Hasil untuk "Mechanics of engineering. Applied mechanics"

Chen Thomas, Muñoz Ewald Patricia

We analyze geometric aspects of the gradient descent algorithm in Deep Learning (DL), and give a detailed discussion of the circumstance that, in underparametrized DL networks, zero loss minimization cannot generically be attained. As a consequence, we conclude that the distribution of training inputs must necessarily be non-generic in order to produce zero loss minimizers, both for the method constructed in [2, 3], or for gradient descent [1] (which assume clustering of training data).

Esteban Aedo-Muñoz, Pablo Merino Muñoz, Luciano Bernardes Leite et al.

<b>Background/Aims:</b> Asymmetry of the internal (IR) and external (ER) shoulder rotators can increase the risk of injuries in judokas. Discrete analyses are usually performed in time series data, but they can have biases by removing trends, so other approaches have been proposed to avoid these biases such as statistical parametric mapping (SPM) and principal component analysis (PCA). This study analyzed the asymmetry in the shoulder rotators in female judokas, comparing dominant (D) vs. non-dominant (ND) upper limbs. <b>Methods:</b> For this, 11 elite athletes (age: 20.1 ± 2.9 yrs.; experience: 4.0 ± 0.5 yrs.; body mass: 66.0 ± 14.6 kg; height: 1.6 ± 0.1 m; BMI: 24.8 ± 4.3 kg/m²), were evaluated in an isokinetic dynamometer (Cybex^® Humac/Norm Dynamometer CSMI, 502140, Stoughton, MA, USA). All participants performed the concentric (CON/CON) isokinetic evaluations of internal and external rotation of the shoulder in 60°/s and 180°/s angular velocities. <b>Results</b>: There was no significative asymmetry between IR vs. ER at 60°/s; similar results were observed at 180°/s when analyzed by PCA or SPM methods (<i>p</i> > 0.05 for all comparison). There was no difference between peak torque at 60°/s or 180°/s (<i>p</i> > 0.05 for all comparison). <b>Conclusions:</b> no asymmetry was observed in IR and ER in elite female athletes, regardless of the analysis method.

Jinle Luo, Haojie Lu, Ming Wen et al.

Powder Plasma Arc Additive Manufacturing (PPA-AM) technique has tremendous potential for the practical application in medium-entropy alloys (MEAs). In this study, we investigated the effect of heat treatment on microstructural evolution, mechanical properties, and the work hardening behavior in the PPA-AM processed (CoCrNi)90Al5Ti5 MEA. The results show that the As-built specimen is a single-phase FCC structure, displaying <001> strong FCC texture in the deposition direction. The stacking faults (SFs) and dislocations were observed in the alloy, which formed the stacking fault networks and the Lomer-Cottrell locks structure. The plasticity of the alloy increased significantly after the high-temperature heat treatment, which can be attributed to the modifications of the microstructure, such as the weakening of the texture strength and the reduction of the stresses. Low-temperature heat treatment decreases the density of dislocations in the alloy, but promotes the generation of the co-lattice phase. The evolution of the dislocation density, texture strength, and precipitates significantly influenced the strain hardening behavior and mechanical properties. The tensile results showed that the strength and plasticity of the samples were increased after two-step heat treatment. The yield strength, ultimate tensile strength, and elongation to failure were 733 MPa, 1080 MPa, and 22.3%, respectively, which were 16.2%, 20.3%, and 15.5% higher than the As-built samples. This work elucidates the underlying mechanisms of heat treatment on the microstructure and mechanical properties of the alloy.

Wei-Qi Sun, Yu-Han Wang, Zhu-Long Xu et al.

