To demonstrate the difference between non-ideal experiments and idealized analytical models, bending vibrations of a frame structure have been analyzed in the context of hands-on teaching in structural dynamics. Both experimental modal analysis and model-based evaluation of system dynamics have been performed. The investigations have been limited to mechanical vibrations in the low-frequency range. It has been found that even simple mechanical models are very useful to explain, understand, and validate experimental results. The latter have been derived from one key principle of analytical dynamics—the Lagrange formalism. The article is written for students in mechanical engineering and related fields as well as for the academic community. The latter could use the results as a benchmark problem in academic teaching as well as in applied research.

The reduction of noise and vibration is possible with passive, semi-active and active control strategies. Especially where self-adaptive control is required, it is necessary to evaluate the noise reduction potential before the control approach is applied to the real-world problem. This evaluation can be based on a virtual model that contains all relevant sub-systems, transfer paths and coupling effects on the one hand. On the other hand, the complexity of such a model has to be limited to focus on principal findings such as convergence speed, power consumption, and noise reduction potential. The present paper proposes a fully coupled electro-vibro-acoustic model for the evaluation of self-adaptive control strategies. This model consists of discrete electrical and mechanical networks that are applied to model the electro-acoustic behavior of noise and anti-noise sources. The acoustic field inside a duct, terminated by these electro-acoustic sources, is described by finite elements. The resulting multi-physical model is capable of describing all relevant coupling effects and enables an efficient evaluation of different control strategies such as the local control of sound pressure or active control of acoustic absorption. It is designed as a benchmark model for the benefit of the scientific community.

Batteries with high energy densities become essential with the increased uptake of electric vehicles. Battery housing, a protective casing encapsulating the battery, must fulfil competing engineering requirements of high stiffness and effective thermal management whilst being lightweight. In this study, a graded lattice design framework is developed based on topology optimisation to effectively tackle the multidisciplinary objectives associated with battery housing. It leverages the triply periodic minimal surfaces lattices, aiming for high mechanical stiffness and efficient heat dissipation considering heat conduction and convection. The effectiveness of the proposed framework was demonstrated through the battery housing design, showcasing its ability to address multidisciplinary objectives as evidenced by the analysis of the Pareto front. This study identifies the potential of lattices in lightweight applications incorporating multiphysics and offers an efficient lattice design framework readily extended to other engineering challenges.

For many engineering applications, it is sufficient to use the concept of simple materials. However, higher gradients of the kinematic variables are taken into account to model materials with internal length scales as well as to describe localization effects using gradient theories in finite plasticity or fluid mechanics. In many approaches, length scale parameters have been introduced that are related to a specific micro structure. An alternative approach is possible, if a thermodynamically consistent framework is used for material modeling, as shown in the present contribution. However, even if sophisticated and thermodynamically consistent material models can be established, there are still not yet standard experiments to determine higher order material constants. In order to contribute to this ongoing discussion, system identification based on the method of self-adaptive filtering is proposed in this paper. To evaluate the effectiveness of this approach, it has been applied to second-order gradient materials considering longitudinal vibrations. Based on thermodynamically consistent models that have been solved numerically, it has been possible to prove that system identification based on self-adaptive filtering can be used effectively for both narrow-band and broadband signals in the field of second-order gradient materials. It has also been found that the differences identified for simple materials and gradient materials allow for condition monitoring and detection of gradient effects in the material behavior.

Theoretical and non-dimensional investigations have been performed to study the vibration control potential of approaches that are not only based on viscoelastic but also on endochronic elements. The latter are known from the endochronic theory of plasticity and provide the possibility of establishing rate-independent schemes for vibration control. The main question that has to be answered is: Can rate-independent damping be efficiently used to reduce mechanical vibrations? To answer this question, non-dimensional models for dynamical systems are derived and analyzed numerically in the time domain as well as in the frequency domain. The results are used to compare the performance of an optimally tuned endochronic absorber to the performance of an optimally tuned dynamic absorber with viscoelastic damping. Based on a novel closed-form representation for non-linear systems with endochronic elements, it has been possible to prove that the rate-independent control of vibration results in an overall control profit that is close to the control profit obtained by the application of well-established approaches. It has also been found that the new concept is advantageous if anti-resonances have to be considered in broadband vibration control. Based on these novel findings, a practical realization in the context of active vibration control is proposed in which the rate-independent control law is implemented with an appropriate signal processing hardware.

