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An accurate model of a foil bearing supported rotor needs to cover rotor dynamics of the shaft, structure dynamics of the foil as well as hydro‐ and thermo dynamics in the fluid film. The paper addresses the incorporation of tilting motions of the shaft and its influence on the foil deflection, which in turn results in a more accurate prediction of the stability threshold of the rotor‐bearing system. [ABSTRACT FROM AUTHOR]

The force response of squeeze film dampers and hydrodynamic bearings is significantly influenced by the occurence of cavitation inside the lubricant films. The viscosity of the occuring mixture of oil and air bubbles is vastly different than that of pure lubricant and therefore changes the pressure build‐up and thereby the stiffness and damping properties of the lubrication films. To accurately predict the force response of a squeeze film damper, the cavitation and its effect on the pressure build‐up therefore has to be taken into account. Well known cavitation algorithms for lubrication problems, like the Elrod algorithm or the two‐phase‐model, neglect the transient nature of outgassing and assume instantaneous bubble formation and collapse. In the presented paper, a transient bubble dynamics model based on the Rayleigh‐Plesset‐Scriven equation is utilised instead and its effect on the rotordynamic behaviour of a turbocharger rotor is examined based on fully transient multi body dynamics simulations. [ABSTRACT FROM AUTHOR]

Lattice structures are lattice‐like assemblies that are inspired by organic systems. The structure inside is made up of cells whose edges form rod‐shaped elements. The size of the cells and the dimensions of the rods can influence the mechanical properties of the entire structure. For the use of lattice structures within engineering applications, stiffness and damping are important parameters. In monolithic designs, the outer contour or the material itself must be modified to change the stiffness and damping. In the case of a lattice structure, moreover, the structure of the inner cells can be adapted, resulting in greater flexibility [1]. Numerical simulations of the structural dynamic behavior will be used to optimize the damping, while heuristic methods are applied to account for the large parameter space. To adjust the simulation model, the damping is measured frequency‐dependent on a real structure which is subsequently used for model adjustment. [ABSTRACT FROM AUTHOR]

It is a well‐known fact, that hydrodynamically supported systems are prone to nonlinear vibrations. Their exact simulative prediction with respect to frequency and amplitude is complicated by the fact that different system properties interact. The paper at hand outlines an approach that takes all relevant influences like rigid body motions, elastic deformations, nonlinear relation between fluid film pressure and bearing kinematics as well as temperature increase due to power loss or adjacent heat sources into account as detailed as necessary. Both journal and thrust bearings are considered as they contribute to the system's stiffness and damping capabilities. The approach is applied to self‐excited pad vibrations of tilting pad thrust bearings as well as the run‐up simulation of a turbocharger rotor under different axial loads. Both models are validated against measurements. [ABSTRACT FROM AUTHOR]

Flow-induced vibration (FIV) is a common phenomenon observed in internal flows and is frequently encountered in technical systems like process plants, nuclear plants, oil-piping or heat exchangers. Compared to single-phase flows, FIV is more difficult to predict and analyze for internal two-phase flows. As a result, experimental data and analysis tools related to two-phase flow are limited to specific aspects or conditions. Another problem is that for real-world applications, FIV analysis is applied to multi-structural components, which becomes complicated due to the size of the technical systems. Thus, experimental studies are usually realized first within the laboratory using a prototype of the original structure. Besides experimental investigations, Computational Fluid Dynamics (CFD) is increasingly adopted and already a prevalent tool for FIV assessment. However, further development in CFD models and methods is necessary in order to complement the experimental database. Additionally, CFD is useful for enhanced understanding of fundamental aspects of two-phase flows, and for gaining insights from situations where experiments are difficult or infeasible, such as in deep-sea borewells, sub-sea riser pipelines, and in nuclear installations. It is also known that there is a lack of sufficiently accurate empirical correlations for terms related to mass, momentum, and energy transfer across the phases for two-phase flows, and CFD can be useful in this respect. Furthermore, for estimating the accuracy of CFD models, comparisons with benchmark results for two-phase, internal, multistructural flows are necessary. Unfortunately, the experimental database involving internal two-phase flows is very limited, and this is a bottleneck for the development of computational techniques. The following contribution presents a review of the research on FIV involving two-phase internal flows with relevance to multistructural components. Methodological literature for two-phase flow measurements along with the latest applications are put forth. Problem areas of two-phase FIV systems have been brought out, and future avenues of research for two-phase, internal FIV are identified. The following specific areas of two-phase FIV are reviewed. Two-phase FIV in subsea risers and in pipeline riser systems is discussed. The slug flow regime is analyzed in particular due its predominant impact on twophase FIV. Parameters affecting two-phase FIV along with two-phase correlations are discussed. Power Spectrum Density (PSD) and Fourier transform applications for two-phase FIV form another section. Latest research efforts involving the two-way interaction of fluid and structure are presented. Both numerical and experimental works have been reviewed. The bulk of the important works for two-phase FIV is experimental in nature. Numerical models and computational power have not been developed enough for simulating more complex, multistructural flows. They are limited to simple cases involving simplified computational models. Experimental efforts for large multistructural components involve the initial use of prototypes and can prove to be costly for fully developed industrial-scale rigs. However, experimentation currently holds an irreplaceable position in two-phase FIV studies. [ABSTRACT FROM AUTHOR]

