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Sound emission from an onshore wind turbine is one of the significant hurdles to use wind energy to its full potential. The vibration caused by the generator is transmitted to the blades, which radiates the sound to the surrounding. The purpose of this experimental study is to present a passive vibration reduction concept, which is based on the high damping properties of granular materials. The efficiency of this concept will be investigated using a laser scanning vibrometer device. For the experimental purpose in the laboratory, small-scale replicas inspired by the original configurations are used as reference geometries for the wind turbine generator and the blades. Vibrations of the prototype, with and without granular material filling, will be determined and compared with each other. The influence of the amount of granular material inside the structure is also investigated. Apart from this, different types of granular filling are examined with respect to their efficiency in reducing the amplitude of vibration of the structure while being as light as possible in order to design a lightweight solution, which increases the overall mass of the wind turbine marginally.

This work aims to improve profile derivation methods for uniaxial and multiaxial vibration testing. Thereby, the focus is put on the inclusion and processing of phase information between the excitation axes. An inherent necessity is the availability of field data. Two existing methods are independently extended by additional phase information and an appropriate processing. The first method is the Fatigue Damage Spectrum for a uniaxial profile derivation. The second method is the enveloping technique for a multiaxial profile derivation. Both methods are theoretically discussed and then evaluated with a fatigue damage calculation of an exemplary structure.

The presented work aims at evaluating the results of uniaxial and multiaxial fatigue failure tests using velocity and acceleration measurements. A specimen containing damaging modes at different eigenfrequencies is introduced. The tests are conducted on an electrodynamic 3D-shaker system using a random vibration environment. Different fatigue times are observed between uniaxial and multiaxial excitation. Based on the velocity and acceleration measurements, fatigue damage values are calculated for each test. While the fatigue damage values of velocities are similar between uniaxial and multiaxial tests, large deviations can be detected when using accelerations as base for the calculation. Thus, experimental verification for recently proposed multiaxial fatigue damage calculations based on different vibrational quantities is made possible.

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.

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.

The vibration behaviour of turbocharger rotors is influenced by the acting loads as well as by the type and arrangement of the hydrodynamic bearings and their operating condition. Due to the highly non-linear bearing behaviour, lubricant film-induced excitations can occur, which lead to sub-synchronous rotor vibrations. A significant impact on the oscillation behaviour is attributed to the pressure distribution in the hydrodynamic bearings, which is influenced by the thermo-hydrodynamic conditions and the occurrence of outgassing processes. This contribution investigates the vibration behaviour of a floating ring supported turbocharger rotor. For detailed modelling of the bearings, the Reynolds equation with mass-conserving cavitation, the three-dimensional energy equation and the heat conduction equation are solved. To examine the impact of outgassing processes and thrust bearing on the occurrence of sub-synchronous rotor vibrations separately, a variation of the bearing model is made. This includes run-up simulations considering or neglecting thrust bearings and two-phase flow in the lubrication gap. It is shown that, for a reliable prediction of sub-synchronous vibrations, both the modelling of outgassing processes in hydrodynamic bearings and the consideration of thrust bearing are necessary.

The paper describes the application of the Narrow Groove Theory (NGT) for Herringbone Grooved Journal Bearings (HGJB) with a complementary set of Dirichlet and Neumann conditions, which enables the algorithm to handle different initial film fraction values. Therefore, the NGT-modified Reynolds Equation is solved in combination with the system’s equation of motion in a common time integration scheme.

Automatic ball balancers (ABB) can be applied to rotating machinery in order to reduce the effective unbalance excitation and resulting deflections of the system. The passive working mechanism omits active components such as sensors, control units and actuators. In an ABB several balls are enclosed in a cylindrical cavity filled with a viscous fluid and can orbit on a circular track positioned centrically to the axis of rotation of the equipped rotor. Inherent to the functional principle, the rotating speed has to exceed the first critical frequency of the system for the balls to be positioned at beneficial orbit positions and counterbalancing the primary unbalance.

