DIRECT DIGITAL DESIGN AND SIMULATION OF MESHING IN WORM-GEAR DRIVE

A direct digital design method （DDDM） of worm-gear drive is proposed. It is directly based on the simulation of manufacturing process and completely different from the conventional modeling method. The loaded tooth contact analysis （LTCA） method is analyzed, in which the advanced surface to surface searching technique is included. The influence of misalignment errors and contact deformations on contact zone and transmission error （TE） is discussed. Combined modification approach on worm tooth surface is presented. By means of DDDM and LTCA, it is very conven- ient to verify the effect of worm-gear drive＇s modification approach. The analysis results show that, the modification in profile direction reduces the sensitivity of worm-gear drive to misalignment errors and the modification in longitudinal direction decreases the TE. Thus the optimization design of worm-gear drive can be achieved prior to the actual manufacturing process.

An elastic model for bioinspired design of carbon nanotube bundles

Collagen fibers provide a good example of making strong micro-or mesoscale fibers from nanoscale tropocollagen molecules through a staggered and crosslinked organization in a bottom-up manner.Mimicking the architectural features of collagen fibers has been shown to be a promising approach to develop carbon nanotube（CNT）fibers of high performance.In the present work,an elastic model is developed to describe the load transfer and failure propagation within the bioinspired CNT bundles,and to establish the relations of the mechanical properties of the bundles with a number of geometrical and physical parameters such as the CNT aspect ratio and longitudinal gap,interface cross-link density,and the functionalizationinduced degradation in CNTs,etc.With the model,the stress distributions along the CNT-CNT interface as well as in every individual CNT are well captured,and the failure propagation along the interface and its effects on the mechanical properties of the CNT bundles are predicted.The work may provide useful guidelines for the design of novel CNT fibers in practice.

闭环液压系统及其对驱动器设计的影响

Hydraulic systems provide a clean and stable supply of hydraulic fluid for subsea valves and actuators installed on the subsea bed in subsea production systems.Subsea control systems are used for contemporary subsea fields instead of installing the control system on topside.Although all-electric subsea systems are state-of-the-art with benefits such as health,safety,and environment improvement,as well as efficiency and lower cost,hydraulic systems are still used for the development of many subsea fields.One of the main questions in the selection of a subsea hydraulic field is whether to choose an open or closed loop hydraulic system.The main characteristic of an open loop hydraulic system is that the hydraulic fluid is discharged into the marine environment during the actuation of the subsea valves.Conversely,the hydraulic fluid is returned to the topside facilities through an umbilical system in a closed loop system.Given that closed loop systems are more eco-friendly,the main question in this research is to examine the effect of the actuator connection of the closed loop system on actuator design.Two cases of actuated valves connected to a closed loop system are analyzed in this paper.The first is a 71/16-in.subsea slab gate valve in the pressure class of 517 bar with a linear spring return fail-safe close(FSC)actuator located on a manifold branch.The data indicates that the piston rod and cylinder diameter of the FSC linear actuator should be increased by some millimeters due to the accumulation of hydraulic oil at the bottom of the actuator.The hydraulic oil in the closed loop system helps in closing the actuator and spring force,so the spring constant and torque should be reduced as a result.The second case involves a 16-in.subsea ball valve in the pressure class of 517 bar with a double-acting fail-as-is rack and pinion actuator.The conclusion in this case is to avoid making any change in the design of double-acting actuator in connection to the closed loop system.

Flap side-edge noise mechanism and shape modification noise reduction design

Flap side-edge noise is a significant noise source for airplane at takeoff and landing stages. The generation mechanism of flap side-edge noise is analyzed by numerical simulation on unsteady flow field using Very Large Eddy Simulation （VLES）. Two kinds of flap side-edge shape modifications are proposed, and their frequency spectrum and directivity of far-field noise are compared with the baseline configuration using permeable integral surface Ffowcs Williams and Hawkings （FW-H） acoustic analogy method to investigate their effects on noise reduction. Via the numerical simulation of flow field and acoustic field, it proves that the flap side-edge noise is broadband noise in nature. The different shapes of flap side-edge change the pattern of flow field, vortex structures and the development of vortex, thus having influences on noise source distributions and characteristics of far-field noise. The result shows that at the given 5° angle of attack, the proposed flap side-edge shape modifications can reduce the overall sound pressure level （OASPL） by 1 to 2 dB without decreasing the lift and drag aerodynamic performances.