Iranian Journal of Science and Technology, Transactions of Mechanical Engineering

Các tiến bộ gần đây trong công nghệ sản xuất gia tăng cho vật liệu kim loại đã mở ra con đường cho việc tạo ra các implant đặc thù cho bệnh nhân với các thuộc tính cơ học được điều chỉnh cho việc tái tạo mô xương. Để giải quyết vấn đề bảo vệ áp lực và cải thiện tích hợp xương, các implant có cấu trúc bên trong được kiến trúc với một thiết kế độc đáo có khả năng mô phỏng các thuộc tính cơ học của xương bị hỏng. Nghiên cứu này đề xuất một phương pháp nhanh chóng, đơn giản và có thể áp dụng trong lâm sàng cho việc thiết kế các cấu trúc giống như xương xốp cho các implant được điều chỉnh, đặc biệt cho thành phần xương ống trong thay khớp gối. Các cấu trúc lưới với các tỷ lệ thể tích khác nhau đã được thiết kế và chế tạo bằng kỹ thuật nung chảy bằng laser chọn lọc (SLM) và hợp kim Ti-6Al-4V. Hành vi cơ học của các cấu trúc đã được đánh giá thông qua phân tích tính toán và thực nghiệm, cùng với đó là so sánh với xương ống tự nhiên. Hơn nữa, độ bền sản xuất của các cấu trúc in được đã được đánh giá bằng cách sử dụng chụp cắt lớp vi tính bằng tia X và kiểm tra vi mô. Kết quả cho thấy độ thấm của các cấu trúc chế tạo dao động từ 0.16 × 10–9 đến 0.38 × 10–9 m2, tương đương với xương xốp. Độ cứng và sức bền của các cấu trúc được thiết kế dao động từ 1.08 đến 4.47 GPa và 147 đến 295 MPa, một cách hợp lý tương thích với xương tự nhiên. Cuối cùng, nghiên cứu đề xuất một khung thiết kế concept mà phân lập mối tương quan giữa tỷ lệ thể tích của các lưới và hành vi sinh học cơ học dự kiến. Nhìn chung, nghiên cứu đã nhấn mạnh tiềm năng của sản xuất gia tăng trong việc tạo ra các implant có hình học phức tạp và được điều chỉnh về mặt cơ học cho việc tái tạo mô xương.

In this paper, the use of the inverse solution method for estimating the mass of moving load on an inclined functionally graded material (FGM) Timoshenko beam is discussed based on the measured displacements. Fletcher–Reeves (FR) method is used to solve the inverse problem. Also, in the process of solving the inverse problem and in order to solve the direct problem, Newmark method is applied for discretization of the time domain and finite element method (FEM) is used for discretization of the space domain. According to many other similar types of research, instead of conducting an experiment and measuring displacements of the beam as inputs of the inverse solution, those inputs are obtained from the direct problem and then random errors are added. Furthermore, an inclined functionally graded (FG) beam with different boundary conditions and power-law exponents due to different speeds of the moving mass has been studied to evaluate the performance of the proposed method. The accuracy of results is very high in all cases.

In order to weaken the strict geometric constraint relationship between the axes of joints so as to reduce manufacturing/assembling errors of overconstrained mechanism, a configuration design methodology for single-loop non-overconstrained mechanism with inactive joints is proposed in this paper based on the screw theory. After completing analysis of degrees of freedom, the design principle and corresponding process of single-loop non-overconstrained mechanism with inactive joints are presented. By introducing two inactive R (R: single-degree-of-freedom revolute joint) joints to an active R joint of Goldberg overconstrained mechanism, the corresponding Goldberg non-overconstrained mechanism is obtained. It is verified that the velocities of two inactive joints in the Goldberg non-overconstrained mechanism are zero via investigating motion screws of branches. By further solving input and output kinematic parameters of Goldberg non-overconstrained mechanism, it is discovered that the overconstrained mechanism and corresponding non-overconstrained mechanism have the identical input–output relationship. Above results confirm that the overconstrained mechanism and its non-overconstrained counterpart with inactive joints are completely equivalent kinematically, which thereby demonstrate fully correctness of the configuration design principle and method of single-loop non-overconstrained mechanism proposed in this paper.

