Vietnam Journal of Mechanics

Trong nghiên cứu này, phân tích dao động tự do của các vi mô Timoshenko làm từ Vật liệu Phân lớp Chức năng (FGM) trên nền móng đàn hồi Winkler-Pasternak được thực hiện dựa trên Lý thuyết Căng thẳng Kết hợp Đã Điều chỉnh (MCST). Đặc tính vật liệu của vi mô thay đổi xuyên suốt độ dày theo phân phối công suất và được ước lượng thông qua các kỹ thuật đồng hóa Mori–Tanaka, Hashin-Shtrikman và Voigt. Mô hình vi mô Timoshenko xem xét tham số độ dài được áp dụng. Các phương trình vi phân dao động tự do của các vi mô FGM được thiết lập dựa trên Phương pháp Phần tử Hữu hạn (FEM) và các hàm hình dạng của Kosmatka. Ảnh hưởng của hiệu ứng kích thước, nền móng, vật liệu và các tham số hình học đến tần số dao động sau đó được phân tích. Kết quả cho thấy rằng nghiên cứu này có thể áp dụng cho các FGM khác cũng như các cấu trúc vi mô phức tạp hơn.

This paper addresses the problem of repairing multiple cracked beams subjected to static load using piezoelectric patches. First, the problem is formulated and solved analytically for the case of two cracks that results in ratio of restoring moments produced by employed piezoelectric patches. Since the ratio is dependent only on crack positions but not their depth, the result obtained for case of two cracks has been extended for the case of multiple cracks. This proposition is then validated by finite element simulation where repairing piezoelectric patches are replaced by mechanical moment load equivalent to the restoring bending moments produced by the piezoelectric patches. The excellent agreement between analytical solution and numerical simulation results in case of single and double cracks allows making a conclusion that a piezoelectric patch could productively repair a cracked beam by producing a restoring moment due to its piezoelectricity. Thus, the problem of repairing multiple cracked beam using piezoelectric patches is solved.

This report presents an analytical approach to the natural frequency analysis of a porous beam consisting of a host porous layer reinforced with graphene platelets (GPLs), namely GPL-reinforced porous core, and two piezoelectric outer layers. In the modelling, symmetric distributions of both porosity and GPLs in the core are supposed. The effective mechanical properties of the GPL-reinforced porous core are estimated by Halpin–Tsai model and the rule of mixture. The electric potential in each piezoelectric layer is assumed to vary linearly across its thickness. Two types of electrical boundary conditions, which are open- and closed-circuits, are considered for the free surfaces of the piezoelectric layers. Parabolic shear deformation beam theory associated with Hamilton’s principle is adopted to derive the governing equations of the free vibration. Afterwards these equations are solved analytically by Navier’s solution. Comparative and comprehensive studies are carried out to examine the accuracy and effects of parameters and conditions, such as GPL weight fraction, porosity coefficient, and electrical boundary conditions on the natural frequencies of the beam.

Vibration of micro-scale composite beams reinforced by carbon nanotubes (CNTRC beams) carrying a moving concentrated load is studied considering CNT agglomeration. The Eshelby-Mori-Tanaka method is adopted to predict the elastic moduli of the CNTRC. The modified couple stress theory and a refined high-order theory are employed to establish the mathematical model. The governing equation in terms of finite element analysis is established and solved by a direct integration method. The effects of the CNT reinforcement, the agglomeration of CNTs, the size scale parameter, and the load speed on the vibration of the beams are investigated in detail.

This paper presents the approach of building a mathematical model for a parallel robotic manipulator with flexible links and elastic joints. The links to the base are assumed to be rigid bodies, and the thin connecting rods are assumed to be flexible links. The elasticity of the transmission from the actuators to the transmission is modeled by a torsional spring and viscous damper. This is a mixed system of rigid bodies, spring, and flexible links. The deformation motion of the elastic link is approximated by shape functions similar to the finite element method. The differential equations of motion are established by combining the substructure method and the Lagrange equation of the 2nd kind for the serial multibody system. Based on the differential equation established for the parallel robot manipulator of five bars, numerical simulations were carried out to investigate the response of the system.

Bài báo này sẽ trình bày một phương pháp để xác định các kiểu dòng (dòng bọt và dòng slug) trong dòng hai pha khí-nước theo chiều dọc bằng cách đo phân số thể tích (sử dụng đầu dò điện trở) tại Viện Cơ học Hà Nội.

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The form of Lyapunov exponents proposed in the part I is verified and illustrated by examining some differential equations with well-known exact solutions.

In the realm of soft robotics, investigating the effect of design parameters on the deformation of complex structures like soft composite actuators is a challenging task. Existing mathematical models often rely on limiting assumptions, while traditional simulation approaches demand substantial computational time and resources, hindering concurrent investigations of multiple design parameters. To address these issues, this paper introduces a new technique to expedite the deformation simulation of composite soft actuators. This automation program enables automatic modification of input parameters while preserving critical properties, constraints, and boundary conditions, resulting in a significant reduction in simulation time. Compared to traditional methods requiring approximately 60 minutes for a single task, our technique achieves the same in merely 10 minutes. The developed program is applied to analyze the impact of design parameters on the curvature of composite soft actuators, leading to the identification of optimal parameters. Through experimental verification, the reliability and efficiency of our technique are demonstrated, showing simulation results with less than a 10% error when compared to physical experiments. The proposed approach enables swift investigation of design parameter influence, facilitating the identification of optimal soft robotic structures for specific objectives. As a result, it has the potential to become a promising tool for advancing soft robotics design and analysis.

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