Miha Boltežar

Miha Boltežar
University of Ljubljana · Faculty of Mechanical Engineering

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137
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Publications

Publications (137)
Article
Full-text available
In noise and vibration engineering, a structure’s passive dynamic properties are often evaluated in terms of its frequency response functions (FRFs). The typical FRF measurement campaign consists of controlled structure excitation and the capturing of its response. However, exploiting operational excitation for FRF acquisition is not feasible, with...
Chapter
pyFBS is an open-source Python package for frequency-based substructuring. The package implements an object-oriented approach for dynamic substructuring. This tutorial is intended to introduce structural dynamics and NVH engineers to the research toolbox in order to overcome vibration challenges in the future. The focus will be on experimental mode...
Article
Full-text available
Hybrid modeling is an increasingly common procedure for predicting the structural dynamics of complex products. System equivalent model mixing (SEMM), a dynamic substructuring-based method, is a recent addition to the field. Its implementation within frequency-based substructuring has great potential. Therefore, it is reasonable to explore the opti...
Article
This paper focuses on the development of a method for the accurate representation of the strong structural–acoustic coupling between an elastic Helmholtz resonator, a heavy fluid and an impedance tube. The Helmholtz resonator has an elastic wall and is connected to the impedance tube, yielding a system with two acoustic cavities coupled through a n...
Article
Full-text available
A reliable experimental application of frequency based substructuring requires very accurate acquisition of frequency response functions (FRFs). Even a relatively small error introduced during the measurement can result in erroneous substructuring results. The measurement errors can be either random or systematic, with the latter often referred to...
Article
Full-text available
When determining the critical paths for the transmission of sound and vibration in assembly products, transfer path analysis (TPA) is a reliable and effective tool. TPA represents a source with a set of forces that replicate the operational responses. However, admittance-based TPA methods are prone to experimental errors, as small measurement inacc...
Chapter
Accurate determination of the high-resolution dynamic response is a crucial step for the dynamic properties characterization in the development phase of a modern product. The conventional experimental procedure for the identification of the structure’s dynamic properties is an experimental modal analysis, where a high spatial resolution can be obta...
Article
Full-text available
Identifying the local properties of a structure, either to perform structural health monitoring or to fine tune a numerical model, requires the updating of a large number of parameters. With a high spatial density, but a low dynamic range response information, high-speed-camera measurements have the potential to identify a large number of localized...
Article
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The application of a speckle pattern to the surface of a structure is usually required for Digital Image Correlation (DIC)-based displacement identification. A speckle pattern generally requires the modification (e.g., painting) of the structure’s surface. An improved method of laser-light speckle formation for DIC measurement of relatively large s...
Article
Full-text available
A high-resolution dynamic response is important for characterizing a system’s dynamic properties. Measurements involving a limited number of points on the structure can be expanded to unmeasured points through approximation or model-based expansion techniques that rely on the introduction of a numerical model. Recently, an expansion method called S...
Conference Paper
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40 papers presented at the 2nd Circular Packaging Conference which was held in hybrid system (live in Slovenj Gradec, Slovenia on 9-10th of September 2021 and online) published in form of full reviewed papers in Proceedings of the conference.
Article
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Modal substructuring is an established subdomain of dynamic substructuring in which the handling of multi-point connections between subcomponents proves to be a problematic task. This is particularly the case with experimental models, where even small inconsistencies in the interface dynamics can greatly affect the accuracy of the substructuring pr...
Article
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A reconstructed displacement field using near-field acoustic holography (NAH) serves as an alternative to conventional measurement methods when it comes to obtaining the high-resolution vibration response of a structure. The method is highly applicable as it enables direct, non-contact measurement of the 3D structural response based on a single aco...
Article
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To measure high-frequency 3D vibrations, multi-camera, high-speed imaging hardware is normally required. An alternative using still-frame cameras was recently introduced with the Spectral Optical Flow Imaging (SOFI) method. In this research, the SOFI method is extended to multiview measurements of spatial operating deflection shapes. This is achiev...
Article
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Fused-filament fabrication, one of the most accessible additive manufacturing technology, has already been used to manufacture piezoresistive static/quasistatic strain sensors, force sensors and wind sensors. Recent research showed that fused-filament fabrication could also be used for the manufacturing of dynamic sensors. However, the anisotropic...
Chapter
Full-text available
pyFBS is an open-source Python package for Frequency Based Substructuring. The package implements an object-oriented approach for dynamic substructuring. State-of-the-art methodologies in frequency based substructuring, such as virtual point transformation and system equivalent model mixing, are available within the pyFBS. Each method can be used a...
Article
Full-text available
Structural dynamics relates the excitation profile to the dynamic loads at a particular location of the structure. Spectral methods fatigue-life estimation is based on the assumptions of stationarity and the Gaussianity. This research proposes a method for a fatigue-life estimation for non-stationary excitation. The method is based on the short-tim...
