DSpace :: Browsing by Author "Petrů, Michal"

Browsing by Author "Petrů, Michal"

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A Comparative Study of the Data-Driven Stochastic Subspace Methods for Health Monitoring of Structures: A Bridge Case Study
(MDPI, 2020-03-29) Shokravi, Hoofar; Shokravi, Hooman; Bakhary, Norhisham; Koloor, Seyed Saeid Rahimian; Petrů, Michal
Subspace system identification is a class of methods to estimate state-space model based on low rank characteristic of a system. State-space-based subspace system identification is the dominant subspace method for system identification in health monitoring of the civil structures. The weight matrices of canonical variate analysis (CVA), principle component (PC), and unweighted principle component (UPC), are used in stochastic subspace identification (SSI) to reduce the complexity and optimize the prediction in identification process. However, researches on evaluation and comparison of weight matrices’ performance are very limited. This study provides a detailed analysis on the effect of different weight matrices on robustness, accuracy, and computation efficiency. Two case studies including a lumped mass system and the response dataset of the Alamosa Canyon Bridge are used in this study. The results demonstrated that UPC algorithm had better performance compared to two other algorithms. It can be concluded that though dimensionality reduction in PC and CVA lingered the computation time, it has yielded an improved modal identification in PC.
A Review on Vehicle Classification and Potential Use of Smart Vehicle-Assisted Techniques
(MDPI, 2020-06-08) Shokravi, Hoofar; Shokravi, Hooman; Bakhary, Norhisham; Heidarrezaei, Mahshid; Koloor, Seyed Saeid Rahimian; Petrů, Michal
Vehicle classification (VC) is an underlying approach in an intelligent transportation system and is widely used in various applications like the monitoring of traffic flow, automated parking systems, and security enforcement. The existing VC methods generally have a local nature and can classify the vehicles if the target vehicle passes through fixed sensors, passes through the short-range coverage monitoring area, or a hybrid of these methods. Using global positioning system (GPS) can provide reliable global information regarding kinematic characteristics; however, the methods lack information about the physical parameter of vehicles. Furthermore, in the available studies, smartphone or portable GPS apparatuses are used as the source of the extraction vehicle’s kinematic characteristics, which are not dependable for the tracking and classification of vehicles in real time. To deal with the limitation of the available VC methods, potential global methods to identify physical and kinematic characteristics in real time states are investigated. Vehicular Ad Hoc Networks (VANETs) are networks of intelligent interconnected vehicles that can provide traffic parameters such as type, velocity, direction, and position of each vehicle in a real time manner. In this study, VANETs are introduced for VC and their capabilities, which can be used for the above purpose, are presented from the available literature. To the best of the authors’ knowledge, this is the first study that introduces VANETs for VC purposes. Finally, a comparison is conducted that shows that VANETs outperform the conventional techniques.
Acoustic, Mechanical and Thermal Properties of Green Composites Reinforced with Natural Fibers Waste
(MDPI, 2020-03) Hassan, Tufail; Jamshaid, Hafsa; Mishra, Rajesh; Khan, Muhammad Qamar; Petrů, Michal; Novák, Jan; Chotěborský, Rostislav; Hromasová, Monika
The use of acoustic panels is one of the most important methods for sound insulation in buildings. Moreover, it has become increasingly important to use green/natural origin materials in this area to reduce environmental impact. This study focuses on the investigation of acoustic, mechanical and thermal properties of natural fiber waste reinforced green epoxy composites. Three different types of fiber wastes were used, e.g., cotton, coconut and sugarcane with epoxy as the resin. Different fiber volume fractions, i.e., 10%, 15% and 20% for each fiber were used with a composite thickness of 3 mm. The sound absorption coefficient, impact strength, flexural strength, thermal conductivity, diffusivity, coefficient of thermal expansion and thermogravimetric properties of all samples were investigated. It has been found that by increasing the fiber content, the sound absorption coefficient also increases. The coconut fiber-based composites show a higher sound absorption coefficient than in the other fiber-reinforced composites. The impact and flexural strength of the cotton fiber-reinforced composite samples are higher than in other samples. The coefficient of thermal expansion of the cotton fiber-based composite is also higher than the other composites. Thermogravimetric analysis revealed that all the natural fiber-reinforced composites can sustain till 300 degrees C with a minor weight loss. The natural fiber-based composites can be used in building interiors, automotive body parts and household furniture. Such composite development is an ecofriendly approach to the acoustic world.
