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  • ItemArtigo
    Experimental investigation of vibration control of flexible rotors using shape memory alloys
    (IOPscience, 2023-06-20) Preto, Eduardo [UNESP]; Abreu, Gustavo Luiz Chagas Manhães de [UNESP]; Gonçalves, Aparecido Carlos [UNESP]; Chavarette, Fábio Roberto [UNESP]; Savi, Marcelo Amorim; Universidade Federal do Rio de Janeiro, COPPE - Mechanical Engineering, Center for Nonlinear Mechanics
    Vibration is an essential subject for the design of rotordynamic systems, being responsible for compromising the integrity and causing risks to operational functioning. This work deals with an experimental investigation of the semi-active vibration controller for a rotordynamic system using shape memory alloy (SMA) elements. SMAs are smart materials that present thermomechanical coupling represented by solid phase transformations that promote either stiffness change or hysteretic dissipation. In this regard, they are useful in controllers employing thermal actuation from electric current through the Joule effect. This paper presents a proof of concept of a controller using SMA elements. An experimental apparatus is proposed considering a typical rotor system using SMA wires at the bearings. In this regard, proper temperature variations allow the system to cross critical resonant conditions.
  • ItemTrabalho de conclusão de curso
    Aprimoramento da transferência de aprendizado utilizando análise de similaridade entre estruturas de viga
    (Universidade Estadual Paulista (Unesp), 2023-11-17) Almeida, Estênio Fuzaro de; Silva, Samuel da [UNESP]
    Um dos grandes desafios na implementação de algoritmos de aprendizado de máquina para a detecção de danos é a reutilização dos classificadores previamente treinados. Em resposta a essa problemática, técnicas de transferência de aprendizado são comumente empregadas, com a maioria delas centrada no mapeamento de atributos, notadamente os parâmetros modais em estruturas dinâmicas. No entanto, é imperativo reconhecer que as condições de contorno exercem uma influência significativa no comportamento mecânico associado à vibração, indo além da influência dos parâmetros modais. Outros fatores, como geometria, modo de vibração e estado de dano, também desempenham papéis relevantes. Dentre esses, as condições de contorno destacam-se como fator preponderante, substancialmente impactando a transferência de aprendizado entre estruturas. A dificuldade reside na determinação das combinações ideais de atributos de modos e contornos distintos que resultam em uma transferência bem-sucedida. Neste contexto, este trabalho propõe uma abordagem inovadora, introduzindo uma análise de similaridade prévia à transferência de aprendizado. O objetivo é determinar as combinações mais eficazes de atributos para cada situação, inclusive avaliando o impacto do estado de dano na similaridade. A hipótese subjacente sustenta que uma maior similaridade conduz a uma transferência de aprendizado mais eficiente. A metodologia empregada envolve a utilização da similaridade cosseno para a seleção dos casos mais similares, fundamentada na premissa de que maior similaridade resulta em uma transferência mais eficaz. Após a seleção de atributos, a transferência de aprendizado é conduzida por meio do algoritmo Transfer Component Analysis (TCA). A análise compara casos de baixa similaridade com aqueles de alta similaridade, corroborando a hipótese de que maior similaridade está associada a uma transferência de aprendizado eficaz. Dois conjuntos de dados são analisados: o primeiro composto por vigas variando as condições de contorno, obtidas por simulação numérica utilizando o método de elementos finitos; o segundo proveniente de uma bancada experimental de junções parafusadas com danos de desaperto. O estudo visa verificar se a análise de similaridade pode indicar combinações superiores, especialmente em cenários com variação de contorno e presença de danos.