A combined experimental and numerical approach for the analysis of convective heat transfer from a multifunctional flat plate specimen under aircraft icing conditions is presented. The experimental setup including a heat control and measurement system that is installed in a de-icing test bed. The ambient temperature (θa=[253,283]K), air velocity (va={0,15,30}ms), and angle of attack (α={10,30}∘) are varied, and their influence on heat transfer during local Joule heating is discussed. The numerical approach utilises the results to compute the convective heat transfer coefficients (HTC) based on Newton’s convective heat transfer condition. Results indicate that the numerical model represents the heat transfer behaviour with high accuracy. The HTC for free convection was found to hold h¯≈2.5Wm2K and h¯≈[10,40]Wm2K for forced convection conditions with minor scattering. The increase in HTC under forced convection conditions has a significant effect on the overall heat transfer behaviour, resulting in high temperature gradients within the material. The functional optimisation of multifunctional structures will benefit from including application related convection conditions, dealing with resulting temperature fields by structural design. It is expected that multifunctional structures for de-icing as well as for structural energy storage, morphing structures, or stiffness adaptive structures with similar material constituents will benefit from this recognition.

A smart exciter coupled to cabin panels can be used as a new type of loudspeaker for emergency announcements in the aircraft cabin. The same device can also be used as a semi-active vibration control system which is effective in reducing the amplitude of structural vibration. The objective of this paper is to investigate the potential of vibration reduction using a smart exciter in combination with an optimized resistive-inductive shunt circuit, which serves as an absorbing network. First, the vibration reduction effect has been analyzed numerically using a simulation framework realized with COMSOL and MATLAB/Simulink. In a second step, the reduction effect of the smart exciter together with a resistive-inductive shunt circuit, which is produced by the Center of Applied Aeronautical Research (Zentrum für Angewandte Luftfahrtforschung GmbH, Hamburg, Germany), has been investigated experimentally. The results presented here prove that the smart exciter together with a resistive-inductive shunt can be highly effective in reducing structural vibrations.

Multifunctional composites including polymer electrolyte coated carbon fibres and polymer matrix systems gained recent interest in light-weight design related research areas. Compared to classical fibre reinforced plastics, the interphase, made by electropolymerisation on the fibre surface, represents a new, third material phase. The coating serves as ion-conducting separator in structural batteries and as insulating layer in energy transmitting multifunctional composites. The importance of this study is related to the fact, that multifunctional applications, based on such composites, are exposed to temperature changes in many cases. The coating material, acting as thin interphase, shows a significant temperature dependant Young’s modulus, determining the overall macroscopic behaviour under thermal loads. The new influences on the effective elastic properties of the composite are determined in this work in a 3D microstructural simulation approach based on a unit cell geometry. For the first time, the resulting effective properties are discussed towards the state of research and future work. First, the effective elastic stiffness is computed by isothermal virtual material testing, applying unit strain modes on the unit cell. Second, a uniform temperature change is applied and the effective thermal expansion coefficients are computed. The results show that a change of stiffness in the coating domain has a great influence on the effective stiffness in the transversal isotropic plane. The effective thermal expansion of the composite is also highly sensitive to the thermal expansion behaviour of the coating phase. Main conclusions are drawn towards multiphysical material simulation: Influences of the coating material properties have to be taken into account to compute effective properties. In particular, it is necessary to include the temperature dependant stiffness and the coefficients of thermal expansion of the interphase, which affect effective properties significantly. A thermo-mechanic coupled microscale model is needed to represent in-situ properties of such composites for applications with heat exposure.

significant reduction of disturbing noise can be achieved by passive, semi-active and fully active control approaches. Passive noise treatments such as dynamic vibration absorber are very robust and can be applied to obtain a broadband performance. Active noise control systems are designed to control harmonic or broadband noise. They are very effective, if the control volume is small as known from single-input/single-output systems used in active headphones. However, if distributed control is required, the control profit is not scalable, because the required multiple-input/multiple output systems must be adjusted to specific acoustic modes as known from the active control of propeller-aircraft interior noise. Semi-active control that is based on the principle of dissipation allows to combine several single-input/single-output systems without coupling. Thus semi-active approaches are capable to solve the problem of scalability. The present paper reports on a specific approach that is based on a dynamic absorber attached to a vibrating structure and coupled with a dissipating electrical network. The electrical components of this network can be adjusted to the mechanical impedance to realize dissipation. To focus on the performance principle, the theoretical investigations are presented in a dimensionless analysis.

