Hasil untuk "Mechanics of engineering. Applied mechanics"

Yoshihiro Kangawa, Akira Kusaba, Toru Akiyama et al.

Chemical vapor deposition (CVD) is fundamental to semiconductor nanotechnology, yet many aspects of its processes and underlying physical and chemical phenomena remain unexplained. This is because CVD is a complex system involving the elementary growth processes of (1) gas-phase reactions, (2) surface processes, and (3) solid-phase diffusion. This review introduces the following research topics, utilizing theoretical approaches that integrate simulations of each fundamental process: the influence of CVD conditions on the residual impurity concentration, surface morphology, and heterointerface flatness. Through integrated simulation, physical and chemical insights that cannot be obtained from simulations of individual elementary growth processes are revealed.

S. Noor Arshika, P.G. Siddheshwar, S. Tarannum et al.

The effect of variable gravity fields that vary through the height of a viscous fluid layer in a Rayleigh-Bénard convection (RBC) is investigated in the paper. A minimal Fourier-series expansion leads to a boundary eigenvalue problem with variable coefficients. Using the Maclaurin-series approach, the recurrence relations for six cases of gravity fields are generated. The eigenvalue of the problem is located using the Newton-Raphson method with an error tolerance of 10-8. The main novelty of the present work is studying the influence of variable gravity fields on the nonlinear dynamics of the problem. A weakly nonlinear stability analysis is performed by first identifying the convective mode and by further arriving at the scaled Lorenz model. Comparison is made with the results of three boundary conditions viz., free-free, rigid-free and rigid-rigid. In the absence of the gravity variation parameter, the results of RBC with constant gravity are recovered. The influence of varying gravity fields on the dynamics is studied using indicators: rH-plots, bifurcation-diagram, periodicity-diagram and trapping-region of the trajectories. It is found that the effect of increasing the strength of gravity is to delay the appearance of chaos for all cases of gravity fields except for the positively linear case. Furthermore, by varying the gravity fields, one can witness shifts in the chaotic and periodic regimes. Moreover, the first largest periodic burst almost overlaps for cubic and biquadratic cases of gravity fields. The shrinking in the size of the ellipsoid with change in the gravity fields is highlighted in the paper.

Julian Lißner, Felix Fritzen

Abstract Two approaches are presented to improve the capabilities of machine learning models in multiscale modeling for microstructure homogenization (graphical abstract in Fig. 1). The first approach features a Bayesian data mining scheme with a human in the loop, halving the prediction error compared to [1] using four novel and efficient to evaluate feature descriptors. The second purely machine learning-driven approach utilizes convolutional neural networks, where we introduce a novel module (the deep inception module) designed to capture characteristics of different length scales within the image. The new module features a new normalization block, which aids in calibrating the differently obtained feature characteristics. Further improvements, universally applicable to artificial neural networks, are found with a novel hyperparameter insensitive learning rate schedule, which adapts to the training progress of the model. A further improvement is given by a pre-trained feature bypass which utilizes global low-level features to serve as baseline prediction such that the model is able to dedicate its attention to high-level features. The proposed schemes have been applied to different literature models, yielding significant improvements in any of the investigated convolutional neural networks. The improvements found by the two overarching contributions, i.e., derived through feature development with a human in the loop, and via convolutional neural networks, are critically assessed in a thermal and mechanical setting. It is further expanded to variable material parameters while allowing for variable microstructural elements, yielding drastically reduced prediction errors across the board.

Jordi Arboix-Alió, Guillem Trabal, Bernat Buscà et al.