  • ItemAnais
    Experimental analysis of the flow around ahmed bodies in tandem position
    (ABCM, 2022) Martins, Gustavo Xavier [UNESP]; Aranda, Gabriel dos Santos; Campos, Henrique Matos; Pantaleão, Aluisio Viais [UNESP]
    Use of experimental methods is fundamental for the automobile industry, as it allows one to analyze aerodynamic phenomena that are crucial for the development of automobiles. A coherent method is to use Ahmed bodies with different rear inclination angles as a reference model, considering that it has been used in studies that aim to analyze the flow of land vehicles, whilst generating satisfactory results. So, in this experimental work, we explored the impact of the rear inclination angle and the spacing between Ahmed bodies in tandem (simulating a truck convoy), aiming to determine the best configuration concerning the drag reduction. The experimental methodology used flow visualization techniques in the horizontal hydrodynamic tunnel. The flow was visualized and registered by a camera for different rear inclination angles (10°, 20°, 30° and 35°) and different gap ratios (0.5 to 1.0) between the Ahmed bodies at a fixed Reynolds number of 2:06 103. Thus, we observed that, even if differences in the flow were presented in all cases, the body with a rear slant angle of 30° has the biggest wake region not mattering the spacing between models. Additionally, the impact of the gap ratio varied for each rear inclination angle.
  • ItemArtigo
    A detailed implementation of multithreading and out-of-core computation to the conventional boundary element algorithm with minimum code changes
    (2023-02-01) de Souza Schiara, Leandro; Paschoalini, Amarildo Tabone [UNESP]; Petrobras S.A; Universidade Estadual Paulista (UNESP)
    The boundary element method (BEM) poses some significant advantages over other numerical methods. Nevertheless, the generation of fully populated unsymmetrical matrices can induce some important problems for the conventional BEM algorithm concerning memory limitations. Furthermore, special integration procedures are used in BEM demand substantial computational power, and these characteristics can compromise BEM applicability for large problems unless more sophisticated approaches are used. A relatively straightforward way to extend BEM usability is to employ multithreading and out-of-core capabilities. This work presents detailed algorithms that can be easily implemented in conventional BEM codes. The improvements obtained are evaluated and commented.
  • ItemArtigo
    Population evaluation of the adapted particle swarm optimization algorithm applied for control in view of unknown parameter changes in the system
    (2023-02-01) Karmouche, Diogo Cunha José [UNESP]; Chavarette, Fábio Roberto [UNESP]; de Abreu, Gustavo Luiz Chagas Manhães [UNESP]; Gonçalves, Aparecido Carlos [UNESP]; Universidade Estadual Paulista (UNESP)
    A proposed particle swarm optimization algorithm is analyzed to adapt the controller to an inverted pendulum system, where the physical parameters of the system will be changed throughout for iterations. The parameters to be changed will be the friction coefficients, the length of the pendulum rod, and the mass of the car at different times of the iterations. The five populations used to evaluate the performance of the algorithm in the adaptation of control vectors were generated in different ways using a random normal distribution, the linear–quadratic regulatory technique, and the description of the linear–quadratic regulatory technique in linear matrix inequality, thus occupying different regions of the search space and having different characteristics. The study shows that the proposed algorithm adapts the control vector independent of the origin of the populations and without knowledge of the changes in the system, thus demonstrating the contribution of this work.
  • ItemTrabalho apresentado em evento
    On the Formation of a Super Attenuation Band in a Mono-coupled Finite Periodic Structure Comprising Asymmetric Cells
    (2023-01-01) Germanos Cleante, Vinicius [UNESP]; Brennan, Michael John [UNESP]; Paupitz Gonçalves, Paulo José [UNESP]; Carneiro, Jean Paulo [UNESP]; Universidade Estadual Paulista (UNESP)
    Metamaterials are employed to reduce vibration levels by exploiting the effects of structural periodicity. When structural elements are arranged in a periodic pattern, they act as mechanical filters, creating stop-bands. The term stop-band is often used for infinite structures, but a more appropriate term for a finite structure is attenuation band. A way of obtaining this effect is by attaching vibration absorbers, which create a local resonance stop-band plus a Bragg stop-band. The local resonance stop-band is controlled only by the properties of the attached device. The Bragg stop-band depends on the interaction between the host cell and the device. The combination of these two effects can create an attenuation zone – the so-called super attenuation band. Recent works on finite mono-coupled metamaterials have shown that asymmetric periodic structures have better attenuation properties when compared to the symmetric ones, if they are correctly orientated. This paper investigates the formation of a super attenuation band in a finite mono-coupled structure using vibration absorbers. The system is defined by the formation of a cell, which repeats along with the whole structure. The cell can be divided into sub-cells with equal or different dynamic properties. The dynamic features to form the super attenuation band are determined from the displacement transmissibility of a single cell. This analysis is extended to several cells. The results show that a super attenuation band can only occur when each attached vibration absorber is optimally tuned to its corresponding host cell in a structure comprising cells with dynamical asymmetry.