The precise calculation of drag forces in the technical application of automatic balancing of rotating machinery provides important information about efficiency and stability. With increasing geometric complexity of the design, this poses a challenge that can be solved with computer-aided fluid dynamic approaches. In rolling element bearings, the influence of drag induced by the lubricant is predominantly considered in the context of efficiency loss estimations, whereas the movement of the rolling elements is mainly constrained by the contact with the bearing rings and, if present, the cage. Automatic ball balancers, which are installed in rotating machinery to reduce unbalance excitation, are in design very similar to fully lubricated ball bearings missing the cage, the inner ring and the majority of the balls. Inherent to the functional principle, the balancing efficiency and stability are significantly influenced by the choice of lubricant and resulting drag forces. Therefore, the estimation of the drag coefficient based on the geometry and lubrication of automatic ball balancers plays an important role in the engineering process. With a focus on the Stokes flow regime, the drag coefficient for a single sphere in an annular flow domain is determined numerically with finite volume discretization and the SIMPLE steady state solution scheme. Based on a parameter study utilizing the presented solution approach, a simple empirical relation between the design of the automatic ball balancer and resulting drag coefficients is derived. As a result, a drag force formulation based on the balancer geometry and the lubrication fluid properties is presented, which helps to supplement a large number of published kinetic models regarding the analysis of automatic ball balancer stability and transient behavior, giving a better understanding of the influences of design decisions regarding geometry and lubricant. [ABSTRACT FROM AUTHOR]

A common problem in transient rotordynamic simulations is the numerical effort necessary for the computation of hydrodynamic bearing forces. Due to the nonlinear interaction between the rotordynamic and hydrodynamic systems, an adequate prediction of shaft oscillations requires a solution of the Reynolds equation at every time step. Since closed-form analytical solutions are only known for highly simplified models, numerical methods or look-up table techniques are usually employed. Numerical solutions provide excellent accuracy and allow a consideration of various physical influences that may affect the pressure generation in the bearing (e.g., cavitation or shaft tilting), but they are computationally expensive. Look-up tables are less universal because the interpolation effort and the database size increase significantly with every considered physical effect that introduces additional independent variables. In recent studies, the Reynolds equation was solved semianalytically by means of the scaled boundary finite element method (SBFEM). Compared to the finite element method (FEM), this solution is relatively fast if a small discretization error is desired or if the slenderness ratio of the bearing is large. The accuracy and efficiency of this approach, which have already been investigated for single calls of the Reynolds equation, are now examined in the context of rotordynamic simulations. For comparison of the simulation results and the computational effort, two numerical reference solutions based on the FEM and the finite volume method (FVM) are also analyzed. [ABSTRACT FROM AUTHOR]

This paper presents the development of a compact torsion spring for use as an elastic element in a lightweight series elastic actuator for an active orthosis. This orthosis is going to be utilised as an assistive device for motorically impaired stroke-patients. In the design a two-step optimisation strategy was implemented to meet all requirements for the torsion spring. The first step was to identify a promising topology for the element. In the second step, the shape was optimised based on a finite element model using two different optimisation methods in order to minimise the von Mises equivalent stresses. Four promising variants of the identified topology were extracted from these calculations, one of which was then chosen as the final design. A prototype was manufactured by a laser cutting process, which is a new procedure in the context of elastic elements for series elastic actuators. The calculation results were validated successfully by measurement of the spring properties of this prototype. [ABSTRACT FROM AUTHOR]

The numerical effort of transient rotordynamic simulations is often dominated by the computation of nonlinear hydrodynamic bearing forces. These forces are described by the Reynolds equation and need to be computed at every time step. Usually, numerical models, analytical approximations, or look‐up table techniques are employed, depending on the desired tradeoff between accuracy and computational cost. In recent studies, a semi‐analytical approach based on the scaled boundary finite element method (SBFEM) has been developed as an efficient alternative to these methods. The partial differential equation is transformed into a system of ordinary differential equations, leading to an eigenvalue problem. Here, the numerical effort can be further decreased by means of a modal reduction, which is investigated in this study. The shaft eccentricity determines the smoothness of the hydrodynamic pressure field and is identified as an adequate indicator as to what subset of eigenvalues and eigenvectors should be considered in the solution. [ABSTRACT FROM AUTHOR]

