Hasil untuk "Mechanics of engineering. Applied mechanics"

Xu Guo, Weisheng Zhang, Wenliang Zhong

Elisa Y. M. Ang, Aminu Yusuf, Chew Beng Soh et al.

To break the cycle of traditional air conditioning, rising carbon emissions, and increasing urban heat, a fundamental redesign of how humans achieve thermal comfort is essential. This review explores emerging technological trends in alternative cooling solutions from two perspectives. First, localized or personal cooling devices are gaining attention as a sustainable alternative to conventional space cooling. However, current technologies remain insufficient to fully replace traditional air conditioning. This review examines the limitations of commercial personal cooling devices and highlights advancements aiming to bridge this gap. Second, given the improbability of personal cooling entirely replacing space cooling in the near future, alternative large-scale cooling approaches must also be considered. This review discusses current and emerging cooling cycles, along with complementary technologies designed to enhance energy efficiency, including district cooling, radiative cooling, cooling paints, and the integration of green spaces.

Juan Granados, Rafael Gallego

A classical problem in computational mechanics is the quadrature of nearly singular and hypersingular integrals, such as those that arise in the boundary element method (BEM) when the collocation point is near the integration element. Due to the rapid variation of the integrand in these nearly singular and nearly hypersingular cases, standard procedures cannot compute the integrals accurately. To address this, a complete cubic polynomial transformation is developed in this work, significantly outperforming the Telles cubic polynomial, which is traditionally regarded as the reference cubic transformation for regularizing such integrals. In contrast with the Telles polynomial, which includes a free parameter determined through an ad hoc optimization procedure, the new polynomial proposed here is complete and contains no free parameters, as all of them result from a rational method. This enhancement is achieved by regularizing the 1/r2 singularity at the complex pole within isoparametric elements, which leads to a fully defined cubic polynomial transformation whose Jacobian mirrors the isolated singularity and vanishes at the complex pole, effectively neutralizing it. Numerical integration results over canonical straight and curved elements are presented, comparing standard numerical integration, the Telles cubic polynomial, and the new cubic polynomial for near singularities of the kind ln 1/r, 1/r, 1/r2, 1/r3, ultimately demonstrating the superior performance of the proposed method.

Keitaro Seki, Shota Kikuchi, Kunihiro Okamura et al.

<b>Purpose</b>: This study explores the impact of take-off distance on hurdling and interval running kinematics in sprint hurdles, recognizing its potential to improve performance. While beginners often use shorter take-off distances, a deeper understanding could inform coaching strategies aimed at improving hurdle technique. <b>Methods</b>: Ten male elite and highly trained hurdlers ran 60 m hurdles under original, short, and long take-off distances (OTD, STD, and LTD, respectively). The sagittal plane kinematics of the fourth hurdle and interval running were obtained using two high-speed cameras at a rate of 120 frames per second. Intraindividual step parameters were compared between conditions. <b>Results</b>: Running speed and step frequency were significantly lower in the STD than in the OTD and LTD. Significant interactions were found for step length with a significantly longer recovery step length in the STD than in the LTD. Furthermore, the hurdling distance was significantly longer in the LTD than in the OTD. In addition, the touchdown distance was significantly shorter in the LTD and longer in the STD compared to the OTD. Therefore, an STD is associated with a shorter acceleration distance between hurdles, whereas an LTD is associated with a longer acceleration distance. Therefore, the take-off distance influenced the distance for acceleration between hurdles, and the recovery step was related to the take-off distance. <b>Conclusions</b>: STD has negative effects on hurdling and interval running, even among elite and highly trained hurdlers.

Ali Alnujaie, Abderrahmane Berkani, Karim Negadi et al.

The increased use of renewable energy in modern power grids has led to a demand for innovative technologies that can efficiently harness intermittent energy sources. Multi-Point Absorber (MPA) systems have emerged as a promising solution for capturing wave and tidal energy sustainably. This study focuses on developing advanced control strategies for MPA systems to improve their performance and coordination in power generation and grid integration for both AC and DC networks. The research begins with a comprehensive review of MPA technologies, highlighting their challenges and opportunities. It then explores the development of control algorithms that dynamically adjust MPA parameters in real-time, optimizing energy extraction efficiency. The paper also addresses the crucial aspect of grid integration, investigating power electronics interfaces and synchronization techniques to enhance grid stability. Additionally, bidirectional power flow capabilities are discussed, enabling functions like frequency regulation and voltage control. The novelty of this work lies in the development of adaptive control algorithms for MPA systems, surpassing previous efforts by incorporating real-time data for parameter adjustments. The study demonstrates the effectiveness of these advanced control strategies through simulations and implementation, evaluating energy conversion efficiency, grid compatibility, and system reliability across various conditions compared to conventional methods. The results emphasize the significance of bidirectional power flow capabilities in achieving enhanced functionality, such as frequency regulation and voltage control. This paper provides valuable insights into optimizing MPA systems, showcasing their potential to revolutionize sustainable energy capture and integration into modern power grids.

