Hasil untuk "Mechanics of engineering. Applied mechanics"

M. Geers, V. Kouznetsova, W. Brekelmans

Jun Wu, O. Sigmund, J. Groen

Multi-scale structures, as found in nature (e.g., bone and bamboo), hold the promise of achieving superior performance while being intrinsically lightweight, robust, and multi-functional. Recent years have seen a rapid development in topology optimization approaches for designing multi-scale structures, but the field actually dates back to the seminal paper by Bendsøe and Kikuchi from 1988 (Computer Methods in Applied Mechanics and Engineering 71(2): pp. 197–224). In this review, we intend to categorize existing approaches, explain the principles of each category, analyze their strengths and applicabilities, and discuss open research questions. The review and associated analyses will hopefully form a basis for future research and development in this exciting field.

R. Glowinski, J. Oden

Daichi Yamashita, Frederick James Henderson, Yuko Ishida

Background/Objectives: This study evaluated the reliability and validity of three methods to measure jump height during countermovement jumps performed with (CMJ_AS) and without (CMJ_NAS) arm swing: (1) an impulse–momentum method with force platforms (FP_imp), (2) a flight time method with force platforms (FP_time), and (3) an inertial measurement unit (PUSH Band 2.0; PUSH2). Methods: Eighteen physically active men performed CMJ_AS and CMJ_NAS on force platforms while wearing PUSH2 over two days. Besides jump height, we computed intraclass correlation coefficients (ICC) and the absolute and relative increases in jump height due to arm swing, compared to CMJ_NAS. Results: The reliability of intra-session, inter-session, and concurrent measures were good to excellent (intra-session ICC_2,1 = 0.957–0.979, inter-session ICC_2,1 = 0.806–0.990, concurrent ICC_3,1 = 0.940–0.973) for CMJ_AS and CMJ_NAS heights, in all three methods. The three methods showed high to very high reliability for both the absolute and relative indices of arm swing contribution (ICC_2,1 = 0.649–0.812). FP_time significantly overestimated CMJ_NAS height relative to FP_imp (<i>p</i> < 0.01). The absolute index of arm swing contribution was similar in FP_imp and FP_time (<i>p</i> = 0.38) but higher in PUSH2 (<i>p</i> < 0.01), indicating that arm swing amplified overestimation. Conclusions: All three methods demonstrated high reliability for jump height measurements, but FP_time and PUSH2 misestimated jump height depending on jump modalities. Caution is advised when assessing the absolute and relative contribution of arm swing, because errors in CMJ_NAS and CMJ_AS height measurements can affect these values and their interpretation.

Eleftherios Nikolaou, Spyridon Kilimtzidis, Efthymios Giannaros et al.

The increasing power density of Unmanned Aerial Vehicles (UAVs) has intensified the need for the efficient thermal management of their propulsion and electronic subsystems. This paper presents a systematic multi-fidelity methodology for the design and validation of a ducted forced convection cooling system for a Class-I mini-UAV. The approach combines analytical sizing and computational fluid dynamic (CFD) analyses. In the preliminary design phase, a surrogate-based optimization (SBO) framework was implemented to determine the optimal geometric characteristics of a NACA-type inlet duct, enabling the efficient exploration of the design space using a limited number of CFD simulations. SBO employed a Kriging surrogate model trained on a Design of Experiments (DoE) dataset to capture nonlinear interactions between duct geometry and performance metrics such as pressure recovery, total-pressure loss, and outlet flow uniformity. The optimized configuration was then refined and validated through detailed external and internal CFD studies under representative flight conditions. The optimized NACA duct configuration achieved an average increase of 10.5% in volume flow rate (VFR) and a 9.5% reduction in velocity distortion while maintaining a drag penalty below 1% compared to the benchmark Frick’s NACA duct. The presented methodology demonstrates that the early integration of surrogate-based optimization in UAV inlet design can significantly improve aerodynamic and thermal performance.

Jan Klusák, Zdeněk Knésl

This paper presents a simple method for evaluating the threshold value for fatigue cracks that emanate from a V-notch. The proposed method is based on the similarities between the elastic-stress fields around the tip of a crack and the tip of a V-notch. Threshold values for fatigue cracks that emanate from a V-notch are expressed by means of the threshold value for the propagation of a high-cycle-fatigue crack and the opening angle of the V-notch. The corresponding calculations were performed by the finite-element method.