The rotary friction welding (RFW) is nowadays an industrial well-established and common welding technique since it allows the combination of a wide range of ferrous and non-ferrous materials, for instance, aluminium alloy and steel in order to create a lightweight structure. Therein, the major challenge is, due to the diverging physical properties, to determine suitable and stable parameters for the welding process. In this context, there is a great industrial demand for appropriate simulation tools to capture the relevant physical phenomena within the welding process and thereby to identity the optimal welding parameters. Various holistic models have been constituted to simulate the RFW process. Whereby, the major differences concern the methods of modelling the material and frictional behaviour. In a recent work, a straightforward material model based on a Carreau fluid formulation together with a shear strength confined Coulomb friction model has been adopted. The main motivation of this paper is to validate the capability and the precision of this proposed modelling approach as well as to represent some modelling aspects in a more tangible way. For that purpose the RFW process of a couple of aluminium to steel welded joints with different process parameters were simulated. Subsequently, a validation of the simulated and measured process variables was done concerning the comparison of the flash formation, the final shortening, the transient shortening rate and temperature evolution. • Representation of an approach for modelling the rotary friction welding process. • Detailed derivation of the used finite element model. • Explanation concerning to the friction and contact modelling. • Description of the applied meshing and remeshing procedure. • Comparison of experimental and simulation results. [ABSTRACT FROM AUTHOR]

A particle damper is a passive damping technique, which is based on the high damping properties of granular materials. The energy dissipation rate of a particle damper depends on several factors, like the type of granular materials, filling ratios, particle size, and shape, etc. Out of all these factors, the type of granular materials used to design a particle damper plays a major role. Therefore, this contribution aims to investigate the influence of eleven different granular materials on vibration attenuation. Furthermore, the application of particle dampers for reducing the low‐frequency vibration amplitude of a wind turbine generator has been demonstrated. For this, two different approaches, namely the damping plate concept and the existing cavity concept have been introduced. It has been found that both concepts are capable of reducing the vibration amplitude tremendously. The material investigation has shown that rubber granulate can reduce the vibration amplitude of the test specimen significantly higher in comparison to the other materials by increasing the additional mass to the entire system marginally. The material test is independent of any particular application. Hence, the results can be used to reduce the vibration amplitude of any mechanical structure. [ABSTRACT FROM AUTHOR]

This work proposes a new method for the fatigue damage evaluation of vibrational loads, based on preceding investigations on the relationship between stresses and modal velocities. As a first step, the influence of the geometry on the particular relationship is studied. Therefore, an analytic expression for Euler Bernoulli beams with a non-constant cross section is derived. Afterward, a general method for obtaining geometric factors from finite element (FE) models is proposed. In order to ensure a fast fatigue damage evaluation, strongly simplified FE-models are used for the determination of both factors and measurement locations. The entire method is demonstrated on three mechanical structures and indicates a better compromise between effort and accuracy than existing methods. For all examples, the usage of velocities and geometric factors obtained from simplified FE models enables a sufficient fatigue damage calculation. [ABSTRACT FROM AUTHOR]

Although the use of combustion engines will decrease in passenger cars due to ecological reasons, turbochargers (TC) as typical applications with floating ring bearings will furthermore be applied in other applications like combined heat and power plants, ships or emergency backup generators for data processing service center and similar systems. Thus, the development of TC concerning rotor‐ and hydrodynamics is an important task, which leads due to the non‐linear behaviour to the necessity of advanced simulations for improving the performance. [ABSTRACT FROM AUTHOR]

Squeeze film dampers (SFDs) are commonly used in turbomachinery in order to introduce external damping, thereby reducing rotor vibrations and acoustic emissions. Since SFDs are of similar geometry as hydrodynamic bearings, the REYNOLDS equation of lubrication can be utilised to predict their dynamic behaviour. However, under certain operating conditions, SFDs can experience significant fluid inertia effects, which are neglected in the usual REYNOLDS analysis. An algorithm for the prediction of these effects on the pressure build up inside a finite-length SFD is therefore presented. For this purpose, the REYNOLDS equation is extended with a first-order perturbation in the fluid velocities to account for the local and convective inertia terms of the NAVIER-STOKES equations. Cavitation is taken into account by means of a mass conserving two-phase model. The resulting equation is then discretized using the finite volume method and solved with an LU factorization. The developed algorithm is capable of calculating the pressure field, and thereby the damping force, inside an SFD for arbitrary operating points in a time-efficient manner. It is therefore suited for integration into transient simulations of turbo machinery without the need for bearing force coefficient maps, which are usually restricted to circular centralized orbits. The capabilities of the method are demonstrated on a transient run-up simulation of a turbocharger rotor with two semi-floating bearings. It can be shown that the consideration of fluid inertia effects introduces a significant shift of the pressure field inside the SFDs, and therefore the resulting damper force vector, at high oil temperatures and high rotational speeds. The effect of fluid inertia on the kinematic behaviour of the whole system on the other hand is rather limited for the examined rotor. [ABSTRACT FROM AUTHOR]