Xiang DING, Yong LIU, Zhiming HAN et al.

To study the calculation method of rock pressure in jointed rock tunnels, based on the theory of tunnel pressure arch, the influence of rock hardness, integrity, and shear strength of structural planes on tunnel pressure arch was analyzed through discrete element numerical simulation. Multiple linear regression was applied to fit the multi factor rock pressure formula, and the applicability of the fitting formula was analyzed in combination with engineering support. The results indicate that the range of pressure arch in jointed rock tunnels is the deflection point from the arch crown to the direction of maximum principal stress; The height of tunnel pressure arch decreases with the increase of joint spacing and shear strength of structural planes, and the influence of rock mechanics parameters on the height of pressure arch is relatively small; Compared with the measured rock pressure on site, the calculation error is within 15%. The proposed formula for surrounding rock pressure has good applicability and provides a new approach for calculating the surrounding rock pressure of jointed rock.

Amira Elkodama, Amr Ismaiel, A. Abdellatif et al.

In recent years, the increasing environmental problems, especially the issue of global warming, have motivated demand for a cleaner, more sustainable, and economically viable energy source. In this context, wind energy plays a significant role due to the small negative impact it has on the environment, which makes it among the most widespread potential sustainable renewable fuel nowadays. However, wind turbine control systems are important factors in determining the efficiency and cost-effectiveness of a wind turbine (WT) system for wind applications. As wind turbines become more flexible and larger, it is difficult to develop a control algorithm that guarantees both efficiency and reliability as these are conflicting objectives. This paper reviews various control strategies for the three main control systems of WT, which are pitch, torque, and yaw control, in different operational regions considering multi-objective control techniques. The different control algorithms are generally categorized as classical, modern (soft computing) and artificial intelligence (AI) for each WT control system. Modern and soft computing techniques have been showing remarkable improvement in system performance with minimal cost and faster response. For pitch and yaw systems, soft computing control algorithms like fuzzy logic control (FLC), sliding mode control (SMC), and maximum power point tracking (MPPT) showed superior performance and enhanced the WT power performance by up to 5% for small-scale WTs and up to 2% for multi-megawatt WTs. For torque control systems, direct torque control (DTC) and MPPT AI-based techniques were suitable for reducing generator torque fluctuations and estimating the torque coefficient for different wind speed regions. Classical control techniques such as PI/PID resulted in poor dynamic response for large-scale WTs. However, to improve classical control techniques, AI algorithms could be used to tune the controller’s parameters to enhance its response, as a WT is a highly non-linear system. A graphical abstract is presented at the end of the paper showing the pros/cons of each control system category regarding each WT control system.

Surya Mani Tripathi, R. Muthukumar, S Anup

The dual thickness dished shells are made of conical frustum with a closed stiff top at the smaller diameter end of the frustum. The dished shells are categorized as dual-thickness because of higher thickness of the top circular region than that of the conical region. The higher thickness of top flat circular portion makes this more stiffer. The buckling behaviour of these shells is similar to that of arches, spherical caps and shallow conical frustums. The variation in curvature of these shells and different stiffnesses of the conical and top circular region makes them very interesting and innovative. Making the top circular region stiffer avoids the need for stiff support in the top circular region for practical applications under uniform pressure. In the present study, a nonlinear finite element analysis on metallic dished shells of dual-thickness is attempted by varying different geometrical parameters such as thickness of conical region, height and top flat region radius of the shell under uniform pressure. This parametric analysis is carried out to find out the effect of elastic and elastic-perfectly-plastic material properties, boundary conditions and imperfection sensitivity of Eigen-mode type axisymmetric imperfections on the critical buckling pressure. It is found that material plasticity has a significant effect on the critical buckling pressure of dual-thickness dished shells. The effect of the axisymmetric Eigen-mode imperfections on critical buckling pressure is significant for the elastic material model and very small with elastic-perfectly-plastic material models. The information collected from the current study can be used for the detailed design of dual thickness dished shells.

