Numerical combination for nonlinear analysis of structures coupled to layered soils

This paper presents an alternative coupling strategy between the Boundary Element Method (BEM) and the Finite Element Method (FEM) in order to create a computational code for the analysis of geometrical nonlinear 2D frames coupled to layered soils. The soil is modeled via BEM, considering multiple inclusions and internal load lines, through an alternative formulation to eliminate traction variables on subregions interfaces. A total Lagrangean formulation based on positions is adopted for the consideration of the geometric nonlinear behavior of frame structures with exact kinematics. The numerical coupling is performed by an algebraic strategy that extracts and condenses the equivalent soil's stiffness matrix and contact forces to be introduced into the frame structures hessian matrix and internal force vector, respectively. The formulation covers the analysis of shallow foundation structures and piles in any direction. Furthermore, the piles can pass through different layers. Numerical examples are shown in order to illustrate and confirm the accuracy and applicability of the proposed technique.

Interactive simulation of flexible parts

Computer simulations play an ever growing role for the development of automotive products. Assembly simulation, as well as many other processes, are used systematically even before the first physical prototype of a vehicle is built in order to check whether particular components can be assembled easily or whether another part is in the way. Usually, this kind of simulation is limited to rigid bodies. However, a vehicle contains a multitude of flexible parts of various types: cables, hoses, carpets, seat surfaces, insulations, weatherstrips... Since most of the problems using these simulations concern one-dimensional components and since an intuitive tool for cable routing is still needed, we have chosen to concentrate on this category, which includes cables, hoses and wiring harnesses. In this thesis, we present a system for simulating one dimensional flexible parts such as cables or hoses. The modeling of bending and torsion follows the Cosserat model. For this purpose we use a generalized spring-mass system and describe its configuration by a carefully chosen set of coordinates. Gravity and contact forces as well as the forces responsible for length conservation are expressed in Cartesian coordinates. But bending and torsion effects can be dealt with more effectively by using quaternions to represent the orientation of the segments joining two neighboring mass points. This augmented system allows an easy formulation of all interactions with the best appropriate coordinate type and yields a strongly banded Hessian matrix. An energy minimizing process accounts for a solution exempt from the oscillations that are typical of spring-mass systems. The use of integral forces, similar to an integral controller, allows to enforce exactly the constraints. The whole system is numerically stable and can be solved at interactive frame rates. It is integrated in the DaimlerChrysler in-house Virtual Reality Software veo for use in applications such as cable routing and assembly simulation and has been well received by users. Parts of this work have been published at the ACM Solid and Physical Modeling Conference 2006 and have been selected for the special issue of the Computer-Aided-Design Journal to the conference.

Mechanical microcontacts of powder particles studied with the quartz crystal microbalance