Full-floating ring between shaft and housing leading to two fluid films in serial arrangement. Analogously, a thrust bearing with an additional separating disk between journal collar and housing can be designed. The disk is allowed to rotate freely only driven by drag torques, while it is radially supported by a short bearing against the journal. This paper addresses this kind of thrust bearing and its implementation into a transient rotor dynamic simulation by solving the Reynolds PDE online during time integration. Special attention is given to the coupling between the different fluid films of this bearing type. Finally, the differences between a coupled and an uncoupled solution are discussed. [ABSTRACT FROM AUTHOR]

Hydrodynamic bearings are commonly used to support fast rotating rotors. Due to their nonlinear bearing properties, they strongly influence the rotor response behaviour, which can be observed by the occurrence of sub-harmonic oscillations. The appearance of sub-synchronous vibrations depends on the operating bearing conditions, which are determined by the kinematics of bearing partners, the thermodynamic processes and especially the occurrence of cavitation. In this contribution, the rotor response behaviour of a full-floating ring supported Jeffcott-rotor is investigated under the consideration of lubricant film cavitation. The two-phase model is applied as a mass-conserving cavitation theory and compared with the assumptions of Half-Sommerfeld. [ABSTRACT FROM AUTHOR]

The aim of this work is to numerically calculate the effective cutting forces during orthogonal turn‐milling using the well‐known analytical approach introduced by Victor/Kienzle in connection with a multi‐body system. Starting with a routine that numerically computes the mill's infeed with the implemented dexel model, it is possible to reconstruct and follow the tool's outline and track caused by its rotation. Hence, the acting cutting forces can be determined. [ABSTRACT FROM AUTHOR]

In this paper, a method is presented to determine the vibrational behavior of an electric motor and the associated structure. Therefore, a holistic simulation approach is used, which takes into account the mutual influence of structural mechanics and electrodynamics. For this purpose, a multi body simulation (MBS) is extended so that electromagnetic loads can be considered, which are calculated by using the finite element method (FEM). In electric machines an undisturbed and constant magnetic field is of great importance. Even small variations of the air gap lead to changes in the magnetic field compared to the ideal geometry, which cause a change in the resulting torque and vibration excitation. Especially local and global asymmetric air gap changes due to load‐ and operation‐dependent deformations of the stator and rotor are problematic. Such deformations result on the one hand from the electromagnetically excited structural vibrations and on the other hand from the rotordynamic loads. For these reasons, it is necessary to consider the electro‐ and structural‐dynamic effects together. The developed method is presented on a simple generic motor to show the influence of the coupling. [ABSTRACT FROM AUTHOR]

The acoustic behavior of a combustion engine is primarily dominated by the sound radiation of the oil pan. Therefore, the vibration behavior of the oil pan as the prominent noise emission source is investigated in this paper. The aim of this study is to present a new vibration reduction concept, which is based on the property of high damping possessed by granular materials. The efficiency of this concept is proven by measurements via a scanning laser vibrometer. Finally, it is shown that it is possible to create a lighter oil pan which shows much lower vibration amplitudes than the original one. [ABSTRACT FROM AUTHOR]

In the paper at hand, a holistic virtual engineering approach for the acoustic analysis of combustion engines is presented, which uses an elastic multi-body simulation to calculate the excitation forces of the engine during the combustion process. These forces are caused by the piston motion and affect the main bearings and the cylinder walls. Due to the fact that both the crankshaft and the piston are supported against the housing by fluid films, it is important to consider the hydrodynamics in the simulation of the crank drive dynamics. Based on the excitation forces, the vibration analysis of the engine is carried out, which provides the input data for the acoustic simulations. The entire simulation workflow is demonstrated on a four-stroke combustion engine. Finally, the presented approach is validated by sound pressure measurements of a running engine in an anechoic room. [ABSTRACT FROM AUTHOR]

