyzed, with the aid of a program implemented with the Python® language, to reinforce the effectiveness of the program and, consequently, to promote the improvement of student learning.

Optics, mechanics, and energetics of two-dimensional MoS2 nanostructures from a theoretical perspective.

CONSPECTUS: Nanostructures based on molybdenum disulfide (MoS2) are by far the most common and well-studied systems among two-dimensional (2D) semiconducting materials. Although still being characterized as a "promising material", catalytic activity of MoS2 nanostructures has been found, and applications in lubrication processes are pursued. Because exfoliation techniques have improved over the past years, monolayer MoS2 is easily at hand; thus, experimental studies on its electronic properties and applicability are in scientific focus, and some MoS2-based electronic devices have been reported already. Additionally, the improvement of atomic force microscopy led to nanoindentation experiments, in which the exceptional mechanical properties of MoS2 could be confirmed. In this Account, we review recent results from density-functional based calculations on several MoS2-based nanostructures; we have chosen to follow several experimental routes focusing on different nanostructures and their specific properties. MoS2-based triangular nanoflakes are systems that are experimentally well described and studied with a special focus on their optical absorption. The interpretation of our calculations fits well to the experimental picture: the absorption peaks in the visible light range show a quantum-confinement effect; they originate from excitations into the edge states. Additionally, delocalized metallic-like states are present close to the Fermi level, which do not contribute to photoabsorption in the visible range. Additionally, nanoindentation experiments have been simulated to obtain mechanical properties of the MoS2 material and to study the influence of deformation on the system's electronics. In these molecular-dynamics simulations, a tip penetrates a MoS2 monolayer, and the obtained Young's modulus and breaking stress agree very well with experimentally obtained values. Whereas the structural properties, such as bond lengths and layer contraction, vary locally differently upon indentation, the electronic structure in terms of the density of states, the gap between occupied and unoccupied states, or the quantum transport change only slightly. The robustness of the material with respect to electronic and mechanical properties makes monolayer MoS2 special. However, it is important to note that this robustness refers to a local disturbance through deformation and still seems to be dependent on the defect concentration. Finally, we present a comparison of the thermodynamic stabilities of different MoS2-based nanostructures with a focus on nanoflakes, fullerene-like nanooctahedra, and smaller Chevrel-type and non-Chevrel-type clusters (nanowires). All studied systems are stable in comparison to MoS2, Mo bulk, and the S8 crown, but only the studied nanoflakes and nanowires show specific stoichiometries, either sulfur-rich or sulfur-poor, whereas the nanooctahedra may adopt both. From the thermodynamic stabilities, it should be possible to deliberately choose specific nanostructures by thoughtful choices of the synthesis conditions. In conclusion, we present in this Account exceptional properties of MoS2-based nanostructures studied by means of density-functional theory. The focus lies on optical absorption in the visible range observed in triangular nanoflakes, which originate in the system's edge states, the robustness of monolayer MoS2 with respect to punctual loads regarding both mechanical and electronic properties, and the thermodynamic stability of most studied MoS2-based nanosystems revealing a correlation between composition and preferred morphology, particularly for 2D systems.

Extension of Euskalduna Conference Centre and Concert Hall: A Contemporary Application of Irregular Reciprocal Frames

Reciprocal frame structures, formed by a set of self-supported elements in a closed circuit, have long been used since antiquity to cover large spans with small elements.The roof structure of the Euskalduna conference centre and concert hall extension in Bilbao, covering an irregular geometry of 3000 m2 with a maximum span of 45 m, presented an interesting opportunity to revisit the concept and to apply these classical systems.Furthermore, its analysis and development led to an interesting discussion on reciprocal frames. They showed great sensitivity of these systems to the local modification of a particular element, establishment of irregular load paths, mobilisation of almost the entire system when locally applying a punctual load and, finally, its large deformability.Besides, reciprocal frames present particular construction complexities and possibilities due to the moderate length of the structural elements, the predominance of shear-only connections and the necessity of the entire system to be completely erected to guarantee its stability.Euskalduna extension, completed in 2012, is one of the largest and a very particular case of irregular reciprocal frame structures built in the world. It shows the formal possibilities and potentiality of reciprocal frames to respond to free and irregular geometries.