Within this work, a particle-polymer surface system is studied with respect to the particle-surface interactions. The latter are governed by micromechanics and are an important aspect for a wide range of industrial applications. Here, a new methodology is developed for understanding the adhesion process and measure the relevant forces, based on the quartz crystal microbalance, QCM. rnThe potential of the QCM technique for studying particle-surface interactions and reflect the adhesion process is evaluated by carrying out experiments with a custom-made setup, consisting of the QCM with a 160 nm thick film of polystyrene (PS) spin-coated onto the quartz and of glass particles, of different diameters (5-20µm), deposited onto the polymer surface. Shifts in the QCM resonance frequency are monitored as a function of the oscillation amplitude. The induced frequency shifts of the 3rd overtone are found to decrease or increase, depending on the particle-surface coupling type and the applied oscillation (frequency and amplitude). For strong coupling the 3rd harmonic decreased, corresponding to an “added mass” on the quartz surface. However, positive frequency shifts are observed in some cases and are attributed to weak-coupling between particle and surface. Higher overtones, i.e. the 5th and 7th, were utilized in order to derive additional information about the interactions taking place. For small particles, the shift for specific overtones can increase after annealing, while for large particle diameters annealing causes a negative frequency shift. The lower overtones correspond to a generally strong-coupling regime with mainly negative frequency shifts observed, while the 7th appears to be sensitive to the contact break-down and the recorded shifts are positive.rnDuring oscillation, the motion of the particles and the induced frequency shift of the QCM are governed by a balance between inertial forces and contact forces. The adherence of the particles can be increased by annealing the PS film at 150°C, which led to the formation of a PS meniscus. For the interpretation, the Hertz, Johnson-Kendall-Roberts, Derjaguin-Müller-Toporov and the Mindlin theory of partial slip are considered. The Mindlin approach is utilized to describe partial slip. When partial slip takes place induced by an oscillating load, a part of the contact ruptures. This results in a decrease of the effective contact stiffness. Additionally, there are long-term memory effects due to the consolidation which along with the QCM vibrations induce a coupling increase. However, the latter can also break the contact, lead to detachment and even surface damage and deformation due to inertia. For strong coupling the particles appear to move with the vibrations and simply act as added effective mass leading to a decrease of the resonance frequency, in agreement with the Sauerbrey equation that is commonly used to calculate the added mass on a QCM). When the system enters the weak-coupling regime the particles are not able to follow the fast movement of the QCM surface. Hence, they effectively act as adding a “spring” with an additional coupling constant and increase the resonance frequency. The frequency shift, however, is not a unique function of the coupling constant. Furthermore, the critical oscillation amplitude is determined, above which particle detach. No movement is detected at much lower amplitudes, while for intermediate values, lateral particle displacement is observed. rnIn order to validate the QCM results and study the particle effects on the surface, atomic force microscopy, AFM, is additionally utilized, to image surfaces and measure surface forces. By studying the surface of the polymer film after excitation and particle removal, AFM imaging helped in detecting three different meniscus types for the contact area: the “full contact”, the “asymmetrical” and a third one including a “homocentric smaller meniscus”. The different meniscus forms result in varying bond intensity between particles and polymer film, which could explain the deviation between number of particles per surface area measured by imaging and the values provided by the QCM - frequency shift analysis. The asymmetric and the homocentric contact types are suggested to be responsible for the positive frequency shifts observed for all three measured overtones, i.e. for the weak-coupling regime, while the “full contact” type resulted in a negative frequency shift, by effectively contributing to the mass increase of the quartz..rnThe interplay between inertia and contact forces for the particle-surface system leads to strong- or weak-coupling, with the particle affecting in three mentioned ways the polymer surface. This is manifested in the frequency shifts of the QCM system harmonics which are used to differentiate between the two interaction types and reflect the overall state of adhesion for particles of different size.rn

Rheology of arrested colloids : a parameter study using novel experimental methods

The steadily increasing diversity of colloidal systems demands for new theoretical approaches and a cautious experimental characterization. Here we present a combined rheological and microscopical study of colloids in their arrested state whereas we did not aim for a generalized treatise but rather focused on a few model colloids, liquid crystal based colloidal suspensions and sedimented colloidal films. We laid special emphasis on the understanding of the mutual influence of dominant interaction mechanisms, structural characteristics and the particle properties on the mechanical behavior of the colloid. The application of novel combinations of experimental techniques played an important role in these studies. Beside of piezo-rheometry we employed nanoindentation experiments and associated standardized analysis procedures. These rheometric methods were complemented by real space images using confocal microscopy. The flexibility of the home-made setup allowed for a combination of both techniques and thereby for a simultaneous rheological and three-dimensional structural analysis on a single particle level. Though, the limits of confocal microscopy are not reached by now. We show how hollow and optically anisotropic particles can be utilized to quantify contact forces and rotational motions for individual particles. In future such data can contribute to a better understanding of particle reorganization processes, such as the liquidation of colloidal gels and glasses under shear.