Despite many advantages, hydrodynamic bearings tend to induce nonlinear vibrations on rotor systems at low external loads. The occurrence and also the amplitudes of these vibrations are very sensible to the operating conditions of the system such as occurrence of gaseous cavitation, oil viscosity (strongly dependent on oil temperature), bearing clearance (dependent on metal temperature and thermal expansion coefficients) or rotor imbalance. This contribution shows the calculation of nonlinear rotor oscillations with the help of a detailed transient 3D‐thermo‐hydrodynamic bearing model. Referring to experimental data of a real exhaust turbocharger with semi‐floating ring bearings, this holistic approach is used for a separate investigation of a) the influences of the temperature‐dependent oil viscosity in the lubricating films and b) the influences of temperature‐related changes in the lubricating gap on the nonlinear oscillations of the rotor. [ABSTRACT FROM AUTHOR]

In this paper, a method for vibration analysis of electric engines and associated structure is presented. For this purpose, a multi‐body simulation (MBS) is extended in such a way that electromagnetic loads can be considered using the finite element method (FEM). Subsequently, the determined loads lead to an excitation of the structural vibrations and a sound radiation of the engine, which is analyzed at selected operating points. A test rig will be used to validate the implemented method. Finally, different design variations of the engine are evaluated with respect to their acoustic behavior. The developed method is not limited to the presented application, but it can be applied to any system with electric drives. [ABSTRACT FROM AUTHOR]

This contribution investigates the influence of outgassing processes on the vibration behavior of a hydrodynamic bearing supported turbocharger rotor. The examined rotor is supported radially by floating rings with outer squeeze-film damping and axially by thrust bearings. Due to the highly nonlinear bearing properties, the rotor can be excited via the lubricating film, which results in subsynchronous vibrations known as oil-whirl and oil-whip phenomena. A significant influence on the occurrence of oil-whip phenomena is attributed to the bearing stiffness and damping, which depend on the kinematic state of the supporting elements, the thermal condition, and the occurrence of outgassing processes. For modeling the bearing behavior, the Reynolds equation with mass-conserving cavitation regarding the two-phase model and the three-dimensional (3D) energy as well as heat conduction equation is solved. To evaluate the impact of cavitation, run-up simulations are carried out assuming a fully (half-Sommerfeld) or partially filled lubrication gap. The resulting rotor responses are compared with the shaft motion measurement. Also, the normalized eccentricity, the minimum lubricant fraction, and the thermal bearing condition are discussed. [ABSTRACT FROM AUTHOR]

The vibration behaviour of fast rotating rotors is significantly influenced by the bearing properties. Lubricant film induced excitations can cause sub‐synchronous rotor oscillations known as oil‐whirl and oil‐whip phenomena. The non‐linear bearing properties depend primarily on the lubricant properties, kinematics of bearing partners and especially on the occurrence of cavitation. Outgassing processes lead to a two‐phase flow consisting of gas and oil, which can influence the bearing stiffness and damping respectively and consequently the rotor response behaviour. In this contribution, the oscillations of a semi‐floating ring supported turbocharger rotor are investigated under the influence of lubricant film cavitation. For this purpose, run‐up simulations are carried out under the assumption of mass‐conserving cavitation according to the two‐phase model and compared with measurements. In order to illustrate the influence of outgassing processes, a comparison is made with non‐mass‐conserving cavitation theory according to the assumptions of Half‐Sommerfeld. [ABSTRACT FROM AUTHOR]

The rotary friction welding (RFW) is a robust, precise, productive and economical joining process that is used in many areas of mechanical engineering to produce lightweight structures consisting of combinations of ferrous and non-ferrous materials, for instance aluminium alloy and steel. Crucial for the design of such lightweight structures is the knowledge about the bonding strength. The bonding strength is the result of the bond formation depending on the present transient kinematic, kinetic and thermal states during the welding process being directly determined by the welding process parameters. Despite several years of empirical research, no reliable numerical modelling approach exists for the RFW process to analyse the bonding strength based on these transient state variables. For this reason, an improvement of the bond formation and therefore an increase in the bonding strength can only be tested experimentally. The main motivation of this paper is to develop an appropriate modelling approach for the estimation of the bonding strength for friction welded lightweight structures manufactured of an aluminium alloy and a structural steel. Therefore, a couple of aluminium alloy and steel welding experiments with different process parameters were performed and subsequently analysed concerning to the resulting bonding strength. Moreover, all the welding experiments were simulated in regard to the corresponding welding process in order to determine the present kinematic, kinetic and thermal state variables, like the strain rate, the stress and the temperature. Thus, a model for the characterization of the bond formation can be developed, which allows a correlation between the bond formation and the resulting bond strength based on the chosen welding process parameters. Finally, the model will be examined and discussed in terms of its plausibility and applicability. • Process simulation of friction welded lightweight structures made of aluminium alloy and structural steel. • Estimation of the transient kinematic, kinetic and thermal state variables in the welding contact zone. • Detailed derivation of a numerical modelling approach to analyse the bonding strength based on the state variables. • Experimental validation. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present a framework for modelling the deformation behaviour of friction welded hybrid structures. The constitutive model is developed for large deformations and nonlinear material behaviour. Moreover, to demonstrate the model's applicabilities, it was implemented into a finite element system (ABAQUS). Subsequently, the simulation results were critically evaluated using experimental data. [ABSTRACT FROM AUTHOR]