  • ItemArtigo
    Analysis of the Influence of Gasoline Adulteration on Lubricant Degradation and Internal Combustion Engine Performance
    (2022-09-27) Gonçalves, Aparecido Carlos [UNESP]; Ferreira, Ronaldo Lourenço [UNESP]; Preto, Eduardo [UNESP]; Karmouche, Diogo [UNESP]; Chavarette, Fábio Roberto [UNESP]; Outa, Roberto [UNESP]; Universidade Estadual Paulista (UNESP); UniRV─University of Rio Verde
    In internal combustion engines, studies of the effects of fuel adulteration focus on problems that occur in the fuel system and pollutants, but little attention is paid to lubricants. Some of these research studies are focused on detecting adulteration rather than the impact of this tampering on the internal combustion engine and lubricant degradation. This work evaluates, in addition to the problems in the supply system, the early degradation of the lubricant from the physical and chemical changes it undergoes when using adulterated gasoline in an internal combustion engine. For that, a 160cc Honda stationary engine mounted on a bench and connected to an alternator through a transmission belt was used. Fuels adulterated with ethanol, kerosene, and thinner were used in proportions of 5, 10, 15, and 20%. The cycles were 40 h each, which is equivalent to approximately 2000 km covered. To measure the engine time and rotation, a tachometer/hourmeter was used, where the time of each cycle was recorded. Particle quantifier analysis (PQA) tests and infrared spectrometry (sulfation, nitriding, oxidation, and total acid number (TBN)) were performed, in addition to changes in engine behavior in relation to rotation. The results showed changes in rotation according to the concentration and type of contaminants. Engine wear was small for the 2000 km covered. The sulfation, nitriding, oxidation, and TBN levels were altered, indicating the degradation of the lubricating oil.
  • ItemArtigo
    Global Sensitivity and Stability Analysis of a Parametrically Excited Energy Harvesting System
    (2023-01-01) Cauz, Luiz Oreste [UNESP]; Chavarette, Fábio Roberto [UNESP]; de Almeida, Estev˜ao Fuzaro [UNESP]; Universidade Estadual Paulista (UNESP); Universidade Estadual de Mato Grosso do Sul (UEMS)
    Energy harvesting is the process of capturing and transforming ambient energy into a useable form. Solar energy, thermal gradients, acoustical and mechanical vibrations are all examples of energy harvesting sources. Vibration Energy Harversting Systems (VEHS) are systems that employ vibrations as a source. VEHS-based energy harvesters are known as a supplementary power source, which provide small amounts of energy for slow-load applications or to charge and operate remote devices and sensors whose require small amounts of energy to operate, such as hearing aids, pacemakers, spinal cord stimulators, and microelectromechanical systems. The objective of this work is to analyze the stability of a parametrically excited energy harvesting system that uses piezoelectric materials as a transducer. The objective is to optimize the energy produced by analyzing the system’s behavior while the physical parameter values are changed. In this regard, it is essential to do a preliminary global sensitivity analysis of the physical parameters in order to determine which parameters, when altered, influence more to energy production. The Sobol’ indices are used to do the sensitivity analysis. The stability analysis is then performed using the results of Floquet’s Theory and the state transition matrix approximation techniques developed by Sinha and Butcher. Sinha and Butcher’s technique, based on Picard iterations and Chebyshev polynomial expansions, aims to find approximate solutions for periodic systems in time. An essential characteristic that is well documented in the literature is that vibrational energy harvesting systems have efficient responses when the physical parameters of the system are set so that the system operates in resonance with the parametric excitation source. As a result, when the system is in resonance with the external excitation source, significant system stability outcomes are obtained.