The rotating shafts of automotive turbochargers are commonly supported in floating ring bearings with two fluid films in serial connection. They are – due to the high rotational shaft speed – often designed as full-floating ring bearings with a free rotating ring between shaft and housing. The ring is driven by the shear stresses on the inner and outer surface of the fluid films, which depend on the rotational speed gradient in the fluid and the pressure distribution in the fluid films. If this frequency meets a natural frequency of the system the oil-whirl locks in an oil-whip and causes a circular motion of the shaft in the bearing with very high amplitudes. Finding an optimal bearing design as a result of these nonlinear relations is a sophisticated task. Several parameters of the floating rings could be tuned to avoid such oil-whip effects. Hence, a holistic simulation approach is used to calculate the run-up of an investigated turbocharger by using the simulation software EMD, which contains solution methods for the nonlinear fluid film equations in order to solve them in every time step. However, the simulation has to be validated against measurements. For this sake, the ring speed is measured using a miniature eddy current sensor during an electric driven run-up on a test rig, yielding an integral quantity containing all relevant effects.

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 semifloating 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.

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.

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.

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.

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.

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.

Concerning dynamical systems an integral part of the construction is the support. Due to favourable thermal and mechanical properties, journal bearings are widely used, from steam or gas turbines of power plants over main bearings of combustion engines to automotive exhaust gas turbochargers, with its comparatively small turbines. The latter shows due to the floating ring bearings an increased level of complexity. The focus of the present study lies on the non-linear effects of floating ring bearings, which have a significant influence on the maximum vibration amplitude, especially in the context of fast rotating and/or slightly loaded rotor systems. The typical resonance conditions of linear systems are inadequate for predicting the system’s behaviour and must therefore be supplemented with non-linear effects. The acting principles of subharmonic excitation and their interaction with the eigenfrequencies of rotor systems supported by journal bearings will be investigated and characterised using the example of an exhaust gas turbocharger. Because the mutual influence between rotor system and support is essential for a detailed illustration of the main effects, a holistic simulation for transient conditions is performed including analysis of eigenbehaviour in form of linear and non-linear Campbell diagrams.

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.

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.

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.

Journal bearings are still widely used, and – in combination with the omnipresent trend of light weight construction – there is an increasing focus on transient behaviour. Therefore, the structure, or more precisely, the aspect of rotordynamics has to be considered in conjunction with the hydrodynamics. Existing tools either address rotordynamics accurately while simplifying the bearings, or they model the bearings profoundly, including cavitation, but oversimplify the rotor to a point mass. The paper at hand addresses an approach to close the gap between both worlds. Therefore, a cavitation algorithm for the use in transient rotor dynamic applications is developed based on a regularised formulation of the Elrod–Adams model. Due to the achieved smoothness of the cavitation boundary, the solution of the hydrodynamic task yields to a more robust and faster calculation with respect to the classical approach. Therefore an application in transient simulations including rotor or multibodydynamic interactions under arbitrary conditions is realizable. For validating purposes, other approaches as well as experimental data were considered. The comparison shows an excellent agreement and additionally underlines the numerical advantages. As a result, the influences of rotordynamic aspects like the shaft's time dependent skew positioning can be considered and lead to a more precise representation of the system's behaviour, e.g. bearing damping or minimal fluid film gap.

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.

The present work aims at finding an approach to calculate fatigue damage from three-dimensional vibration measurements, with a key objective to define a reliable measurement quantity to predict local stresses. Existing theoretical concepts highlight an exploitable relation to modal velocity. A hysteresis counting based on velocity measurements as well as damage accumulation using S–N curves is proposed. While existing methods consider only uniaxial shaker test setups, there is also a need for fatigue calculation under a three-dimensional shaker setup. This paper also derives a method for fatigue calculation for structures under three-dimensional excitation using the equivalent stress concept. The proposals are also validated using a real mechanical structure and the results indicate better applicability than existing methods.

The improvement in sound quality is an important aspect in the development of automobiles, as it influences the customers comfort and therefore the purchase decision. Furthermore, the legislature has passed several bills that aim at tightening the sound radiation threshold within the next decade. In order to improve the sound emission properties of lightweight designs, extensive research efforts have been devoted to develop sophisticated concepts that achieve an excellent noise reduction at a low mass.