In tribological systems, the surface topography is influencing the friction and wear behaviour and therefore the component lifetime. These functional surfaces can be found for example in roller bearings, where a lubricating property between rolling elements affects the functionality. Currently, the grinding process is mainly used for finishing the rolling elements. Compared to grinding, the turn-milling process is able to modify the machined surface structure in a deterministic way. Furthermore, this process can be driven under dry conditions, which causes an ecological benefit. The industrial relevance of turn-milling forces a pre-process modelling of the surface structure concerning the turn-milling strategy and process parameters. This article presents opportunities to predict textured surfaces by the tangential and orthogonal turn-milling process. An analytical approach was written in Matlab and connected with Microsoft Visual Studio Express. The results were examined in relation to experimental manufactured surfaces. Thus, conclusions for the structuring of functional surfaces by turn milling can be achieved to enhance the process in an analytical way. Furthermore, a numerical approach is introduced, which enlarges the analytical model by means of the implementation of the dynamic behaviour of the workpiece and the tool. [ABSTRACT FROM AUTHOR]

The numerical effort of rotordynamic simulations with hydrodynamic bearings is often dominated by the solution of the Reynolds equation. Because of the nonlinear fluid–structure interaction, this equation needs to be solved in every time step. Although computationally efficient analytical approximations and look-up table techniques exist, these approaches often do not provide the necessary modeling depth and accuracy. Thus, in many cases, numerical methods are preferred despite their computational cost. In recent studies, a semi-analytical solution of the Reynolds equation has been developed based on the scaled boundary finite element method (SBFEM) with the objective of improving the numerical efficiency. The developed approach assumed Gümbel conditions, which means that cavitation was handled in a highly simplified manner. In this work, the SBFEM solution is for the first time combined with a more complex, nonlinear cavitation model based on the Elrod algorithm. Because of the semi-analytical technique, this requires a simplification of the switch function that defines the locations of the pressure and cavitation zones. However, as demonstrated in this paper, the resulting bearing forces are still in good agreement with a standard numerical reference solution based on the finite volume method (FVM). Since the SBFEM model uses only a one-dimensional discretization, its high-order formulation is very straightforward, even in case of a non-equidistant grid with varying shape functions that take the smooth and non-smooth regions of the solution into account. As a result, the numerical effort is reduced significantly in comparison to the standard FVM. [Display omitted] • An SBFEM solution of the Reynolds equation is combined with an Elrod cavitation model. • The accuracy of the hydrodynamic forces computed with this approach is adequate. • The developed method is numerically efficient compared to the standard FVM. [ABSTRACT FROM AUTHOR]

For the numerical simulation of the rotary friction welding process in prior works a modified Carreau fluid law has been successfully adopted, which can so far not be used for the residual stress prediction due to the basic assumptions in this model. Therefore, an extension is proposed accounting for elastic effects, thermal induced stresses and hardening of steels using the data of continuous cooling transformation (CCT) phase diagrams. For the validation of the model, measurements from literature as well as own measurements utilizing partial cut-outs are used. The numerical results correlate well with experimental data for first order residual stresses. [ABSTRACT FROM AUTHOR]

In this paper, the damping effect of granular materials is explored to reduce the vibration and noise of mechanical structures. To this end, a honeycomb structure with high stiffness is used to contain a granular filling which presents the possiblity for the distribution of the granular material to be designed. As a particular application example, the oil pan bottom of a combustion engine is used to investigate the influence on the vibration behavior and the sound emission. The effect of the honeycomb structure along with the granular mass, distribution, and type on the vibration behaviour of the structure is investigated via laser scanning vibrometry. From this, an optimized filling is determined and then its noise suppression level validated on an engine test bench through measurements with an acoustic array. [ABSTRACT FROM AUTHOR]