  • ItemResenha
    An enhanced approach for damage detection using the electromechanical impedance with temperature effects compensation
    (2023-04-01) Dias, Lorena Lopes [UNESP]; Lopes, Kayc Wayhs [UNESP]; Bueno, Douglas D. [UNESP]; Gonsalez-Bueno, Camila Gianini [UNESP]; Universidade Estadual Paulista (UNESP)
    Damage detection is one of the great challenges of the maintenance tasks and it has involved numerous researches to develop techniques in the field of structural health monitoring (SHM). Among different techniques, electromechanical impedance (EMI) technique has attracted attention due to its important and promising results. However, the sensitivity of this technique to variations in environmental conditions can lead to false diagnoses, and the temperature is one of the most critical factors for EMI technique. In view of this point, different researchers have developed compensation techniques to minimize the effects caused by temperature variation in electromechanical impedance measurements. Another important issue related to electromechanical Impedance curves is about the frequency range chosen to be analyzed. Then, the present article introduces an improved approach for damage detection by adding a new step for the temperature compensation technique proposed in a well-established approach in the literature. The proposal comprises a strategy to select the frequency range to compute damage detection indexes, and the technique is demonstrated for an aluminum beam in three different structural conditions: corresponding to the healthy and two types of damaged structure. The results are investigated for four different frequency ranges. The findings demonstrate the effectiveness of the proposed approach to reduce false alarms in damage detection using the EMI technique.
  • ItemArtigo
    Numerical and Optimization-Based Study on Split Hemispherical Shaped Fins for Augmenting Heat Transfer Rate
    (2023-01-01) Ranjan, Alok; Das, Ranjan; Gajghate, Sameer S.; Barik, Debabrata; Majumder, Himadri; Cardoso, Elaine M. [UNESP]; Majumder, Arindam; Pal, Sagnik; Deb, Madhujit; National Institute of Technology; Indian Institute of Technology; G H Raisoni College of Engineering & Management; Karpagam Academy of Higher Education; Universidade Estadual Paulista (UNESP)
    This paper deals with the numerical investigation of split hemispherical fins mounted staggered over a base plate. The thermal and flow analyses have been carried out to evaluate the Nusselt number (Nu), pressure drop ðΔPÞ, and hydrothermal performance factor (HTPF) with air as a medium and Reynolds number (Re = /3000 to 15000). The cylindrical fin (CF) and hemispherical fin (HF, of radius R) of the same volume and height have been formed and placed in the computational domain. Results reveal that the Nu for CF compared to HF is 1.3-1.4 times higher, with approximately 1.5 times higher ΔP for the given Re range. The value of HTPF for HF is greater than unity (/1.13-1.20) for all the considered Re values. Secondly, the HF gets split into longitudinal and transverse flow directions for better solid-fluid interaction. The geometrical parameters are transverse offset TO (/=0 − R/8), longitudinal offset LO (/=0 − R/8), and Re. Results show that the highest value of Nu (/=384.10) and HTPF (/=1.33) have been obtained at TO = R/10 (at LO =0) and TO = R/10 (at LO = R/10) for the highest Re (/=15000). At last, the cuckoo search algorithm (CSA) coupled with the response surface method (RSM) has been performed to fetch the optimum value of Nu based upon dimensionless TO∗, dimensionless LO∗, and Re. The optimum value (obtained at TO∗ =0:1, LO∗ =0, and Re = 15000) of Nu (=/392.16) from CSA is promising, with the numerically obtained Nu value (=/384.1059) with an error of 2.05%.
  • ItemArtigo
    Correction of Phase Balance on Nd:YAG Pulsed Laser Welded UNS S32750 Using Cobalt Electroplating Technique
    (2023-02-01) Da Cruz Junior, Eli J.; Seloto, Bruna B. [UNESP]; Ventrella, Vicente A. [UNESP]; Varasquim, Francisco M. F. A.; Zambon, Andrea; Calliari, Irene; Gennari, Claudio; Settimi, Alessio G.; Science and Technology; Universidade Estadual Paulista (UNESP); University of Padua
    Super-duplex stainless steel (SDSS) shows high mechanical and corrosion resistance because of the balanced structure of austenite and ferrite. However, maintaining this phase ratio after welding is a challenge. The use of austenite stabilizing components is recommended to balance the microstructure. The addition of alloying elements presents a challenge because of the characteristics of Nd:YAG pulsed laser welding. An approach, which has proven to be effective, is to use metal electroplating to prepare the surfaces of the mechanical SDSS components that will be welded, therefore promoting the phase balance in the fusion zone. While the effects of metals such as nickel as an austenite stabilizer are well recognized, cobalt’s effects require more research. The present work investigated the influence of the use of cobalt addition in the joining process by preliminary electroplating on UNS S32750 SDSS Nd: YAG pulsed laser welding, specifically regarding microstructure and microhardness. Three conditions were investigated, changing the thickness of the deposited cobalt layer. The addition of cobalt modified the morphology and increased the volume fraction of austenite. An austenite volume fraction of around 48% was obtained using a 35 μm thick cobalt coating. The microhardness was affected by austenite/ferrite proportions. The microhardness dropped from about 375 HV to 345 HV as the cobalt layer’s thickness rose, being similar to that of the base metal. The effect of cobalt as an austenite stabilizer was observed, and the cobalt electroplating technique was effective to correct the phase balance on UNS S32750 laser welding.