Polymer electrolyte coated carbon fibres embedded in polymeric matrix materials represent a multifunctional material with several application scenarios. Structural batteries, thermal management materials as well as stiffness adaptive composites, made from this material, are exposed to significant joule heat, when electrical energy is transferred via the carbon fibres. This leads to a temperature increase of up to 100 K. The thermal behaviour of this composite material is characterized in this numerical study based on a RVE representation for the first time. Compared to classical fibre reinforced plastics, this material comprises a third material phase, the polymer electrolyte coating, covering each individual fibre. This material has not been evaluated for effective thermal conductivity, specific heat and thermal behaviour on the microscale before. Therefore, boundary conditions, motivated from applications, are applied and joule heating by the carbon fibres is included as heat source by an electro-thermal coupling. The resulting temperature field is discussed towards its effect on the mechanical behaviour of the material. Especially the temperature gradient is pronounced in thickness direction, leading to a temperature drop of 1 °Cmm, which needs to be included in thermal stress analysis in future thermo-mechanically coupled models. Another important emphasis is the identification of suitable homogenization and model reduction strategies in order to reduce the numerical effort spent on the thermal problem. Therefore, traditional analytical homogenization methods as well as a newly proposed “Two-Level Lewis-Nielsen” approach are discussed in comparison to virtually measured effective quantities. This extensive comparison of analytical and numerical methods is original compared to earlier works dealing with PeCCF composites. In addition, the accuracy of the new Two-Level Lewis-Nielsen method is found to fit best compared to classical methods. Finally, a first efficient and accurate 2D representation of the thermal behaviour of the PeCCF composite is shown, which reduces computational cost by up to 97%. This benefit comes with a different Temperature drop prediction in thickness direction of 1.5 °Cmm. In the context of future modelling of multifunctional PeCCF composite materials with multiphysical couplings, this deviation is acceptable with respect to the huge benefit for computational cost.

Multifunctional structures like the structural energy storage are investigated for enhanced lightweight design. Polymer electrolyte coated carbon fibres (PeCCF) function as a battery half-cell, combining negative electrode and structural electrolyte of the energy storage. The new material combination results in unknown mechanical and multiphysical effective characteristics. Looking forward to future multifunctional CFRP structures made from PeCCF, an influence of the multiphysical PeCCF properties on the CFRP laminate characteristics is expected. This paper presents experimental work, focusing on the first multiphysical characterization of state of the art PeCCF. Thereby, physical effects like the thermo-mechanical coupling in a temperature domain of 193 K<T<720 K and the temperature induction by resistive heating are characterized. Important finding is a temperature dependent complex modulus of the material compound, which is related to the temperature dependent mechanical behaviour of the polymer coating. In addition, the ability to adapt and to predict the materials temperature, which is influenced by resistive heating, is shown. Furthermore, first indications of durability of the coating after cyclic mechanical loading are presented. In addition, new experimental methods for PeCCF investigation are proposed, e.g. the application of conductive epoxy resin for electrical connections.

Cultural assets are witnesses of past times with versatile worth. The irreplaceability of those treasures of art makes their protection our major task. This article reflects the commitment and results of 40 years of conservators' research to protect canvas - objects of cultural heritage - particularly from mechanical loads. It gives a classification of mechanical loads that act upon canvas during transport, exhibition and storing in depot. Furthermore, it gives an overview of different approaches which were used over years to protect canvas from various mechanical loads. This article tends to bridge the gap between restorers' knowledge and methods and concepts known from engineering dynamics. Restorers' first steps using engineers' methods are brought up and the necessity of theoretical modeling which has not started so far are pointed out.

Shaft seals shall prevent the leakage of oil and the intrusion of dirt particles in rotating machineries. A loss of contact between shaft and seal results in leakage. In order to ensure the functionality of the sealing system, the followability of the seal needs to be ensured. To analyze this problem, a model of a Polytetrafluorethylen (PTFE) shaft seal is coupled with an unbalanced rotor. PTFE has pronounced viscous and plastic characteristics. This leads – combined with other non neglectable nonlinearities – to a numerically challenging problem. To reduce the complexity and to increase the computational efficiency, the PTFE shaft seal is discretized by a quasi‐axisymmetric lattice model. The results show that loss of contact at rotor speeds close to the eigenfrequency of the rotor (high amplitude) and at high rotor speeds (high frequency) is possible and shall be avoided to prevent leakage. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

To analyze the vibration behavior of an unbalanced flexible rotor considering both internal damping and a constant driving torque, the Laval-rotor-model is applied. The resulting set of nonlinear ordinary differential equations is transformed into a dimensionless formulation to enable numerical integration using an explicit Runge-Kutta-schema. Applying this approach it is possible to study two different phenomena, the well known “stalling” effect of the shaft that occurs just below the bending critical speed when the drive torque is too weak to pass the resonance as well as the effect of self-excitation that occur at very high speeds because of negative damping. It is shown that both problems can be solved, if the radial displacements of the shaft are controlled by a shaft seal. The latter is modeled as a lumped system – considering mass, stiffness and viscosity effects. The seal influences both the horizontal and vertical displacement of the shaft, and the speed of rotation. Because shaft seals are already used as sensors to determine the speed of rotation, it should be possible to develop a control approach to adjust the pressure between seal and shaft in such a way that stalling and self-excitation can be avoided or at least reduced.

