Combination of Boundary Element Method and Genetic Algorithm for Optimization of T-shape Noise Barrier

This paper presents the acoustic and visual optimization of the T-shape noise barrier cap by using the Boundary Element Method (BEM) fused with the Genetic Algorithm (GA). This paper investigates whether the established methodology in reducing the traffic noise pollution can be applied to the geometry of the T-shape noise barrier cap. By performing the optimization with Genetic Algorithm, it is shown that it is possible to create a noise barrier that provides satisfactory acoustic efficiency at all audio frequencies, from 125 Hz to 1 kHz. The obtained noise barriers are shown to be more efficient compared to conventional wooden T-shape noise barriers. Furthermore, by considering the parameter termed "Visual Pleasantness" it is shown that the opaque barriers are perceived as visually unpleasant when compared to the transparent ones. Based on these findings an optimized design of plain transparent noise barrier which does not diminish the aesthetic performance is proposed

Possibilities of Reliable Ultrasonic Detection of Subwavelength Pipework Cracks

An occurrence of cracks in pipework could lead to potentially very dangerous malfunction in some critical engineering systems such as power plants. There is a clear trend of replacing traditional manual testing with non-invasive in-situ methods that should detect crack formation in its early stage. Such as approach would enable replacing of unhealthy pipe components during the regular periodic outages. Ultrasonic testing is known to be a rather mature and reliable technology. However, it suffers from serious problems in detection of the cracks of subwavelength size. This paper attempts to soften aforementioned problems by investigating the influence of a duration of the unipolar excitation signal on the achieved resolution. In addition, the transducer input electricalimpedance of NDT transmitter was measured by using different excitation pulses and their levels and the results are compared with those obtained using traditional frequency sweeping method at low excitation levels. Finally, use of some advanced signal processing algorithms that might lead to the automatic detection of subwavelength voids, in scenarios with low signal-to-noise ratio, is discusse

Laboratorij za određivanja svojstava kompleksnih materijala akustičkim metodama - LOSKSAM

U radu će se opisati rad Istraživačkog laboratorija za određivanja svojstava kompleksnih materijala akustičkim metodama-LOSKSAM osnovanog u sklopu Zavoda za elektroakustiku, Fakulteta elektrotehnike i računarstva, Sveučilišta u Zagrebu. U LOSKSAM-u se provodi karakterizacija elektroakustičkih i ultrazvučnih pretvarača i, kao i pripadajućih elektroničkih i akustičkih komponenata. Razvijaju se sonde za bio-medicinsko djelovanje (terapija, kirurgija) kao i za nedestruktivno ispitivanje materijala. Obavljaju se mjerenja isijane ultrazvučne snage u realnom okruženju, detekcija pojave kavitacije kod ultrazvučnih mjerenja, njeno korištenje u kirurške svrhe te kalibracija svih vrsta elektroakustičkih pretvarača i mjerenja na akustičkim elementima i sustavima

Laboratorij za određivanja svojstava kompleksnih materijala akustičkim metodama - LOSKSAM

U radu će se opisati rad Istraživačkog laboratorija za određivanja svojstava kompleksnih materijala akustičkim metodama-LOSKSAM osnovanog u sklopu Zavoda za elektroakustiku, Fakulteta elektrotehnike i računarstva, Sveučilišta u Zagrebu. U LOSKSAM-u se provodi karakterizacija elektroakustičkih i ultrazvučnih pretvarača i, kao i pripadajućih elektroničkih i akustičkih komponenata. Razvijaju se sonde za bio-medicinsko djelovanje (terapija, kirurgija) kao i za nedestruktivno ispitivanje materijala. Obavljaju se mjerenja isijane ultrazvučne snage u realnom okruženju, detekcija pojave kavitacije kod ultrazvučnih mjerenja, njeno korištenje u kirurške svrhe te kalibracija svih vrsta elektroakustičkih pretvarača i mjerenja na akustičkim elementima i sustavima

The influence of body position on cerebrospinal fluid pressure gradient and movement in cats with normal and impaired craniospinal communication

