Buoyancy-driven single bubble behaviour in a vertical Hele-Shaw cell with various gap Reynolds numbers Re(h/d)2 has been studied. Two gap thicknesses, h = 0.5 mm (Re(h/d)2 = 1.0–8.5) and 1 mm (Re(h/d)2 = 6.0–50) were used to represent low and high gap Reynolds number flow. Periodic shape oscillation and path vibration were observed once the gap Reynolds number exceeds the critical value of 8.5. The bubble behaviour was also numerically simulated by taking a two-dimensional volume of fluid method coupled with a continuum surface force model and a wall friction model in the commercial computational fluid dynamics package Fluent. By adjusting the viscous resistance values, the bubble dynamics in the two gap thicknesses can be simulated. For the main flow properties including shape, path, terminal velocity, horizontal vibration, and shape oscillation, good agreement is obtained between experiment and simulation. The estimated terminal velocity is 10%–50% higher than the observed one when the bubble diameter d ≤ 5 mm, h = 0.5 mm and 9% higher when d ≤ 18 mm, h = 1.0 mm. The estimated oscillation frequency is 50% higher than the observed value. Three-dimensional effects and spurious vortices are most likely the reason for this inaccuracy. The simulation confirms that the thin liquid films between gas bubbles and the cell walls have a limited effect on the bubble dynamics.
Additive manufacturing (AM) is now capable of fabricating geometrically complex geometries such as a variable-density lattice structure. This ability to handle geometric complexity provides the designer an opportunity to rethink the design method. In this work, a novel topology optimization algorithm is proposed to design variable-density lattice infill to maximize the first eigenfrequency of the structure. To make the method efficient, the lattice infill is treated as a continuum material with equivalent elastic properties obtained from asymptotic homogenization (AH), and the topology optimization is employed to find the optimum density distribution of the lattice structure. Specifically, the AH method is employed to calculate the effective mechanical properties of a predefined lattice structure as a function of its relative densities. Once the optimal density distribution is obtained, a continuous mapping technique is used to convert the optimal density distribution into variable-density lattice structured design. Two three-dimensional (3D) examples are used to validate the proposed method, where the designs are printed by the EOS direct metal laser sintering (DMLS) process in Ti6Al4V. Experimental results obtained from dynamical testing of the printed samples and detailed simulation results are in good agreement with the homogenized model results, which demonstrates the accuracy and efficiency of the proposed method.
The RMS value of total HOAs, coma-like, trefoil-like, third-order, fourth-order, and fifth-order aberrations are correlated with age, and the RMS values and Zernike coefficients of aberrations were different in different age stages of the subjects. This study described the distribution of HOAs in children and adolescents and established 95% statistical normal values of HOAs for different ages of children and adolescents by analyzing the HOAs in a large number of the Han Chinese clinical population.
This study aims to investigate the inbound open innovation and firm performance in different time periods across different organisations. Specifically, a conceptual model at firm level analysis was proposed based on literature review. The model was tested with structural equation modeling, using the empirical data which were collected from 60 research centre projects and 62 business unit projects in 2008. Results reveal the causal relationship between the implementation of inbound open innovation and the firm performance in both research centre and business unit. Comparative results showed that regarding research centre, increasing the frequency of inbound open innovation, efficient interal R&D activities and the higher degree of product newness make projects stable and efficient; consequently, the success of firm performance is achieved. As for the business unit, the frequently inbound open innovation practices are necessary for terms of generating efficiency and outcomes, and efficient inter R&D stargeties are significant conditioned by the degree of product newness, contributing to the firm performance as well.
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