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3D computer tomography for measurement of femoral position in acl reconstruction
(2015) FERNANDES, TIAGO LAZZARETTI; MARTINS, N. M. M. F.; WATAI, F. A.; ALBUQUERQUE, Cyro; PEDRINELLI, A.; HERNANDEZ, A. J.
A CFD analysis of the flow dynamics of a directly-operated safety relief valve
(2018) Scuro N.L.; Angelo E.; Angelo G.; Andrade D.A.
© 2018 Elsevier B.V.A three-dimensional numerical study on steady state was designed for a safety relief valve using several openings and inlet pressures. The ANSYS-CFX® commercial code was used as a CFD tool to obtain several properties using dry saturated steam revised by IAPWS-IF97. Mass flow and discharge coefficient calculated from simulations are compared to the ASME 2011a Section 1 standard. The model presented constant behavior for opening lifts smaller than 12 mm and is very reasonable when compared to the standard (ASME). In addition, the conventional procedure to design normal disc force assumes that all the fluid mechanical energy was converted into work; however, the CFD simulations showed that average normal disc force is about 19% lower than theoretical ASME force, which could prevent the valve oversizing. A numerical validation was conducted for a transonic air flow through a converging–diverging diffuser geometry to verify the solver's ability to capture the position and intensity of a shockwave: the results showed good agreement with the benchmark experiments.
A comparison of different assistance strategies in power assisted wheelchairs using an optimal control formulation
(2016-08-18) CUERVA, V. I.; Marko Ackermann; Fabrizio Leonardi
Power assisted wheelchairs are a promising solution to overcome problems associated with manual wheelchair propulsion, such as the incidence of upper limbs injuries and muscle fatigue. However, there are still open questions regarding the most appropriate assistance strategy. The main goal of this paper is to compare three different types of assistance in power assisted wheelchairs: constant force, proportional force and a novel type of assistance inspired on the impedance control theory. The comparison was performed using a simple model and an optimal control formulation that searched for optimal user actuation and controller parameters so as to minimize the user effort. The fairness of the comparison was ensured by imposing an upper bound on the energy consumption by the motors. The results show that the proportional and impedance controlbased strategies are the most appropriate steady state conditions. In typical daily activities such as obstacle avoidance, the impedance control has advantage as it permits a faster system's response.
A computational study of the swing phase of the gait with standard and spring-loaded crutches
(2012-06-12) Marko Ackermann; TAISSUN, B. A.
Crutches have suffered few functional modifications over their long history, with improvements largely limited to aesthetics and weight reduction aspects. The large energetic cost of the gait with crutches and problems associated to their long-term use impose a heavy burden to the users. In order to mitigate some of the mentioned problems, alternative designs have been proposed over the past few decades. Among them, the idea of incorporating an elastic element to the crutches to reduce impact forces transmitted to the upper extremities and to promote energy storage and release has been indicated in the specialized literature as a potential solution, in particular for the crutch gait styles more similar to the normative human gait such as the two-point and the swing-through. In fact, tendon elasticity has been shown to reduce energy consumption during animal and human locomotion by means of energy storage in the initial and mid stance-phase and release in the push-off phase of the gait cycle. In spite of the great potential of this idea, appropriate stiffness curves for the elastic element are poorly studied in the literature. This study aims at investigating appropriate stiffness values for the elastic element of spring-loaded crutches by means of computational simulations using a model of the swing phase of the swing-through gait style. The findings show that the stiffness should be tuned carefully to ensure improved gait quality. Spring-loaded crutches undoubtedly reduce impact forces transmitted to upper limbs and shoulder at touch down but they can deteriorate performance with respect to foot clearance and effort at the shoulder when compared to stiff crutches if stiffness is not carefully selected. © 2012 IEEE.
A low-cost anthropometric walking robot for reproducing gait lab data
(2008-12-05) Da Silva Santana R.E.; De Toledo Fleury A.; Menegaldo L.L.