Intracranial hypertension is a severe therapeutic problem, as there is insufficient knowledge about the physiology of cerebrospinal fluid (CSF) pressure. In this paper a new CSF pressure regulation hypothesis is proposed. According to this hypothesis, the CSF pressure depends on the laws of fluid mechanics and on the anatomical characteristics inside the cranial and spinal space, and not, as is today generally believed, on CSF secretion, circulation and absorption. The volume and pressure changes in the newly developed CSF model, which by its anatomical dimensions and basic biophysical features imitates the craniospinal system in cats, are compared to those obtained on cats with and without the blockade of craniospinal communication in different body positions. During verticalization, a long-lasting occurrence of negative CSF pressure inside the cranium in animals with normal cranio-spinal communication was observed. CSF pressure gradients change depending on the body position, but those gradients do not enable unidirectional CSF circulation from the hypothetical site of secretion to the site of absorption in any of them. Thus, our results indicate the existence of new physiological/pathophysiological correlations between intracranial fluids, which opens up the possibility of new therapeutic approaches to intracranial hypertension

Promjene radnih parametara ultrazvučnog pretvarača izlaznog kuta ultrazvučnog snopa 0° za nerazorna ispitivanja uslijed različitih električnih pobuda

The electrical excitation dependence of working parameters of a normal beam non-destructive evaluation ultrasound transducer has been investigated. Noteworthy differences between the transducer input electrical impedance and acoustic properties at low excitation voltages (~1V), most often used in electromechanical characterizations by performing frequency sweeps, and at high excitation voltages (~250V), generally used to drive ultrasound transducers in non-destructive evaluation applications, were emphasized. For the purpose of this work, a circular normal beam ultrasound transducer of centre frequency 2 MHz was constructed by using a PZT piezoelectric disk, epoxy- based acoustically passive front matching and backing layers, an electrical impedance matching element, housing and coaxial cable. The transducer was characterized around the thickness extensional vibration mode both by using low and high voltage electrical excitation signals. The characterization of the electromechanical properties was conducted at several different stages of the transducer construction and for several excitation signal waveforms and levels.Svojstva i ponašanje radnih parametara ultrazvučnog pretvarača (izlaznog kuta ultrazvučnog snopa 0°) za kontrolu bez razaranja ispitani su u ovisnosti o vrsti električne pobude. Pokazane su zamjetne razlike između ulazne električne impedancije i akustičnih svojstava pretvarača pri malim električnim pobudnim amplitudama (~1V), koje se u pravilu koriste u elektromehaničkim karakterizacijama mjerenjem frekventne ovisnosti impedancije pretvarača, te pri visokim pobudnim nivoima (~250V), u pravilu korištenih za radnu pobudu ultrazvučnih pretvarača pri obavljanju kontrole bez razaranja. Za ovaj rad konstruiran je osnosimetrični ultrazvučni pretvarač izlaznog kuta ultrazvučnog snopa od 0°, središnje frekvencije 2MHz; u izradi su korišteni akustički aktivan piezoelektrični PZT (olovo-cirkonij-titanat) keramički disk, akustički pasivni prednji i prigušni slojevi na bazi epoksidnih smola, elektronički element za prilagodbu električne impedancije, kućište od nehrđajućeg čelika i koaksijalni kabel. Svojstva pretvarača karakterizirana su oko longitudinalnog ekstenzijskog titrajnog moda korištenjem električnih pobudnih signala i malih i velikih amplituda. Ispitivanje elektromehaničkih svojstava pretvarača napravljeno je pri nekoliko različitih stadija njegove konstrukcije i za nekoliko valnih oblika pobudnih električnih valnih oblika

