A computational approach for predicting the hydroelasticity of flexible structures based on the pressure Poisson equation

This work is concerned with the modeling of the interaction of fluid flow with flexible solid structures. The flow under consideration is governed by the Navier–Stokes equations for incompressible viscous fluids and modeled with low‐order velocity–pressure finite elements. The motion of the fluid domain is accounted for by the arbitrary Lagrangian–Eulerian formulation. The structure is represented by means of an appropriate standard finite element formulation. The spring smooth analogy is used to mesh control. The time integrating algorithm is based on the predictor–multi‐corrector algorithm. An important aspect of the present work is the introduction of a new monolithic approach based on the fluid pressure Poisson equation (PPE) to solve the hydroelasticity problem of an incompressible viscous fluid with an elastic body that is vibrating due to flow excitation. The PPE is derived to be consistent with the coupled system equation for the fluid–structure interaction (FSI). Based on this approach, an efficient monolithic method is adopted to simulate hydroelasticity between the flexible structure and the flow. The fluid pressure is implicitly derived to satisfy the incompressibility constraint, and the other unknown variables are explicitly derived. The coefficient matrix of the PPE for the FSI becomes symmetric and positive definite. To demonstrate the performance of the proposed approach, two working examples, a beam immersed in incompressible fluid and a guide vane of a Francis turbine passage, were used. The results show the validity of the proposed approach. Copyright © 2007 John Wiley & Sons, Ltd.     

Initial stages of the cubic-InN growth with the technique of the pre-deposition of indium

The initial stages of the cubic indium nitride film growth at 350 °C were studied using low-pressure metal-organic chemical vapor deposition. The technique of the pre-deposition of indium was applied, that is, a layer of indium was first deposited on sapphire surface before the growth of InN. X-ray diffraction and X-ray photoelectron spectroscopy show that the pre-deposition of indium is able to promote the growth of InN films, and meanwhile, suppress the indium aggregation in the as-grown films. Atomic force microscopy images of InN films indicate that the pre-deposition of indium not only enhances the density of nucleate sites, but also facilitates the coalescence among the InN islands. The free energy calculations reveal that the pre-deposited indium atoms preferentially react with NH and N radicals after NH₃ introduction, which leads to the formation of InN on the sapphire surface. The preferentially formed InN is then supposed to be responsible for the above phenomena.     

ADAPTIVE CONTROL DESIGN FOR NONLINEARLY PARAMETERIZED SYSTEMS WITH A TRIANGULAR STRUCTURE

A novel adaptive backstepping design for a class of nonlinearly parameterized systems with a triangular structure is proposed. Under the Lipschitz condition with respect to unknown parameters of the system, an effective adaptive controller is designed without the requirement on the compactness of the unknown parametric set. Especially, the proposed adaptive control enables the advantage of “tuning function concept”, which results in only one estimation law for the unknown parameters. Our simulation with induction motor model particularly shows the viability of the obtained results.     

Organic thin-film field-effect transistors with MoO3/Al electrode and OTS/SiO2 bilayer gate insulator

An organic thin-film transistor (OTFTs) having OTS/SiO₂ bilayer gate insulator and MoO₃/Al electrode configuration between gate insulator and source–drain (S–D) electrodes has been investigated. Thermally grown SiO₂ layer is used as the OTFT gate dielectric and copper phthalocyanine (CuPc) for an active layer. We have found that using silane coupling agents, octadecyltrichlorosilane (OTS) on SiO₂, surface energy of SiO₂ gate dielectric is reduced; consequently, the device performance has been improved significantly. This OTS/SiO₂ bilayer gate insulator configuration increases the field-effect mobility, reduces the threshold voltage and improves the on/off ratios simultaneously. The device with MoO₃/Al electrode has similar source–drain current (I_DS) compared to the device with Au electrode at same gate voltage. Our results indicate that using double-layer of insulator and modified electrode is an effective way to improve OTFT performance.     

Titanium based cranial reconstruction using incremental sheet forming

In this paper, we report recent work in cranial plate manufacturing using incremental sheet forming (ISF) process. With a typical cranial shape, the ISF process was used to manufacture the titanium cranial shape by using different ISF tooling solutions with and without backing plates. Detailed evaluation of the ISF process including material deformation and thinning, geometric accuracy and surface finish was conducted by using a combination of experimental testing and Finite Element (FE) simulation. The results show that satisfactory cranial shape can be achieved with sufficient accuracy and surface finish by using a feature based tool path generation method and new ISF tooling design. The results also demonstrate that the ISF based cranial reconstruction has the potential to achieve considerable lead time reduction as compared to conventional methods for cranial plate manufacturing. This outcome indicates that there is a potential for the ISF process to achieve technological advances and economic benefits as well as improvement to quality of life.     