Ligament balancing in TKA: Evaluation of a force-sensing device and the influence of patellar eversion and ligament release

Ligament balancing in total knee arthroplasty may have an important influence on joint stability and prosthesis lifetime. In order to provide quantitative information and assistance during ligament balancing, a device that intraoperatively measures knee joint forces and moments was developed. Its performance and surgical advantages were evaluated on six cadaver specimens mounted on a knee joint loading apparatus allowing unconstrained knee motion as well as compression and varus-valgus loading. Four different experiments were performed on each specimen. (1) Knee joints were axially loaded. Comparison between applied and measured compressive forces demonstrated the accuracy and reliability of in situ measurements (1.8N). (2) Assessment of knee stability based on condyle contact forces or varus-valgus moments were compared to the current surgical method (difference of varus-valgus loads causing condyle lift-off). The force-based approach was equivalent to the surgical method while the moment-based, which is considered optimal, showed a tendency of lateral imbalance. (3) To estimate the importance of keeping the patella in its anatomical position during imbalance assessment, the effect of patellar eversion on the mediolateral distribution of tibiofemoral contact forces was measured. One fourth of the contact force induced by the patellar load was shifted to the lateral compartment. (4) The effect of minor and major medial collateral ligament releases was biomechanically quantified. On average, the medial contact force was reduced by 20% and 46%, respectively. Large variation among specimens reflected the difficulty of ligament release and the need for intraoperative force monitoring. This series of experiments thus demonstrated the device's potential to improve ligament balancing and survivorship of total knee arthroplasty.

Discrete element methods for asphalt concrete : development and application of user-defined microstructural models and a viscoelastic micromechanical model

As an important Civil Engineering material, asphalt concrete (AC) is commonly used to build road surfaces, airports, and parking lots. With traditional laboratory tests and theoretical equations, it is a challenge to fully understand such a random composite material. Based on the discrete element method (DEM), this research seeks to develop and implement computer models as research approaches for improving understandings of AC microstructure-based mechanics. In this research, three categories of approaches were developed or employed to simulate microstructures of AC materials, namely the randomly-generated models, the idealized models, and image-based models. The image-based models were recommended for accurately predicting AC performance, while the other models were recommended as research tools to obtain deep insight into the AC microstructure-based mechanics. A viscoelastic micromechanical model was developed to capture viscoelastic interactions within the AC microstructure. Four types of constitutive models were built to address the four categories of interactions within an AC specimen. Each of the constitutive models consists of three parts which represent three different interaction behaviors: a stiffness model (force-displace relation), a bonding model (shear and tensile strengths), and a slip model (frictional property). Three techniques were developed to reduce the computational time for AC viscoelastic simulations. It was found that the computational time was significantly reduced to days or hours from years or months for typical three-dimensional models. Dynamic modulus and creep stiffness tests were simulated and methodologies were developed to determine the viscoelastic parameters. It was found that the DE models could successfully predict dynamic modulus, phase angles, and creep stiffness in a wide range of frequencies, temperatures, and time spans. Mineral aggregate morphology characteristics (sphericity, orientation, and angularity) were studied to investigate their impacts on AC creep stiffness. It was found that aggregate characteristics significantly impact creep stiffness. Pavement responses and pavement-vehicle interactions were investigated by simulating pavement sections under a rolling wheel. It was found that wheel acceleration, steadily moving, and deceleration significantly impact contact forces. Additionally, summary and recommendations were provided in the last chapter and part of computer programming codes wree provided in the appendixes.

Ankle joint pressure changes in a pes cavovarus model: supramalleolar valgus osteotomy versus lateralizing calcaneal osteotomy