Human gait analysis is one of the resources that may be used in the study and treatment of pathologies of the locomotive system. This paper deals with the modelling and control aspects of the design, construction and testing of a biped walking robot conceived to, in limited extents, reproduce the human gait. Robot dimensions have been chosen in order to guarantee anthropomorphic proportions and then to help health professionals in gait studies. The robot has been assembled with low-cost components and can reproduce, in an assisted way, real-gait patterns generated from data previously acquired in gait laboratories. Part of the simulated and experimental results are addressed to demonstrate the ability of the biped robot in reproducing normal and pathological human gait.
A method to simulate motor control strategies to recover from perturbations: Application to a stumble recovery during gait
(2011-09-03) FORNER-CORDERO, A.; Marko Ackermann; DE LIMA FREITAS, M.
Perturbations during human gait such as a trip or a slip can result in a fall, especially among frail populations such as the elderly. In order to recover from a trip or a stumble during gait, humans perform different types of recovery strategies. It is very useful to uncover the mechanisms of the recovery to improve training methods for populations at risk of falling. Moreover, human recovery strategies could be applied to implement controllers for bipedal robot walker, as an application of biomimetic design. A biomechanical model of the response to a trip during gait might uncover the control mechanisms underlying the different recovery strategies and the adaptation of the responses found during the execution of successive perturbation trials. This paper introduces a model of stumble in the multibody system framework. This model is used to assess different feedforward strategies to recover from a trip. First of all, normal gait patterns for the musculoskeletal system model are obtained by solving an optimal control problem. Secondly, the reference gait is perturbed by the application of forces on the swinging foot in different ways: as an instantaneous inelastic collision of the foot with an obstacle, as an impulsive horizontal force or using a force curve measured experimentally during gait perturbation experiments. The influence of the type of perturbation, the timing of the collision with respect to the gait cycle, as well as of the coefficient of restitution was investigated previously. Finally, in order to test the effects of different muscle excitation levels on the initial phases of the recovery response, several muscle excitations were added to selected muscles of the legs, thus providing a simulation of the recovery reactions. These results pave the way for future analysis and modeling of the control mechanisms of gait. © 2011 IEEE.
A modeling framework to investigate the radial component of the pushrim force in manual wheelchair propulsion
(2015-11-25) Marko Ackermann; COSTA, H. R.; Fabrizio Leonardi
© Owned by the authors, published by EDP Sciences, 2015.The ratio of tangential to total pushrim force, the so-called Fraction Effective Force (FEF), has been used to evaluate wheelchair propulsion efficiency based on the fact that only the tangential component of the force on the pushrim contributes to actual wheelchair propulsion. Experimental studies, however, consistently show low FEF values and recent experimental as well as modelling investigations have conclusively shown that a more tangential pushrim force direction can lead to a decrease and not increase in propulsion efficiency. This study aims at quantifying the contributions of active, inertial and gravitational forces to the normal pushrim component. In order to achieve this goal, an inverse dynamics-based framework is proposed to estimate individual contributions to the pushrim forces using a model of the wheelchair-user system. The results show that the radial pushrim force component arise to a great extent due to purely mechanical effects, including inertial and gravitational forces. These results corroborate previous findings according to which radial pushrim force components are not necessarily a result of inefficient propulsion strategies or hand-rim friction requirements. This study proposes a novel framework to quantify the individual contributions of active, inertial and gravitational forces to pushrim forces during wheelchair propulsion.
A study on friction coefficient and wear coefficient of coated systems submitted to micro-scale abrasion tests
(2013) Cozza R.C.