  • ItemArtigo
    Analysis of the Inconel 718 properties after roller burnishing
    (2022-01-01) Casarin, Samuel José [UNESP]; de Godoi, Eduardo Luiz; de Angelo Sanchez, Luiz Eduardo [UNESP]; de Alcântara, Anne Caroline Melo [UNESP]; Gonçalves, Aparecido Carlos [UNESP]; Universidade Estadual Paulista (UNESP); Estrada Municipal Paulo Eduardo de Almeida Prado
    Experimental studies were performed to investigate the influence of roller burnishing (RB) parameters, as the temperature and the number of RB operations, on the subsurface microstructures and microhardness, surface roughness and roundness deviation of the Inconel 718 alloy. The experimental results indicate that the RB enhance the surface quality, reduces the surface roughness by 76.7% and increase the microhardness by 20.9% compared to the turned part. RB affects the microstructural morphology of the subsurface grains and improves roundness deviation of Inconel 718 parts. The presence of precipitates in the plastic deformation zone contributes to increase the mechanical strength of the subsurface. The RB operation, both at room temperature and at 310°C, proved to be very efficient in reducing the surface roughness of the Inconel 718. About roundness deviation, the increase of the RB temperature induces a greater specimen roundness deviation, and the hot RB operation is not favourable to improve the circularity of the specimen.
  • ItemArtigo
    On the modeling of circular piezoelectric transducers for wave propagation-based structural health monitoring applications
    (2023-01-01) Lopes, Kayc W [UNESP]; Gonsalez-Bueno, Camila G [UNESP]; Inman, Daniel J; Bueno, Douglas D [UNESP]; Universidade Estadual Paulista (UNESP); University of Michigan
    Structural Health Monitoring (SHM) techniques have an important role in the performance of mechanical structures. In particular, piezoelectric transducers (PZT) have been employed for establishing damage detection processes in SHM systems. However, despite their wide use, there is limited information in the literature regarding important characteristics for SHM applications, such as the shape, dimensions and frequencies to use, which can affect the performance of the system used to detect the damage. This article investigates longitudinal and flexural waves for applications using circular piezoelectric transducers bonded to thin plates. The methodology allows one to obtain optimal frequencies to create and capture both types of waves and understand the influence of the geometric characteristics of these transducers on the damage detection. Numerical simulations are carried out to show that a change in the parameters of the piezoelectric transducers can maximize the waves amplitudes incoming at the sensor. Results from experimental tests are presented to demonstrate the proposed methodology. New equations are introduced and they compute output voltage and determine optimal frequencies to monitor the structure. The findings contribute to establishing a more efficient design of a damage detection process involving plate-like structures in SHM systems based on wave propagation.