Manipulating the flow of water wave energy is crucial for ocean wave energy extraction or coastal protection, and the emergence of metamaterials paves a potential way for controlling water waves. In this work, by introducing a local disorder in a cavity-type metamaterial constructed by split-tube resonators, we show that water waves can be guided in an open channel with multiple energy flow paths formed merely by surrounded disconnected concurrent resonators that can serve as invisible walls without the requirement of a whole array system such as general periodic structures or waveguides. Specifically, we numerically and experimentally validate that a T-shaped metamaterial can achieve free guiding of water waves in a narrow band and a band-edge state along a distinct path. This open-space water waveguiding is found to be dominated by Fano-type interference and Fabry–Pérot resonance. Two distinct propagating modes, a low-frequency “trapping mode” and a high-frequency “following mode”, are identified. By simply rotating two configuration-dependent unit cells at the intersection of the metamaterial, we achieve a variety of water waveguiding paths tuning along rectilinear or bending (splitting or turning) directions, which rely on the two different propagating modes.

Gennadiy Baglyuk, Stepan Kyryliuk

В статті наведені результати дослідження еволюції  деформованого стану заготовок, енергосилових параметрів процесу і розподілу поруватості по об'єму поковки на всіх етапах гарячого штампування поруватих порошкових поковок у відкритому штампі. Моделювання процесу проводили методом скінченних елементів з використанням програмного комплексу DEFORM 2D/3D. В результаті моделювання встановлено, що на початковій стадії процесу відбувається головним чином ущільнення заготовки при мінімальній радіальній течії матеріалу. Помітна течія металу в зону облойної канавки починається лише при досягнення матеріалом поковки середньої відносносної густини, що перевищує 90 %. Відзначено суттєво відмінний характер розподілу по об’єму поковки осьових ez та радіальних er деформацій. Зона з підвищеними рівнями значень осьових деформацій формується в центральному шарі поковки, рівновіддаленому від верхньої та нижньої поверхонь порожнини штампу, а значення радіальних деформацій зменшуються по мірі віддаленості від зони, яка межує з вільною боковою поверхею заготовки в радіальному (доцентровому) напрямку. Мінімальні значення ez та er проявляються в верхній та нижній кутових застійних зонах поковки. Показано, що графік залежності зусилля деформування від переміщення пуансона відзначається наявністю щонайменше трьох характерних ділянок, обумовлених співвідношенням між процесам ущільнення та формозміни поковки на кожному етапі процесу.

Antonelli Dario, Aliev Khurshid

Integrated robotic systems combining manipulators with mobile robots provide outstanding improvement opportunities for semi-automatic assembly processes leveraged by Industry 4.0. Factory operations are released from the rigid layout constraints imposed by conventional fixed robots. Thus, they introduce new challenges in managing the recharge cycles as the energy consumption of mobile manipulators is not simply related to the travelled distance but to the overall tasks executed. Its estimation requires a systemic approach. In the proposed solution, an intelligent monitoring system is implemented on board. Data gathered online, and Key Performance Indicators (KPIs) calculated during the working tasks are exploited by Machine Learning (ML) to optimize energy recharging cycles. Although the development of an intelligent monitoring framework for a mobile manipulator was the original objective of the research, the monitoring system is exploited here for energy management only, leaving space for other future applications.

Feng Chen, Zhihu Liu, Yonghao Huo et al.

In the drilling process of horizontal and highly deviated well sections, cuttings are deposited on the lower side of annulus under the action of gravity during its transport, which affects the normal drilling operation. A variety of cuttings removal tools have emerged and achieved good results, but they are only effective when the drill string is rotating, while it is difficult to ensure the removal effect of cuttings in sliding drilling. In the drilling process of directional well and horizontal well, rotary drilling is sometimes difficult to meet the requirements of wellbore control, and sliding drilling is often used at this time. Therefore, there is an urgent need for a tool that can effectively remove cuttings in sliding drilling. In the present work, an efficient vortexing cuttings removal tool (VCRT) has been developed and the Computational Fluid Dynamics (CFD) simulation technology was used to study the cuttings removal mechanism of VCRT. The cuttings removal effect under the action of VCRT was compared with that of the conventional cuttings removal tool (CCRT) and the conventional drill pipe. The results show that VCRT has good cuttings removal effect in both sliding and rotary drilling conditions. The average cuttings volume fraction under the action of VCRT during sliding drilling is 59% lower than that of the conventional drill pipe, and 26% lower than that of CCRT. The average cuttings volume fraction under the action of VCRT during rotary drilling is 78% lower than that of the conventional drill pipe, the removal efficiency is similar to CCRT, but VCRT can send more cuttings into the annulus. The research reveals the mechanical mechanism of VCRT which provides a scientific basis for the cuttings removal mechanism of VCRT.