Article
Full-text available
The dynamic properties of modern products are analysed using an experimental approach through the measurement of frequency-response functions (FRFs). For an individual measurement, the coherence offers an online check during the system acquisition. More general tools for determining the consistency of the complete measurement set are based on a com...
Chapter
Ch. 3 gives the theoretical background on the experimental modal analysis, which is an important tool for model validation; this chapter is divided into three sections: Types of excitation, Frequency response function estimation, and Modal parameter identification. Types of excitation in experimental modal analysis and vibration fatigue are very im...
Chapter
Ch. 12 presents an experiment with the identification of nonstationary and non-Gaussian excitation. Further, the significance of nonstationary vs. non-Gaussian excitation is researched.
Chapter
Ch. 4 gives the theoretical background on the uniaxial vibration fatigue. The goal of this chapter is giving the theoretical background on the uniaxial high-cycle loads typical in vibration fatigue. The uniaxial approach will be given in the subsequent Ch. 5 generalized to the multiaxial case. In the first section the basics of the time-domain stre...
Chapter
Ch. 1 gives the theoretical background on the structural dynamics. This chapter is organized in two sections. The first section gives the theoretical background on the single-degree-of-freedom systems, whereas the second section is on the multi-degree-of-freedom systems. Initially, damping-free systems are discussed, but then the damping in the for...
Chapter
Ch. 5 extends the uniaxial loads theory to the multiaxial loads theory in three sections. The first section Time domain basics discusses the historic origins of multiaxial loads and presents relevant basic prior research and the nomenclature. The second section Random stress response relates the multiaxial stress state introduced in Ch. 1 to the ra...
Chapter
Ch. 8 presents an experimental approach for the harmonic accelerated vibration testing with concurrent identification of fatigue and structural parameters.
Chapter
Ch. 6 discusses the modal decomposition based vibration fatigue analysis. Whereas this could be considered a multiaxial criterion, it presents a theoretical generalization of the multiaxial loads. As is discussed in Ch. 1, the dynamic model can be researched using the spatial, modal, or response model. The FEM model presents a spatial model and is...
Chapter
Ch. 7 presents the vibration fatigue at nonstationary and non-Gaussian excitation. All previous chapters are based on the assumptions of stationary and Gaussian excitation. However, dynamical systems are frequently nonstationary and non-Gaussian excited, and this chapter is divided into two sections: the first deals with the identification on nonst...
Chapter
Ch. 11 presents an experimental setup where the Y-sample has been multiaxially excited. The different theoretical methods are compared and discussed on the experimental data.
Chapter
Ch. 9 presents an experimental approach accelerated vibration fatigue testing with random and harmonic excitation. A comparison of experimental and numerical results is also given.
Chapter
Ch. 10 experimentally compares the methods presented in Ch. 4.
Chapter
Ch. 2 gives the theoretical background on signal processing and is divided into two sections, the deterministic process and the random process. The deterministic process section discusses the Fourier transform and the discrete Fourier transform. It further discusses the properties of the Fourier transform, which are especially important when handli...
Article
Full-text available
Experimental modal analysis (EMA) is a well-established procedure for determining the modal parameters of a structure. Typically, a point-force is used to excite the structure and the translational response is measured. When performing an EMA, problems with a reliable modal-parameter estimation can arise whenever a selected reference point is locat...
Article
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In structural dynamics, different damping models are used; however, due to modal decomposition, those models typically result in the use of the damping ratio as the modal damping parameter. If proportional viscous damping is used, the damping ratio can be related to the mass and stiffness parameters of a particular dynamic system, i.e. the damping...
Chapter
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Polyvinylidene fluoride (PVDF) piezoelectric thin film sensors are already well-known as low-cost vibrational sensors. One of the primary reasons, in addition to the overall cost, is also the PVDFs high chemical resistance, thermal stability and flexibility, which makes them a compelling alternative to piezoelectric ceramic. The PVDF sensors can al...
Article
Full-text available
The use of a high-speed camera for dynamic measurements is becoming a compelling alternative to accelerometers and laser vibrometers. However, the estimated displacements from a high-speed camera generally exhibit relatively high levels of noise. This noise has proven to be problematic in the high-frequency range, where the amplitudes of the displa...
Article
Full-text available
The Virtual Point Transformation (VPT) makes it possible to experimentally identify the full DoF FRF matrix by projecting the measured displacements onto the Interface Deformation Modes (IDMs). The VP FRFs were already successfully used in Frequency-Based Substructuring (FBS); however, the VPT is susceptible to deviations in the impact location and...
Chapter
Optical vibration measurement methods have, due to their non-contacting nature and high spatial resolution, steadily been gaining in adoption with the developments in high-speed camera technology in recent years. In high-frequency applications, however, where observed displacements of the vibrating structure are particularly small in amplitude, the...