An analytical conductance model for gas detection based on a zigzag carbon nanotube sensor
(MDPI, 2020) Hosseingholipourasl, Ali; Ariffin, Sharifah Hafizah Syed; Ahmadi, Mohammad Taghi; Koloor, Seyed Saeid Rahimian; Petrů, Michal; Hamzah, Afiq
Recent advances in nanotechnology have revealed the superiority of nanocarbon species such as carbon nanotubes over other conventional materials for gas sensing applications. In this work, analytical modeling of the semiconducting zigzag carbon nanotube field-effect transistor (ZCNT-FET) based sensor for the detection of gas molecules is demonstrated. We propose new analytical models to strongly simulate and investigate the physical and electrical behavior of the ZCNT sensor in the presence of various gas molecules (CO2, H2O, and CH4). Therefore, we start with the modeling of the energy band structure by acquiring the new energy dispersion relation for the ZCNT and introducing the gas adsorption effects to the band structure model. Then, the electrical conductance of the ZCNT is modeled and formulated while the gas adsorption effect is considered in the conductance model. The band structure analysis indicates that, the semiconducting ZCNT experiences band gap variation after the adsorption of the gases. Furthermore, the bandgap variation influences the conductance of the ZCNT and the results exhibit increments of the ZCNT conductance in the presence of target gases while the minimum conductance shifted upward around the neutrality point. Besides, the I-V characteristics of the sensor are extracted from the conductance model and its variations after adsorption of different gas molecules are monitored and investigated. To verify the accuracy of the proposed models, the conductance model is compared with previous experimental and modeling data and a good consensus is observed. It can be concluded that the proposed analytical models can successfully be applied to predict sensor behavior against different gas molecules.
An Energy-Based Concept for Yielding of Multidirectional FRP Composite Structures Using a Mesoscale Lamina Damage Model
(MDPI, 2020) Rahimian Koloor, Seyed Saeid; Karimzadeh, Atefeh; Yidris, Noorfaizal; Petrů, Michal; Ayatollahi, Majid Reza; Nasir Tamin, Mohd
Composite structures are made of multidirectional (MD) fiber-reinforced polymer (FRP) composite laminates, which fail due to multiple damages in matrix, interface, and fiber constituents at different scales. The yield point of a unidirectional FRP composite is assumed as the lamina strength limit representing the damage initiation phenomena, while yielding of MD composites in structural applications are not quantified due to the complexity of the sequence of damage evolutions in different laminas dependent on their angle and specification. This paper proposes a new method to identify the yield point of MD composite structures based on the evolution of the damage dissipation energy (DDE). Such a characteristic evolution curve is computed using a validated finite element model with a mesoscale damage-based constitutive model that accounts for different matrix and fiber failure modes in angle lamina. The yield point of composite structures is identified to correspond to a 5% increase in the initial slope of the DDE evolution curve. The yield points of three antisymmetric MD FRP composite structures under flexural loading conditions are established based on Hashin unidirectional (UD) criteria and the energy-based criterion. It is shown that the new energy concept provides a significantly larger safe limit of yield for MD composite structures compared to UD criteria, in which the accumulation of energy dissipated due to all damage modes is less than 5% of the fracture energy required for the structural rupture.