BACKGROUND: A fixed cavovarus foot deformity can be associated with anteromedial ankle arthrosis due to elevated medial joint contact stresses. Supramalleolar valgus osteotomies (SMOT) and lateralizing calcaneal osteotomies (LCOT) are commonly used to treat symptoms by redistributing joint contact forces. In a cavovarus model, the effects of SMOT and LCOT on the lateralization of the center of force (COF) and reduction of the peak pressure in the ankle joint were compared. METHODS: A previously published cavovarus model with fixed hindfoot varus was simulated in 10 cadaver specimens. Closing wedge supramalleolar valgus osteotomies 3 cm above the ankle joint level (6 and 11 degrees) and lateral sliding calcaneal osteotomies (5 and 10 mm displacement) were analyzed at 300 N axial static load (half body weight). The COF migration and peak pressure decrease in the ankle were recorded using high-resolution TekScan pressure sensors. RESULTS: A significant lateral COF shift was observed for each osteotomy: 2.1 mm for the 6 degrees (P = .014) and 2.3 mm for the 11 degrees SMOT (P = .010). The 5 mm LCOT led to a lateral shift of 2.0 mm (P = .042) and the 10 mm LCOT to a shift of 3.0 mm (P = .006). Comparing the different osteotomies among themselves no significant differences were recorded. No significant anteroposterior COF shift was seen. A significant peak pressure reduction was recorded for each osteotomy: The SMOT led to a reduction of 29% (P = .033) for the 6 degrees and 47% (P = .003) for the 11 degrees osteotomy, and the LCOT to a reduction of 41% (P = .003) for the 5 mm and 49% (P = .002) for the 10 mm osteotomy. Similar to the COF lateralization no significant differences between the osteotomies were seen. CONCLUSION: LCOT and SMOT significantly reduced anteromedial ankle joint contact stresses in this cavovarus model. The unloading effects of both osteotomies were equivalent. More correction did not lead to significantly more lateralization of the COF or more reduction of peak pressure but a trend was seen. CLINICAL RELEVANCE: In patients with fixed cavovarus feet, both SMOT and LCOT provided equally good redistribution of elevated ankle joint contact forces. Increasing the amount of displacement did not seem to equally improve the joint pressures. The site of osteotomy could therefore be chosen on the basis of surgeon's preference, simplicity, or local factors in case of more complex reconstructions.

Dynamic Analysis of high Speed Railway Traffic Loads on Ballasted Track

This paper reports the studies carried out to develop and calibrate the optimal models for the objectives of this work. In particular, quarter bogie model for vehicle, rail-wheel contact with Lagrangian multiplier method, 2D spatial discretization were selected as the optimal decisions. Furthermore, the 3D model of coupled vehicle-track also has been developed to contrast the results obtained in the 2D model. The calculations were carried out in the time domain and envelopes of relevant results were obtained for several track profiles and speed ranges. Distributed elevation irregularities were generated based on power spectral density (PSD) distributions. The results obtained include the wheel-rail contact forces, forces transmitted to the bogie by primary suspension. The latter loads are relevant for the purpose of evaluating the performance of the infrastructure

Models for Lateral Dynamic Interaction of High-Speed Trains and Bridges

In this work a methodology for analysing the lateral coupled behavior of large viaducts and high-speed trains is proposed. The finite element method is used for the structure, multibody techniques are applied for vehicles and the interaction between them is established introducing wheel-rail nonlinear contact forces. This methodology is applied for the analysis of the railway viaduct of the R´ıo Barbantino, which is a very long and tall bridge in the north-west spanish high-speed line.

Comparison of dynamic effects of high-speed traffic load on ballasted track using a simplified two-dimensional and full three-dimensional model.

The vertical dynamic actions transmitted by railway vehicles to the ballasted track infrastructure is evaluated taking into account models with different degree of detail. In particular, we have studied this matter from a two-dimensional (2D) finite element model to a fully coupled three-dimensional (3D) multi-body finite element model. The vehicle and track are coupled via a non-linear Hertz contact mechanism. The method of Lagrange multipliers is used for the contact constraint enforcement between wheel and rail. Distributed elevation irregularities are generated based on power spectral density (PSD) distributions which are taken into account for the interaction. The numerical simulations are performed in the time domain, using a direct integration method for solving the transient problem due to the contact nonlinearities. The results obtained include contact forces, forces transmitted to the infrastructure (sleeper) by railpads and envelopes of relevant results for several track irregularities and speed ranges. The main contribution of this work is to identify and discuss coincidences and differences between discrete 2D models and continuum 3D models, as wheel as assessing the validity of evaluating the dynamic loading on the track with simplified 2D models

