Stephan Becker, Robin Göddel, Carlo Dindorf
et al.
Background: Individuals may exhibit altered foot pronation during gait when fatigue sets in. Therefore, a more evidence-based understanding of these fatigue-induced changes may be helpful for future gait analysis and return-to-play tests since fatigue can provide new insights that might explain a person’s complaints. Methods: A total of 25 healthy individuals (12♂, 13♀; 24.3 ± 2.7 years; 174.9 ± 9.09 cm; 70 ± 14.2 kg; BMI: 22.7 ± 2.8) participated in this controlled non-randomized study of unilateral fatigue of the right foot’s stabilizing muscles with regard to the pronation of the foot, measured by navicular drop (ND) in static (statND; standing) and dynamic (dynND; walking) states. The left foot served as the control. Surface electromyography was used to verify fatigue. Results: While the statND did not change, the dynND increased significantly by 1.44 ± 2.1 mm (=22.3%) after the foot-stabilizing muscles experienced fatigue. No correlation was found between the statND and dynND. Conclusions: Muscular fatigue can affect foot pronation. The dynND appears to be more representative of the loads in everyday life, whereby most studies use the statND.
Mechanics of engineering. Applied mechanics, Descriptive and experimental mechanics
Sergey E. Yakush, Yuli D. Chashechkin, Andrey Y. Ilinykh
et al.
The impingement of a short-duration water jet on a pool of molten Rose’s metal is studied experimentally herein. Short-duration water jet impacting on the free surface of a molten metal pool with a temperature of 300 °C are generated with a pneumatic water delivery system, with two-camera high-speed video registration. A total of 14 experimental series, each containing 5 repeated tests, are performed for a water volume of 0.2–1 mL and a jet impact velocity of 4.1–9.0 m/s. The cavity development in the melt layer is studied, with the main stages described herein. Despite the significantly higher density of melt in comparison with water, the cavity can reach the melt pool bottom; furthermore, its further collapse results in the formation of a central jet rising to the height of a few centimeters. The maximum height of the central jet is shown to depend linearly on the total momentum of the water jet, and a semi-logarithmic correlation is found for the maximum diameter of the cavity. Repeatability analysis is performed within each experimental series, and the relative standard deviation for the melt splash height is shown to be from 8.8% to 26.8%. The effects of the pool depth, the vessel shape, and the water temperature are weaker in the range of the experimental parameters used here.
Thermodynamics, Descriptive and experimental mechanics
Mohsen Abdolahzadeh, Ali Tayebi, Mehrdad Ahmadinejad
et al.
In this study, a numerical investigation of the effect of different magnetic fields on ferrofluid-fluid mixing processes in a two-dimensional microchannel is performed An improved version of smoothed particle hydrodynamics, SPH, by shifting particle algorithm and dummy particle boundary condition, is implemented to solve numerical continuity, ferrohydrodynamics-based momentum and mass transfer equations. SPH is formulated through the irregular arrangement of the nodes where the fields are approximated using the fifth-order Wendland kernel function. After validating the computational approach, the influence of the number (from one to three) of parallel electrical wires positioned perpendicular to the microchannel on the mixing efficiency is studied for the first time. It has originally been found that the mixing efficiency highly non-linearly depends on the Reynolds number and the number of electrical wires. For <i>Re</i> ≤ 20 the mixing efficiency is almost the same for two and three electrical wires and about two times higher than one electrical wire. For <i>Re</i> ≥ 80, the mixing efficiency of three wires is much higher than one and two electrical wires. Optimum performance of the micromixer is achieved with three electrical wires, since the mixer performs well on a broader range of <i>Re</i> than the other two studied cases. The outcomes of this study, obtained by a meshless method, are important for the industrial design of micromixers.
