Documents published in Scipedia

• Power dissipation modelling in rolling contact

  A. Myśliński, A. Chudzikiewicz

  WCCM2024.

  
  

  Abstract

  This paper is concerned with the modeling of power dissipation due to friction and its relation with wear estimation in wheel–rail contact. In contact models, wear is usually described in terms of the wear depth function. This function modifies the gap between the contacting bodies as well as the shape of the surfaces of the wheel and rail in contact. In this paper, besides the wear depth function, the dissipated energy, rather than the contact stress, is taken into account to evaluate the wear impact on rail or wheel surfaces. The dissipated energy allows us to more precisely evaluate the wear debris amount as well as the depth of wear and its distribution along the contact interface. A two-dimensional rolling contact problem with frictional heat flow is considered. The elasto-plastic deformation of the rail is assumed. This contact problem is governed by a coupled system of mechanical and thermal equations in terms of generalized stresses, displacement and temperature. The finite element method is used to discretize this problem. The generalized Newton method is applied to numerically solve this mechanical subproblem. The dissipated power is evaluated based on the resultant force and slip at a reference point. Numerical results including the distribution of slip velocity, power factor and wear rate are provided and discussed.

  Abstract
  This paper is concerned with the modeling of power dissipation due to friction and its relation with wear estimation in wheel–rail contact. In contact models, wear is usually [...]

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• How does friction affect sliding contact mechanics?

  N. Menga, C. Mueller, G. Carbone, M. Mueser

  WCCM2024.

  
  

  Abstract

  Dealing with semi-infinite solids, interfacial friction is usually neglected, as normal and tangential displacements fields are independent on each other (unless material dissimilarity occurs). However, contacts involving a sufficiently thin layer, do not stick to such a simplified assumption, as thickness related normal/tangential coupling occurs, and surface frictional shear stresses do matter. It is the case, for instance, of classical rotary seals in boundary lubrication regimes, where rough frictional contacts between thin polymeric sealing lips and rotating shafts occur. Also, functional coatings to control the interface (adhesive, frictional, chemical, etc.) behavior, may be very thin and compliant, and usually experience frictional sliding during operation. All the same, these examples indicates that conditions exists where elastic coupling between in plane and out of plane displacements cannot be neglected and must be considered, instead. Here, we present our results on the rough contact mechanics of elastic and viscoelastic thin layers. We assume sliding conditions and friction at the interface, and we investigate the contact problem in the framework of linear (visco)elasticity, by relying on the Green’s functions approach. We show that, due to the friction and coupling, the presence of interfacial friction may lead to a significant increase of the contact area (up to 10%), compared to the frictionless case, which may affect specific functional response of the interface, such as electrical and thermal conductivity. Since the normal gap distribution is also affected by coupling and friction, the leak rate at the interface turns out significantly altered too. Coupling and friction also affect the contact pressure, which presents a certain degree of asymmetry leading (even for purely elastic materials) to an additional interlocking contribution to the tangential force opposing the relative motion at the interface. Therefore, the overall macroscale friction cannot be predicted by summing-up the local friction contributions occurring at microscale as commonly expected; it should instead include an additional coupled-induced term. The surface stress tensor is also affected, as due to friction and coupling very high tensile stresses are localized at the contact trailing edge, which are likely to induce material failure. In conclusion, we show that the common practice to neglect in-plane interactions in contact mechanics may lead to misleading tribological predictions.

  Abstract
  Dealing with semi-infinite solids, interfacial friction is usually neglected, as normal and tangential displacements fields are independent on each other (unless material [...]

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• Hyper-dimensional gap finite elements for the enforcement of interfacial constraints

  B. Giffin

  WCCM2024.

  
  

  Abstract

  In the classical theory of two-body contact, a single shared contact interface is considered between two continuum bodies, and is further discretized as such in the finite element setting. In general, however, the finite element mesh topology of two contacting bodies will be non-conforming at this shared interface, requiring the definition of a preferred or intermediate surface over which integral constraints may be evaluated. The specification of this interface is deemed to be somewhat arbitrary, but in practice the numerical solution of contact problems may exhibit sensitivity to the particular choice of intermediate surface. A further complication concerns the need to establish projective mappings between the discretized finite element surfaces and the chosen intermediate surface, particularly for the sake of evaluating the contact gap function between pairs of points on each of the two bodies. In this work, a new methodology for the enforcement of contact constraints in the context of finite element analyses is proposed. The method entails an alternative representation of contact surface integrals by equivalently integrating over the interstitial – albeit degenerate gap volume between two contacting bodies. An auxiliary indicator field is defined on each body, and is used to represent the degenerate interstitial volume as a non-degenerate hyper-dimensional gap volume. Over this domain, the gradient of the continuously interpolated displacement field with respect to the indicator field yields the oriented displacement gap, which may be used in the formulation of contact inequality constraints. Discretization of the hyper-dimensional gap volume into conforming finite elements is explored, and is observed to offer several advantages over existing contact discretization methods: the proposed method does not require the computation of geometric intersections or projections; it exploits conventional Gaussian quadrature schemes to integrate the hyper-dimensional gap integrals with a sufficient degree of accuracy; and may be naturally and efficiently extended to represent contact between higher-order surfaces. The efficacy of the method is demonstrated on several benchmark problems. Continuing and future work is also discussed, with a focus on intended applications and extensions of the method.