  • ItemArtigo
    A new predictive model for a photovoltaic module's surface temperature
    (2022-11-01) Silva, Domisley Dutra [UNESP]; Marson, Vinicius [UNESP]; de Souza, Reinaldo Rodrigues; de Oliveira, Jeferson Diehl; Silva, João Batista Campos [UNESP]; Cardoso, Elaine Maria [UNESP]; Universidade Estadual Paulista (UNESP); University of Minho; Center of Innovation and Technology
    The current study developed an analytical model to predict the PV module's operating temperature based on an experimental database, which considers cell temperature, local meteorological data (irradiance, ambient temperature, wind velocity, and humidity), voltage, and current generated by the photovoltaic system associated with the purely resistive load. Based on the analysis of the 172-day database, it was possible to compare the most used correlations in the literature with the analytical model developed in the current work. For all conditions, the model showed a better response to climate variation – with 100% of the data within an error band of ± 20% and an absolute mean percentage error of 3.1% – predicting well the PV module's operating temperature for both sky conditions (clear or cloudy) and demonstrated that the thermal capacity of the PV module to climatic variations should not be neglected. Moreover, the new model considered the PV module's thermal response capacity to include the variations in the incident solar irradiance caused by the presence of clouds (shading effect). By considering a global heat capacity as a mean value of the heat capacities of the layers of the PV module, the term transient – generally neglected in several works – is considered in the energy equation in the current work, which gives a better response to the variations in the incident radiation.
  • ItemTrabalho apresentado em evento
    On the Pipe Localization Based on the Unwrapped Phase of Ground Surface Vibration Between a Roving Pair of Sensors
    (2023-01-01) Iwanaga, Mauricio Kiotsune [UNESP]; Brennan, Michael John [UNESP]; Scussel, Oscar; de Almeida, Fabrício César Lobato [UNESP]; Karimi, Mahmoud; Universidade Estadual Paulista (UNESP); University of Southampton; University of Technology Sydney
    Buried pipes are used worldwide to transport water. Although they are convenient, a large amount of water is wasted during the transportation. To minimize such a problem, water companies apply different technologies to locate leaks in their pipe networks, where the buried pipe is usually located first. Electromagnetic techniques can be used to locate buried pipes, but their performance is limited by the moisture content of the surrounding soil. Active vibro-acoustic techniques have also been investigated to locate buried pipes, in which vibro-acoustic energy is introduced into the soil by an excitation source. Although they are promising, their practical application can be expensive and complex due to the setup of an excitation mechanism. The aim of this paper is to present a passive vibro-acoustic localization technique for buried water pipes, in which a leak is the source of excitation. The localization technique is based on the calculation of an approximate slope for the unwrapped phase between a pair of sensors placed on the ground surface. The performance of the two-sensor technique is tested with two datasets, one extracted from a numerical model of the buried pipe system and the other extracted from an experiment carried out on a test rig. The results highlight the potential of the two-sensor technique in locating buried water pipes.
  • ItemTrabalho apresentado em evento
    An Investigation into the Factors Affecting the Bandwidth of Measured Leak Noise in Buried Plastic Water Pipes
    (2023-01-01) Scussel, Oscar; Brennan, Michael J. [UNESP]; de Almeida, Fabricio C. L. [UNESP]; Iwanaga, Mauricio K. [UNESP]; Muggleton, Jennifer M.; Joseph, Phillip F.; Gao, Yan; University of Southampton; Universidade Estadual Paulista (UNESP); Chinese Academy of Sciences
    Inspection and preservation of buried water pipelines is of importance in the modern world. The wastage of water due to leaks is a global problem and existing technologies/methods to detect leaks in buried pipelines still face challenges, such as how to predict the bandwidth of measured leak noise using acoustic correlators, and what are the main factors affecting this frequency range. The leak noise bandwidth is useful information for operators to know before carrying out tests in the field, and currently there is no practical way of predicting this frequency range. This paper presents an approach to predict the bandwidth and investigates the main factors affecting it such as the distance between the sensors, wave speed and attenuation of the fluid-dominated wave, which is the main carrier of leak noise. To achieve this, a water-pipe-soil-sensor model is represented in terms of filters, allowing an investigation into the corresponding physical/geometric characteristics that affect the bandwidth of the measured leak noise. It is shown that the dominant factors are the material and geometry of the pipe, the properties of the surrounding soil and the type of transducer used.
