MU-SYNTHESIS BASED ACTIVE ROBUST VIBRATION CONTROL OF AN MRI INLET

In this paper, a robust control technique based on μ-synthesis is employed in order to investigate the vibration control of a funnel-shaped structure that is used as the inlet of a magnetic resonance imaging (MRI) device. MRI devices are widely subjected to the vibration of the magnetic gradient coil which then propagates to acoustic noise and leads to a series of clinical and mechanical problems. In order to address this issue and as a part of noise cancellation study in MRI devices, distributed piezo-transducers are bounded on the top surface of the funnel as functional sensor/actuator modules. Then, a reduced order linear time-invariant (LTI) model of the piezolaminated structure in the state-space representation is estimated by means of a predictive error minimization (PEM) algorithm as a subspace identification method based on the trust-region-reflective technique. The reduced order model is expanded by the introduction of appropriate frequency-dependent weighting functions that address the unmodeled dynamics and the augmented multiplicative modeling uncertainties of the system. Then, the standard D-K iteration algorithm as an output-feedback control method is used based on the nominal model with the subordinate uncertainty elements from the previous step. Finally, the proposed control system implemented experimentally on the real structure is to evaluate the robust vibration attenuation performance of the closed-loop system

Frequency Domain Subspace Identification of Multivariable Dynamical Systems for Robust Control Design

Black-box system identification is subjected to the modelling uncertainties that are propagated from the non-parametric model of the system in time/frequency-domain. Unlike classical H1/H2 spectral analysis, in the recent robust Local Polynomial Method (LPM), the modelling variances are separated to noise contribution and nonlinear contribution while suppressing the transient noise. On the other hand, without an appropriate weighting on the objective function in the system identification methods, the acquired model is subjected to bias. Consequently, in this paper the weighted regression problem in subspace frequency-domain system identification is revisited in order to have an unbiased estimate of the frequency response matrix of a flexible manipulator as a multi-input multi-output lightly-damped system. Although the unbiased parametric model representing the best linear approximation (BLA) of the system in this combination is a reliable framework for the control design, it is limited for a specific signal-tonoise (SNR) ratio and standard deviation (STD) of the involved input excitations. As a result, in this paper, an additional step is carried out to investigate the sensitivity of the identified model w.r.t. SNR/STD in order to provide an uncertainty interval for robust control design

Adrb2 gene polymorphisms and salbutamol responsiveness in Serbian children with asthma

Inhaled beta 2 adrenergic receptor (beta 2-AR) agonists are the mainstay of asthma therapy. The beta 2-AR protein is encoded by the ADRB2 gene and variants within this gene can have significant consequences for modulating the response to asthma therapy. This cross-sectional study performed at the University Children's Hospital in Belgrade, included 54 children with asthma. The subjects were genotyped for ADRB2 +46A gt G (Arg16Gly, rs1042713) and +79C gt G (G1n27G1u, rs1042714) polymorphisms and the association with asthma severity and response to inhaled salbutamol was examined. In Serbian asthmatic children, allele +46A was detected with a frequency of 41.7% and allele +79G was detected with a frequency of 23.1%. Allele +460 was found to be associated with a better response to inhaled salbutamol (p lt 0.05) and with mild form of asthma (p lt 0.05). Polymorphism ADRB2 +46A gt G may be a determinant of asthma severity and response to salbutamol in children with asthma. We did not find any association of +79C gt G polymorphisms with the asthma severity and bronchodilator response to inhaled salbutamol. The results of this study can be potentially useful for personalization of asthma treatment

The case of hip dysplasia of an adult from the Roman Period site of Velebit (Serbia)

Objective: This study is designed to reveal the diagnosis of a rare hip condition with an estimation of the possible cause of death. Materials: Archaeological site of Velebit dated between the 3rd and 4th century AD is located in northern Serbia. Grave No 24 differs from others in the unusual position of the skeletal remains in situ. Methods: The bioanthropological analyses included an estimation of skeletal preservation, cranial and postcranial skeletal measurements, estimation of sex and age at the moment of death, dental analysis and a paleopathological examination. This skeleton was analysed for signs of bone disease, using diagnostic paleopathological procedures comprising gross examination and CT scanning. Results: The results revealed that the analysed male individual was 40 to 55 years of age. The bioanthropological analyses showed two deformities of the pelvic bones, each on the outer surface, located posteriorly and superiorly of the acetabular area. The observed lesions were characterised as type 4 of developmental dysplasia of the hip. In addition, a sharp lesion was observed in the right posterior region of squama of the occipital bone. Conclusions: Our results clearly suggest that this individual had been suffering from hip dysplasia. The possible cause of death could be the observed head lesion. In addition, there is no skeletal conformation of unfavourable living conditions related to physiological stress and diet

Optimal Input Excitation Design for Nonparametric Uncertainty Quantification of Multi-Input Multi-Output Systems

In this paper, the impact of various input excitation scenarios on two different MIMO linear non-parametric modeling schemes is investigated in the frequency-domain. It is intended to provide insight into the optimal experiment design that not only provides the best linear approximation (BLA) of the frequency response functions (FRFs), but also delivers the means for assessing the variance of the estimations. Finding the mathematical representations of the variances in terms of the estimation coherence and noise/nonlinearity contributions are of critical importance for the frequency-domain system identification where the objective function needs to be weighted in the parametrization step. The input excitation signal design is tackled in two cases, i.e., multiple single-reference experiments based on the zero-mean Gaussian and the colored noise signal, the random-phase multisine, the Schroeder multisine, and minimized crest factor multisine; and multi-reference experiments based on the Hadamard matrix, and the so-called orthogonal multisine approach, which additionally examines the coupling between the input channels. The time-domain data from both cases are taken into the classical H1 spectral analysis as well as the robust local polynomial method (LPM) to extract the BLAs. The results are applied for data-driven modeling of a flexible beam as a model of a flexible robotic arm