Nonlinear models for lateral dynamics of railway vehicles on bridges subject to wind action

The study of lateral dynamics of running trains on bridges is of importance mainly for the safety of the traffic, and may be relevant for laterally compliant bridges. These studies require threedimensional coupled vehicle-bridge models, wheree consideration of wheel to rail contact is a key aspect. Furthermore, an adequate evaluation of safety of rail traffic requires nonlinear models. A nonlinear coupled model is proposed here for vehicle-structure vertical and lateral dynamics. Vehicles are considered as fully three-dimensional multibody systems including gyroscopic terms and large rotation effects. The bridge structure is modeled by means of finite elements which may be of beam, shell or continuum type and may include geometric or material nonlinearities. The track geometry includes distributed track alignment irregularities. Both subsystems (bridge and vehicles) are described with coordinates in absolute reference frames, as opposed to alternative approaches which describe the multibody system with coordinates relative to the base bridge motion. The wheelrail contact employed is a semi-Hertzian model based on realistic wheel-rail profiles. It allows a detailed geometrical description of the contact patch under each wheel including multiple-point contact, flange contact and uplift. Normal and tangential stresses in each contact are integrated at each time-step to obtain the resultant contact forces. The models have been implemented within an existing finite element analysis software with multibody capabilities, Abaqus (Simulia Ltd., 2010). Further details of the model are presented in Antolín et al. (2012). Representative applications are presented for railway vehicles under lateral wind action on laterally compliant viaducts, showing the relevance of the nonlinear wheel-rail contact model as well as the interaction between bridge and vehicle.

Führungsbauteile aus faserverstärkten Kunststoffen in intralogistischen

In vielen Anwendungen der Intralogistik lassen sich Führungssysteme mit Stützrollen finden, die hohen Belastungen ausgesetzt sind. Hierbei werden oftmals Profilträger aus Stahlwerkstoffen als führende Bauteile eingesetzt. Deren Bewegung erfordert aufgrund der hohen Eigenmassen einen erheblichen Energiebedarf. Im vorliegenden Artikel wird die Entwicklung von derartigen Komponenten aus faserverstärkten Kunststoffen beschrieben. Der Fokus liegt auf der Eintragung hoher Kontaktkräfte in das Bauteil. Es werden die notwendigen Anforderungen dargestellt sowie die Entwicklung eines speziellen Rollenprüfstandes erläutert. Zudem beinhaltet der Artikel die systematische Entwicklung neuer Funktionselemente und die Herleitung einer Methodik zur Untersuchung der Belastbarkeit des faserverstärkten Kunststoffes beim Einwirken einer Rolle als Teilergebnisse des Forschungsvorhabens.

On the study of train-track dynamic interactions caused by rail welds on discrete supported rails

The paper studies the influence of rail weld dip on wheel-rail contact dynamics, with particular reference to freight trains where it is important to increase the operating speed and also the load transported. This has produced a very precise model, albeit simple and cost-effective, which has enabled train-track dynamic interactions over rail welds to be studied to make it possible to quantify the influence on dynamic forces and displacements of the welding geometry; of the position of the weld relative to the sleeper; of the vehicle's speed; and of the axle load and wheelset unsprung mass. It is a vertical model on the spatial domain and is drawn up in a simple fashion from vertical track receptances. For the type of track and vehicle used, the results obtained enable the quantification of increases in wheel-rail contact forces due to the new speed and load conditions.