Thermodynamics, Descriptive and experimental mechanics
Published theories and observations have shown that dissipation of gravity waves implies frequency downshifting of wave energy. Hence, for wind-waves, the wind energy input to the highest frequencies is of special interest. Here it is shown that this input is vital, because the direct wind energy input obtained by the air-pressure’s work on most gravity waves is slightly less than what the waves need to grow. Further, the wind’s input of the angular momentum that waves need to grow is found to be absent at most gravity wave frequencies. The capillary waves that appear at the surface of the sea when the wind is blowing solve these problems. To demonstrate this, an extension of linear wave theory is established to study possibilities and limitations for transfer of energy and angular momentum from the wind to waves through these frequencies. The theory describes regular, gravity–capillary waves with constant amplitude under laminar conditions. It includes surface tensions, viscosity, gravity and a wind-generated shear current, and shows that these waves—contrary to most gravity waves—receive more energy from the wind than they dissipate and angular momentum they cannot keep. Hence, the problem of the missing input of energy and angular momentum from wind to gravity waves is solved by transfers through the capillary waves. This implies that capillary waves are vital to obtain growing gravity waves.
Thermodynamics, Descriptive and experimental mechanics
Kamel Guedri, Abdullah A. Abdoon, Omar S. Bagabar
et al.
Tunnel fires are one of the most dangerous catastrophic events that endanger human life. They cause damage to infrastructure because of the limited space in the tunnel, lack of escape facilities, and difficulty that intervention forces have in reaching the fire position, especially in highly crowded areas, such as Makkah in the Hajj season. Unfortunately, performing experimental tests on tunnel fire safety is particularly challenging because of the prohibitive cost, limited possibilities, and losses that these tests can cause. Therefore, large-scale modeling, using fire dynamic simulation, is one of the best techniques used to limit these costs and losses. In the present work, a fire scenario in the Makkah’s King Abdulaziz Road tunnel was analyzed using the Fire Dynamics Simulator (FDS). The effects of the heat released per unit area, soot yield, and CO yield on the gas temperature, radiation, concentrations of the oxygen and combustion products CO and CO<sub>2</sub>, and air velocity were examined. The results showed that the radiation increased with the heat released per unit area and the soot yield affected all parameters, except the oxygen concentration and air velocity. The CO yield significantly affects CO concentration, and its influence on the other studied parameters is negligible. Moreover, based on the validation part, the results proved that FDS have limitations in tunnel fires, which impact the smoke layer calculation at the upstream zone of the fire. Therefore, the users or researchers should carefully be concerned about these weaknesses when using FDS to simulate tunnel fires. Further comprehensive research is crucial, as tunnel fires have severe impacts on various aspects of people’s lives.
Thermodynamics, Descriptive and experimental mechanics
Ocean waves deliver an immense amount of energy to coasts around the planet, powering high-velocity flows that interact with nearshore marine plants and animals. Although some of these interactions are beneficial, it is often advantageous for subtidal and intertidal ecological communities if wave-induced water velocities can be reduced by safely dissipating wave energy. This function is often fulfilled by seaweeds and marine plants, which thereby act as ecosystem engineers, modifying the environment to the benefit of the community. Recent advances in hydro-mechanical theory help to explain the mechanisms by which vegetation dissipates wave energy, highlighting the role that organisms’ tendency to bend in flow—their structural flexibility—plays in their ability to engineer wave-induced flows. Here, I review these theories and their application to salt marsh plants, seagrasses, mangroves, and seaweeds, focusing on the ways that marine vegetation serves a foundational role in community function.
Thermodynamics, Descriptive and experimental mechanics
Free vibration of functionally graded (FG) sandwich plates partially supported by a Pasternak elastic foundation is studied. The plates consist of three layers, namely a pure ceramic hardcore and two functionally graded skin layers. The effective material properties of the skin layers are considered to vary in the plate thickness by a power gradation law, and they are estimated by Mori-Tanaka scheme. The quasi-3D shear deformation theory, which takes the thickness stretching effect into account, is adopted to formulate a finite element formulation for computing vibration characteristics. The accuracy of the derived formulation is confirmed through a comparison study. The numerical result reveals that the foundation supporting area plays an important role on the vibration behavior of the plates, and the effect of the layer thickness ratio on the frequencies is governed by the supporting area. A parametric study is carried out to highlight the effects of material distribution, layer thickness ratio, foundation stiffness and area of the foundation support on the frequencies and mode shapes of the plates. The influence of the side-to-thickness ratio on the frequencies of the plates is also examined and discussed.