  Abstract
  In the classical theory of two-body contact, a single shared contact interface is considered between two continuum bodies, and is further discretized as such in the finite [...]

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• Development of a Mixed Reality visualization system using a location-based method for the underwater objects

  R. Nakaso, K. Kashiyama, T. Kotoura

  WCCM2024.

  
  

  Abstract

  This paper presents a development of a hybrid Mixed Reality visualization system using location-based and marker-based methods. The Microsoft Hololens 2 is employed for the MR device. In open-sky environment, location-based method was used for the superimposition method. To obtain location information, GNSS (Global Navigation Satellite System) receivers are used, which can obtain highly accurate location information by network RTK positioning at open-sky environment. The system is capable of superimposed 3D models into real space accurately and automatically. Also, by allowing the switch to marker-based method, this system can be applied to non-open-sky environment. The present system is applied to the visualization of underwater objects in order to check the validity and effectiveness.

  Abstract
  This paper presents a development of a hybrid Mixed Reality visualization system using location-based and marker-based methods. The Microsoft Hololens 2 is employed for the [...]

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• Development of a land use classification model based on semantic segmentation using aerial photographs and its application to Tsunami simulation

  Y. Habutsu, T. Miyake, H. Okawa, K. Kashiyama

  WCCM2024.

  
  

  Abstract

  This paper presents a development of land use classification model based on semantic segmentation using aerial photographs and its contribution to the efficiency of 2D tsunami inundation simulations. The proposed method uses Artificial Intelligence(AI)-based image classification to generate a roughness coefficient mesh, which is then applied to a 2-D tsunami run-up simulation using the finite element method on real geometry. Numerical results are compared to evaluate the improvement in simulation efficiency, and the potential benefits of the proposed method are discussed by analyzing the differences in simulation results.

  Abstract
  This paper presents a development of land use classification model based on semantic segmentation using aerial photographs and its contribution to the efficiency of 2D tsunami [...]

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• Research on heat distribution design of carbon ceramic brake discs and shape optimization of rib for high-speed train

  Y. Zhou, S. Yao

  WCCM2024.

  
  

  Abstract

  High speed and lightweight are the development trends of high-speed trains in the world. Air braking technology is the last line of defense to ensure the safety and reliability of trains. The complex working environment and huge braking power put forward higher requirements for brake disc configuration and material. Carbon-ceramic composite materials have the characteristics of large specific heat capacity, thermal shock resistance, lightweight and high temperature resistance, and are considered to be high-performance friction materials. By imitating the distribution of animal and plant nutrients transportation pipelines, a carbon-ceramic composite brake disc structure with #-shaped heat dissipation ribs was designed that take into account the anisotropy of the thermal conductivity of carbon-ceramic composite materials. The branched rib structure realizes rapid heat transmission in the disc material, thereby achieving high efficiency and uniform temperature distribution, prevents the concentration of heat generated by friction, which can reduce the maximum temperature value under braking conditions. Then combined with the shape optimization and size optimization design of the local heat dissipation ribs of the brake disc. Further research on the uniform temperature performance and heat dissipation under emergency braking conditions of 400km/h was carried out. The LSR model was used to analyze the different outlet angle, inlet angle and number of the cooling ribs in the same reference flow field. By comprehensively considering parameters as the average maximum temperature, convection heat transfer coefficient, an optimal design that balances cooling efficiency and aerodynamic loss is obtained.

  Abstract
  High speed and lightweight are the development trends of high-speed trains in the world. Air braking technology is the last line of defense to ensure the safety and reliability [...]

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• Pratt truss characteristics for optimal weight

  A. Neiburgs

  WCCM2024.

  
  

  Abstract

  This paper presents a study on the characteristics of Pratt trusses under conditions of optimal or near-optimal weight. Trusses with varying numbers of panels, spans, and heights are selected for analysis. Several characteristics describing truss geometry and internal forces are examined. Four dimensioning approaches are developed to perform calculations and obtain data for analysis. A parametric model of truss geometry is developed and integrated with a finite element calculation algorithm in the Rhino8/Grasshopper software. The data are processed and analyzed using the machine learning software Weka and the statistical analysis software RStudio. Results show correlations between various truss characteristics. This study focuses on truss weight and height-span ratio to find the optimal weight. Based on truss height at optimal weight for each span, other characteristics are analyzed. It is observed that a larger number of panels increases the truss weight but also makes the results more consistent and predictable. The objective of this work is to better understand Pratt truss performance, which can be used to reduce the size of optimization tasks.