Noise reduction - noise barriers

U ovom preglednom radu razmotrit će se problem buke u smislu zagađivanja okoliša te će se izložiti moguća rješenja. Zvuk je oblik energije koja se prenosi zvučnim valovima, s time da postoje poželjni i nepoželjni zvukovi. Svaki nepoželjni zvuk naziva se bukom, dok je percepcija buke subjektivna i individualna. Drugim riječima, jedna osoba može određeni zvuk okarakterizirati kao ugodan, dok druga kao nepoželjan i neugodan. Stoga, u ovom radu je detaljno objašnjen sam pojam buke, indikatori buke kao fizikalne veličine, te način na koji buka negativno djeluje na čovjeka. Čak i danas, zagađenje bukom ima naizgled malo značenje jer naoko nema izravni utjecaj na zdravlje ljudi. Međutim, kao i kod svih zagađenja, izloženost buci ima akumulirajući karakter, dakle uočava se tek nakon duljeg vremena i može se manifestirati kao loše raspoloženje, umor, nesanica, glavobolja i gubitak koncentracije, te time izravno utječe na kvalitetu života. Fokus samog rada je postavljen na buku prometa, te moguća rješenja za smanjenje takve buke. Glavnina zvučne energije buke prometa, nalazi se u području srednjih frekvencija, što također odgovara i području najveće osjetljivosti ljudskog uha. Kod projektiranja novih prometnica, smanjenje utjecaja buke na ljude i okoliš moguće je postići odabirom trase izvan naseljenih mjesta i uklapanjem u postojeći reljef. S obzirom na već postojeće prometnice u blizini naseljenih mjesta, predlažu se zaštitne barijere, odnosno bukobrani. Stoga je u radu detaljno objašnjen pojam bukobrana te je dan pregled vrsta bukobrana. Također su razmotrene prednosti i nedostaci svake vrste bukobrana.This paper deals with the issue of noise as an environmental pollutant, and furthermore it suggests possible solutions for this issue. Sound is a form of energy transmitted by sound waves. In general, sounds may be perceived as desirable or undesirable. Sounds which are considered undesirable and unwanted can be observed as noise, however the perception of sound in general is significantly subjective and individual. In particular, one person can perceive a certain sound as pleasant, whereas another could characterize it as annoying, unpleasant, and generally undesirable. This paper explains the term “noise” in detail, noise indicators as numerical values, and the ways noise can have a negative impact on people. Even today, noise pollution is often neglected compared to other environmental pollutions (i.e. water pollution, soil pollution, air pollution etc.). However, exposure to noise has an accumulative character. The consequences are noticeable after a prolonged exposure and can manifest themselves as bad mood, fatigue, insomnia, headache and loss of concentration, thereby having a direct influence on the quality of life. The focus of this paper is traffic noise and acoustical solutions which can reduce it. The dominant part of sound energy produced by traffic is in the middle-frequency range, which coincides with the range of maximum sensitivity of human hearing. When planning a new traffic route the negative influence of noise on people and the environment can be reduced by choosing the route which is remote from populated areas. In cases when the roads are fitted into the existing terrain and near populated areas, they can be equipped with protective noise barriers. The paper gives a detailed explanation on what noise barriers are, and an overview of different types of noise barriers that are currently in use. In addition, the advantages and disadvantages of different types of noise barriers are discussed

A case study of different sound environments - a way to a more pleasant and more efficient work environment

Koncept zvučnih okolina uveden je kako bi se izmijenila i nadopunila procjena buke i njezinih utjecaja na čovjeka. Istraživanje zvučnih okolina predlaže pomalo drugačiji pristup istraživanju buke uzimajući u obzir njezinu složenost i multidisciplinarnost. Stoga istraživanje zvučnih okolina nije istraživanje same buke, već uvjeta i razloga njezinog nastanka, razine opažanja i procjene, prvenstveno od strane čovjeka odnosno ljudi. Jedna zvučna okolina obuhvaća određeni okoliš odnosno sredinu, a samim time i veliki broj zvučnih izvora čije karakteristike utječu na uobičajene čovjekove aktivnosti, njegovu koncentraciju i raspoloženje. S obzirom da ljudi danas većinu vremena provedu na poslu, poželjno je da su im radne okoline ugodne i s akustičkog aspekta kako bi zaposlenici bili što zadovoljniji i uspješniji u izvršavanju radnih zadataka. Ovaj rad u tom smislu diskutira utjecaj četiriju radnih zvučnih okolina na čovjeka. One su redom: dječji vrtić, dionica autoputa, industrijska hala i trgovački centar. Ove četiri okoline su odabrane jer su generalno percipirane kao stresne za svoje zaposlenike.The concept of soundscape was introduced to modify and complement noise assessment and the effect of different sound environments on people. Soundscape research poses a somewhat different problem than the study of noise as such, for it is a more complex phenomenon that requires a multidisciplinary approach. Therefore, sound environments study is not a study of noise but of the conditions and causes, the level of perception and the effects on people. Any sound environment will be subjected to a substantial number of sound sources that affect ordinary human activities, people\u27s concentration and mood. Most people today spend a great deal of time at work, so it would be desirable that their work environment is acoustically pleasant in order to ensure effective work and satisfaction of the workers. The paper discusses four sound environments: kindergarten, expressway, industrial plant, and shopping centre. These four have been selected for they are generally perceived as stressful for the employees