An experimental evaluation of convective heat transfer in multi-layered fibrous materials composed by different middle layer structures
(SAGE PUBLICATIONS INC, 2455 TELLER RD, THOUSAND OAKS, CA 91320 USA, 2019-10) Xiong, Xiaoman; Venkataraman, Mohanapriya; Jašíková, Darina; Yang, Tao; Mishra, Rajesh; Militký, Jiří; Petrů, Michal
In this work, three types of multi-layered fibrous materials with different middle layer structures, including Struto nonwoven, Struto nonwoven with air pockets and Struto nonwoven with air pockets filled by aerogel particles, were prepared based on laser engraving technique and laminating method. A custom-built new device was fabricated to evaluate convective thermal behaviour of the multi-layered materials in cross flow. It was found that in cross flow the heat transfer coefficient of the multi-layered material with encapsulated aerogels is directly proportional to Reynolds number. There are considerable variances in heat transfer rates of the three structures at low airflow velocity (less than 10 m/s), but the values are very close at high airflow velocity. It is concluded that the air pockets and aerogels present in the multi-layered fibrous material have significant effect on convective thermal behaviour of the overall structure in cross flow. The finding is a new contribution to the field of aerogel-based fibrous materials as thermal insulators in building and industrial facilities.
Analytical Approach to Study Sensing Properties of Graphene Based Gas Sensor
(MDPI, 2020-03) Hosseingholipourasl, Ali; Ariffin, Sharifah Hafizah Syed; Al-Otaibi, Yasser D.; Akbari, Elnaz; Hamid, Fatimah K. H.; Rahimian Koloor, Seyed Saeid; Petrů, Michal
Over the past years, carbon-based materials and especially graphene, have always been known as one of the most famous and popular materials for sensing applications. Graphene poses outstanding electrical and physical properties that make it favorable to be used as a transducer in the gas sensors structure. Graphene experiences remarkable changes in its physical and electrical properties when exposed to various gas molecules. Therefore, in this study, a set of new analytical models are developed to investigate energy band structure, the density of states (DOS), the velocity of charged carriers and I-V characteristics of the graphene after molecular (CO, NO2, H2O) adsorption. The results show that gas adsorption modulates the energy band structure of the graphene that leads to the variation of the energy bandgap, thus the DOS changes. Consequently, graphene converts to semiconducting material, which affects the graphene conductivity and together with the DOS variation, modulate velocity and I-V characteristics of the graphene. These parameters are important factors that can be implemented as sensing parameters and can be used to analyze and develop new sensors based on graphene material.
Analytical Prediction of Highly Sensitive CNT-FET-Based Sensor Performance for Detection of Gas Molecules
(Institute of Electrical and Electronics Engineers Inc., 2020-03-27) Hosseingholipourasl, Ali; Syed Ariffin, Sharifah Hafizah; Rahimian Koloor, Seyed Saeid; Petrů, Michal; Hamzah, Afiq
In this study, a set of new analytical models to predict and investigate the impacts of gas adsorption on the electronic band structure and electrical transport properties of the single-wall carbon nanotube field-effect transistor (SWCNT-FET) based gas sensor are proposed. The sensing mechanism is based on introducing new hopping energy and on-site energy parameters for gas-carbon interactions representing the charge transfer between gas molecules (CO2, NH3, and H2O) and the hopping energies between carbon atoms of the CNT and gas molecule. The modeling starts from the atomic level to the device level using the tight-binding technique to formulate molecular adsorption effects on the energy band structure, density of states, carrier velocity, and I-V characteristics. Therefore, the variation of the energy bandgap, density of states and current-voltage properties of the CNT sensor in the presence of the gas molecules is discovered and discussed. The simulated results show that the proposed analytical models can be used with an electrical CNT gas sensor to predict the behavior of sensing mechanisms in gas sensors.
Application of the Subspace-Based Methods in Health Monitoring of Civil Structures: A Systematic Review and Meta-Analysis
(MDPI, 2020-05) Shokravi, Hoofar; Shokravi, , Hooman; Bakhary, Norhisham; Heidarrezaei, Mahshid; Koloor, Seyed Saeid Rahimian; Petrů, Michal
A large number of research studies in structural health monitoring (SHM) have presented, extended, and used subspace system identification. However, there is a lack of research on systematic literature reviews and surveys of studies in this field. Therefore, the current study is undertaken to systematically review the literature published on the development and application of subspace system identification methods. In this regard, major databases in SHM, including Scopus, Google Scholar, and Web of Science, have been selected and preferred reporting items for systematic reviews and meta-analyses (PRISMA) has been applied to ensure complete and transparent reporting of systematic reviews. Along this line, the presented review addresses the available studies that employed subspace-based techniques in the vibration-based damage detection (VDD) of civil structures. The selected papers in this review were categorized into authors, publication year, name of journal, applied techniques, research objectives, research gap, proposed solutions and models, and findings. This study can assist practitioners and academicians for better condition assessment of structures and to gain insight into the literature.