Dynamics model and analysis of the lifting system of automatic catwalk北大核心CSCD

When the field test of rope pulled automatic catwalk was carried out, the load fluctuation of rope was obvious, and it was difficult to complete the lifting of the target weight column. Therefore, the structure and motion characteristics of rope pulled automatic catwalk were analyzed, and dynamic model based on the D'Alemebert principle was established, MATLAB software was used to analyze the influence of the distance between the block on the base and the bottom of the ramp, the hinge position of the transfer arm and the support arm, and the length of the support arm on the load of rope. The analysis results showed that adjusting the position of block on the base to the bottom of the ramp, and reducing the length of support arm could reduce the required force of rope in the process of lifting. According to the analysis results, the structure size of automatic catwalk was adjusted to carry out the field test, the test result showed that the maximum lifting oil pressure of the hydraulic which was decreased by more than 2 MPa, the lifting capacity of automatic catwalk was improved. The analysis and experimental results can guide the design and optimization of rope pulled automatic catwalk.     

Modified and Trefftz unsymmetric finite element models

The unsymmetric finite element method employs compatible test functions but incompatible trial functions. The pertinent 8-node quadrilateral and 20-node hexahedron unsymmetric elements possess exceptional immunity to mesh distortion. It was noted later that they are not invariant and the proposed remedy is to formulate the element stiffness matrix in a local frame and then transform the matrix back to the global frame. In this paper, a more efficient approach will be proposed to secure the invariance. To our best knowledge, unsymmetric 4-node quadrilateral and 8-node hexahedron do not exist. They will be devised by using the Trefftz functions as the trial function. Numerical examples show that the two elements also possess exceptional immunity to mesh distortion with respect to other advanced elements of the same nodal configurations.     

Study of Half-Metallic Ferromagnetism in Be0.75Ti0.25Y (Y = S,Se, and Te) Using Ab Initio Calculations: Potential Candidate for Spintronic Devices

The structural, elastic, electronic, and magnetic properties of Be_0.75Ti_0.25Y (Y = S, Se, and Te) have been investigated to understand their potential applications in spintonic devices. Crystals of BeS, BeSe, and BeTe, individually doped with Ti with a dopant concentration of x = 0.25, have been evaluated by using full-potential linearized augmented plane-wave plus local orbital method within the framework of density functional theory. We employed the Wu–Cohen generalized gradient approximation for optimizing the crystal structure and evaluating elastic properties. In order improve bandgap values and optical parameters, the modified Becke and Johnson (mBJ) potential has been employed. The theoretical investigation of band structure and density of states confirms the half-metallic ferromagnetic nature of these compounds. The elastic constants are calculated by the charpin method which shows that the compounds under consideration are brittle and anisotropic. Moreover, it is noted that tetrahedral crystal field splits the 3d state of Ti into triple degenerate t_2g and double degenerate e_g states. The exchange splitting energies Δ _x (d) and Δ _x (pd) and exchange constants (N ₀ α) and (N ₀ β) are predicted from triple degenerate t_2g states, and negative values of N ₀ β justify that the nature of effective potential is more attractive in spin down case rather than that in the spin up case. We also find the crystal field splitting (ΔE _crystal = E _t2g?E _eg) energy and reduction of the local magnetic moment of Ti from its free space charge value and creation of small local magnetic moments on the non-magnetic Be, S, Se, and Te sites by p–d hybridization.     

Erratum to “Finding the most efficient DMUs in DEA: An improved integrated model” [Comput. Indus. Eng. 52 (2007) 71–77]

There are two errors existing in “Finding the most efficient DMUs in DEA: An improved integrated model” (Amin & Toloo, 2007), one exists in the process of proving the theorem that “Theorem:model (3) is feasible (p. 75)”, while the other is that model (3) and model (4) are incorrectly built.     

基于改进蚁群算法的网格资源调度研究

为进一步掌握网格资源动态运行状态,以便合理调度网格资源,提高任务执行效率,提出了一种基于改进蚁群算法的网格资源调度策略。该算法引入了一个网格资源空闲所需时间向量F,通过向量F动态调整网格资源负载情况,达到快速实现遥感资源空间检索的目的。从仿真实验结果可以看出,改进蚁群算法比蚁群算法和其他算法更优,网格资源的利用效率更高。