Andrei Zemskov, Le Hao, Dmitry Tarlakovskii

The article describes the problem of unsteady vibrations of a Bernoulli-Euler beam taking into account the relaxation of temperature and diffusion processes. The initial mathematical model includes a system of equations for unsteady bending vibrations of the beam with consideration of heat and mass transfer. This model is obtained from the general model of thermomechanodiffusion for continuum using the D'Alembert's variational principle. The solution of the problem is obtained in the integral form. The kernels of the integral representations are Green's functions. For finding of Green's functions the expansion into trigonometric Fourier series and Laplace transform in time are used. The calculation example is investigated for a freely supported three-component beam made of zinc, copper and aluminum alloy under the action of unsteady bending moments, including the interaction of mechanical, temperature and diffusion fields.

Y. Ju, Zhangyu Ren, Jiangtao Zheng et al.

Abstract Discontinuous structures such as pores, fractures, joints, and faults govern the physical and mechanical behavior of subsurface rock masses in underground engineering applications. The excavation of subsurface energy resources and construction activities extensively change the discontinuous structures and stress distribution in the surrounding rock masses. These hidden and dynamic changes are extremely difficult to detect and characterize using conventional methods and techniques, and this has greatly impeded the study of the intrinsic mechanisms governing the deformation and failure of rock masses. In the past few years, discontinuous rock structure imaging methods and three-dimensional printing (3DP) technology have been successfully applied to replicate rock mass samples for geological and geophysical research purposes. The combination of these methods has led to innovative ways to investigate the behavior of complex rock and guide underground engineering applications. This review focuses on the characterization and visualization of (1) the interior discontinuities of rock masses, and (2) the stress distribution and its continuous evolution in the discontinuous rock masses. Recent progress in experimental and computational methods in identifying and characterizing the discontinuous structures are presented. In particular, we discuss the development and process of integrating computed tomography (CT), 3DP technology, transparent rock models, and optical mechanics methods to quantitatively and visually present the interior structures and stress evolution inside rock masses.

Peixing Chen, Linhao Li, Lili Dong et al.

Enthesis injury repair remains a huge challenge because of the unique biomolecular composition, microstructure, and mechanics in the interfacial region. Surgical reconstruction often creates new bone-scaffold interfaces with mismatched properties, resulting in poor osseointegration. To mimic the natural interface tissue structures and properties, we fabricated a nanofibrous scaffold with gradient mineral coating based on 10 × simulated body fluid (SBF) and silk fibroin (SF). We then characterized the physicochemical properties of the scaffold and evaluated its biological functions both in vitro and in vivo. The results showed that different areas of SF nanofibrous scaffold had varying levels of mineralization with disparate mechanical properties and had different effects on bone marrow mesenchymal stem cell growth and differentiation. Furthermore, the gradient scaffolds exhibited an enhancement of integration in the tendon-to-bone interface with a higher ultimate load and more fibrocartilage-like tissue formation. These findings demonstrate that the silk-based nanofibrous scaffold with gradient mineral coating can regulate the formation of interfacial tissue and has the potential to be applied in interface tissue engineering.

Gerald C. Hsu

This paper discusses the author’s biomedical research work based on the GH-Method: math-physical medicine (MPM) approach over the past decade. This is significantly different from the traditional medical research using biochemical approach and simple statistical methods. He uses his own type 2 diabetes (T2D) metabolic conditions as a case study including several application examples as illustrations and explanations of the MPM methodology. The MPM methodology will be described, then followed by 10 application examples to show how he applied his knowledge and disciplines in mathematics, physics, engineering modeling, computer science tools, and psychology during his 10-years of biomedical research, especially in the domain of lifestyle, metabolism, chronic diseases, diabetes, cardiovascular diseases, and renal complications. The following list highlights the math-physical concepts, theories, principles, or equations used in the 10 application examples: 1. Topology, finite element method 2. Time-domain analysis, correlation and regression model, pattern recognition, segmentation analysis 3. Signal processing, trial and error method, regression analysis 4. Artificial intelligence (AI) auto-correction, quantum mechanics, safety margin of engineering design 5. Optical physics, AI, perturbation theory of quantum mechanics 6. Wave theory, Fourier transform, frequency-domain analysis 7. Structural engineering modeling, solid mechanics (both elastic and plastic), fluids dynamics, energy theory 8. Pattern recognition, behavior psychology 9. Spatial analysis, time-series analysis 10. Big data analytics, AI, software engineering Using MPM, a non-traditional medical research methodology, provides many quantitative proofs with a high degree of accuracy (higher precision) compared to other disease research results. Medicine is based on biology and chemistry, while biology, chemistry, and engineering are based on physics, and physics is based on mathematics. Logically, mathematics is the mother of all sciences. When we explore our application problems down to the foundation level, we can discover more facts and deeper truths. This is the logical essence of “math-physical medicine.” Using this MPM model, the accuracy of medical evaluations, along with the precision of predictive models can be greatly improved, with dramatic benefits to the patients.

