Researcher:
Uçar, Hakan

Profile Picture
ORCID

Job Title

PhD Student

First Name

Hakan

Last Name

Uçar

Name

Name Variants

Uçar, Hakan

Email Address

Birth Date

Filters

2011 - 20184

Advanced Search

Filter by

Settings

Researcher Of Publications: search.filters.isAuthorOfPublication.8d39e46a-b5f8-4df4-9609-058bc8f4a805

Search Results

Now showing 1 - 4 of 4
  • Placeholder
    PublicationMetadata only
    Vibration response prediction on rubber mounts with a hybrid approach
    (Int Inst Acoustics & Vibration, 2018) N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Uçar, Hakan; Başdoğan, İpek; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Engineering; N/A; 179940
    Accurate prediction of the vibration response at a point on a complex structure, where the operational behavior cannot be measured directly, is an important engineering problem for design optimization, component selection and condition monitoring. Identifying the exciting forces acting on the structure is a major step in the vibration response prediction (VRP). At the point where direct measurement is impossible or impractical due to physical constraints, a common approach is to identify the exciting forces based on multiplication of an inverted frequency response function (FRF) matrix and a vector of vibration responses measured at the points where the exciting forces are transmitted through. However, in some cases measuring FRFs are almost impossible. In other cases, where measuring is possible, they may be prone to significant errors. Furthermore, the inverted FRF matrix may be ill-conditioned due to the one or few modes that dominate the dynamics of the structure. In order to improve the force identification step and reduce the experimental challenges, previous studies focused on either conditioning methods or numerical models. However, conditioning methods result in additional measurements, and using only numerical models causes reduced accuracy due to incongruities between the simulation model and the real system. Considering these problems, a hybrid VRP methodology that incorporates the numerical modeling and experimental measurement results is proposed in this study. Creating an accurate numerical model and properly selecting the force identification points are the main requirements of the proposed methodology. A structure coupled with rubber mounts is used to demonstrate the proposed methodology. The numerical model includes hyperelastic and viscoelastic modeling of the rubber to represent the system behavior accurately. The selection of force identification points is based on a metric that is composed of the average condition number of the FRF matrix across the whole frequency of interest. The results show that the proposed hybrid methodology is superior to other alternative methods where predictions are solely based on numerical results or experimental measurements.
  • Placeholder
    PublicationMetadata only
    A validation study of the structural modification technique for vibro-acoustic analysis
    (ICSV, 2011) Department of Mechanical Engineering; Department of Mechanical Engineering; Başdoğan, İpek; Uçar, Hakan; Faculty Member; PhD Student; College of Engineering; Graduate School of Sciences and Engineering; 179940; N/A
    The structure-borne noise inside the passenger cabin of automobiles, which is mainly caused by the vibrating panels enclosing the vehicle, dominates the low frequency noise. The structural design of the panels can be modified to improve the sound pressure level (SPL). The sound pressure level (SPL) can be predicted using a vibro-acoustic model which includes the Finite Element Model (FEM) for the structural analysis and the Boundary Element Model (BEM) for the acoustic analysis. However, when the designer is making changes on the structural model to improve the SPL, the vibration analysis must be repeated after every modification before the reanalysis of the vibro-acoustic model. Such changes require considerable computational time especially in case of very complex structures. In our previous studies, it has been shown that the structural modification technique can be implemented to reduce the computational time significantly by skipping the modal analysis of the modified structure. This technique utilizes the frequency response functions (FRFs) of the original model for the reanalysis of the structure that is subjected to structural modification. In this study, a demonstration testbed of a rectangular box with the flexible mid-panel is constructed in order to validate the structural modification technique experimentally and determine the effect of modification. The differences between the numerical and experimental models are discussed then the structural/acoustic performance of the rectangular box is compared before and after the modification using the testbed results.
  • Thumbnail Image
    PublicationOpen Access
    Dynamic characterization and modeling of rubber shock absorbers: a comprehensive case study
    (Sage, 2018) Department of Mechanical Engineering; Department of Mechanical Engineering; Uçar, Hakan; Başdoğan, İpek; PhD Student; College of Engineering; N/A; 179940
    Rubber or elastomeric materials are widely used for shock absorbers having elastic and viscous properties such as high inherent damping, deflection capacity, and energy storage. The dynamic properties of these components are of primary concern in designing rubber absorbers to reduce the shock loading given as well as the structure-borne noise transmissibility. Besides, the dynamic response of the mechanical systems, at where the rubber shock absorbers are used, is directly associated with the properties of the shock absorbers. In order to determine these properties of the rubber, mathematical models are created in terms of hyperelasticity and viscoelasticity. The hyperelastic and viscoelastic material models represent the nonlinear elastic and strain rate dependencies of the overall rubber behavior, respectively. Hyperelastic material model captures the material's nonlinear elasticity with no-time dependence whereas viscoelastic model describes the material response which contains an elastic and viscous part depending on time, frequency, and temperature. This paper presents the dynamic characterization of rubber shock absorbers, having different shore hardness values, in terms of hyperelastic and viscoelastic constitutive models. The parameters of the constitutive models are determined from the uniaxial tensile and relaxation tests. These parameters are used for the numerical model of the rubber components and the accuracy of the characterization is presented by means of a numerical case study.
  • Thumbnail Image
    PublicationOpen Access
    Operational response prediction for rigidly linked structures via direct inversion method
    (Sage, 2016) Department of Mechanical Engineering; Department of Mechanical Engineering; Uçar, Hakan; Başdoğan, İpek; PhD Student; College of Engineering; N/A; 179940
    Most of the mechanical systems are composed of different subsystems connected and coupled by several links. Any excitation acting on the system is divided into several internal forces which propagate through these links or so-called transfer paths. For these kinds of systems, it is important to predict the structure's response due to this excitation which is transmitted via propagation paths. Predicting the operational response as much as accurate at the point of interest is of great importance in terms of design optimization and condition monitoring at where the response cannot be measured due to some physical constraints. In accordance with this purpose, the identification of operational internal forces is necessary. In cases where direct measurement of the operational forces is impossible or impractical, especially for complex structures, a common approach is to identify the operational forces based on measured frequency response functions and a set of measured operational responses. The classical approach is the Moore-Penrose pseudo inversion, which needs significant number of frequency response function measurements and huge time consumption and effort since the coupled system is to be disassembled at all interfaces. Noting that, real complex structures have some physical limitations to be disassembled, more practical and faster approaches are required for real-life applications. The aim of this study is to present direct inversion method to identify the operational forces and hence, predict the operational response for rigidly linked vibrating structures and also demonstrate the effect of mass loadings of the transducers and noise during frequency response function measurements. The algorithms investigated herein are applied in numerical and experimental setups composed of rigidly linked structures.