Multi-scale filling simulation of micro-injection molding process

This work proposes a multi-scale simulation method that can simulate filling during the micro-injection molding process. The multiscale simulation is comprised of two steps. In the first step, the macro-scale flow is analyzed using the conventional method. In the second step, the micro-scale simulation is conducted taking the slip and surface tension into consideration to investigate the filling of microcavity. Moreover, a conservative level set method is employed to accurately track the flow front. First, numerical tests have been done for circular micro-channels. The results show that slip and surface tension play important roles in the micro-regime. Second, to verify the multi-scale method, filling of a thin plate with micro-channel patterns has been simulated. The results show that the proposed multi-scale method is promising for micro-injection molding simulations.     

Study on the compressible viscous flows through a straight pipe

When sonic nozzles of significantly smaller diameter are used as standard flow meters, the critical backpressure ratio is affected by the boundary layer at the nozzle throat. It is known that, as the flow pathway is complicated in actual valves, the critical pressure ratio differs from the ideal value. However, the effect of the boundary layer thickness on choking criteria is still controversial. Choking phenomenon in a sonic nozzle fitted with a straight circular pipe of variable length is investigated numerically and the results are compared with experimental and theoretical ones. The results show that the actual critical pressure ratio is less than the ideal value and it decreases with increase in pipe length. The effect of boundary layer thickness on main flow Mach number is also made clear in this work. In addition, sonic conductance and pressure loss in actual viscous flows computed are compared with the ISO 6358 standard.     

Dynamic modeling and simulation of electrodynamic tether system in stationkeeping phase

Dynamics is one of the fundamentally important aspects of all space tether research. This paper derives the dynamic equations of electrodynamic tether system (EDT) in stationkeeping phase using Newton’s laws. This paper further analyzes the tether system motion rules under electrodynamic drag, gravity induced force, and tether tension. Numerical simulation of electrodynamic tether system in station-keeping phase is calculated using an approach that combines the central difference method, fourth-order Runge-Kutta method, and predictor-corrector method, among others. The simulation results show that the motion of electrodynamic tether in stationkeeping phase not only contains librations caused by the motion of endmass, but also contains vertical and longitudinal vibrations of tether. If the motion of endmass is ignored, it is much similar to the vibration of cable with two immovable pinned-supports, in which the mid-span has the largest amplitude of vibration. Based on this, the main satellite and the endmass at both ends of tether can be treated as immovable pinned-supports when the tether vibration and tension of electrodynamic tether system in impermanency are investigated.     

The difference in the uplift force at each support point of a container crane between FSI analysis and a wind tunnel test

We analyzed the difference between FSI (fluid-structure interaction) analysis and a wind tunnel test regarding the uplift force at each support point of a container crane and also design stowing devices — a tie-down rod and a stowage pin — and an alarm system to prevent overturning of a container crane under wind loads. We know that FSI analysis agrees more with wind tunnel tests than with structural analysis, but the results of FSI analysis are different from those of the tests. To evaluate the effect of the wind load on the stability of the crane, two container cranes that are widely used in container terminals-50 ton-class and 61 ton-class container cranes-are adopted for the analytic model and 19 values are considered for the wind direction as the design parameter. First, a wind tunnel test for the reduced-scale container crane model is performed according to the wind direction using an Eiffel-type atmospheric boundary-layer wind tunnel. Next, FSI analysis for a full-scale container crane is conducted using ANSYS and CFX. Then, the uplift force obtained from FSI analysis is compared with that yielded by the wind tunnel test. Finally, a formula is suggested to compensate the difference between FSI analysis and the wind tunnel test.     

Local stiffness control for reducing vehicle interior noise by using FRF-based synthesis method

This paper explores the feasibility of estimating the interior noise of a vehicle compartment when the attachment stiffness (i.e., the local stiffness of the mounting point at which operational force is applied) is altered. In order to change the local stiffness of the vehicle body, it was assumed that the local stiffness could be changed by attaching some additional systems to the vehicle body. The frequency response function (FRF)-based synthesis method is used herein to estimate the change in the local stiffness of the modified vehicle body. In addition, the change in the noise transfer function (NTF) can also be estimated using this method. Since the operational force transmitted from the source excitation to the body attachment is required to predict the interior noise of the vehicle body in the operational condition, a transfer path analysis (TPA) technique was performed. Various vehicles and additional systems were utilized to estimate the dynamic properties of the modified vehicle body. Results indicated that the synthesis technique is an appropriate method to estimate the change in the local stiffness and NTF of the modified vehicle body. The results also show that the interior noise of the body can be estimated accurately by using the synthesis technique and TPA procedure when the vehicle body is locally modified.     