Several works on friction coefficient during abrasive wear tests are available in the literature, but only a few were dedicated to the friction coefficient in micro-abrasive wear tests conducted with rotating ball. This work aims to study the influence of titanium nitride (TiN) and titanium carbide (TiC) coating hardness on the friction coefficient and wear coefficient in ball-cratering micro-abrasive wear tests. A ball of AISI 52100 steel and two specimens of AISI D2 tool steel, one coated with TiN and another coated with TiC, were used in the experiments. The abrasive slurry was prepared with black silicon carbide (SiC) particles and distilled water. Two normal forces and six sliding distances were defined, and both normal and tangential forces were monitored constantly during all tests. The movement of the specimen in the direction parallel to the applied force was also constantly monitored with the help of an electronic linear ruler. This procedure allowed the calculation of crater geometry, and thus the wear coefficient for the different sliding distances without the need to stop the test. The friction coefficient was determined by the ratio between the tangential and the normal forces, and for both TiN and TiC coatings, the values remained, approximately, in the same range (from μ= 0.4 to μ= 0.9). On the other hand, the wear coefficient decreased with the increase in coating hardness. © 2012 Elsevier B.V.
A transient three-dimensional heat transfer model of the human body
(2009-08-05) FERREIRA, M. S.; YANAGIHARA, J. I.
The objective of this work is to develop an improved model of the human thermal system. The features included are important to solve real problems: 3D heat conduction, the use of elliptical cylinders to adequately approximate body geometry, the careful representation of tissues and important organs, and the flexibility of the computational implementation. Focus is on the passive system, which is composed by 15 cylindrical elements and it includes heat transfer between large arteries and veins. The results of thermal neutrality and transient simulations are in excellent agreement with experimental data, indicating that the model represents adequately the behavior of the human thermal system. © 2009 Elsevier Ltd. All rights reserved.
Adoção de materiais resistentes ao desgaste em projetos industriais
(2015) COZZA, Ronaldo Câmara; RODRIGUES, Lucas Cremonese; SCHON, Cláudio Geraldo
Adressing Energy Demand and Climate Change through the Second Law of Thermodynamics and LCA towards a Rational Use of Energy in Brazilian Households
(2022-10-25) PEREIRA, M. T. R. M.; CARVALHO, M.; Carlos Mady
© 2022 by the authors.This study focuses on a typical Brazilian household through the lens of sustainable development, regarding energy demand and GHG emissions. The analysis encompasses both the direct and indirect energy, exergy consumption, and GHG emissions (quantified by life cycle assessment) associated with the usual routine of a household. The household is modeled as a thermodynamic system to evaluate inputs (food, electricity, fuels for transportation) and outputs (solid and liquid residues). The hypothesis is that each input and output contains CO (Formula presented.) emissions and exergy derived from its physical-chemical characteristics or production chains. Each household appliance is modeled and tested as a function of external parameters. The contribution of several industries was obtained to the total GHG emissions and exergy flows entering and exiting the household (e.g., fuels for transportation, food, gas, electricity, wastewater treatment, solid waste). It was verified that urban transportation was the flow with the highest GHG and exergy intensity, ranging between 1.49 and 7.53 kgCO (Formula presented.) /day and achieving 94.7 MJ/day, almost five times higher than the calculated exergy demand due to electricity. The second largest flow in GHG emissions was food due to the characteristics of the production chains, ranging from 1.6 to 4.75 kgCO (Formula presented.) /day, depending on the adopted diet. On the other hand, the electricity presented low GHG emissions due to the main energy sources used to generate electricity, only 0.52 kgCO (Formula presented.) /day. Moreover, the chemical exergy of the solid waste was 9.7 MJ/day, and is not irrelevant compared to the other flows, representing an interesting improvement opportunity as it is entirely wasted in the baseline scenario.
Advanced multi-metallic SOFC anode development by mechanical alloying route
(2010-01-05) TESTIVO, T. A. G.; LEITE, D. W.; MELLO-CASTANHO, S. R. W.