Apparent negative mass in QCM sensors due to punctual rigid loading

Quartz Crystal Microbalances (QCM) are highly sensitive piezoelectric sensors able to detect very small loads attached to them. These devices are widely employed in many applications including process control and industrial and environmental monitoring. Mass loading is usually related to frequency shift by the well-known Sauerbrey's equation, valid for thin rigid homogeneous films. However, a significant deviation from this equation can occur when the mass is not uniformly distributed over the surface. Whereas the effects of a thin film on a QCM have been thoroughly studied, there are relatively few results on punctual loads, even though particles are usually deposited randomly and non-uniformly on the resonator surface. In this work, we have studied the effect of punctual rigid loading on the resonant frequency shift of a QCM sensor, both experimentally and using finite element method (FEM). The FEM numerical analysis was done using COMSOL software, 3D modeling a linear elastic piezoelectric solid and introducing the properties of an AT-cut quartz crystal. It is shown that a punctual rigid mass deposition on the surface of a QCM sensor can lead to positive shifts of resonance frequency, contrary to Sauerbrey's equation.

Wave propagation in finite structures due to transient loading with application to pyroshock simulation

AbstractPyroshocks are transient motions of a structure caused by e.g. explosion of ordnance devices. Prior to their launching space modules have to be tested for fulfillment of strict requirements concerning the expected acceleration during a space mission. Since, in practical applications, this is still based on empirical knowledge and time consuming testing procedures, an analytical way to face this problem is the modelling of a pyroshock test device for the simulation of mechanical impacts on plates carrying the module to be tested. From the mechanical point of view, the problem is described by the wave propagation in a disk or a plate carrying a point mass and being exposed to a punctual load caused by the impact of a sphere. The displacement field is calculated semi‐analytically by the use of a modal approach, HERTZian contact theory as well as the GALERKIN procedure. In order to systematically determine the optimum setup leading to a desired acceleration signal an evolution strategy is used as well as comparisons with experimental and FEM results have been made. The present procedure allows for a better and faster simulation and predictability of pyroshock tests. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The motion planning problem and exponential stabilisation of a heavy chain. Part I†

A model of a heavy chain system with a punctual load (tip mass) in the form of a system of partial differential equations is interpreted as an abstract semigroup system on a Hilbert state space. Our aim is to solve the output motion planning problem of the same nature as in the case of an unloaded heavy chain (Grabowski, P. (2003), ‘ Semigroup Model of Heavy Chain System with Application to a Motion Planning Problem’, in Proceedings of 9th IEEE International Conference: Methods and Models in Automation and Robotics, 25–28 August, Międzyzdroje, Poland, pp. 77–86 (IS1-2-3.PDF)). In order to solve this problem we first analyse its well-posedness and some basic properties. Next, we solve the output motion planning problem using a substitute of the inverse of the input–output operator represented in terms of the Laplace transforms. A problem of exponential stabilisation is also formulated and solved using a stabiliser of the colocated type. The exponential stabilisation is proved using the method of Lyapunov functionals combined with some frequency-domain tools. The method of Lyapunov functionals can be replaced by the spectral or exact controllability approach as shown in the second part (Grabowski, P. (2008), ‘The Motion Planning Problem and Exponential Stabilisation of a Heavy Chain. Part II’, Opuscula Mathematica, 28 (2008) (Special issue dedicated to the memory of Professor Andrzej Lasota), 481–505) of the present article. A laboratory setup which allows verification of the results in practice is described in detail. Its dynamical model is used as an example to illustrate the theoretical results. †Dedicated to Frank M. Callier on the occasion of his 65th birthday.

Experimental Study of Stress Induced Martensite Transformation under Plane State of Stress

An experimental study of stress induced martansite transformation by electrical strain gauges is present. The studies were performance on polycrystalline Cu-Al-Be Shape Memory Alloys. Beams and a bar in cantilever flexion hold to punctual load were instrumented with electrical strain gauges in several points where the state of stress is: a) simple tension, b) simple shear and b) tension-shear. Employing the trasforational load values in each plot was calculated critical principal stresses. Employing the results obtained, 1 2 σ −σ plots were constructed and a comparison with the yield Von-Mises criteria, Patoor model and Buchheit model for the critical stress were do.

Sur les opérateurs différentiels symétrisants relatifs aux systèmes non-conservatifs

For nonconservative systems, which we call systems with follower loads, a study is proposed concerning the differential operators which lead to a self-adjoint problem for a generalization of the Rayleigh quotient.In the case of punctual loads, we give the general expression for the identification of these operators. For some systems under follower loads, a new method is developed for the identification of the eigenvalues (critical load and critical frequency) when these operators do not exist. A numerical comparison is presented when the exact solutions do exist. PACS Nos. : 02.00 et 03.00