  Abstract
  This paper presents a study on the characteristics of Pratt trusses under conditions of optimal or near-optimal weight. Trusses with varying numbers of panels, spans, and [...]

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• Finite element-based simulation of large wind turbines wake using the actuator line method

  V. Morici, V. Barnabei, A. Castorrini, F. Rispoli

  WCCM2024.

  
  

  Abstract

  The numerical simulation of wind turbines and wind farms aerodynamics represents an open challenge in computational mechanics. It involves multi-physics and multi-scale phenomena, turbulent flows at very large Reynolds numbers, atmospheric boundary layer features, and rotor machinery flow features and dynamics. The geometrically resolved Computational Fluid Dynamics (CFD) is recognized as the highest-fidelity approach for wind turbine simulations but it has still a too high computational cost if employed for wind farm flow analysis. For this application, several reduced-order models have been formulated to obtain reliable results at a sustainable computational effort. Among the others, Large Eddy Simulations (LES) with Actuator Line Model (ALM) represents a valid middle-fidelity alternative for accurately simulating the wind turbine wakes dynamics and its interaction with the atmospheric boundary layer turbulence. Most implementations of the ALM are derived for volume-based CFD solvers. In this work we present the implementation of this model in a Finite Element Method (FEM) framework, which allows the use of a Residual Based Variational Multiscale (RBVMS) method to model the turbulent flow field, instead of the standard LES formulation. The ALM-VMS formulation is applied to study a 5MW and a 15MW wind turbine rotors, comparing the results with data available in literature in terms of aerodynamic variables of main interest, such as rotor loads and aerodynamics and near and far wake features.

  Abstract
  The numerical simulation of wind turbines and wind farms aerodynamics represents an open challenge in computational mechanics. It involves multi-physics and multi-scale phenomena, [...]

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• Compressive stocking optimization for lymphedema treatment at lower-limb

  A. Garcia Llona, M. Aguirre, F. Verdugo, S. Avril

  WCCM2024.

  
  

  Abstract

  Lymphedema is a chronic disease that causes swelling in the soft tissues, mostly taking place in the extremities. This research focuses on the treatment of lymphedema through compression, which is widely applied to reduce the volume of edemas. Although effective at a clinical level, the use of off-the-shelf stockings with predefined sizes, reduces the efficiency at the patient-specific level. With the long-term goal of designing patient-specific stockings, this study aims to develop a real-time simulation tool, able to predict the efficiency of a given compression stocking for a given patient. For such purpose, the use of standard Finite Element Method (FEM) falls short due to high computational cost. Therefore, a solution based on Reduced Order Modeling (ROM) is developed to compute, in real-time, the hydrostatic pressure distribution at the location of the lymphatic dysfunction. It is assumed that hydrostatic pressure improves lymph circulation and increase the drainage capacity. This method enables to design the most efficient compressive stockings considering the particularities of each patient.

  Abstract
  Lymphedema is a chronic disease that causes swelling in the soft tissues, mostly taking place in the extremities. This research focuses on the treatment of lymphedema through [...]

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• Study of the dynamic behavior of cellular structures for the absorption of mechanical vibrations

  M. Silva, L. Ramos

  WCCM2024.

  
  

  Abstract

  Vibration is a prevalent issue in structural engineering, encompassing a wide array of problems that, if left unaddressed, can lead to severe consequences. These consequences can vary from causing discomfort for pedestrians traversing a perceptibly moving bridge to inducing premature fatigue in aeronautical structural components, ultimately resulting in catastrophic failures and loss of human life. Various sources can induce vibration in structural components, such as misalignment of rotating systems, seismic excitations, road loads on vehicles, and aerodynamic loads. To address these phenomena, in addition to appropriate structural design, various mechanisms, which can operate actively or passively, are used to attenuate oscillatory effects and minimize their impact. Active systems use electronic controllers to generate a response via actuators, reducing the signal transmissibility level based on specific oscillatory signals. Passive systems, on the other hand, mainly rely on viscoelastic polymeric materials, utilizing the reduction of the natural frequency associated with their use and a characteristic phenomenon of these materials for energy dissipation, hysteresis [1]. Hysteresis is a phenomenon where mechanical deformation energy is dissipated in the form of heat. In other words, part of the energy that would be transmitted to the structure is dissipated, thereby increasing the system's damping. Active systems are extremely efficient in their purpose, as they can isolate vibrations across a wide frequency spectrum and can be applied to structures of different magnitudes, from small and lightweight systems using piezoelectric actuators to large structures using hydraulic actuators, such as in active stabilization systems for reducing vibrations caused by seismic activities in buildings. However, they tend to be quite costly and imply an additional layer of systems, which, if not properly designed, can reduce the structure's reliability [2].

  Abstract
  Vibration is a prevalent issue in structural engineering, encompassing a wide array of problems that, if left unaddressed, can lead to severe consequences. These consequences [...]

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