Na presente dissertação pretende-se avaliar a influência das condições de produção nos ciclos térmicos, no binário e na força axial em soldaduras pelo processo Tool Assisted Friction Spot Welding (TAFSW) para uma vasta gama de aços com baixo teor de carbono. Para tal, estudaram-se soldaduras com diferentes parâmetros e condições de fixação. Os ciclos térmicos e as condições termomecânicas foram comparados com os valores obtidos para as diferentes condições de ensaio.Os materiais base utilizados nesta investigação foram o aço macio DC01 com e sem revestimento, o aço de elevada resistência HC220, o aço dual phase DP600, assim como o aço galvanizado DX51D com diferentes espessuras de revestimento. As medições de temperatura foram realizadas com o auxílio de uma câmara termográfica, as características morfológicas foram observadas através de análise metalográfica e as propriedades mecânicas avaliaram-se recorrendo a medições de dureza. Os valores relativos ao binário e à força axial durante o processo foram registados pelo equipamento de soldadura. A investigação desenvolvida permitiu concluir que as condições de ensaio apresentam forte influência na aquisição das temperaturas. Mais precisamente, uma fixação menos exigente conduz ao desenvolvimento de deformação das chapas de material base que levam, não só à incorreta aquisição dos ciclos térmicos, mas também a condições de dissipação de calor diferentes das desenvolvidas aquando de um procedimento de fixação mais rigoroso, resultando ainda em diferenças na geração de calor durante o processo.

The purpose of this study was to analyze the hydrodynamic characteristics of a realistic model of an elite swimmer hand/forearm using three-dimensional computational fluid dynamics techniques. A three-dimensional domain was designed to simulate the fluid flow around a swimmer hand and forearm model in different orientations (0°, 45°, and 90° for the three axes Ox, Oy and Oz). The hand/forearm model was obtained through computerized tomography scans. Steady-state analyses were performed using the commercial code Fluent. The drag coefficient presented higher values than the lift coefficient for all model orientations. The drag coefficient of the hand/forearm model increased with the angle of attack, with the maximum value of the force coefficient corresponding to an angle of attack of 90°. The drag coefficient obtained the highest value at an orientation of the hand plane in which the model was directly perpendicular to the direction of the flow. An important contribution of the lift coefficient was observed at an angle of attack of 45°, which could have an important role in the overall propulsive force production of the hand and forearm in swimming phases, when the angle of attack is near 45°.

The main aim of this study was to investigate the effect of finger spread on the propulsive force production in swimming using computational fluid dynamics. Computer tomography scans of an Olympic swimmer hand were conducted. This procedure involved three models of the hand with differing finger spreads: fingers closed together (no spread), fingers with a small (0.32 cm) spread, and fingers with large (0.64 cm) spread. Steady-state computational fluid dynamics analyses were performed using the Fluent code. The measured forces on the hand models were decomposed into drag and lift coefficients. For hand models, angles of attack of 0°, 15°, 30°, 45°, 60°, 75°, and 90°, with a sweep back angle of 0°, were used for the calculations. The results showed that the model with a small spread between fingers presented higher values of drag coefficient than did the models with fingers closed and fingers with a large spread. One can note that the drag coefficient presented the highest values for an attack angle of 90° in the three hand models. The lift coefficient resembled a sinusoidal curve across the attack angle. The values for the lift coefficient presented few differences among the three models, for a given attack angle. These results suggested that fingers slightly spread could allow the hand to create more propulsive force during swimming.

The purpose of this study was to analyse the effect of wearing a swimsuit on swimmer's passive drag. A computational fluid dynamics analysis was carried out to determine the hydrodynamic drag of a female swimmer's model (i) wearing a standard swimsuit; (ii) wearing a last generation swimsuit and; (iii) with no swimsuit, wearing light underwear. The three-dimensional surface geometry of a female swimmer's model with different swimsuit/underwear was acquired through standard commercial laser scanner. Passive drag force and drag coefficient were computed with the swimmer in a prone position. Higher hydrodynamic drag values were determined when the swimmer was with no swimsuit in comparison with the situation when the swimmer was wearing a swimsuit. The last generation swimsuit presented lower hydrodynamic drag values, although very similar to standard swimsuit. In conclusion, wearing a swimsuit could positively influence the swimmer's hydrodynamics, especially reducing the pressure drag component.