Yu Lu, Kaiguo Chen, Cheng Cheng et al.

Abstract This paper reports on the development of a magnetically driven high-velocity implosion experiment conducted on the CQ-3 facility, a compact pulsed power generator with a load current of 2.1 MA. The current generates a high Lorentz force between inner and outer liners made from 2024 aluminum. Equally positioned photonic Doppler velocimetry probes record the liner velocities. In experiment CQ3-Shot137, the inner liner imploded with a radial converging velocity of 6.57 km/s while the outer liner expanded at a much lower velocity. One-dimensional magneto-hydrodynamics simulation with proper material models provided curves of velocity versus time that agree well with the experimental measurements. Simulation then shows that the inner liner underwent a shock-less compression to approximately 19 GPa and reached an off-Hugoniot high-pressure state. According to the scaling law that the maximum loading pressure is proportional to the square of the load current amplitude, the results demonstrate that such a compact capacitor bank as CQ-3 has the potential to generate pressure as high as 100 GPa within the inner liner in such an implosion experiment. It is emphasized that the technique described in this paper can be easily replicated at low cost.

Chonlada Luangarpa, Hideo Koguchi

Singular stress fields in three-dimensional piezoelectric bonded joints are investigated at a vertex and along a free edge (the singular line) of an interface. Two perfectly bonded joints, which are different in the side surface shapes, are considered. The joints consist of multi-terms of singularity. Two-major terms of singularity are investigated in details. The orders of singularity at the vertex and along the singular line are calculated using three-dimensional finite element eigen-analysis. The intensities of singularity are calculated using the conservative integral. The intensities of singularity at several points located on the singular line are examined. The relationships between the intensities of singularity and the distances from the vertex are plotted to determine how the vertex singularity affects the singularity along the singular line. Finally, the relationships between singular stress fields at the vertex and along the singular line are considered.

Muhamad Shahirul Mat Jusoh, Mohd Yazid Yahya, Haris Ahmad Israr Ahmad

Presently, the application of natural fibres widely gains attention from academia and industries as an alternative material in the composite system. The introduction of the hybrid composite using natural and synthetic fibres is extensively investigated on the static mechanical properties. However, the investigation on the high strain-rates effect is less reported due to the difficulty of the experimental set-up as well as the limitation of dynamic testing apparatus. The split Hopkinson pressure bar (SHPB) was utilised in this present study to characterise the dynamic mechanical properties of the hybrid composite between E-glass with jute fibres at three different strain rates of 755, 1363, and 2214 s−1. Results showed that the dynamic compression stress and strain of the tested samples significantly influenced by the value of strain rates applied. The E-glass/jute sample exhibited the strain-rate dependent behaviour, whereby the higher dynamic mechanical properties were recorded when the higher strain rates were imposed. The difference between maximum dynamic stress was 12.1 and 23.9% when the strain rates were increased from 755 to 1363 s−1 and 1363 to 2214 s−1, respectively. In terms of compressive strain, the maximum compressive strain was recorded when the lower strain rates were imposed during testing.

Mohammad Mafi, Behrooz Ghasemi, Omid Mirzaee

Production of aluminum matrix composites is widespread because these material provide enhanced mechanical properties compared to aluminum. One the most important parameters of metal matrix composite production is uniform distribution of reinforcing nanoparticles in matrices using the stir-casting method. Second is ensuring high wettability, which is determined by evaluating the properties of materials on a nano-scale. In this study, aluminum composites were reinforced with titanium carbide nanoparticles coated with aluminum to increase wettability. Particles were prepared and added to a molten aluminum alloy. After stirring the particle mixture as a variable parameter, casting was conducted in a sand mold. To evaluate the mechanical properties of the composite, the Brinell test was used to determine hardness and the pin-on-disk test was used to measure wear rate and the friction coefficient. The results showed that the hardness of the composite increased from 84 BHN to 134 BHN as nanoparticles were added to the alloy. Additionally, as stirring time increased, weight loss decreased with respect to the base alloy, while the coefficient of friction increased.