Mechanical engineering and machinery, Descriptive and experimental mechanics
We consider steady, laminar, compressible lubrication flows in a high-speed two-dimensional journal bearing governed by the appropriate Reynolds equation. The thermodynamic states correspond to pressurized gases and are in the single-phase regime. Simple explicit formulas for the load capacity, power loss, and attitude angle are derived by applying the virial (or small density) expansions of pressure and shear viscosity to results developed in previous studies. The present virial approximation was compared to the exact numerical solutions to the Reynolds equation. It was shown that the results based on our virial expansions are quite accurate at thermodynamic states corresponding to dense and supercritical gases. The first virial correction is seen to significantly improve predictions based on the ideal gas theory.
Thermodynamics, Descriptive and experimental mechanics
The receptance function has been studied and applied widely since it interrelates the harmonic excitation and the response of a structure in the frequency domain. This paper presents the derivation of the exact receptance function of continuous cracked beams and its application for crack detection. The receptance curvature is defined as the second derivative of the receptance. The influence of the crack on the receptance and receptance curvature is investigated. It is concluded that when there are cracks the receptance curvature has sharp changes at the crack positions. This can be applied for the crack detection purpose. In this paper, the numerical simulations are provided.
Mechanical engineering and machinery, Descriptive and experimental mechanics
In this study, the finite element method (FEM) is used to investigate the dynamic response of continuous girder bridge due to moving three-axle vehicle . Vertical reaction forces of axles that change with time make bending vibration of girder significantly increase. The braking in the first span is able to create response in other spans. In addition, the dynamic impact factors are investigated by both FEM and experiment for Hoa Xuan bridge. The results of this study provide an improved understanding of the bridge dynamic behavior and can be used as additional references for bridge codes by practicing engineers.
Mechanical engineering and machinery, Descriptive and experimental mechanics
Nguyen Minh Nhan, Dinh Cong Du, Vo Duy Trung
et al.
The paper presents a new indicator called normalized energy index (nei) in damage locating vector method (DLV) for detecting multiple damaged positions in beam and truss structures. In the DLV method, a set of load vectors, which is extracted from the change in flexibility matrix between an undamaged structure and a damaged one, is applied as static loads to the undamaged structure which are evaluated via the finite element modeling. Then, the nei values are computed for each element by using the displacements. In order to verify the accuracy and efficiency of a proposed indicator, a cantilevered beam and a 14-bay planar truss are considered.
Mechanical engineering and machinery, Descriptive and experimental mechanics
Stabilization control of networked robot system faces uncertain factors caused by the network. Our approach for this problem consists of two steps. First, the Lyapunov stability theory is employed to derive control laws that stabilize the non-networked robot system. Those control laws are then extended to the networked robot system by implementing a predictive filter between the sensor and controller. The filter compensates influences of the network to acquire accurate estimate of the system state and consequently ensures the convergence of the control laws. The optimality of the filter in term of minimizing the mean square error is theoretically proven. Many simulations and experiments have been conducted. The result confirmed the validity of the proposed approach.
Mechanical engineering and machinery, Descriptive and experimental mechanics
The averaging method is a useful tool for investigating both deterministic and stochastic quasilinear system. In the stochastic problems, however, the method has often been developed only for mechanical systems subjected to white noise excitations.In the paper this method is applied to high order stochastic differential equations. The nonlinear oscillations in high order deterministic differential equations were investigated in the fundamental work of Prof. Nguyen Van Dao. As an application of high order stochastic differential equations the nonlinear oscillation of single degree of freedom systems subjected to the excitation of a class of colored noises is outlined. The results obtained show that the higher order averaging method can also be successfully extended to the cases of colored noise excitation.
Mechanical engineering and machinery, Descriptive and experimental mechanics