This study aimed to investigate the influence of stick grasping on the performance of elite youth rink hockey players in 10 m linear sprints and 180° change of direction (COD) tasks. Forty-nine rink hockey players (age = 18.40 ± 2.12 year; body mass = 73.52 ± 6.02 kg; height = 1.82 ± 0.07 m; BMI = 23.61 ± 1.69; sports experience = 6.42 ± 1.41 years; 4.89 ± 0.68 years’ post-peak height velocity) participated in this cross-sectional study. Measurements included 10 m sprint time and COD 180° performance with and without stick grasping. Results revealed non-significant differences when carrying a stick in the 10 m linear sprint (1.90 s ± 0.08 with stick vs. 1.89 s ± 0.08 without stick; <i>p</i> = 0.71; <i>d</i> = 0.05), neither did COD 180° for the left limb (2.75s ± 0.11 with stick vs. 2.76 s ± 0.11 without stick; <i>p</i> = 0.91; <i>d</i> = 0.02). However, for the right limb, significantly better performance in COD 180° was found when players held the stick (2.72 s ± 0.11 with stick vs. 2.75 s ± 0.09 without stick; <i>p</i> = 0.03; <i>d</i> = 0.32). These findings imply that the distinctive biomechanics and requirements of rink hockey, especially the lateral movements inherent in skating, might alleviate the negative impacts associated with implement grasping observed in other sports. This study highlights that stick grasping did not hinder COD ability and may even have a facilitating effect on certain movements, emphasizing the importance of considering sport-specific biomechanics in rink hockey performance analysis.

Daniel Antoniak, Piotr Konderla

The paper presents a general numerical model for the analysis of prestressed concrete with the application to beam, thin shell and volume type of prestressed structures. Discrete, embedded approach is used to model curved, bonded or unbonded tendons. Also a partial bond may be introduced by the friction between the tendon and the surrounding body. In the finite element model, two types of elements are obtained. One is a typical finite element for the kind of structure modeled, and the other is an embedded, three noded, subparametric tendon element. Equations of the finite element method have been obtained from the incremental form of the principle of virtual work providing geometrical linearity and possibility of nonlinear physical relations. Numerical examples illustrate application to modeling of beam, thin shell and volume type of prestressed structures as well as the impact of the friction on the axial force distribution in prestressing tendon.

Han-Sheng Chuang, Han-Sheng Chuang, Yu-Jui Fan et al.

Artur Krowiak

In this paper, a meshless pseudospectral method is applied to solve problems possessing weak discontinuities on interfaces. To discretize a differential problem, a global interpolation by radial basis functions is used with the collocation procedure. This leads to obtaining the differentiation matrix for the global approximation of the differential operator from the analyzed equation. Using this matrix, the discretization of the problem is straightforward. To deal with the differential equations with discontinuous coefficients on the interface, the meshless pseudospectral formulation is used with the so-called subdomain approach, where proper continuity conditions are used to obtain accurate results. In the present paper, the differentiation matrix for this method is derived and the choice of a proper value of the shape parameter for radial functions in the context of the subdomain approach is studied. The numerical tests show the effectiveness of the method when using regular or unstructured node distribution. They confirm that the approach preserves well-known advantages of the radial basis function collocation method, i.e., rapid convergence, simplicity of the implementation and extends its usage for problems with weak discontinuity.

Maciej Dutkiewicz, Taras Dalyak, Ivan Shatskyi et al.

This paper studied the distribution of stresses near damage in the form of axial surface cracks in a pipeline reinforced with a spiral-wound composite coating. The authors applied the homogenization method to determine the effective elastic characteristics of a structurally anisotropic layered package. By means of the classical momentless theory of shells, it was established that the stress state of the coated intact pipe under the pressure of the pumped product depends on the parameters of the geometry of the capacity strip, as well as on the component composition of the heterogeneous coating. The finite element method was applied to solve the problem of plane deformation of a piecewise homogeneous ring with an internal crack perpendicular to the interface. This problem assumes the linearity of the materials and the ideal mechanical contact with the layers. The effect of the composite coating and the size of the damage on the magnitudes of the energy flow into the crack tip, and on the stress intensity factor, was studied in detail. Various variants of the coating were considered, namely, winding of the coating on an unloaded pipe and reinforcement of the pipe under repair pressure.

Olha Kauss, Susanne Obert, Iurii Bogomol et al.