Chapter
Vibration measurements with a high-speed camera are becoming a compelling alternative to accelerometers and laser vibrometers. However, estimated FRFs from the high-speed camera are usually displaying relatively high levels of noise. The noise has proven to be problematic especially in the higher frequency range, where the amplitude of the displace...
Article
Full-text available
With recent developments in additive manufacturing (AM), new possibilities for fabricating smart structures have emerged. Recently, single-process fused-filament fabrication (FFF) sensors for dynamic mechanical quantities have been presented. Sensors measuring dynamic mechanical quantities, like strain, force, and acceleration, typically require co...
Article
Full-text available
Fused-filament-fabrication (FFF) technology is promising for the production of fully embedded piezoresistive dynamic sensors. However, the lack of experimental identification of the dynamic piezoresistivity limits the scientific and applied progress. Dynamic piezoresistivity of 3D printed structures is hard to research due to: structural anisotropy...
Article
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The response of linear dynamic structures can be decomposed into modal components, where each natural frequency is also represented by a corresponding mode shape and damping ratio. While vibration-fatigue-damage identification was recently expanded using modal decomposition, this research proposes a modal-decomposition-based thermoelastic damage id...
Article
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In vibration fatigue, three unique types of loads are typical: random, harmonic and impulse. In an application any of these loads are possible. A fatigue-life analysis is possible in the time and frequency domains using the frequency-response function of a structure. Recent studies demonstrated that the impulse loads influence the accuracy of a fat...
Article
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The use of high-speed camera systems in vibration measurements is typically limited to identifying motion, transversal to the optical axis, due to an inherent limitation of 2D imaging systems. Depth information, lost in the imaging process , can be recovered by using the well-established 3D DIC technique, but is still limited to a single face of th...
Article
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Dynamic substructuring methods serve as a powerful tool in the analysis of modern complex systems. The coupling of substructures has been successful with analytically obtained results. However, substructuring with experimentally obtained data remains challenging. One of the main problems associated with experimental substructuring is the coupling o...
Article
Full-text available
Pulse-Width Modulation (PWM) represents a carrier-frequency-dependent structural excitation. The PWM’s excitation harmonics are also reflected in the air gap’s electromagnetic forces, the vibration response and the resulting structure-borne noise. The last of these can be numerically predicted with a multiphysics finite-element-analysis (FEA) conta...
Article
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The theory of frequency-based substructuring enables us to combine the dynamical behavior of multiple subsystems into the common response of the whole system. Subsystem’s properties can be numerically or experimentally obtained in the form of frequency response functions. Response models are then coupled together taking into account a connectivity...
Article
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3D-printing technology is opening up new possibilities for the co-printing of sensory elements. While quasi-static research has shown promise, the dynamic performance has yet to be researched. This study researched smart 3D structures with embedded and printed sensory elements. The embedded strain sensor was based on the conductive PLA (Polylactic...
Article
Full-text available
Three types of loads are typical in vibration fatigue: random, harmonic and impact. In an application, any combination of these loads is possible. In vibration fatigue the random loads can be investigated by using the frequency-response function of the structure. While the theoretical relationship between the frequency-response function and the imp...
Article
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High-speed camera measurements are increasingly being used in modal analysis to instantaneously measure full-field structural responses by extracting the displacement information from images using digital-image-correlation and other optical-flow methods. High-speed cameras capable of filming full frame at high frame rates can be very expensive and...
Article
According to the standard ASTM E2611 an impedance tube can be used to measure the sound transmission and reflection losses in an absorption material. However, application in a liquid medium in the low-frequency range presents difficulties with respect to the size of the structure and the waveguide-related distortion of the plane-wave propagation. I...
Article
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Computational simulations of a multibody dynamic response are an important tool for the analysis and design of various mechanical systems. While the governing dynamic equations of these systems are well known, the identification of model parameters, especially those associated with joints, can prove difficult and time consuming. Traditionally, expe...
Article
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This is a review of well established and recently introduced contact-force models that are used in the dynamical analysis of multibody systems. In particular, two contact groups have been investigated: the general (point contact) and the cylindrical (line contact) models. For the point-contacts group, 20 dierent models are listed and a dozen are us...
Article
Full-text available
Pulse-width modulation (PWM) is widely used in motor control and represents a carrier-frequency-dependent structural excitation. The PWM's excitation harmonics are also reflected in an air gap's electromagnetic forces, the transmitted bearing forces and the resulting structure-borne noise. Inappropriate carrier-frequency selection can cause additio...
Article
We present a new formulation to calculate the response of a system containing rolling-element bearings operating under a radial clearance and a dominant radial load. The nonlinear bearing force-and stiffness-displacement characteristics in combination with the bearing clearance necessitate an advanced numerical analysis. The response of a shaft-bea...