• Experimental study of particle damper materials on vibration attenuation. • Detailed investigation for damping performance of 20 different granular materials and their mixtures with special focus on the required additional mass. • Damping efficiency comparison of several soft and hard granular materials, like rubber granulate, rubber powder, stone powder, lead shot, plastic balls, etc. • A hybrid particle damper is introduced in this paper. • The effects of several parameters on particle damper performance are addressed. A particle damper is a passive vibration control technology that utilizes the high damping properties of granular materials for reducing the vibration amplitude of a structure over a wide frequency range. Energy dissipation of particle damper is a highly nonlinear and complex physical phenomenon [1]. Previous studies have shown that the damping mechanism of a particle damper depends on several factors, like particle size and shape, granular material, filling ratio, and the number of particles [2–5]. Out of these parameters, the type of granular material used in the particle damper plays a major role in reducing the vibration amplitude of a mechanical structure. Therefore, the current contribution aims to investigate the influence of 20 different granular materials on vibration attenuation. The granular materials under investigation are subdivided into two major groups, namely: soft particles, like rubber granulate, and hard particles, like steel balls. Furthermore, this paper proposes a hybrid particle damper in which two different types of granular material mixtures are used, i.e. a particle damper in which for instance soft particles are mixed with hard particles. Moreover, in this contribution, fine particles, like rubber powder are mixed with hard granular materials like lead shot, which can be seen as an extension of the fine particle impact damper concept [6]. The humidity-dependent behavior of particle dampers is also another important issue, which is addressed in this paper. To investigate the vibration attenuation efficiency of all the granular materials and their mixtures including the humidity-dependent behavior, a laser scanning vibrometer device is used. Generally, the relationship between the vibration response and the granular material mass is rarely addressed in the literature, which can restrict the industrial application of particle dampers. Hence, the additional mass of the granular material is also a focus of this paper. The experimental investigation shows that the vibration response of the test specimen is significantly lower for particles with lower densities in the low-frequency range. Furthermore, an excellent damping efficiency can be also observed for the particle damper with a granular material mixture. The results obtained in this study are not restricted to any special structure and can be implemented in several industrial applications, where vibration and noise attenuation plays a major role, like automotive, aerospace, wind turbine, medical technology, mining, etc. [ABSTRACT FROM AUTHOR]

Within a multi‐body simulation (MBS) a three‐dimensional FE model is employed to represent the nonlinear properties of rubber bushings. This is implemented via a sequential force‐displacement coupling between the two solvers. For a first material modelling approach of the elastomer, the modified Neo Hooke model is used in conjunction with the generalized Maxwell model. Later, however, a physically motivated material model will be used. First results for a single‐mass oscillator are presented and show the general functionality of the coupled approach. Since the use of FE models in MBS causes a significantly higher computational effort, it is necessary to realize the coupling between FEM and MBS as efficient as possible, which is also a future task. [ABSTRACT FROM AUTHOR]

A semi‐analytical solution of the Reynolds equation for hydrodynamic bearings in rotordynamic simulations is investigated, which is based on the Scaled Boundary Finite Element Method (SBFEM). The numerical efficiency of this approach is compared to the Finite Element Method (FEM), considering linear as well as higher‐order shape functions. It is observed that the SBFEM requires significantly less computational time than the FEM, especially with respect to high‐order formulations. [ABSTRACT FROM AUTHOR]

Present‐day research in the field of product development are increasingly focused on the efficient use of energy and raw material resources. In the light of this context, the design principle of consistent lightweight construction is gaining more and more importance. One possible approach is the targeted combination of different materials with favourable technological properties in hybrid structures. Against this background, the rotary friction welding (RFW), is particularly advantageous allowing the joining of dissimilar materials, like aluminium and steel in order to create such lightweight structures. The purpose of the paper at hand, is to present a framework for modelling the elastoplastic behaviour of those manufactured structures under the assumption of large deformation and non‐linear material behaviour. Moreover, the presented model was implemented into a finite element analysis program (ABAQUS), in order to simulate a tensile test of a friction welded lightweight structure. Subsequently, the simulation results were critically evaluated using experimental data. [ABSTRACT FROM AUTHOR]

A numerically efficient, semi‐analytical solution of the Reynolds equation for hydrodynamic journal bearings is developed based on the Scaled Boundary Finite Element Method. The pressure field is discretized along the circumferential coordinate of the lubrication gap, while an analytical formulation is used in the axial direction. A system of inhomogeneous ordinary differential equations is obtained, which is solved under consideration of the boundary conditions. The solution is verified, and its numerical efficiency is investigated in comparison to an FEM solution. [ABSTRACT FROM AUTHOR]

