Applied Mechanics and Materials Vol. 736

Abstract: This paper systematically analyzes the interaction law on how the shape parameters of brake magnet yoke affect the magnetic field distribution and the permanent-magnetic attraction by means of parameterized finite element numerical calculations based on the basic principles of train permanent track brake device and the mathematic model of permanent-magnetic attraction [1]. It is found: the permanent-magnetic attraction decreases with the increase of the width of rotor partition board and maximum value of the attraction appears at 16-20nm; the attraction slowly increases along with the increment of slipper chamfering but will decrease when the magnetic induction intensity of the material is saturated; the increase of the rotating angle of rotational magnetic axis leads to decrease of permanent-magnetic attraction; the vertical air gap between permanent-magnetic track brake and steel rail will make the attraction dramatically drop; and the slipper wear almost has little impact on the attraction. The shape parameters of magnetic track brake should be optimized in design by considering the permanent-magnetic attraction so that the efficiency of the brake can be brought into full play.

Abstract: The demand for shape memory alloy (SMA) actuators for technical applications is steadily increasing; however SMA may have poor deactivation time due to relatively slow convective cooling. Convection heat transfer mechanism plays a critical role in the cooling process, where an increase of air circulation around the SMA actuator (i.e. forced convection) provides a significant improvement in deactivation time compared to the natural convection condition. The rate of convective heat transfer, either natural or forced, is measured by the convection heat transfer coefficient, which may be difficult to predict theoretically due to the numerous dependent variables. In this work, a study of free convective cooling of linear SMAactuators was conducted under various ambient temperatures to experimentally determine the convective heat transfer coefficient. A finite difference equation (FDE) was developed to simulate SMA response, and calibrated with the experimental data to obtain the unknown convectiveheat transfer coefficient, h. These coefficients are then compared with the available theoretical equations, and it was found that Eisakhaniet. almodel provides good agreement with the Experiment-FDE calibrated results. Therefore, FDE is reasonably useful to estimate the convective heat transfer coefficient of SMA actuator experiments under various conditions, with a few identified limitations (e.g. exclusion of other associative heat transfer factors).

Abstract: Method of searching for rational shapes of skeletal structures based on the use of Delaunay tetrahedron partition algorithms with constraints and evolutionary modeling has been developed. Topology of load-bearing rod system is synthesized on specified multitude of nodes at fixed number of rods. Established structures are considered redundant and are optimized by means of excluding individual members. Optimization is performed with the modified genetic algorithm pursuant to criterion of minimum weight of structure. An example of synthesis of rectangular rod structure showing performance of suggested approach in terms of shape synthesis of trusses has been given.

Abstract: This paper describes the transient analysis of artificial hip joint during human movement under elastohydrodynamic lubrication (EHL) with non-Newtonian lubricants based on a Carreau model. During walking, the load and velocity are varying with time. The numerical schemes employed perturbation method, Newton-Raphson method and multi-grid multilevel with full approximation technique to solve the time-dependent modified Reynolds equation and elasticity equation with initial conditions. The aim of this study was investigated the characteristics of elastohydrodynamic lubrication, profile of film pressure and film thickness profile in human artificial hip joint during human movement. Numerical results show the transient film thicknessincreased and then decreased because of reverse motion. In smooth surface condition, film thickness for Newtonian fluids is slightly higher than the film thickness for non-Newtonian fluid. The amplitude of surface roughness has significant effect on the film thickness,the minimum film thickness decreased when the amplitude of surface roughness increases.