Automobilová sedačka s nepolyuretanovým materiálem
(Technická Univerzita v Liberci, 2012) Petrů, Michal; Fliegel, Vítězslav
Náhrada polyuretanové pěny za jiný alternativní recyklovaný materiál, snižování hmotnosti a snižování nežádoucích mechanických vibrací je klíčovým problémem nejen současného trendu vývoje automobilové sedačky, ale také všech sedaček pro dopravní kolové stroje. Disertační práce se zabývá studiem a analýzou mechanických vlastností vybraných materiálových struktur aplikovatelných pro konstrukci výplně komfortní vrstvy sedáku automobilové sedačky a také konstrukčním návrhem aktivní regulovatelné výztuhy sedáku automoblové sedačky.
Bio-Composites Reinforced with Natural Fibers: Comparative Analysis of Thermal, Static and Dynamic-Mechanical Properties
(KOREAN FIBER SOC, KOREA SCIENCE TECHNOLOGY CTR #501 635-4 YEOGSAM-DONG, KANGNAM-GU, SEOUL 135-703, SOUTH KOREA, 2020-03) Mishra, Rajesh; Wiener, Jakub; Militký, Jiří; Petrů, Michal; Tomková, Blanka; Novotná, Jana
In the present study, flax, jute and glass woven fabric samples were developed as reinforcement for composites with bio-epoxy resin. Flax fabrics were developed with plain weave, twill weave (different areal densities) and unidirectional (UD) structure. Jute fabrics were woven with three different structures i.e. plain, matt and twill respectively. For comparison purpose, glass woven fabric with plain weave and 3D orthogonal weave were used in this study. Static mechanical properties like flexural strength and impact resistance were studied. Dynamic mechanical properties were investigated by DMA 40XT RMI equipment.. Thermal conductivity has been studied for all composite samples. It is observed that the static mechanical properties of glass fabrics reinforced composites are superior but the flax & jute fabric reinforced composites are more flexible. The specific flexural strength as well as specific impact strength of the flax & jute fabric reinforced composites are competitive. The dynamic mechanical properties are comparable to that of glass fabric reinforced composites. They can be used in relatively lower load bearing applications as they are a sustainable source of materials for bio-composites which reduce the environmental burden and reduce the manufacturing cost.
Carbon Nanoparticle-Based Electro-Thermal Building Block
(MDPI, 2020) Taghi Ahmadi, Mohammad; Mousavi, Neda; Khang Nguyen, Truong; Koloor, Seyed Saeid Rahimian; Petrů, Michal
All around the world, researchers have raised concerns about the superlative geometrical, electronic, thermal, chemical and mechanical properties of carbon nanoparticles (CNPs). CNPs with low cost, high performance and prominent intrinsic properties have attracted extensive interest for numerous applications in various fields. Although CNPs have been studied mainly as transistors and sensors, they could also be considered as heat producers. However, this option has scarcely been studied. In this research, a CNP-based electro-thermal building block is synthesized by the arc discharge method in a carbonic medium (high-density polyethylene), and its behavior is investigated. It is shaped in the form of a metal–semiconductor–metal structure (MSM) between metallic electrodes, and in addition, the formation of two back-to-back Schottky diodes is analyzed and their use as CNP-based electro-thermal building blocks are reported.