Tariq Mahmood, Zain Ali khan, Shahid Hassan et al.

Jatropha is a tropical herb and can be matured in a diverse soil with low to high rainfall. It provides a chunk of the fuel supply in the transportation and energy sectors. Jatropha biodiesel implies a diesel equivalent and consist of methyl esters. It is produced through the transesterification process which is a chemical reaction of jatropha oil with an alcohol in the presence of a catalyst. In the present work, the physical and chemical attributes of jatropha biodiesel were determined. Various blended samples of jatropha biodiesel with mineral diesel were used to run diesel engine to see the variation of the brake power, brake specific fuel consumption and brake thermal efficiency of engine with percentage increase of jatropha biodiesel in the mixture. It was observed that these properties remain unchanged for 5% and 10% blend of jatropha biodiesel to mineral diesel and hence its use is quite feasible without any change in engine design. This provides an edge to the countries having surplus lands in low rain areas to generate 10% of their energy resources for power generation and transport through the cultivation and growth of jatropha plants.

Guangcan Zhou, Zi Heng Lim, Yi Qi et al.

Grating plays an essential role in various optical systems owing to its unique dispersion properties. In recent years, there is increasing demand to miniaturize optical systems for a wide range of field applications. Therefore, the integration of diffraction grating with MEMS technology provides an efficient way to build truly miniaturized optical systems. Till now, MEMS diffraction gratings have mainly been explored in two directions, namely MEMS scanning gratings and MEMS tunable gratings. MEMS scanning gratings are constructed with a variety of MEMS actuators to drive a grating platform to scan across the target, and they play a significant role in various scanning systems. Meanwhile, the dispersive properties of grating scanners make them attractive in wavelength sensing applications, including spectrometers and hyperspectral imaging systems. Tunable gratings typically employ MEMS actuators to dynamically change the diffraction properties, thus tuning its wavelength sensitivity for a specific application. Thus, this review will introduce these two types of MEMS gratings in detail and evaluate their efficiency and advantages in various fields.

A. Mahmoud, J. Olivier, J. Vaxelaire et al.

Jimin Liu, Hua Cheng, Chuanxin Rong et al.

The vertical stability analysis of the drilling shaft lining has long been a technical problem in the construction of underground space development projects. And the critical depth of vertical stability was a key parameter to judge its stability. To determine this parameter, a simple and practical computational method would be helpful. In this paper, a new vertical stability analysis model of shaft lining structure based on catastrophe theory was proposed. In accordance with the mechanical analysis, the catastrophic instability mechanics was analyzed and a new critical depth of drilling shaft lining was deduced. Further, the rationality and feasibility of the catastrophic calculation model was proved by the numerical simulation results in a case. And the sensitivity of the influencing parameters was also analyzed, which provided theoretic reference for optimization design and guiding security construction. The results implied that catastrophic calculation model, as an alternative method for shaft stability analysis, could be applied to theoretical analysis and guiding engineering practice in the study of drilling shaft lining’s vertical stability.

Machi Zawidzki

Extremely Modular Systems (EMSs) are comprised of as few types of modules as possible and allow creating structurally sound free-form structures that are not constrained by a regular tessellation of space. Truss-Z is the first EMS introduced, and its purpose is to create free-form pedestrian ramps and ramp networks in any given environment. This paper presents an overview of various multi-objective optimization methods applied to Truss-Z structures.

D. Srinivasacharya, P. Jagadeeshwar

This article analyses the influence of viscous dissipation and thermoporesis effects on the viscous fluid flow over a porous sheet stretching exponentially by applying convective boundary condition. The numerical solutions to the governing equations are evaluated using a local similarity and non-similarity approach along with a successive linearisation procedure and Chebyshev collocation method. The influence of the pertinent parameters on the physical quantities are displayed through graphs.

Momčilović Nikola, Motok Milorad, Maneski Taško

Development of stress concentration in the corner zone of rectangular plate opening is a well-known fact. It is usually literally taken that the largest stress concentration factor (SCF) occurs exactly in the corner (at angle coordinate of 45 degrees in case of square opening). More rigorous analyses, however, reveal that this is not perfectly true. Although maximum stress never really "leaves the corner", for some hot-spot analyses, more scrupulous investigation of this phenomenon has significance. In this paper, results of some analytical, numerical and experimental investigations of this topic, for plate in tension, are presented and compared.

A. Alvaro, I. T. Jensen, Nousha Kheradmand et al.