Ag2S morphology controllable via simple template-free solution route

Different morphologies of Ag₂S nano- and micro-materials, including spokewise micrometer bars, microfibers, nanowires, worm-like nanoparticles and nanopolyhedrons have been obtained controllably by a facile one-step method at room temperature. Powder X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and scanning electron microscope (SEM) were employed to characterize the structure and compositions of those nanomaterials. Furthermore, ultraviolet visible (UV–vis) spectra of Ag₂S with different morphologies show different spectral features. In this route, no any organic template materials were added into the reaction container. The concentrations of ammonia, Ag⁺, S^2? and their ratios in the solution may play an important role on the morphologies and sizes of the products.     

Numerical simulation of water flow in an axial flow pump with adjustable guide vanes

A new adjustable guide vane (AGV) is proposed in this paper. This vane can reduce hydraulic losses and improve the performance of an axial flow pump. The formula of AGV adjustment was obtained after theoretical analysis. The fluid flow inside the axial flow pump with a fixed guide vane and adjustable guide vane was simulated. The calculated Q-H curves for the fixed guide vane agreed well with the experimental ones. The results show that the attack angle and flow separation have an important contribution to the vortices which create hydraulic losses in the guide vane channel. The AGV can decrease hydraulic losses and significantly enhance the pump head and efficiency by changing the guide vane angle.     

Optimizing location of particle damper using principles of gas-solid flow

Journal of Mechanical Science and Technology - Particle damping is a passive control technology with strong nonlinearity whose damping effect is relative to the vibration intensity where a particle...     

Residual ultimate strength assessment of stiffened panels with locked cracks

The residual ultimate strength of stiffened panels with locked cracks under axial compressive loading is analyzed. The influences of various geometrical characteristics of cracks and panels, such as the length and the orientation angle of cracks, are investigated by the nonlinear finite element analysis. The cracks are prevented from further propagation by holes with a diameter of 2 mm drilled at their tips. The finite element model has two bays in the longitudinal direction, employing periodical symmetrical boundary conditions at the ends of the loading edge. Beam tension test results are used to define the true stress–strain relationship of the material, which is used in the FE analyses to account for the nonlinear material property of steel.     

二元结构岩土基坑“吊脚桩”支护设计数值分析

在山地丘陵地区,上层是土体、下层是岩体的岩土二元结构基坑非常普遍。针对此类基坑支护中常用到的“吊脚桩”的设计和施工特点进行有限元数值模拟与分析,研究了其设计方法及其安全稳定性、桩体嵌岩深度、桩脚处锚杆轴力和预留岩肩宽度等各种影响因素。分析结果表明：此类基坑设计对上层土体按传统设计计算方法进行设计施工时能够保证上层土体开挖基坑的稳定性;增加嵌岩深度或增大桩脚处锚杆预应力都能有效地控制下层岩体开挖时基坑的稳定和变形,锚杆预应力为主要控制因素,施工中要注意对其轴力进行监测;预留岩肩宽度越大,支护桩位移越小,当该宽度大于某定值时,其变化对位移和弯矩的影响作用将不再明显。     

NUMERICAL SIMULATION OF TRANSIENT FLOW AROUND A SHIP IN UNSTEADY BERTHING MOTION

Ship berthing is a specific maneuver operation. The flow around a berthing ship and the forces acting on the hull are quite different from those for a ship in normal navigation. By solving the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations, the transient flow field around a ship undergoing unsteady lateral motion is simulated and the varying lateral hydrodynamic force acting on the hull is evaluated in this article. The numerical results obtained with different turbulence models are analyzed and compared with experimental results and other numerical results published in literature, and a turbulence model more suitable for simulation of the viscous flow around a ship undergoing unsteady berthing is determined.     

An efficient FE model and Least Square Error method for accurate calculation of transverse shear stresses in composites and sandwich laminates

Accurate evaluation of transverse stresses in laminated composites and sandwich plates using 2D FE models involves cumbersome post-processing techniques. In this paper a simple and efficient method has been proposed for accurate evaluation of through-the-thickness distribution of transverse stresses in composites and sandwich laminates by using a displacement based C⁰ FE model (2D) derived from Refined Higher Order Shear Deformation Theory (RHSDT) and a Least Square Error (LSE) method. The C⁰ FE model satisfies the inter-laminar shear stress continuity conditions at the layer interfaces and zero transverse shear stress conditions at the top and bottom of the plate. In this model the first derivatives of transverse displacement have been treated as independent variables to circumvent the problem of C¹ continuity associated with the above plate theory (RHSDT). The LSE method is applied to the 3D equilibrium equations of the plate problem at the post-processing stage, after in-plane stresses are calculated by using the above FE model based on RHSDT. Thus the proposed method is quite simple and elegant compared to the usual method of integrating the 3D equilibrium equations at the post-processing stage for calculation of transverse stresses in a composite laminate. In the proposed method, the first two equations of equilibrium are utilized to compute the transverse shear stress variation through the thickness of a laminated plate whereas the third equation of equilibrium gives the normal stress variation. Accuracy of the proposed method is demonstrated in the numerical examples through comparison of the present results with those obtained from different models based on higher order shear deformation theory (HSDT) and 3D elasticity solutions.     

ISO 6954振动评价标准新旧版本的比较研究

国际标准化组织“机械振动与冲击”技术委员会制定的ISO 6954振动评价标准目前经历了两个版本：1984年版的《商船振动综合评估指南》和2000年版的《客船和商船适居性振动测量、报告和评价准则》。两者的内容存在很大不同：前者是针对船体振动的评估,后者是针对人体对船舶的适居性的评估。但目前基于这两种版本的振动评价标准仍然都被采用,部分船级社关于振动的指导性文件也同时引用了这两种版本,因此在具体使用中存在一定的模糊性。本文旨在比较分析ISO 1984新旧版本在理论和实际测量上的差异性,并结合各主要船级社及相关文献的内容,对如何使用ISO 6954振动评价标准进行初步的探讨。     

A micromechanical model for the mechanical degradation of natural fiber reinforced composites induced by moisture absorption

This paper develops a micromechanical model to study the mechanical degradation of natural fiber reinforced composites (NFRCs) induced by moisture absorption. Since the moisture absorption and the mechanical degradation of the composite are correlated, a modified Mori–Tanaka method with a damage variable is proposed. A set of micromechanical equations are established to describe the modulus loss of NFRCs. After specifying this model with different inclusion shapes, the overall swelling deformation and the mechanical degradation of the randomly oriented and the unidirectional straight natural fiber reinforced composites are studied in detail. Theoretical predicted results of the randomly oriented straight fiber reinforced composite are compared with experimental ones from literature and a good agreement is obtained. Further numerical results demonstrate that a stiffer matrix can reduce both the moisture absorption and the mechanical degradation of natural fibers.     

船舶轴系合理校中及其影响因素分析

针对某一实船的轴系布置,考虑轴承支撑刚度与船体变形,进行轴系的合理校中计算,分析支撑刚度与船体变形对轴系校中计算结果的影响。