Abstract: In a novel approach of task based conceptual design method by proper synthesis and analyzes tools mechanism and function entities are modified, turned into and considered as extendable and squeezable ones , so systemized search of optimal structural solutions inside those entities leads the designer to satisfaction of prior given set of functions. Conceptual design generation procedure includes task simplification phase where a key function (s) based mechanical model is composed and its further development into final concept requires gradual satisfaction of remained pre given functions. Two major sources of mechanical solutions are used for function satisfaction. First is existing knowledge on mechanism available as database and the second source is self-generation of mechanisms by granting DOF action, both procedures strictly implemented in a function targeted manner. The database itself is available in different formats depending on application, tutorial or systemizing purposes. Current study discloses the approaches and methods of modification of mechanisms from database into models and formats applicable and suitable for being used in proposed task based conceptual design method.

Abstract: This study showcases two independent magnetic manipulation systems to remotely control the movement of Fe₃O₄ nanomaterial in microfluidic chips. One system utilizes a homogeneous rotating magnetic field to carry out magnetic stirring in 100 μm and 300 μm flow channels. The mixing results of this system revealed that adding Fe₃O₄ nanoparticles to the solution enhances the efficiency of the micromixer by twice as much that of a device without the nanomaterial. The second manipulation system utilizes oscillating magnetic field for rapid microablation of thrombus in a microchannel. A customizable magnetic platform using 3D-printed material is also constructed. This is proposed as a feasible low-cost and portable magnetic manipulation device that can implement both applications.

Abstract: In times of increasing international business competition forging companies try to increase their competitiveness by optimization of different factors such as efficient use of resources in the forging process, optimization of processes or managing costs. In common forging processes for geometrically complicated parts such as crankshafts, an excess on material (flash) is technically needed to produce a good part, which results often in a material utilization between 60 % and 80 %. But the material costs in forging represent up to 50 % of the total production costs. By decreasing the flash ratio, the material usage and production costs in forging operations can be reduced significantly, helping to increase the competitiveness of companies. Innovative approaches are required, to achieve a significant reduction of the amount of flash in the forging of complicated parts like crankshafts. For a crankshaft, the development of a new forging sequence was necessary, to achieve the reduction of flash. This development was performed for an industrial two-cylinder crankshaft, based on finite element analysis (FEA) simulations. The new forging sequence consists of three flashless preforming operations, an induction reheating followed by a multidirectional forging and the final forging. By use of this forging sequence the flash ratio was reduced from about 54 % to less than 10 %. The whole forging sequence was set up in an industrial environment and the feasibility of this process chain was proven. Due to the huge reduction of the flash ratio, material as well as energy can be saved from now on, thus increasing the competitiveness of the company.

Abstract: In this paper the comparison of simulations of cross wedge rolling processes with real trials using flat cross wedge tools is presented. The investigated materials are titanium and bainitic grade steel. First simulations were used to find the suitable parameter combinations for the investigated materials. Afterwards tools were manufactured with these parameters and additionally with some variations to investigate a field of parameters around this range of parameter values. The purpose of these tests is to find geometrical and process parameters with which a stable cross wedge rolling process for bainitic grade steel and titanium is possible.

Abstract: This paper described a kind of designation method to the power distribution system in the modern computer room .Compared with the traditional power supply socket, The Power Distribution Unit (PDU) with these functions whichcan monitor the RMS current and voltage, line frequency ,energy usage ,load limitation and the relay controlling to current leak ,over load or over current etc., There also has the wired RS-485and reserved the wireless WIFI interfaces in the PDU through which the working conditionsof equipment in the computer room can be connected and monitored by administrator at any time and place.

Abstract: Firewall plays an important role in today's network security, and its rule configuration is reasonable or not directly related to the security of network environment. With the increasing size of the network, firewall configurations are becoming increasingly complex, and the firewall policy audit should be born in order to better play the protective properties of the firewall. Firstly, this paper studies the relationship between firewall rules in detail, analyzes some common types of rules abnormal of audit programs and reviews existing policies. Next, this paper proposes a improved audit program based on the tree structure, discusses and achieves the audit process of the program in detail. Finally, this paper shows a graphical reports and detailed audit findings of the prototype system, and does a comparison and verification between the results of the improved audit program and the traditional strategy tree.