Janusz Skorek, Jan Składzień

The paper presents selected results of the analysis of thermal and mass flow transient processes within the containments of the WWER-440 and the WWER-1000 nuclear reactors during Loss-of-Coolant Accidents based on the mathematical model and computer code for LOCA simulation. General assumptions of the mathematical model (with lumped parameters) are briefly presented. Changes of thermal variables (temperature, pressure etc.) are governed by the fundamental thermodynamic equations. All these equations have the nonlinear, integral form. The whole area of the containment is divided into several control volumes. Control volumes are joined in a given mode (orifices, valves, siphon closures etc.) . The liquid phase (water) and the gaseous phase (air, steam and hydrogen) can appear in a control volume. Thermal equilibrium within an individual phase and a non-equilibrium state between phases is assumed. Heat accumulation in the walls and internal structures of the containment is taken into account and heat transfer between liquid and gaseous phases is also considered. The working mathematical model can be used for the analysis of different scenarios of LOCA within the containment of the PWR and BWR reactors. Later on the sample results of calculations of changes of pressure and temperature within the containment of the WWER-440 nuclear reactor and within the full containment of the WWER-1000 reactor are presented.

Shizhe Feng, Ke Cao, Yue Gao et al.

Graphene is known to display a number of attractive mechanical properties. Here, anisotropy in the fracture toughness of graphene is investigated by in-situ mechanical testing, revealing weak anisotropy between armchair and zigzag directions.

Oluvole D. Makinde

Thermal ignition for a reactive viscous flow between two symmetrically heated walls is investigated. The second order nonlinear boundary value problem governing the problem is obtained and solved analytically using a special type of Hermite-Padé approximation technique. We obtained very accurately the critical conditions for thermal ignition together with the two solution branches. It has been observed that an increase in viscous heating due to viscous dissipation can cause a rapid decrease in the magnitude of thermal ignition critical conditions.

S. Kanth, G. Harmain, Azher Jameel

Abstract The extended finite element (XFEM) has been applied to investigate fatigue crack growth in engineering components containing different types of material irregularities. The standard approximations of finite element method are enriched with additional functions by employing the partition of unity approach. In order to keep track of discontinuities in the domain, level set method is employed. Fatigue crack growth in presence of different material irregularities, such as elliptical, rectangular, hexagonal and octagonal discontinuities, has been the main focus of the study. The effect of geometry, position and material properties of these discontinuities on fatigue behavior of the cracked specimen has been addressed. The fatigue life of the cracked component has been estimated by the generalized Paris law. The mixed mode stress intensity factors have been evaluated by the domain-based interaction integral approach. Several numerical problems are solved by XFEM to study the fatigue crack growth behavior of cracked specimens containing different types of material irregularities.

J. A. Sanz-Herrera, J. Mora‐Macías, J. Ayensa-Jiménez et al.

Goudarzi Masoumeh, Bemanian Mohammadreza, Leylian Mohammadreza

The golden number has been one of the most important measures of beauty from ancient Greece till now. Although the reason still unclear, it is certain that the golden ratio has a direct correlation with beauty. This nice feeling can come from listening to a musical piece or watching a visual art, which is based on this wondrous number. Although the golden number is more suitable from beauty or harmony’s perspective, for some researches it is a requirement to develop Architectural designs. Therefore, in this article a masterpiece (Shah-mosque Isfahan) was investigated to find its golden relations. This mosque was chosen because of the precise and harmonious proportions. In this research: plan, sections, facade and decorations of ceiling tiles in main dome, were analyzed by Phi-matrix software in which, existence of the golden ratio has been proven undoubtedly.

Eko Julianto, Sunaryo Sunaryo, Elkana Bilak Lopo

The purpose of this study was to determine the shape change characteristics of float sheet glass using heat treatment experiments on its surface. This involved the use of a float glass type with a thickness of 5 mm, a width of 840 mm, and length of 1350 mm as the test specimen and the heat transfer experiments and treatment were conducted through conduction with the heat distribution recorded to be between 34 °C and 600 °C at every 5 minutes within 60 minutes in a heating furnace. The analysis focused on the characteristics of the glass surface exposed to fire with emphasis placed on the temperature during the deflection changes in the entire glass surface, the dimensional changes at the edges of the glass which follow the glass printing pattern, and the changes in temperature on the upper and lower surfaces of the curved glass mold. The results showed the existence of a very clear change in each temperature or conduction heat when the shape of the glass is changed to curve with the ideal shape observed to have changed at a temperature of 482.50 °C. Moreover, dimensional changes were 1.0427 m2 and the variations in the temperature were 107.55 °C and the continuous increase in the heat was to have led to a faster change in the glass shape by 11.2°. This, therefore, means a higher temperature or room temperature affects the firing rate of glass bending and also increases the rate of heat absorption.