Anodes composed of Ni-YSZ (yttria-stabilised zirconia) cermets are the key material to allow direct biofuel feeding to Solid Oxide Fuel Cell (SOFC) devices due to its internal reforming capability. The main challenge among these materials is related to carbon deposition poisoning effect when C-bearing fuels are feed. The work deals with these issues by alloying Ni with some metals like Cu to conform a multi-metallic anode material. Mechanical alloying (MA) at shaker mills is chosen as the route to incorporate the metal and ceramic powders in the anode material, also leading to better sintering behaviour. A projected cermet material is conceived where a third metal can be added based on two criteria: low Cu solubility and similar formation enthalpy of hydrides regarding Ni. Refractory metals like Nb, W and Mo, seems to fulfil these characteristics, as well as Ag. The MA resulted powder morphology is highly homogeneous showing nanometric interpolated metal lamellae. The sintering behaviour is investigated by conventional dilatometry as well as by stepwise isothermal dilatometry (SID) quasi-isothermal method to determine the sintering kinetic parameters. Based on these tools, it is found the Cu additive promotes sintering to obtain a denser anode and therefore allowing lower process temperatures. The consolidation is achieved through the sintering by activated surface (SAS) method allied to liquid phase sintering process, where the third metal additive also has influenced. The final cermet can be obtained at one sole process step, dispensing pore-forming additives and reduction treatments. The sintered microstructure demonstrates the material is homogeneous and possesses suitable percolation networks and pore structure for SOFC anode applications. © (2010) Trans Tech Publications.
An integrated model of the thermoregulatory and respiratory systems of the human body
(2020-07-05) Cyro Albuquerque; YANAGIHARA, J.I.
This work aims to develop a mathematical model for computing the distribution of temperature, O2, and CO2 in the human body, depending on the ambient conditions. The body is divided into segments, including layers of tissues and blood compartments, where mass and energy balances are applied. The inclusion of O2 and CO2 transfer mechanisms throughout all segments and tissues of the human body is one of the great novelties of this work. It also includes the exothermic metabolic reactions in the tissues, the transportation of O2 and CO2 by the blood, and the energy exchanged with the environment through the skin and by ventilation. The model also includes the regulation of metabolism, circulation, ventilation, and sweating, depending on the body temperature and the concentrations of O2 and CO2 in the blood. The lungs are represented by alveolar and blood compartments, with diffusion between them. Comparisons with experimental data from the existing literature show that the proposed model is suitable for representing transient exposure to cold and warm ambient temperatures, low concentration of O2, and high concentrations of CO2. In the end, some results demonstrate the effect of ambient temperature on the distribution of temperature, O2, and CO2 across segments, blood, and tissues. Shivering in a cold environment reduces the concentration of O2 and increases the concentration of CO2 in the muscles, which results in increased ventilation and blood circulation. The concentration of gases in the skin depends mainly on variations in the skin's circulation with the environment, which alters the availability of O2 and the elimination of CO2. Small variations were found in the concentrations of O2 and CO2 in the brain and lungs.
An integrated model of the thermoregulatory and respiratory systems of the human body
(2020-07-05) YANAGIHARA, J. I.
© 2020 Elsevier LtdThis work aims to develop a mathematical model for computing the distribution of temperature, O2, and CO2 in the human body, depending on the ambient conditions. The body is divided into segments, including layers of tissues and blood compartments, where mass and energy balances are applied. The inclusion of O2 and CO2 transfer mechanisms throughout all segments and tissues of the human body is one of the great novelties of this work. It also includes the exothermic metabolic reactions in the tissues, the transportation of O2 and CO2 by the blood, and the energy exchanged with the environment through the skin and by ventilation. The model also includes the regulation of metabolism, circulation, ventilation, and sweating, depending on the body temperature and the concentrations of O2 and CO2 in the blood. The lungs are represented by alveolar and blood compartments, with diffusion between them. Comparisons with experimental data from the existing literature show that the proposed model is suitable for representing transient exposure to cold and warm ambient temperatures, low concentration of O2, and high concentrations of CO2. In the end, some results demonstrate the effect of ambient temperature on the distribution of temperature, O2, and CO2 across segments, blood, and tissues. Shivering in a cold environment reduces the concentration of O2 and increases the concentration of CO2 in the muscles, which results in increased ventilation and blood circulation. The concentration of gases in the skin depends mainly on variations in the skin's circulation with the environment, which alters the availability of O2 and the elimination of CO2. Small variations were found in the concentrations of O2 and CO2 in the brain and lungs.