Robotic Sensing and Manipulation of Deformable Linear Objects with Learning-based methods

Nowadays robotic applications are widespread and most of the manipulation tasks are efficiently solved. However, Deformable-Objects (DOs) still represent a huge limitation for robots. The main difficulty in DOs manipulation is dealing with the shape and dynamics uncertainties, which prevents the use of model-based approaches (since they are excessively computationally complex) and makes sensory data difficult to interpret. This thesis reports the research activities aimed to address some applications in robotic manipulation and sensing of Deformable-Linear-Objects (DLOs), with particular focus to electric wires. In all the works, a significant effort was made in the study of an effective strategy for analyzing sensory signals with various machine learning algorithms. In the former part of the document, the main focus concerns the wire terminals, i.e. detection, grasping, and insertion. First, a pipeline that integrates vision and tactile sensing is developed, then further improvements are proposed for each module. A novel procedure is proposed to gather and label massive amounts of training images for object detection with minimal human intervention. Together with this strategy, we extend a generic object detector based on Convolutional-Neural-Networks for orientation prediction. The insertion task is also extended by developing a closed-loop control capable to guide the insertion of a longer and curved segment of wire through a hole, where the contact forces are estimated by means of a Recurrent-Neural-Network. In the latter part of the thesis, the interest shifts to the DLO shape. Robotic reshaping of a DLO is addressed by means of a sequence of pick-and-place primitives, while a decision making process driven by visual data learns the optimal grasping locations exploiting Deep Q-learning and finds the best releasing point. The success of the solution leverages on a reliable interpretation of the DLO shape. For this reason, further developments are made on the visual segmentation.

The effect of elastic modulus and equilibrium vapor adsorption on capillary forces

Die Kapillarkraft entsteht durch die Bildung eines Meniskus zwischen zwei Festkörpen. In dieser Doktorarbeit wurden die Auswirkungen von elastischer Verformung und Flϋssigkeitadsorption auf die Kapillarkraft sowohl theoretisch als auch experimentell untersucht. Unter Verwendung eines Rasterkraftmikroskops wurde die Kapillarkraft zwischen eines Siliziumoxid Kolloids von 2 µm Radius und eine weiche Oberfläche wie n.a. Polydimethylsiloxan oder Polyisopren, unter normalen Umgebungsbedingungen sowie in variierende Ethanoldampfdrϋcken gemessen. Diese Ergebnisse wurden mit den Kapillarkräften verglichen, die auf einem harten Substrat (Silizium-Wafer) unter denselben Bedingungen gemessen wurden. Wir beobachteten eine monotone Abnahme der Kapillarkraft mit zunehmendem Ethanoldampfdruck (P) fϋr P/Psat > 0,2, wobei Psat der Sättigungsdampfdruck ist.rnUm die experimentellen Ergebnisse zu erklären, wurde ein zuvor entwickeltes analytisches Modell (Soft Matter 2010, 6, 3930) erweitert, um die Ethanoladsorption zu berϋcksichtigen. Dieses neue analytische Modell zeigte zwei verschiedene Abhängigkeiten der Kapillarkraft von P/Psat auf harten und weichen Oberflächen. Fϋr die harte Oberfläche des Siliziumwafers wird die Abhängigkeit der Kapillarkraft vom Dampfdruck vom Verhältnis der Dicke der adsorbierten Ethanolschicht zum Meniskusradius bestimmt. Auf weichen Polymeroberflächen hingegen hängt die Kapillarkraft von der Oberflächenverformung und des Laplace-Drucks innerhalb des Meniskus ab. Eine Abnahme der Kapillarkraft mit zunehmendem Ethanoldampfdruck hat demnach eine Abnahme des Laplace-Drucks mit zunehmendem Meniskusradius zur folge. rnDie analytischen Berechnungen, fϋr die eine Hertzsche Kontakt-deformation angenommen wurde, wurden mit Finit Element Methode Simulationen verglichen, welche die reale Deformation des elastischen Substrats in der Nähe des Meniskuses explizit berϋcksichtigen. Diese zusätzliche nach oben gerichtete oberflächenverformung im Bereich des Meniskus fϋhrt zu einer weiteren Erhöhung der Kapillarkraft, insbesondere fϋr weiche Oberflächen mit Elastizitätsmodulen < 100 MPa.rn