Carbon-Based Band Gap Engineering in the h-BN Analytical Modeling
(MDPI, 2020-04-27) Ahmadi, Mohammad Taghi; Razmdideh, Ahmad; Koloor, Seyed Saeid Rahimian; Petrů, Michal
The absence of a band gap in graphene is a hindrance to its application in electronic devices. Alternately, the complete replacement of carbon atoms with B and N atoms in graphene structures led to the formation of hexagonal boron nitride (h-BN) and caused the opening of its gap. Now, an exciting possibility is a partial substitution of C atoms with B and N atoms in the graphene structure, which caused the formation of a boron nitride composite with specified stoichiometry. BC2N nanotubes are more stable than other triple compounds due to the existence of a maximum number of B-N and C-C bonds. This paper focused on the nearest neighbor's tight-binding method to explore the dispersion relation of BC2N, which has no chemical bond between its carbon atoms. More specifically, the band dispersion of this specific structure and the effects of energy hopping in boron-carbon and nitrogen-carbon atoms on the band gap are studied. Besides, the band structure is achieved from density functional theory (DFT) using the generalized gradient approximations (GGA) approximation method. This calculation shows that this specific structure is semimetal, and the band gap energy is 0.167 ev.
Compression resilience and impact resistance of fiber-reinforced sandwich composites
(2019) Mishra, Rajesh; Wiener, Jakub; Militký, Jiří; Petrů, Michal; Tomková, Blanka; Novotná, Jana
This paper presents an experimental investigation on the compression behavior of fiber-reinforced sandwich composites. In this study, five different types of sandwich composites were prepared with warp knitted spacer fabric as middle layer. Four different types of woven Kevlar fabric structures were used as outer layers (skin) along with one sample of woven basalt fabric. The middle layer used is 100% polyester spacer fabric. Sandwich composites were fabricated using epoxy resin by wet lay-up method under vacuum bagging technique. Compression behavior, ball burst, and knife penetration were tested for all samples. The effect of outer layer of these composites on the mechanical performance was studied using the compression stress-strain curves. It is known that spacers have excellent compression elasticity and cushioning. Maximum knife penetration resistance is obtained with twill weave on surface because of maximum yarn cohesion and resin impregnation. Higher amount of cohesive friction results in higher resistance against penetration of sharp objects like the knife edge. Plain and twill fabrics offer sufficient resistance again ball burst. The yarn deformation allows formation of dome shape after ball impact. Maximum impact resistance in ball burst is obtained for plain weave because of highest level of interyarn binding. The results provide new understanding of knitted spacer fabric-based sandwich composites under compression and impact loading condition.
Cooperation of Virtual Reality and Real Objects with HoloLens
(SPRINGER INTERNATIONAL PUBLISHING AG, 2020) Cýrus, Jindřich; Krčmařík, David; Petrů, Michal; Kočí, Jan
We propose several approaches when programming applications for Microsoft HoloLens. These applications aim at close cooperation of real world with holographic objects (virtual reality). Often a precise placement that does not change with the position of a user can be challenging. One way of avoiding such problems is to use technology of anchors. Another way proposed in this paper is a prior scanning of object of interest with an application aimed for Vuforia plugin. Both concepts use close cooperation with user-friendly environment for developing of mixed reality applications - Unity. We present and discuss examples in this article. The area of precise location for mixed reality (augmented reality mixed with real reality in a way that one can interact witch each other) is of paramount importance. If we know precise position of virtual objects in the scene and precise position of the device in the scene, we can alleviate the burden of massive computing within HoloLens. As a result, we gain better experience from mixed reality.