An optimal control framework to predict gait patterns resulting from changes in musculoskeletal properties
(2016-08-18) SANTOS, G. F.; GOMES, A. A.; SACCO, I. C. N.; Marco Ackermann
A musculoskeletal model allows the analysis of the human gait and may aid the investigation of different strategies employed by the human body to perform this important task. This study presents a planar multibody model of the musculoskeletal system and an optimal control approach to obtain the time history of motion and muscle activation during the gait. Passive joint moments and muscle properties of the model are modified to represent potential changes caused by different diseases, such as diabetic neuropathy. The system adaptation is predicted on the basis of an optimal control framework and the results show many global adaptations as a response to local changes in the properties of the musculoskeletal system and evidences the great potential of this framework to predict patient adaptations to disease, assistive devices or surgical interventions.
ANÁLISE COMPORTAMENTAL DOS COEFICIENTES DE ATRITO E DESGASTE DE SISTEMAS REVESTIDOS SUBMETIDOS A DESGASTE MICRO-ABRASIVO
(2010) COZZA, Ronaldo Câmara; Recco, Abel André Candido; Tschiptschin, André Paulo; Souza, Roberto Martins de; Tanaka, Deniol Katsuki
ANÁLISE SOBRE A REPRODUTIBILIDADE DE RESULTADOS E FRAGMENTAÇÃO DE PARTÍCULAS ABRASIVAS EM ENSAIOS BALL-CRATERING
(2013) COZZA, Ronaldo Câmara
Analysis of Surface Integrity for DIN 100Cr6 Steel Conical Bearing Rings after Hard Turning
(2011) DELIJAICOV, Sergio; SALAZAR, C. E. V.; BORDINASSI, Éd Cláudio; PADOVESE, L. R.
Analysis of surface integrity for din 100cr6 steel conical bearing rings after hard turning
(2011-11-12) Sergio Delijaicov; SALAZAR, C. E. V.; BORDINASSI, E. C.; PADOVESE, L. R.
This work studies the influence of machining parameters, such as cutting speed and forces, feed rate, cutting depth, and tool flank wear, on the generation of surface residual stresses in DIN 100Cr6 steel conical bearing rings submitted to a hard turning process. A complete factorial planning was used to perform the tests and projected measurement. Cutting forces were measured by a piezoelectric dynamometer and residual stresses were determined by the hole-drilling method using strain gage. Results showed that after 2000 m of tool machining, phase transformations had been observed on sample surfaces, with white layer formation, and deeper, a dark layer whose thickness varied depending on the severity level of turning and the tool wear (in machined distance). Increase in tool wear generated minor values of compressive residual stresses and the surface roughness presented almost the same values in all experiments, except when the bigger parameters were used. © (2011) Trans Tech Publication.
Analysis of the Metallurgical Bonding between Inconel and NiCrAlY Coatings by HVOF and with CO2 Laser Beam
(2016-08-05) OLIVEIRA, ANA CLAUDIA COSTA; Gustavo Donato; Rodrigo Magnabosco; TELEGINSKI, VIVIANE; CHAGAS, DANIELE CRISTINA; VASCONCELOS, GETÚLIO DE; CAMARGO, F.
Coatings are applied on turbine blades’ surfaces to provide protection not only against high temperature but also against aggressive environment. Ceramic coatings are employed to avoid metallic substrate overheating, while at the same time increasing turbine work temperature and performance. A bond coat (BC) base of particulate material based on Ni-Al powders is necessary to assure oxidation protection, a good adhesion and gradual decrease in thermal expansion coefficient between the blades’ metallic substrate and the ceramic top coating. One of the most important parameters of such coatings is the adhesion strength. In this work, a NiCrAlY bond coat was deposited on Inconel 625 substrate employing High-Velocity Oxygen-Fuel (HVOF) thermal spraying technology and CO2 laser beam irradiation to enhance coating–substrate adherence and metallurgical bonding. Microstructural features were examined by optical and scanning electron microscopy (SEM), X-ray diffraction and microhardness analysis. The results indicate that the laser treatment provided an efficient metallurgical bond between the (BC) and Inconel 625 substrate.

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