Mo-Si-B alloys are one of the most promising candidates to substitute Ni based superalloys in gas turbines. The optimization of their composition can be achieved more effectively using multi-scale modeling of materials behavior and structural analysis of components for understanding, predicting, and screening properties of new alloys. Nevertheless, this approach is dependent on data on the properties of the single phases in these alloys. The focus of this investigation is Mo₃Si, one of the phases in typical Mo-Si-B alloys. The effect of 100 h annealing at 1600 °C on phase stability and microhardness of its three near-stoichiometric compositions—Mo-23Si, Mo-24Si and Mo-25Si (at %)—is reported. While Mo-23Si specimen consist only of Mo₃Si before and after annealing, Mo-24Si and Mo-25Si comprise Mo₅Si₃ and Mo₃Si before annealing. The latter is then increased by the annealing. No significant difference in microhardness was detected between the different compositions as well as after annealing. The creep properties of Mo₃Si are described at 1093 °C and 1300 °C at varying stress levels as well as at 300 MPa and temperatures between 1050 °C and 1350 °C. Three constitutive models were used for regression of experimental results—(i) power law with a constant creep exponent, (ii) stress range dependent law, and (iii) power law with a temperature-dependent creep exponent. It is confirmed that Mo₃Si has a higher creep resistance than Mo_ss and multi-phase Mo-Si-B alloys, but a lower creep strength as compared to Mo₅SiB₂.

Tarek S. Amer, Roman Starosta, Abdelkarim S. Elameer et al.

This work looks at the nonlinear dynamical motion of an unstretched two degrees of freedom double pendulum in which its pivot point follows an elliptic route with steady angular velocity. These pendulums have different lengths and are attached with different masses. Lagrange’s equations are employed to derive the governing kinematic system of motion. The multiple scales technique is utilized to find the desired approximate solutions up to the third order of approximation. Resonance cases have been classified, and modulation equations are formulated. Solvability requirements for the steady-state solutions are specified. The obtained solutions and resonance curves are represented graphically. The nonlinear stability approach is used to check the impact of the various parameters on the dynamical motion. The comparison between the attained analytic solutions and the numerical ones reveals a high degree of consistency between them and reflects an excellent accuracy of the used approach. The importance of the mentioned model points to its applications in a wide range of fields such as ships motion, swaying buildings, transportation devices and rotor dynamics.

Xiaolei Yang, Daniel Foti, Christopher Kelley et al.

Subscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of a subscale turbine, which is located closer to the ground and faces different incoming turbulence, is also similar to that of a full-scale wind turbine. In this work we investigate the wakes from a full-scale wind turbine of rotor diameter 80 m and a subscale wind turbine of rotor diameter of 27 m using large-eddy simulation with the turbine blades and nacelle modeled using actuator surface models. The blade aerodynamics of the two turbines are the same. In the simulations, the two turbines also face the same turbulent boundary inflows. The computed results show differences between the two turbines for both velocity deficits and turbine-added turbulence kinetic energy. Such differences are further analyzed by examining the mean kinetic energy equation.

Nicola Simon, Maximilian Krause, Paul Heinemann et al.

Multi-phase materials often times consist of constituents with high contrasts in phase-specific mechanical properties. Here, even after homogeneous plastic deformation phase-specific residual stresses develop that may affect the components behaviour in service. For numerical simulation of phase-specific residual stresses, knowledge of the particular phase-specific strain hardening behaviour is essential. In this study, the strain hardening of ferrite and austenite in cold rolled duplex stainless steel of type X2CrNiN23-4 is investigated. By means of X-ray diffraction, the phase-specific load partitioning and residual stress evolution are analysed for uniaxial load application in three directions within the sheets plane, taking into account the sheet metals phase specific anisotropy. In order to assess the necessity for experimental determination of anisotropic phase specific behaviour, the strain hardening parameters, derived from only one loading direction, are implemented in a mean-field approach for prediction of phase-specific stresses. A simplified simulation approach is applied that only considers macroscopic plastic anisotropy and results are compared to experimental findings. For all investigated loading directions, it was observed that austenite is the high-strength phase. This load partitioning behaviour was confirmed by the evolution of phase-specific residual stresses as a result of uniaxial elasto-plastic loading. With the simplified and fast numerical approach, satisfying results for prediction of anisotropic phase-specific (residual) stresses are obtained.