Combined acoustical and economical noise barrier optimization using genetic algorithms

U ovom radu proučavana je optimizacija zvučnih barijera pomoću numeričke metode rubnih elemenata i genetičkog algoritma. Zvučne barijere su optimizirane po akustičkim, tehnološkim i ekonomskim značajkama u svrhu dobivanja optimalne zvučne barijere. Kako bi se optimizirale akustičke i ekonomske karakteristike zvučne barijere korišten je genetički algoritam koji od danih oblika slaže zvučnu barijeru. U radu je definiran i novi parametar, nazvan parametar troška zvučne barijere (Ke). Primjenom genetičkog algoritma i parametra troška zvučne barijere (Ke) lako je stvoriti, razviti i konstruirati odgovarajuću zvučnu barijeru.This paper studies noise barrier optimization using the Boundary Element Method (BEM) as a numerical technique and Genetic Algorithms (GA). Noise barriers are optimised according to acoustical, technological and economical properties so as to obtain an optimum noise barrier. In order to optimise acoustical and economical properties of noise barriers, the use is made of a genetic algorithm that forms a noise barrier out of given shapes. A new noise barrier evaluation parameter, named the noise barrier cost parameter (Ke), is also defined in the paper. Using the genetic algorithm and the noise barrier cost parameter (Ke), it is easy to create, develop and construct an appropriate noise barrier

Accoustic solutions for detection of drones with the goal of increasing general safety

U današnje doba male bespilotne letjelice postaju sve popularnije. Postoje njihove razne inačice, ali po svojoj popularnosti prednjače kvadrokopteri odnosno dronovi. Primjenu nalaze većinom u komercijalnim svrhama ili kao nečiji hobi, međutim mogu biti korišteni i u ilegalne svrhe poput krijumčarenja ili prijenosa eksploziva. Veliki problem predstavljaju i ako se koriste na točno određenim lokacijama poput zračnih luka. Dronove je iznimno teško detektirati zbog njihovih relativno malenih dimenzija, prednjeg dijela napravljenog od plastike te električnih motora koji emitiraju vrlo male količine toplinske energije. U tom smislu konvencionalni radari ili infracrvene kamere jednostavno nisu dovoljne u detekciji dronova. Cilj istraživanja opisanog u ovom članku je ustanoviti koje su mogućnosti akustičkog rješenja za detekciju dronova, odnosno utvrditi zvučne razine malih UAV letjelica i na temelju te zvučne razine odrediti koja je teoretska granica udaljenosti na kojoj je moguće akustički detektirati dron. Također je istraženo koliko ta udaljenost raste ako se kao akustički detektor koristi akustička kamera. Očekuje se da će ishodi ovog istraživanja poboljšati opću sigurnost jer optimiziraju nekoliko vrsta pristupa u svrhu bolje detekcije dronova.In this day and age, small unmanned aerial vehicles are becoming more and more popular. Different types of these craft have been built over the years, with drones (quadrocopters) being the most popular. They are used mostly for commercial purposes and as a support in different hobbies, but they can also be used for illegal activities such as smuggling or transport of explosives. The use of drones in the vicinity of airports is a major problem. Drones are exceptionally difficult to detect due to their small size, their front end made of plastic, and their electric-powered engines that generate very little heat. For these reasons, conventional radars and infrared cameras are not sufficient for detection of drones. The purpose of this research is to determine the possibilities of acoustic detection of drones. The sound pressure levels of noise emitted by drones have been measured. Based on this data, the theoretical limit distance at which a drone can still be detected acoustically has been determined. A possible increase of this limit distance has been examined, if an acoustic camera is used as the acoustic detector. The outcomes of this research are expected to improve general safety due to the optimization of several different approaches to drone detection