Numerical investigation of the stress field near a crack normal to ceramic-metal interface

Ceramic-metal interfaces are often present in composite materials. The presence of cracks has a major impact on the reliability of advanced materials, such as fiber or particle reinforced ceramic composites, ceramic interfaces and laminated ceramics. The understanding of the failure mechanisms is very important, as is as the estimation of fracture parameters at the tip of the crack approaching an interface and crack propagation path. A cracked sandwich plate loaded with axial uniform normal stress was numerically investigated using plane strain Finite Element Analysis. The numerical results for the singularity orders were compared with the analytical solution. The influences of the material combination and crack length on the radial and circumferential stresses and displacement distributions were investigated. The Stress Intensity Factors were determined based on numerical results using a displacement extrapolation method. The results for the non-dimensional stress intensity factors show that at lower crack lengths the influence of material mismatch is lower, but this influence increases with increasing crack length.     

Magnetic field effect on fluid flow characteristics in a pipe for laminar flow

The influence of a magnetic field on the skin friction factor of steady fully-developed laminar flow through a pipe was studied experimentally. A mathematical model was introduced and a finite difference scheme used to solve the governing equations in terms of vorticity-stream function. The model predictions agree favourably with experimental results. It is observed that the pressure drop varies in proportion to the square of the product of the magnetic field and the sine of the magnetic field angle. Also, the pressure drop is proportional to the flow rate. This situation is similar to what applies in the absence of a magnetic field. It is found that a transverse magnetic field changes the axial velocity profile from the parabolic to a relatively flat shape. At first, the radial velocity rises more rapidly and then gradually decreases along the pipe until falling to zero. A numerical correlation can be written for the considerable distance required for the new axial velocity profile to establish. Owing to the changes taking place in the axial velocity profile, it exhibits a higher skin friction factor. The new axial velocity profile asymptotically approaches its limit as the Hartmann number becomes large.     

Gear fault identification and classification of singular value decomposition based on Hilbert-Huang transform

An improved singular value decomposition method of gear fault identification based on Hilbert-Huang transform was proposed to overcome the problem of reconstructing a feature matrix of singular value decomposition. The method includes three steps. First, the instantaneous frequency and amplitude matrices were acquired by Hilbert-Huang transform from faulted gear signals. Second, after the matrices were decomposed by singular value decomposition, the defined distances of singular value vectors and the optimal threshold of the distance for classification were calculated. Third, the fault characteristics of a gearbox were identified and classified by the threshold of the distances. The result demonstrates that the proposed method effectively identifies the gear fault and can realize an automatic gear fault diagnosis.     

Concentration measurement with optical fibers for small sample

It is valuable to physically detect concentration of small quantity of liquid with suspended particles. In this paper, light scattering in different directions and optical lengths is simulated and analyzed based on Mie theory. Then, an equipment is designed with two receiving beams of optical fibers, one is for scattering and the other is for transmitting. Scattering angle can be adjustable in order to locate the most sensitive direction. The method of ratio of scattering light to transmitted light is used to reduce the influence of fluctuations of light source and the method of transmitting light is used to satisfy the large measure range. Under room temperature conditions, concentration of yeast extract is tested with 785 nm laser. The results indicate at 0 to 5%, there is linear relationship between ratio of scattering light to transmitted light and concentration. While, for 5 to 10%, there is linear relationship between transmitting light and concentration. Furthermore, it’s notable that maximum relative error on experiment is less than ±0.2%.     

Effect of constraint on fracture behavior of welded 17mn4 and aisi304 steels

In this study, 17Mn4 (P295GH) pressure vessels steel and AISI304 stainless steel were welded with ER309L austenitic consumable. In experimental part of the study, tensile tests were conducted on welded plates and variation of hardness values along specimen was measured. J-integral fracture toughness values were investigated for different crack locations. In order to determine the regions where plastic deformation did not take place due to constraint, uni-axial tensile test was performed on welded tensile specimen after attaching strain gauges. In numerical part of the study, finite element (FE) analyses were conducted by fixing 2-D models precracked on different locations by using ANSYS software. In these models, stress triaxiality and plastic deformation characteristics around crack tip were determined for each crack locations after stress — strain analyses. The limitation on the extension of plastic deformation at diffusion line causes extra increase in stress triaxiality at crack tip.