Bassam A. Alwan, Muhsin J. Jweeg, Zaid S. Hammoudi

To initate a datebase on material properties on typical laminations used in belwo knee prosthetic socket (Trans-Tibial). The authors subjected samples of common prosthetic socket laminations to tensile, bending, and fatigue tests. Two varieties of lay up material (fibers) were each laminated separately with common resins (acrylic), resulting in four combinations of fiber/acrylic resin. Fibers made of carbon fiber and perlon fiber were used at different volume fractions. The result showed that socket prosthesis made of carbon fiber and perlon fiber (12 layers) has highest tensile and flexural strenght when compared to other laminations. Material test results indicate that the composite material (12 Layers) have better tensile and fatigue properties than composite material (8 layers). The ultimate tensile strength, and the modulus of elasticity composite material (12 layers) are higher than those of the composite material (8 layers) by 0.124% and 0.072% respectively, and by 0.1% and 0.185 for composite material (8 layers ) with volume fraction of matrix equal 0.72). Vacuum technique is good process and this prevented cavites or defects in specimens

Van Tinh Nguyen, Kiem Anh Nguyen, Van Linh Nguyen

Nowadays, self-climbing formworks are commonly used in the construction of concrete buildings with a great height, such as high-rise buildings, silos, and bridge piers. A regular formwork can be improved to have more functions, e.g., the formwork itself can climb to the desired construction site. Climbing characteristics of the formwork as well as opening and closing characteristics of the formwork shell are essential criteria for evaluating the performance of a self-climbing formwork. The effective ones were mentioned in different studies, where most of them were published in patents of countries, e.g., the United States and China. Dissimilar from these studies, this paper presents several improvements for some certain groups to enhance the features of a hydraulic self-climbing formwork. Based on the analysis of the composition and the working principle of the actual climbing formwork types, a new opening and closing method of the formwork shells and a new rail clamping device are suggested. They are applied to design a self-climbing formwork with the shell’s working size of 4 m x 3 m. Their load capacity, as well as the flatness of the concrete surface after casting, are assessed. The proposed solutions can result in various advantages, e.g., the shorter initial alignment time, the increase of the quality concrete surface, and the maximal automation for construction operations.

Fan Guo, Yanqiu Jiang, Zhen Xu et al.

Improved compressive elasticity was lately demonstrated for carbon aerogels but the problem of reversible stretchability remained a challenge. Here the authors use a hierarchical structure design and synergistic effects between carbon nanotubes and graphene to achieve high stretchability in carbon aerogels.

Nae-Hyun KIM

Heat transfer and friction characteristics of the radial slit-finned heat exchangers under wet condition are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on j and f factor is negligible. Louver fin samples yield higher f factors than slit fin samples. For one row configuration, the average f factor ratio between slit fin sample and plain fin sample is 1.61, which decreases to 1.37 for two row configuration, and to 1.36 for three row configuration. As for the j factor, the ratios are approximately the same. The j factor increases as the number of tube row decreases. The f factor, however, is independent of the number of tube row. The j/f ratios of the slit fin are higher than those of louver fin. A new correlation is developed based on the present data.

