A new triangular composite shell element with damping capability

This paper presents a new triangular composite shell element with damping capability. Formulation of the composite triangular shell element is based on stacking individual homogeneous triangular shell ele- ments on top of each other. The homogeneous shell element is an assembly of a triangular membrane element with drilling degrees of freedoms and a plate element. Damping capability is provided by means of complex element stiffness matrix of individual flat layers of the composite element. These elements with damping capability allow modelling general structures with damping treatments. A few test cases are modelled using triangular finite element developed here and the results of the complex eigenvalue analyses are compared with those of the quadrilateral shell elements proposed recently. The results obtained using the presented triangular and previous quadrilateral composite elements are also com- pared with those based on modal strain energy method and experimental results. Comparisons of the experimental and the theoretical results confirm that the modal properties including modal damping lev- els of structures with damping treatments can be predicted with high accuracy using the proposed finite element.WOS:000343838900033Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ1ArticleUluslararası işbirliği ile yapılmayan - HAYIRAralık2014YÖK - 2014-1

Detection of air leakage into vacuum packages using acoustic measurements and estimation of defect size

Air leakages in food and ingredient packages which are sealed in vacuum environments may cause a marked deterioration of the product, leading to a loss of functionality. Manufacturers of such products have very stringent but rather costly quality control procedures and there is a pressing need for developing more economical ways of automated quality control techniques to test the vacuum packages reliably. However, due to the fact that the defect size of a typical package with a leakage problem could be micro- or nano-scale, such faults are not detectable using conventional techniques. In this paper, the performance of a proposed acoustic method is assessed for the detection of air leakage in instant dry yeast packages sealed in a vacuum environment, which are typical of food and ingredients packaged under vacuum conditions. The investigation is carried out in both laboratory and in-situ environments. The acoustic pressure created by leaking air into the faulty packages is measured using a low-noise microphone in an acoustic chamber. Faulty packages are then identified using the changes in measured sound pressure levels within a certain frequency band. A mathematical model is also proposed to predict the pressure inside a yeast package with certain defect size as a function of time. The mathematical model is then used to determine the size of a defect causing the leakage, using the time required for the pressure inside a faulty yeast package to reach to a threshold level. The results of this investigation show that, using the state of the art measurement techniques, it is possible to detect packages with leakage problem if the diameter of the defect is greater than a few tens of micrometres.WOS:000447112700030Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ1ArticleUluslararası işbirliği ile yapılmayan - HAYIROcak2019YÖK - 2018-1

Application of ultrasonic vibrations for minimization of the accumulation of limescale in steam irons

The accumulation of limescale in steam irons can significantly reduce the ironing efficiency. It is this problem that inspired us to introduce ultrasonic vibrations to irons in order to minimize limescale accumulation. This study describes a methodology for designing, modelling and optimizing an iron fitted with an ultrasonic exciter in an attempt to minimize limescale accumulation. In our methodology, first, an experimental demonstration of the potential benefits of ultrasonic vibrations in steam irons was conducted, using two existing irons, one of which was equipped with an ultrasonic exciter. Having confirmed the benefits, an experimental iron was designed and then optimized to maximise ultrasonic vibrations using finite element analyses within a predefined frequency range. To validate the results of the finite element analyses, a prototype iron base was built, and forced vibrations of this prototype, at ultrasonic frequencies ranging from 35 to 40 kHz, were measured using a laser vibrometer. The results of the theoretical and experimental vibration analyses as well as the physical experiments on the steam irons indicate that it is possible for ultrasonic vibrations to be utilized in irons to minimize the accumulation of limescale.WOS:000428484500003Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ2ArticleUluslararası işbirliği ile yapılmayan - HAYIRHaziran2018YÖK - 2017-1

Testing non-magnetic materials using Oberst Beam method utilising electromagnetic excitation

The use of a non-contact electromagnetic excitation system is highly recommended in the literature to identify the mechanical properties of materials using the Oberst Beam Method. However, it is not possible to test a specimen made of non-magnetic material using the Oberst beam test rig, comprising of an electromagnetic exciter, unless the specimen is modified using some magnetic particles or small discs made of a ferromagnetic material. Although doing so makes it possible to perform the test, this results in an undesirable modification to the test specimen, leading to unquantified levels of errors in the estimated material properties. This study proposes an approach for eliminating the adverse effects of such mass modification to the test specimen, and also allows subsequent removal of the electromagnetic stiffening effects produced by the electromagnetic exciter. The proposed method is validated using both finite element (FE) simulations and experimental data. Results confirm that the proposed method for the removal of the adverse effects of mass modification, combined with the subsequent removal of the electromagnetic stiffening effects, is very effective, making it possible to determine the material properties of non-magnetic materials with a very good accuracy.WOS:000471250400007Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ1ArticleUluslararası işbirliği ile yapılmayan - HAYIREylül2019YÖK - 2019-2