Numerical simulation can be performed; however the implementation into the design process is small due to the fact that the accepted validation processes are still not established. Especially the coupling to optimization problems is still not a simple approach. Also the sufficient modelling of room acoustical problems involves a number of parameters (e.g. material-based absorption coefficients) which are currently not easy to implement.

Because of standing waves, noise source ident ification in an enclosed sound field is nearly impossible, if the damping ratio is low. In such a case, it can be advantageous to apply an inverse method. The novel approach presented in this paper starts with sound pressure measurements in a subspace of the investigated inte rior. In a second step, these data are associated to a time-harmonic finite element model f the cavity. If all sources are located on the boundary, the set of equations can be split int o two subsets. The first can be used to determine all unknown pressure data. The second all ows for calculating the particle velocity. The solution of the inverse problem is found by min i izing a cost function that corresponds to the acoustic energy of the enclosure. In additio n he method of Lagrange multipliers has been used to consider constraints defined by subset one. Using internal as well as external sources, this approach has been applied to sound so urce localization in a fully equipped longrange aircraft section. Internal sources have been localized with success. Furthermore, it has been possible to compute reliable data, if the cabi n noise field has been excited by external sources. Acknowledgement The second and third section of this paper contains results of applied research that has been conducted at the Helmut-Schmidt-University / Univer sity of the Federal Armed Forces Hamburg (HSU) between 2004 and 2011. At this time t he author was employed by the HSU and worked as chief engineer with the chair for Mec hatronics. The experimental investigations described in section three would hav e been impossible without a specific test environment that that has been made available by th e TU Hamburg-Harburg. The support of both institutions is gratefully acknowledged by the author. Furthermore, the author wishes to acknowledge the support of Mr. Daniel Sadra by comp iling this paper.

Noise field analysis is usually the first design task of an ANC-system design process whose procedure has been discussed in Chap. 8. Such an analysis may also include noise source identification in order to develop an ANC concept that is capable of shielding the interior effectively against exterior noise. For this purpose it is essential to determine both positions and source strengths of the primary noise sources. These information are required for an appropriate placement and control of actuators and sensors. A powerful ANC-system design tool that can be used for noise source identification is the IFEM. This tool was described in Sect. 7.2. The upcoming chapter reports on investigations in which the IFEM has been applied to identify acoustic hot spots in a cross-section of a long-range airliner. The sound field in this cavity that represents the basic system was excited by internal as well as by external sources and mapped with a custom-built microphone array. A matching finite element model was developed. As it will be shown in the following chapter, the acoustic variables were calculated from the measured data with success.

Before we start with a detailed analysis of active noise control systems and their application to enclosed sound fields, it is necessary to motivate both the idea and the limits of active control. Furthermore, it will be necessary to describe the interior noise problem and to distinguish between different concepts that can be used to reduce interior noise by means of active control. The upcoming chapter is therefore subdivided into four sections. The first is focused on the fundamental idea of active control, whereas the second contains remarks on active control of interior noise and, to motivate the active noise control approach, an illustrative example concerning aircraft cabin noise caused by propeller rotation. The intention of the third section is to provide some information on the state of the art, while the last section describes both objective and structure of this book.

Active systems for noise reduction are especially of interest when considering applications in which low frequency noise is a main source of disturbance and only limited amounts of installation space and payload are available. This makes the adaptation and implementation of such systems plausible in vehicles such as automobiles and aircraft where passive reduction methods are restricted. Taking into account that both automobiles and aircraft are (usually) equipped with an audio entertainment system, it is self-evident to analyze an active control concept that uses the loudspeakers of the entertainment system as canceling sources driven by a combination of audio signal and control signal. As another example for the application of the proposed design methodology (compare Chap. 8) and the usage of the ANC-system design tools (discussed in Chap. 7), the upcoming chapter reports therefore on a project that was carried out to evaluate the feasibility of broadband ANC combined with in-flight entertainment in a very light jet aircraft cabin. Various problems in design, test and optimization such as optimal transducer placement and choice of adaptive control algorithm were taken into account as reported in (Sachau et al. in Audio Interior fur Kleinflugzeuge (AIK). Final Report. Hamburg Aircraft Research Program (Lufo Hamburg 2), HH 107 B "AIK," Helmut-Schmidt-University/University of the Federal Armed Forces Hamburg, 2008b). The project was conducted at the Helmut-Schmidt-University/University of the Federal Armed Forces Hamburg in cooperation with Innovint-Aircraft Interior GmbH. Financial support by the city of Hamburg is gratefully acknowledged.