Correction: Effect of Hygrothermal Aging and Surface Treatment on the Dynamic Mechanical Behavior of Flax Fiber Reinforced Composites. Materials 2019, 12(15), 2376
(MDPI, 2019-10-17) Wang, Xiaomeng; Petrů, Michal
Coulomb Blockade Effect in Well-Arranged 2D Arrays of Palladium Nano-Islands for Hydrogen Detection at Room Temperature: A Modeling Study
(MDPI, 2020) Khaje, Mahdi; Sedghi, Hassan; Goudarzi, Hadi; Taghi Ahmadi, Mohammad; Koloor, Seyed Saeid Rahimian; Petrů, Michal
The fast growth of hydrogen usage as a clean fuel in civil applications such as transportation, space technology, etc. highlights the importance of the reliable detection of its leakage and accumulation under explosion limit by sensors with a low power consumption at times when there is no accumulation of hydrogen in the environment. In this research, a new and efficient mechanism is presented for hydrogen detection—using the Coulomb blockade effect in a well-arranged 2D array of palladium nano-islands—which can operate at room temperature. We demonstrated that under certain conditions of size distribution and the regularity of palladium nano-islands, with selected sizes of 1.7, 3 and 6.1 nm, the blockade threshold will appear in current-voltage (IV) characteristics. In reality, it will be achieved by the inherent uncertainty in the size of the islands in nano-scale fabrication or by controlling the size of nanoparticles from 1.7 to 6.1 nm, considering a regular arrangement of nanoparticles that satisfies single-electron tunneling requirements. Based on the simulation results, the threshold voltage is shifted towards lower ones due to the expansion of Pd nanoparticles exposed to the environment with hydrogen concentrations lower than 2.6%. Also, exploring the features of the presented structure as a gas sensor, provides robustness against the Gaussian variation in nano-islands sizes and temperature variations. Remarkably, the existence of the threshold voltage in the IV curve and adjusting the bias voltage below this threshold leads to a drastic reduction in power consumption. There is also an improvement in the minimum detectable hydrogen concentration as well as the sensor response.
Degradation of bending properties of flax fiber reinforced polymer after natural aging and accelerated aging
(Elsevier Ltd, 2020) Wang, Xiaomeng; Petrů, Michal
In this paper, the effect of natural aging and accelerated aging on the bending properties of flax fiber reinforced polymer (FFRP) is studied. Test results show that the flexural strength decreases by 11.2%, 14.9%, 15.5%, and the flexural modulus decreases by 21.3%, 32.3%, 35.8%, after 60 days, 120 days and 180 days of natural aging, respectively. Then accelerated test is carried out to predict the long-term performance of FFRP. The results show that short-term exposure test (just considering the temperature and humidity) cannot achieve the same effect on mechanical property degradation as natural aging. A modified residual mechanical property model of FFRP is established according to the test results.
DESIGN OF COMPOSITE FRAMES USED IN AGRICULTURAL MACHINERY
(CZECH UNIVERSITY LIFE SCIENCES PRAGUE, DEPT SYSTEMS ENG, KAMYCKA 129, PRAGUE 6 165 21, CZECH REPUBLIC, 2019) Mlýnek, Jaroslav; Petrů, Michal; Martinec, Tomáš
At present, composite materials are increasingly used in agricultural machinery. The light weight, long lifespan and minimal maintenance of composites are among the main reasons for their use in agricultural machinery. Frame composites are often produced for the needs of agriculture. The production technology of these composites is based on the winding of fibres (from carbon or glass) on a frame (usually from polyurethane). A fibre processinghead and industrial robot are used in the production of composite frame. This paper describes the calculation of an appropriate off-line trajectory of the industrial robot during the passage of frame through the fibre-processing head. The described mathematical model of the winding process and matrix calculus are used to calculate suitable robot trajectory.
Effect of Electrospun Nanofiber Deposition on Thermo-physiology of Functional Clothing
(2019-07-23) Akshat, T. M.; Misra, Srabani; Gudiyawar, M. Y.; Salačová, Jana; Petrů, Michal
The present work focuses on developing electrospun nanofibers using wire electrospinning and deposition of such nanofibrous layer on the clothing textiles. The porosity and permeability of the fabrics are substantially influenced by deposition of nanofibers on woven textiles. Cotton, Kevlar and Nomex fabrics have been selected as the substrate material. They are extensively used in the military sector for uniform of defence personnel. The emergence of nanofiber technology with the advent of needle-less electrospinning has enabled researchers to apply such materials to existing fabrics. Nylon 6 (PA6) nanofibers are spun by wire electrode spinning and deposited on selected clothing fabrics. The fabrics so developed are compared with control fabric samples for understanding the influence on thermal and physiological properties. The thermal comfort is influenced mainly by porosity and thickness of the fabric ensemble. Air permeability results are significantly influenced by nanofiber deposition. A further study on moisture management properties is also carried out. The thermal and physiological comfort is influenced mainly by porosity and thickness of the fabric ensemble. The nanofiber deposition on base fabric significantly influences water vapor and liquid water transmission related properties.

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