In this work, a ship motion simulator based on a parallel manipulator able to replicate the seakeeping trial is introduced. The mobility of the moving platform is explained through the theory of screws which reveals the existence of three constraint systems reciprocal to the motion-screw system of a central passive kinematic chain. Thereafter, the forward displacement analysis leads to five quadratic equations which are solved by means of homotopy continuation methods. On the other hand, the input–output equations of velocity and acceleration of the parallel manipulator are systematically obtained by resorting to the theory of screws. Finally, the dynamics of the parallel manipulator is approached through a harmonious combination of the theory of screws and the principle of virtual work. A case study is included with the purpose to numerically exemplify the application of the method.

This research aims to study the photo-thermoelastic interactions in an infinite semiconducting spherical shell in the context of the Moore-Gibson-Thompson-Photo-Thermo elasticity theory. The spherical shell is influenced by a high magnetic field acting along its axis. The inner and outer boundary surface of the spherical shell is traction free and subjected to time-dependent heating. The numerical expressions for the components of displacement, temperature field, carrier density, and thermal stresses are obtained in the Laplace transform domain. The numerical inversion technique is used to obtain the solution in the physical domain. The impact of Hall current on the displacement, temperature, thermal stresses, and carrier density are represented graphically for silicon material using MATLAB software.

Laminar heat transfer characteristics of non-Newtonian power-law fluids from a long (heated) triangular prism in the time-periodic regime have been explored. Momentum and energy equations were solved using finite volume methodology over the range of non-dimensional control parameters: Reynolds number (Re) = 50–150, Prandtl number (Pr) = 1–50 and power-law index (n) = 0.4–1.8. For the fixed Pr, the local and the time-averaged Nusselt numbers increase with rising Re irrespective of n. However, the local and the time-averaged Nusselt numbers decrease as the fluid nature alters from pseudo-plastic (n < 1) to dilatant (n > 1) for the fixed Re and Pr. Maximum enhancements in the values of time-averaged Nusselt numbers for Pr = 10, 20 and 50 with respect to Pr = 1 are observed to be approximately 180, 273 and 438%, respectively. Further, it is observed that for the fixed n and Pr, the Colburn heat transfer factor (or the jh factor) decreases with rising Re. Finally, the various values of the jh factor at different Re, n and Pr have been correlated via a simple expression, thus enabling its estimation in a new application.

A comparative study is performed to investigate the improved heat-driven refrigeration systems. The systems use a low-temperature heat source to produce low-temperature cooling (− 55 °C). The base system consisted of a hybrid GAX (HGAX) cycle and a Rankine cycle. Three major features for the HGAX cycle are proposed in four configurations to reduce the high temperature of the compressed fluid exiting the compressor. The operating parameters of the systems having the maximum exergy efficiency are computed, and the corresponding performance parameters are applied in all configurations. The results show that the best configuration that has higher exergy efficiency is the one utilizing two compressors in the HGAX cycle. For the heat source temperature of 133.5 °C, this configuration has 34.7% higher energy utilization factor, 33% higher exergy efficiency, 11% lower total product cost, and 28% lower circulating cooling water of the cooling tower than the base system.

Free vibration of cracked multistep beam made of functionally graded material is studied on the basis of the Timoshenko beam theory and actual position of neutral plane of functionally graded beam. Crack model is adopted using a pair of translational and rotational springs of stiffness calculated from the same crack depth. An exact dynamic shape function is proposed and used to conduct a simplified transfer matrix for cracked uniform functionally graded beam element. Frequency equations of the cracked multistep beam established in the form of 3 × 3-dimensional determinant for different cases of boundary conditions are employed for analysis of natural frequencies in dependence on the crack position and depth, material properties and size of beam steps. It was shown that abrupt variation of beam thickness has significant effect on the sensitivity of natural frequencies to cracks. This is demonstrated by numerous results obtained for beam with three steps in different boundary condition cases.

This paper uses the whole flow field numerical simulation method to study the axial force and balance device of a seawater desalination pump (SDP) with high capacity and pressure. The axial force on the impeller is divided into the forces acting on the outer and inner surface and then monitored separately in the numerical calculation. The pressure distribution law of the pump chamber and blade surface of all levels of the impeller were studied to obtain the distribution law of the cover plate force, dynamic reaction force, and axial force of each stage impeller. The total axial force distribution law is summarized and found to change nonlinearly with the flow rate, and the axial force is closely related to the pump operation state. The principle of the balancing device and its internal flow state were studied. The relative error between the axial force calculated by the numerical calculation and the axial force balanced by the balance device was 6.1%. Considering the complexity of the internal flow of the balance device and the simulation error, it is possible to conclude that the balance device can better balance the axial force of the SDP.