D.S. Volkov, A.V. Shcherbina

An analysis of mathematical model of the Process of granulation of the raw materials. Justified mode granulator

Yuri Petrakov

Grinding of non-round surfaces, in particular polygonal surfaces of dies, is characterized by substantial non stationary. At different sections of the profile, the change in the main characteristic (Material Removal Rate – MRR) process reaches tens of times. To stabilize the grinding process, it is recommended to control the spindle speed of the workpiece CNC grinding machine. Created software that allows to design the control program on the basis of mathematical model of the system. The determination of MRR is realized automatically in the simulation of the grinding process which uses the algorithm developed for solving problems in geometric interaction of the workpiece and the wheel. In forming the control program is possible takes into account the limitations on the maximum circumferential force of cutting, and the maximum allowable acceleration of the machine spindle. Practice has shown that full stabilization is not obtained, even though the performance is increased more than 2 times, while ensuring the quality of the surface. The developed block diagram of the grinding process can serve as a basis for further improvement in the solution of dynamic problems.

Namazian Zafar, Hashemi Heidar, Namazian Farideh

In this study, the turbulent non-premixed methane-air flame is simulated to determine the effect of air velocity on the length of flame, temperature distribution and mole fraction of species. The computational fluid dynamics (CFD) technique is used to perform this simulation. To solve the turbulence flow, k-ε model is used. In contrast to the previous works, in this study, in each one of simulations the properties of materials are taken variable and then the results are compared. The results show that at a certain flow rate of fuel, by increasing the air velocity, similar to when the properties are constant, the width of the flame becomes thinner and the maximum temperature is higher; the penetration of oxygen into the fuel as well as fuel consumption is also increased. It is noteworthy that most of the pollutants produced are NOx, which are strongly temperature dependent. The amount of these pollutants rises when the temperature is increased. As a solution, decreasing the air velocity can decrease the amount of these pollutants. Finally, comparing the result of this study and the other work, which considers constant properties, shows that the variable properties assumption leads to obtaining more exact solution but the trends of both results are similar.

N. Shah

J. Bałchanowski

The paper presents elements of the topology, geometry and the kinematic analysis of a translational parallel mechanism with three degrees of freedom. In such mechanisms the selection of a proper structure and geometry ensures that the driven link maintains a fixed orientation relative to the base. The method of determination of the configuration of mechanisms using contour vector notation was elaborated in the paper. The equations for the analysis of the direct and inverse kinematics task are determined. An analytical procedure for determining the system’s singular positions is presented and illustrated with examples

Zheng Pengqiang

J. Zhang, H. Lu, Y. Sun et al.

Norlida Jamil, Ahmad Razlan Yusoff, Mohamad Hatifi Mansor

Milling is one of the most common manufacturing processes for automotive components, but its productivity is limited by the onset of regenerative chatter. This is a form of unstable self-excited vibration that occurs when the volume of material removed is too large for a particular spindle speed. This form of chatter is undesirable because it results in premature tool wear, poor surface finish on the machined component and the possibility of serious damage to the machine itself. The chatter stability of a milling process can be determined using well-established theory, provided that the frequency response of the flexible structure can be determined. In practice this usually involves the excitation of a stationery (non-rotating) milling tool with a modal hammer, and measurement of the response of the tool with a co-located accelerometer. However, this measurement is not necessarily accurate due to amplitude dependency factor consideration. There is anecdotal evidence that structural nonlinearity can have a significant effect on the chatter stability of some milling machines. This project develops non-contact electromagnetic actuators to measure the frequency response of milling tools to machine automotive parts. In addition it will describe the practical application of this approach, and discuss its amplitude dependency for current excitation during frequency response function measurement using magnetic force generation.

Krishna Rudraraju