• A semi-analytical solution of the Reynolds equation for hydrodynamic journal bearings is derived. • The solution is based on the scaled boundary finite element method (SBFEM). • The SBFEM solution is numerically efficient for bearings with large slenderness ratios. • For simplified oil supply pressure boundary conditions, the numerical effort is further reduced. [Display omitted] The behavior of rotor systems with hydrodynamic bearings can be affected crucially by the nonlinear bearing forces. These forces are incorporated in rotordynamic simulations by solving the Reynolds equation in every step of a time integration scheme. Since closed-form analytical solutions of the Reynolds equation are known only for simplified boundary conditions, numerical methods and look-up table approaches are applied. To obtain accurate and convergent results, numerical solutions require a fine discretization, while the look-up tables require a fine grid of interpolation points. In both cases, the numerical effort of the rotordynamic simulation is dominated by the computation of the bearing forces. In this study, a semi-analytical solution of the Reynolds equation based on the Scaled Boundary Finite Element Method (SBFEM) is developed to reduce the numerical effort of the overall simulation. In contrast to a purely numerical solution, the two-dimensional pressure field is discretized in only one coordinate direction, whereas in the other direction, an analytical formulation is used. This results in a system of non-homogeneous ordinary differential equations, which is solved under consideration of the boundary conditions. Since the complexity of the SBFEM model and the resulting numerical effort depend on the modeling of the oil supply groove, three different models are analyzed in this paper. The equations are derived, the solutions are verified, and their numerical efficiency is investigated in comparison to an FEM solution, which is one of the standard numerical approaches. [ABSTRACT FROM AUTHOR]

Different oil‐film‐induced instabilities have to be accounted for when designing rotor systems supported by hydrodynamic bearings. Because the system's behaviour is strongly dependent on the thermal state, this contribution presents an approach for calculating the thermo‐hydrodynamic behaviour of a bearing‐rotor‐system. It incorporates a solution of the three‐dimensional energy equation for the fluid film and accounts for heat conduction through the surrounding parts of the bearing. The simulation model is validated with the help of experimental data and improvements are pointed out compared to an isothermal approach. [ABSTRACT FROM AUTHOR]

In this paper an experimental method for determining the frequency‐dependent stiffness and damping properties is presented. The aim is to obtain valid input parameters for a simulation model that considers the most important effects of typical damping materials without the necessity of poroelastic material formulations, which require at least five different input parameters. These parameters are difficult and expensive to determine experimentally. Moreover, the determination procedure is not very robust and the results can easily vary [1]. Additionally, such parameters are often phenomenological without having a physical meaning. For these reasons, it is promising to use a simpler material model based on frequency‐dependent stiffness and damping parameters within numerical simulations in order to be able to predict the acoustic behavior of complex systems with different damping and insulation treatments sufficiently. [ABSTRACT FROM AUTHOR]

The wear of automotive chain drive systems after high mileages is numerically calculated based on Fleischer's energetic wear equation. This equation is embedded in a FE-model, consisting of one single chain link only. Their time-variant positions and acting forces are taken from a multi-body simulation. A focus is on ensuring the quality of the FE-model and the contact between pin and bush, where here a penalty approach has provided a stable solution schema. The parameters of the wear model are derived from measurements. After each time increment the wear results in a changed surface geometry, which is used for the simulation of the next time increment. The enormous computation time is reduced by the development of a convenient extrapolation factor. The complex simulation approach is applied to the chain drive of a test vehicle after a mileage of about 50000 km. The comparison of the simulated and measured data demonstrates an agreeing correlation. • For calculating the wear of automotive chains an energetic based wear model is embedded into a FE-Model of the chain. • Only one chain link model is required; its time dependent positions and forces are taken from multi-body simulations. • After each simulation step the wear results in a new surface geometry, which is used for the next time increment. • The enormous computation time is reduced by the development of a convenient extrapolation factor. • The chain wear simulation is in a proper correlation with measurements of a test vehicle after ∼50000 km mileage. [ABSTRACT FROM AUTHOR]

In this paper the measurements of the internal chain friction of a bush chain for various engine parameters are studied with a focus on petrol engines and the influence of engine oil. Due to the combustion of a petrol engine, the engine oil contains numerous particles and chemical bonds that have a significant impact on the internal chain friction. In order to measure the internal chain friction an experimental set-up has been developed excluding the influence of guide rails. The measurements of the internal chain friction at specific working points with different used engine oils allow an estimation of the time-dependent friction coefficients for modern automotive bush chain drive systems. • The application of used oil leads to an increased internal chain friction and a faster onset of mixed/boundary lubrication. • This effect is aided at higher strand force and higher oil temperature. • It is detrimental to operate an engine at elevated temperatures using used oil as opposed to fresh oil. • Varying the strand force at fixed engine speed and 100 °C oil temperature of an used oil verifies Coulomb's friction law. • Within this investigation the internal chain friction should also be a function of the soot content in petrol engine oil. [ABSTRACT FROM AUTHOR]