Energy based three-dimensional damage index for monitoring and damage detection of concrete structures

U radu je prikazan novi pristup koji omogućuje aktivno praćenje stanja konstrukcija i otkrivanje oštećenja na masivnim armiranobetonskim konstrukcijama, a utemeljen je na primjeni piezoelektričnih pametnih agregata. U matričnom je obliku izveden inovativni trodimenzionalni indeks oštećenja baziran na valićnoj dekompoziciji signala i energiji prostiranja valova. Iako se predloženi trodimenzionalni indeks oštećenja može koristiti za sve vrste armiranobetonskih konstrukcija, prije svega se ipak preporučuje za masivne infrastrukturne građevine. Pristup predložen u ovom radu teoretski je izveden za proizvoljni oblik armiranobetonskog elementa, te je numerički provjeren u raznim scenarijima variranjem geometrije armiranobetonskih elemenata, isto kao i položaja, veličine i rasprostranjenosti oštećenja. Kvazistatička analiza piezoelektričnih pametnih agregata modelirana je pomoću standardne metode konačnih elemenata, a u ovom je istraživanju uspješno primijenjena eksplicitna metoda konačnih elemenata za modeliranje prostiranja ultrazvučnih valova. Rezultati bazirani na numerički generiranim simulacijama upućuju na perspektivnost novog pristupa za nerazorno otkrivanje oštećenja pomoću trodimenzionalnih indeksa oštećenja.A novel approach to active structural health monitoring and damage detection of massive reinforced concrete structures using piezoelectric smart aggregates is presented in this paper. An innovative three-dimensional damage index, based on wavelet signal decomposition and energy of wave propagation, is derived in matrix form. Although the proposed three-dimensional damage index can be used for all types of reinforced concrete structures, it is primarily recommended for massive infrastructure buildings. The approach proposed in this paper is theoretically considered for an arbitrary shape of a reinforced concrete element, and it is numerically verified for various scenarios by varying the geometry of reinforced concrete elements, as well as the position, size and quantity of damage. Quasi-static analysis of piezoelectric smart aggregates is modelled using a standard finite element method, and the explicit finite element method is successfully applied in this research for modelling propagation of ultrasonic waves. The results based on numerically generated simulations indicate that the new approach to non-destructive damage detection using three-dimensional damage indexes is quite promising

Model - based active noise control of a piezoelectric structure Aktywny układ redukcji hałasu na bazie modelu struktury piezoelektrycznej /

Tyt. z nagłówka.Bibliografia s.76.Dostępny również w formie drukowanej.ABSTRACT: Methods of active noise and vibration control involve different techniques which combine electroacoustics with integration of active materials and controller into a complex active structural system in order to enable radiation of an anti-phased field for cancellation or attenuation of an original noise in a specific domain. This paper presents a model-based controller design procedure for the active noise attenuation of a piezoelectric structure surrounded by the acoustic fluid. Model development is based on a finite element method approach, which takes into consideration the electro-mechanical-acoustic effects. A FEM-based state-space model obtained after appropriate transformations and modal reduction is used for the controller design. The aim of the control, suppression of the acoustic fluid pressure in a prescribed point or field, is achieved using an optimal LQ controller designed based on a developed state-space model. The controller design involves also a novel approach, with included additional dynamics for the noise control in the presence of periodic excitations. The effects of the suggested method are tested on a smart acoustic box consisting of an aluminium plate with attached piezoelectric patches, surrounded by the acoustic fluid (air) inside the wooden box. The air pressure reduction at a selected point inside the box is observed in the controlled case. STRESZCZENIA:Aktywne metody redukcji drgań i hałasu wymagają zróżnicowanych technik, które łączą elementy elektroakustyczne zintegrowane z elementami czynnymi oraz sterownikami wewnątrz złożonej aktywnej struktury, żeby umożliwić promieniowanie pola w przeciwfazie w celu eliminacji lub redukcji pierwotnego hałasu w wybranej strefie. Artykuł prezentuje projekt regulatora na bazie modelu do aktywnej redukcji hałasu struktury piezoelektrycznej w otoczeniu płynu akustycznego. Opracowany model bazuje na metodzie elementów skończonych, która uwzględnia zjawiska elektro-mechaniczno-akustyczne. Model w przestrzeni stanu powstały na podstawie MES, otrzymany w wyniku stosownych przekształceń i uproszczeń modelu, użyto do syntezy regulatora. Celem sterowania było wytłumienie ciśnienia płynu akustycznego w danym punkcie lub polu, co osiągnięto, wykorzystując regulator optymalny LQ zaprojektowany na podstawie opracowanego modelu w przestrzeni stanu. Projektowanie regulatora wymaga nowatorskiego podejścia uwzględniającego dodatkową dynamikę podczas redukcji hałasu w obecności wymuszeń harmonicznych. Efekty zaprezentowanej metody zostały przetestowane na inteligentnej skrzynce akustycznej zbudowanej z aluminiowej płyty z naklejonymi na niej płytkami piezoelektrycznymi, otoczonej przez płyn akustyczny (powietrze), umieszczonej w drewnianym pudle. Zaobserwowano redukcję ciśnienia powietrza w wybranym punkcie wewnątrz skrzynki dla układu z regulatorem KEYWORDS: active noise control, piezoelectric structure, optimal lq controller, acoustic box. SŁOWA KLUCZOWE: aktywna redukcja hałasu, struktura piezoelektryczna, optymalne sterowanie lq, skrzynka akustyczna