Multi-field coupling prediction for improving aeroacoustic performance of muffler based on LES and FW-H acoustic analogy methods

Based on the large eddy simulation (LES) and Ffowcs Williams and Hawkings (FW-H) equation, a multi-field coupling method is presented for aeroacoustic prediction of a muffler with high-speed and high-temperature exhaust gasflow. A three-dimensional finite-volume model of the muffler is established by using the LES and FW-H acoustic analogy (FW-H-AA) methods. Experimental validations of the simulated results suggest a good accuracy of the combined LES and FW-H-AA approach. Some factors influencing on noise attenuation, such as the gasflow velocity, temperature and the structural parameters of the muffler are analyzed. The results show that the aerodynamic noise and turbulent kinetic energy (TKE) are mainly attributed to the structural mutations in the muffler. The outlet sound pressure level (SPL) increases with the inlet gasflow velocity and decreases with temperature. According to the factor analysis results, the target muffler is modified by adding a fillet transition to the end of inserted tube and redesigning the structures where the TKE concentrated for improving the aerodynamic performance. In terms of the outlet SPL, the inner TKE and the backpressure of the muffler, the modified muffler is significantly improved by the maximum reductions of 3-5dB in SPL, 10–20% in TKE and 0.5–2.5 kPa in backpressure. The presented method might be extended to other kinds of muffler for aeroacoustic calculation and improvement design.

An Efficient Parking Solution: A Cam-Linkage Double-Parallelogram Mechanism Based 1-Degrees of Freedom Stack Parking System

To solve the difficult parking problem, developing a mechanical parking device is a practical approach. Aiming at longitudinal parking, a novel compact double-stack parking system is put forward based on a 1-DOF (degree of freedom) cam-linkage double-parallelogram mechanism. Due to the unique structure, the whole device can be driven by a single motor to realize three motion periods, including lifting, translation, and fillet transition. Meanwhile, all parts of this compact mechanism can be well contained in the filleted rectangular trajectory. This rectangular trajectory is essential that we no longer need to take out the ground vehicles so as to realize stack parking. Furthermore, to overcome the singularity collinear problem of the parallelogram which may lead to the polymorphic state, the double-parallelogram mechanism is proposed to maintain the orientation of the parking platform. The digital simulation and kinetostatic analysis results demonstrate the feasibility that this novel cam-linkage double-parallelogram mechanism can improve the space utilization of the residential area, alleviate the parking problem, and can be quickly put into application on campuses or streets in a short period.

Stress Concentration in a Connectorized Optical Fiber

For the most part, analyses of fiber fractures in connectors have been in the form of postmortem fractography. Typically in these works, characteristics of prefracture stress states have been inferred from fracture surfaces, and plausible qualitative explanations have been advanced about the likely structural mechanics and circumstances leading to fractures. The authors and their colleagues have undertaken a number of investigations of relevant structural mechanics. These have served the useful purpose of elucidating gross mechanisms, but the influence of the fine details of stress distributions have been missing. Considered here is a cylindrical-ferrule connector for which, typically, the ferrule is ceramic with an outside diameter of 2.5mm or 1.25mm. The fiber to be terminated is bonded into a small-bore axial hole (capillary) in the ferrule by an epoxy or similar adhesive. In addition, fiber insertion into the capillary is facilitated by ferrule designs that provide a conical entrance cavity leading to the capillary. A very high percentage of fiber failures, both in the laboratory and the field, occur at the transition region between the fiber and the capillary; so analysis is focused on that region. The stress distribution within an optical fiber adhesively bonded to a ceramic ferrule is determined by the finite element method for uniform remote tension acting on the fiber. An axisymmetric model is constructed to represent the fiber, epoxy, and geometry of the ferrule under this particular loading condition. The resulting stress distribution is determined within the fiber and the epoxy layer using the ANSYS finite element code. Analysis of the stress distribution reveals the presence of two stress concentrations located at the surface of the fiber as the fiber enters the ferrule. One stress concentration occurs as the fiber encounters the epoxy within the conical cavity. The second stress concentration occurs as the fiber enters the capillary. These stress concentrations when combined with surface damage (flaws) may lead to fiber breakage. Further analysis reveals that a smooth fillet transition between entrance and capillary could significantly reduce the stress concentration at the capillary entrance. Finally, a simulation of epoxy debonding within the entrance cone reveals an increase of stress concentration at the capillary entrance.