In this paper the authors present shortly an original method to make the dynamic synthesis of a mechanism with rotary cam and rotated tappet with roll, used with priority at the distribution mechanisms from the heat engines with internal combustion. This type of distribution can improve the changes of gases, and may decrease significantly the level of vibration, noises, and emissions. As long as we produce electricity and heat by burning fossil fuels is pointless to try to replace all thermal engines with electric motors, as loss of energy and pollution will be even larger. However, it is well to continuously improve the thermal engines, to reduce thus fuel consumption. At the heat engine with internal combustion a great loss of power is realized and by the distribution mechanism, reason for that we must try to improve the functionality of this mechanism. The dynamic synthesis of this type of distribution mechanism can be made shortly, by the Cartesian coordinates, but to determine these coordinates we need and some trigonometric parameters of the mechanism. Dynamics and forces of this distribution mechanism are presented as well. One introduce the dynamic coefficient D.

The paper presents an algorithm to set the parameters of the dynamics of the classic mechanism the main of internal combustion. It shows the distribution of the forces (on the main mechanism of the engine) on engines with internal combustion. Dynamic, the gears can be distributed in the same way as forces. Practically, in the dynamic regimes, the velocities have the same synchronization as forces. The method shall be applied separately for two distinct situations: when the engine is working on a compressor and in the system of the motor. For the two individual cases, two independent formulae are obtained for the dynamic cinematic forces (gearbox). The calculations shall be made for an engine with a single cylinder. The change of speed in the dynamics feels like a variation of the angular speed of the engine. It is more difficult to be taken into account (theoretically) effect on an engine with several cylinders.

The paper presents in detail a method of calculating the forces acting on a 2T9R type robot. In order to determine the reactions (forces in the kinematic couples), one must first determine the inertial forces in the mechanism to which one or more useful loads of the robot can be added. The torsor of the inertia forces is calculated with the help of the masses of the machine elements and the accelerations from the centers of mass of the mechanism elements, so the positions, velocities, and accelerations acting on it will be determined, i.e. its complete kinematics. The calculation method applied by a MathCad program intelligently uses data entry through the IFLOG logic function so that the calculations can be automated. So the effective automation of the calculation program is done exclusively through the IFLOG functions originally used in the paper.

The paper presents in detail a method of calculating the forces acting on a 1T6R robot manipulator. To determine the reactions (forces in kinematic torques), you must first determine the inertial forces in the mechanism to which one or more payloads of the robot can be added. The torsion of the inertial forces is calculated using the masses of the machine elements and the accelerations at the centers of mass of the elements of the mechanism, so that the positions, speeds, and accelerations acting on it, ie its complete kinematics, will be determined. Equations of the dynamics are also determined through an original method.

The negative effects due to soil compaction in agricultural soils may result in inappropriate conditions for plant growth. This study was aimed at evaluating the traffic effect on physical and mechanical soil properties as well as its influence on machines and plants by taking into account different managements. An area with an Hapludalf was assessed under different treatments, namely: no-tillage, minimum tillage, and native grassland. The following treatments were evaluated: (a) soil under no-tillage (control) (b) soil under no-tillage with traffic intensity of 24.79 Mg km ha-1 and (c) 49.59 Mg km ha-1; (d) soil after 6 months of minimum tillage; and (e) under under minimum tillage compacted with traffic (10 Mg total weight). Additionally, different treatments were analyzed for a site under native grassland (a) common level of compaction (control); (b) additional compaction; (c) soil with herbicide applications; and (d) additional compaction on soil with herbicide applications. Physical soil properties (porosity, bulk density, and permeability) and mechanical soil properties (preconsolidation stress, compression index, and relative deformation) as well as parameters associated to plant (root biomass and root growth) and machine (horizontal e vertical efforts) were evaluated in this study. The traffic reduced soil porosity and air and water flow, thus increasing soil penetration resistance, but soil density was not increased. The physical soil properties were not altered due to the change in traffic intensity (24.79 Mg km ha-1 and 49.59 Mg km ha-1). The chiseling operation did not reduce soil compaction, thus clearly demonstrating that operations other than mechanical ones should be applied. The machine traffic had influence on physical soil properties in such a way that both microporosity and macroporosity were reduced, whereas bulk density was increased. As a result of these modifications, soil penetration resistance was increased by over 20%. It should be emphasized that even with the traffic intensity used in this study, the current physical conditions allow farmers to use agriculture on the site studied; however, precaution should be taken on this type of land-use.