  • ItemArtigo
    LINEAR QUADRATIC REGULATOR APPLIED TO A MAGNETORHEOLOGICAL DAMPER AIMING ATTENUATE VIBRATION IN AN AUTOMOTIVE SUSPENSION
    (2022-01-01) Roefero, L. G.P. [UNESP]; Chavarette, F. R. [UNESP]; Mishra, L. N.; Universidade Estadual Paulista (UNESP); Vellore Institute of Technology
    Automotive suspension is a mechanical device used in automobiles to attenuate vibrations, which are caused by the undulation of the oor. This device can be modeled by a mass-spring-damper system, and the damper used in most real situations is a viscous medium damper, which dissipates energy passively. In this work, a 1=4 model of automotive suspension was analyzed when the passive shock absorber is exchanged for a magnetorheological shock absorber, whose control current is determined by a law of Optimal Linear Control. Based on the analyzes made in terms of displacement and acceleration, more satisfactory results were obtained in the system containing the AMR, in contrast to the results obtained with the presence of the passive damper.
  • ItemArtigo
    Exact general solutions for the mode shapes of longitudinally vibrating non-uniform rods via Lie symmetries
    (Elsevier B.V., 2022-08-17) Nunes, Afonso W. [UNESP]; Silva, Samuel da [UNESP]; Ruiz, Adrian; Universidade Estadual Paulista (UNESP); Univ Cadiz
    A Lie symmetry method-based approach is proposed for systematically computing general solutions in closed-form for the mode shape equation of non-uniform and unconventional vibrating rods. The mode shape equation is modeled by the elementary rod theory, addressing polynomial, exponential, trigonometric, and hyperbolic cross-section variations. The method provides algorithmic order-reduction steps for solving the investigated mode shape equation, producing a first-order Riccati equation whose integration reveals the aimed solutions for the problem. Illustrative examples are presented, including original solutions in closed-form as well as solutions previously obtained in the literature by other approaches. Mode shapes from general solutions with appropriate rod boundary conditions are also considered for different examples.
  • ItemArtigo
    LINEAR QUADRATIC REGULATOR APPLIED TO a MAGNETORHEOLOGICAL DAMPER AIMING ATTENUATE VIBRATION IN AN AUTOMOTIVE SUSPENSION
    (Turkic World Mathematical Soc, 2022-01-01) Roefero, L. G. P. [UNESP]; Chavarette, F. R. [UNESP]; Mishra, L. N.; Universidade Estadual Paulista (UNESP); Vellore Inst Technol
    Automotive suspension is a mechanical device used in automobiles to attenuate vibrations, which are caused by the undulation of the floor. This device can be modeled by a mass-spring-damper system, and the damper used in most real situations is a viscous medium damper, which dissipates energy passively. In this work, a 1/4 model of automotive suspension was analyzed when the passive shock absorber is exchanged for a magnetorheological shock absorber, whose control current is determined by a law of Optimal Linear Control. Based on the analyzes made in terms of displacement and acceleration, more satisfactory results were obtained in the system containing the AMR, in contrast to the results obtained with the presence of the passive damper.
  • ItemArtigo
    Increasing the corrosion resistance in the UNS S32750 super duplex steel welded joints through Hybrid GTAW-Laser Welding and Nitrogen
    (MDPI, 2023-01-05) Videira, Arthur Moraes e; Mendes, Willians Ribeiro; Ventrella, Vicente Afonso [UNESP]; Calliari, Irene; Universidade Estadual Paulista (Unesp)
    The development of techniques to improve the welding of super duplex steels is necessary in order to ensure that the phase balance and properties of the material are not affected during this process. Hybrid arc-laser welding is a perfect combination of the advantages of both processes, producing deeper weld beads with more balanced phases than the pulsed laser process. Here, the objective was to improve the corrosion resistance of UNS S32750 weld beads by increasing the volumetric austenite percentage in the fusion zone (FZ) with a hybrid process of GTAW (gas tungsten arc welding) and pulsed laser Nd-YAG (neodymium-doped yttrium aluminum garnet). Welds were performed in bead on plate conditions with fixed laser parameters and a varying heat input introduced through the GTAW process. Additionally, welds within a nitrogen atmosphere were performed. After base metal characterization, an analysis of the FZ and heat affected zone were performed with optical microscopy, scanning electron microscopy and critical pitting tests (CPT). The synergy between the thermal input provided by the hybrid process and austenite-promoting characteristic of nitrogen led to a balanced volumetric austenite/ferrite fraction. Consequently, the results obtained in CPT tests were better than conventional welding processes, such as laser or GTAW solely.