نضال عدنان جاسم

تعد مرحلة التصاميم من المراحل الاساسية في دورة حياة المشروع الهندسي حتى ان ما يتحقق من متطلبات الجودة في هذه المرحلة يكون محدداً لجودة ما بعده من مراحل الانشاء والصيانة. يهدف البحث الى دراسة الجودة وتأكيدها في مرحلة التصميم والتخطيط له وكيف يمكن توظيف اسس تقنية (COPRAS) في تقييم ادارة جودة التصاميم لمجموعة من المشاريع الانشائية من خلال تحديد المعايير المستخدمة لتحديد المشروع الامثل من ناحية ادارة جودة التصاميم وكذلك تحديد مجموعة من لمشاريع الانشائية لكي تختار الامثل منها. ولغرض  تحقيق هدف البحث فقد تم جمع البيانات الخاصة به من الادبيات التي تناولت موضوعي ادارة جودة التصاميم الهندسية وطريقة التقييم النسبية المتعددة المعايير المعقدة واخيراً من المقابلات الشخصية من ذوي الاختصاص من المصممين والاستشاريين لهذه المشاريع . اظهرت نتائج تحليل البيانات لافراد العينة ومن ثم طريقة ترتيب النظام الوسطية (ROC) والمميزة في تطبيقها ان معايير السيطرة على مخرجات التصميم، الهيكل التنظيمي وفرق اعداد التصاميم، ضبط مدخلات التصميم والتخطيط للتصميم،  هي اكثر المعايير اهمية لاجراء المقارنات الثنائية بين المشاريع وان محور السيطرة على مخرجات التصميم وفرق اعداد التصاميم والهيكل التنظيمي هي اكثر اهمية من بقية المعايير في المشاريع. واخيراً ومن خلال حساب الاهمية النسبية للمشاريع ودرجة المنفعة لها نجد ان مشروع بناية العيادة الاستشارية في بعقوبة قد حصل على النصيب الاكبر من المنفعة والاهمية بالمقارنة مع المشاريع الاخرى. وقد تم التوصل الى مجموعة من الاستنتاجات والتوصيات لمختلف جوانب الموضوع من بينها الاسراع في تطبيق تقنيات اتخاذ القرار المتعدد المعايير في تقييم المشاريع اضافة الى الاسراع في تطبيق النظم المقترحة من قبل الباحثة لادارة جودة التصاميم الهندسية لمساعدة المهندسين على التطبيق الامثل لهذه الادارة.

Pil Hyong LEE, Sang Soon HWANG

A lean premixed surface flame has many advantages including low CO(Carbon Monoxide) and NOx(Nitrogen Oxide) emission and applicability of a small combustion volume leading to compact design. These advantages make it applicable to burner for condensing boilers with high thermal efficiency. Moreover recent severe regulation of global warming gas favored a lean premixed surface flame in development of a condensing boiler burner. This study focused on emission characteristics of lean premixed flame and the effect of flow distribution on flame stability of a surface flame in a cylindrical porous metal plate burner. For conceptual design of surface flame burner, the numerical calculation of a flow pattern inside the burner was performed and the calculated data were used for design of the burner system including the baffle plate and flame holder. The results show that the surface and stable premixed flame can be generated by implementing the proper baffle plate and flame holder. The surface cylindrical flame mode is changed into green flame, yellow radiation flame, blue flame and blow off with decreasing equivalence ratio. The blue flame has a wide stability region in the stability curve and showed the lowest CO and NOx emission at low equivalence ratio. And CO decreased as the mixture ratio became leaner but NOx showed almost the same emission level. For stability of a surface cylindrical flame, it was found to be very important to select the proper distribution of holes in a baffle plate and install the flame holder to prevent blow off at the rim of the cylindrical burner. NOx was measured below 6 ppm (0% oxygen base) from equivalence ratios 0.706 to 0.769 through the proper design of baffle plate and flame holder. CO which is a very important emission index in residential gas boiler was observed below 49.1ppm under the same equivalence ratio range.

Groenenboom P. H. L., Lobovský L.

Within this study, the implementation of the smoothed particle hydrodynamics (SPH) method solving the complex problem of interaction between a quasi-incompressible fluid involving a free surface and an elastic structure is outlined. A brief description of the SPH model for both the quasi-incompressible fluid and the isotropic elastic solid is presented. The interaction between the fluid and the elastic structure is realised through the contact algorithm. The results of numerical computations are confronted with the experimental as well as computational data published in the literature.

L. Chai, H. Li