Springer Science and Business Media LLC

When a liquid droplet impacts on a solid surface, it recoils to the center of that surface after reaching its maximum spreading diameter. The mechanism of droplet recoiling is not fully understood. To simulate this recoiling of a droplet, a particle method is a good choice because it does not require grids for simulating fluid motions, and can easily handle a large deformation of fluid. In this study, the coupled method of rigid body dynamics and the moving particle semi-implicit (MPS) method (Park and Jeun, 2011) was used to calculate three-dimensional droplet impingement. Also, the previous surface tension model for MPS (Nomura et al., 2001) was revised to get a more realistic surface tension force. A two-step calculation was performed. In the first step, a MPS calculation was performed with particles that were considered to have no mass or volume. In the second step, rigid body dynamics came into the calculation and considered the diameters of particles being slightly lesser than the initial distance between particles. In this study, the calculated results were compared with the measured data (Kim and Chun, 2000) and the recoiling lengths of droplets for the various initial impingement speeds were estimated.

In order to establish a reliable numerical method for solving the transient rotating flow induced by a speed-changing impeller, two numerical methods based on finite volume method (FVM) were presented and analyzed in this study. Two-dimensional numerical simulations of incompressible transient unsteady flow induced by an impeller during starting process were carried out respectively by using DM and DSR methods. The accuracy and adaptability of the two methods were evaluated by comprehensively comparing the calculation results. Moreover, an intensive study on the application of DSR method was conducted subsequently. The results showed that transient flow structure evolution and transient characteristics of the starting impeller are obviously affected by the starting process. The transient flow can be captured by both two methods, and the DSR method shows a higher computational efficiency. As an application example, the starting process of a mixed-flow pump was simulated by using DSR method. The calculation results were analyzed by comparing with the experiment data.

The free vibration and flow-induced flutter instability of cantilever multi-wall carbon nanotubes conveying fluid are investigated and the nanotubes are modeled as thin-walled beams. The non-classical effects of the transverse shear, rotary inertia, warping inhibition, and van der Waals forces between two walls are incorporated into the structural model. The governing equations and associated boundary conditions are derived using Hamilton’s principle. A numerical analysis is carried out by using the extended Galerkin method, which enables us to obtain more accurate solutions compared to the conventional Galerkin method. Cantilevered carbon nanotubes are damped with decaying amplitude for a flow velocity below a certain critical value. However, beyond this critical flow velocity, flutter instability may occur. The variations in the critical flow velocity with respect to both the radius ratio and length of the carbon nanotubes are investigated and pertinent conclusions are outlined. The differences in the vibration and instability characteristics between the Timoshenko beam theory and Euler beam theory are revealed. A comparative analysis of the natural frequencies and flutter characteristics of MWCNTs and SWCNTs is also performed.

Bending tubes are key products in many industries. The geometric parameters of the bending process are considered according to Taguchi’s orthogonal array and then coupled with finite element simulation to predict and improve the formability of the tube bending process for copper JIS25A material. Three parameters, namely, mandrel diameter, distance between mandrel rings, and distance from the tip of the mandrel bar to the center of the base die, are selected to study their effects on the quality of the bending process. The variance analysis shows that the effect distribution of each parameter to bending quality is determined, and optimal conditions are adopted to conduct experiments.

In wire and arc additive manufacturing, the weld bead geometry determined the slicing layer height, which was decided by the welding parameters. Generally, the determination of the welding parameters relied on empirical and experimental data through the trial-and-error methods that incur considerable time and cost. To obtain the proper welding process parameters according to the desired single bead geometry and layer height, a full factorial experimental design matrix was applied to collect the original data of welding parameters and bead geometrical variables. A forward artificial neural network (FANN) was built to predict the bead geometry form the welding parameters. Then, a closed-loop iteration method combined a genetic algorithm (GA) and the FANN model (FANN-GA) was developed to search for the most optimal welding process parameters in accordance with the selected bead geometrical variables. The results confirmed that the FANN-GA model has a good performance on the backward prediction of the welding process parameters compared with the direct backward artificial neural network (BANN). Several groups of single layer multi-bead and multi-layer multi-bead experiment were performed to testify the proposed method, and the relative error between the desired and actual layer height was small. The proposed method makes it possible to fabricate the component with an arbitrary desired layer height, and could be used in the adaptive slicing additive manufacturing or surface coating.

As audio-visual electronic devices such as TV and laptop computer get thinner, vibrations due to speakers bring about sometimes deteriorations in the audio-visual performance. When visco-elastic isolators are installed between speakers and device structures in order to reduce the structural vibration just based on the transmissibility of a single-degree of freedom system, other by-product problems may occur, such as the structural vibration noise inside the devices or the decrease of read/write speed in a hard disk drive system. In this paper, how to isolate speakers is presented so as to reduce the structural vibration of audio-visual electronic devices without reducing the vibration of the cone in speakers. An electro-mechanical vibration model for the whole system, which includes a loud speaker, vibration isolators and a device structure, is derived based on the substructure synthesis method. A dynamic model is derived mathematically for the loud speaker, isolators are treated as lumped springs and damping elements and the device structure is characterized experimentally in terms of compliance. Subsequently, they are coupled using frequency response functions at the connection points. It is claimed that, through simulations on modification of the isolator stiffness and loss factor, a realistically ‘good’ isolator can be designed before making a prototype so that the vibration of the structure may be the minimum, yet without reducing the key performance of a loud speaker in terms of vibration of speaker cone.

Backward-facing step flow is a benchmark problem that has been studied in various fields, such as airfoils, diffusers, boilers, nuclear reactors, electronic devices, and air-conditioning ducts. In this study, a rigid rectangular flapping longitudinal vortex generator was mounted at the step of the channel to investigate the fluid flow and heat transfer characteristics at three flapping frequencies (0.167, 0.25, and 0.5 Hz) in the Reynolds number range of 3000 to 8000, while maintaining at a constant heat flux. When the fluid flowed over the backward-facing step with flapping longitudinal vortex generator, a train of longitudinal vortices developed simultaneously. At a flapping frequency of 0.167 Hz, the developed high-intensity longitudinal vortices were stable and augmented the heat transfer by 38.54 % more than the smooth channel. The friction factor at 0.167 Hz was found to be 19.47 % and 25.33 % greater than at the higher frequencies of 0.25 and 0.5 Hz, respectively.

Based on the analysis of the movement rule of 3D five-way braided yarn, the 3D five-way braided case model is divided into three parts: base, case bottom plate and case wall. According to the characteristics of each part, the braiding and forming principle of a 3D five-way composite case was analyzed. Under the assumption of ignoring the influence of friction, bearing and other factors on the system, the differential equations of motion of the two-stage gear transmission system with case were established. The two-stage gear transmission system was numerically analyzed by Euler method, and the influence of dimensionless meshing frequency, clearance, case mass and damping on the dynamic characteristics of the transmission system was studied. After that, high and low frequency disturbance was applied to the input case. The research shows that the damping ratio of the composite case increases and the low frequency attenuation is accelerated due to the decrease of the case mass, so the composite case has better shock resistance to low frequency interference.