Characterization of viscoelastic materials using free-layered and sandwiched samples: assessment and recommendations

Viscoelastic materials are widely used in many applications in practice. However, determination of the elastic and damping properties of these materials is quite difficult in the sense that the identified results may contain high degree of uncertainty. The characterization of viscoelastic materials using the Oberst beam method, based on non-contact excitation and response measurements, is revisited in this paper. The effects of signal processing parameters such as frequency resolution in Frequency Response Function (FRF) measurements, as well as the effects of various single-degree-of-freedom modal analysis methods, including circle-fit, half-power and line-fit are investigated first. Then, the modal loss factors, Young's modulus and shear modulus of some sample viscoelastic materials are identified using both the free-layered and sandwiched samples. The results obtained from different tests are compared, discussed and some recommendations are made so as to identify the damping and elastic properties of typical viscoelastic materials with better accuracy. Analyses of a large number of FRF measurements show that the selection of the appropriate signal processing parameters and the use of appropriate modal analysis method can be very significant during the identification of viscoelastic materials. By following the approach presented in this paper, the damping and elastic properties of viscoelastic materials can be identified with better accuracy using either free-layered or sandwiched samples. The material properties obtained by this approach can be used for developing valid structural models and/or for damping optimization purposes.WOS:000357937100110Scopus - Affiliation ID: 60105072Science Citation Index Expanded - Conference Proceedings Citation Index- ScienceQ4Article; Proceedings PaperUluslararası işbirliği ile yapılmayan - HAYIRNisan2015YÖK - 2014-1

Elimination of transducer mass loading effects from frequency response functions

Frekans Tepki Fonksiyonlarının (FTF) kalitesinin parazit ve sistematik hatalar gibi faktörlerle olumsuz yönde etkilendiği bilinmektedir. FTF’larını kullanan çeşitli analizlerin doğruluğu ve güvenilirliği de ölçülmüş verilerin kalitesine bağlıdır. Bu çalışma ölçülmüş FTF’larındaki en önemli sistematik hatalardan biri olan transdüser kütle etkisini kaldırmayı amaçlamaktadır. Bu çalışmada ölçülmüş FTF’larındaki transdüser kütle etkisinin kaldırılması için Sherman-Morrison eşitliğine dayalı olarak geliştirilen yeni bir yöntem sunulmaktadır. Burada sunulan formülasyon genel amaçlıdır ve hem sabit hem de hareketli transdüser durumlarına uygulanabilmektedir. Transdüserin gezdirildiği test durumunda yardımcı bir kütle kullanımından yararlanılmaktadır. Bununla beraber, yapının transfer FTF’nun ölçümünde yardımcı kütle kullanımına gerek duyulmaması yeni yöntemin üstün özelliklerinden biridir. Bu sayede transfer FTF’nda ilave etkiler oluşturulmamaktadır. Yöntemin uygulanabilirliği sayısal simülasyonlarla ve deneysel veriler kullanılarak incelenmiştir.Anahtar Kelimeler: Frekans Tepki Fonksiyonu (FTF), transdüser kütle etkisi, Sherman-Morrison eşitliği.It is well known that the quality of measured Frequency Response Functions (FRFs) is adversely affected by many factors, most significant sources being noise and systematic errors. It is also known that the accuracy and the reliability of various analyses using the measured FRFs depend strongly on the quality of measured data. This paper aims to remove one of the major systematic errors in measured FRFs, namely the mass loading effects of transducers. This paper presents a new method based on the Sherman-Morrison identity for the elimination of mass loading effects of transducers from measured FRFs. The formulation presented here is general in the sense that it can be applied for both fixed and moving transducer cases.  In the case of moving transducer type of tests, the use of dummy mass is utilized. However, one of the distinct features of the new method is that it avoids the need for the measurement of cross-FRFs of a structure with a dummy mass attached to the structure, hence avoiding further contamination of cross-FRFs. The applicability of the method is also assessed using experimental as well as simulated data. Keywords: Frequency Response Functions (FRFs), transducer mass effect, Sherman-Morrison identity