Recent progress in Mg-based alloys as a novel bioabsorbable biomaterials for orthopedic applications

Traditional orthopedic metal implants,such as titanium(Ti),Ti alloys,and cobalt-chromium(Co-Cr)alloys,cannot be degraded in vivo.Fracture patients is must always suffer a second operation to remove the implants.Moreover,stress shielding,or stress protection occurs when traditional orthopedic metal implants are applied in fractures surgery.The mechanical shunt produced by traditional orthopedic metal implants can cause bone loss over time,resulting in decreased bone strength and delayed fracture healing.Biodegradable metals that‘biocorrode’are currently attracting significant interest in the orthopedics field due to their suitability as temporary implants.As one of the biodegradable metals,magnesium(Mg)and Mg alloys have gained interest in the field of medicine due to their low density,excellent biocompatibility,high bioresorbability,and proper mechanical properties.Additionally,Mg ions released from the metal implants can promote osteogenesis and angiogenesis during the degradation process in vivo,which is substantially better for orthopedic fixation than other bioinert metal materials.Therefore,this review focuses on the properties,fabrication,biological functions,and surface modification of Mg-based alloys as novel bioabsorbable biomaterials for orthopedic applications.

Numerical Modelling of the Transient Hygroscopic Behavior of Flax-Epoxy Composite

This contribution deals with the development of a three-node triangular plane finite element to analyze the transient hygroscopic behavior of 2/2 twill flax fabric-reinforced epoxy composite.Several plates of this material were fabricated using the vacuum infusion process and composite specimens were then cut and aged in tap water at room temperature until saturation.To simplify,a plane modelling of water diffusion in the aged specimens is adopted and Fick’s model is used to describe the water diffusion kinetics.To highlight the heterogeneity of the flax-epoxy samples,the twill flax fabrics waviness is modelled with a sinusoidal undulation.In particular,we show that the proposed finite element formulation allows estimating the flax fiber radial diffusion coefficient by an inverse approach.

纯钨/310不锈钢异种材料激光熔化沉积探究

采用激光熔化沉积的方法,在310S奥氏体不锈钢钢表面进行纯钨材料的增材制造.结合金相显微镜(OM)、扫描电子显微镜(SEM)、能谱分析(EDS)、X射线衍射(XRD)及显微硬度仪等材料表征手段,对试样的微观组织结构、元素分布、物相组成及显微硬度进行了对比分析.结果表明:沉积层内部存在未完全熔化的钨颗粒,同时也存在完全熔化后重新凝固的富钨组织,其为金属间化合物Fe_(7)W_(6),并且该化合物主要以枝晶形式存在;未完全熔化的钨颗粒与铁基基质呈良好的冶金结合,结合界面生成了Fe_(7)W_(6)/W的核壳结构.

Numerical estimation of bank-propeller-hull interaction effect on ship manoeu-vring using CFD method

This paper presents a numerical investigation of ship manoeuvring under the combined effect of bank and propeller. The incompressible turbulent flow with free surface around the self-propelled hull form is simulated using a commercial CFD software （ANSYS-FLUENT）. In order to estimate the influence of the bank-propeller effect on the hydrodynamic forces acting on the ship, volume forces representing the propeller are added to Navier-Stokes equations. The numerical simulations are carried out using the equivalent of experiment conditions. The validation of the CFD model is performed by comparing the numerical results to the availa- ble experimental data. For this investigation, the impact of Ship-Bank distance and ship speed on the bank effect are tested with and without propeller. An additional parameter concerning the advance ratio of the propeller is also tested.

3-D NUMERICAL SIMULATION OF CONVOY-GENERATED WAVES IN A RESTRICTED WATERWAY

We consider waves generated by the passing of convoys in a restricted waterway. The magnitude of these waves depends mainly on the geometrical and kinematical parameters of the convoy, such as the speed and the hull geometry. The objective of this study is to predict the relationship between these geometrical and kinematical parameters and the amplitude of ship-generated waves as well as the water plane drawdown. Numerical simulations are conducted by solving the 3-D Navier-Stokes equations along with the standard k-c model for turbulent processes. The results are compared first with the empirical model and second with experimental measurements performed by the French company Compagnie National du Rhone （CNR）.

Assessment of ship manoeuvrability by using a coupling between a nonlinear transient manoeuvring model and mathematical programming techniques

In this paper, a numerical method based on a coupling between a mathematical model of nonlinear transient ship manoeuvring motion in the horizontal plane and Mathematical Programming （MP） techniques is proposed. The aim of the proposed procedure is an efficient estimation of optimal ship hydrodynamic parameters in a dynamic model at the early design stage. The proposed procedure has been validated through turning circle and zigzag manoeuvres based on experimental data of sea trials of the 190 000- dwt oil tanker. Comparisons between experimental and computed data show a good agreement of overall tendency in manoeuvring traiectories.

Impacts of ship movement on the sediment transport in shipping channel

The duration of ship-generated waves （wake waves） and accelerated currents can generate significant influences on the sediment transport. A 3-D numerical model is presented to estimate these effects. The hydrodynamic model is the 3-D Reynolds averaged Navier-Stokes （RANS） equations including the standard k - ε model while the 3-D convection-diffusion model is for the resuspended sediment transport. This hydro-sedimentary model is firstly validated with the trench experimental results, and then applied to the open channel with a moving ship. The computed results demonstrate that the resuspension generation mainly depends on ship speeds, barge number, and the relative distance away from ship. The acceleration effects of ship on the sediment transport are analyzed as well.

Numerical Research of Flow past a Circular Cylinder with Splitter Plate at a Subcritical Reynolds Number Region

Numerical research of flow past a circular cylinder with a splitter at the subcritical Reynolds number region of 5 × 10~4—9 × 10~4 was researched based on Computational Fluid Dynamics(CFD) through solving twodimensional incompressible unsteady Reynolds-averaged Navier-Stokes(URANS) equations with the shear stress transport(SST) k-ω turbulence model. Three different grid resolutions were employed in the verification and validation study of the adopted turbulence model. Various fluid characteristics such as Strouhal number, lift coefficient of the cylinder and the splitter with respect to various splitter lengths and different Reynolds numbers were investigated. It was revealed that the lift coefficient ratio of the splitter over the cylinder remains near 1.6 when the splitter length is 1.5—4 times the cylinder's diameter. Vortex shedding is strongly inhibited when the splitter length is greater than a critical value of around four times the cylinder's diameter. The phase difference of the lift coefficient on the upper and lower surface of the splitter varies between-30?and 30?. The maximal lift coefficients are reached when the splitter length is about 2 times the cylinder's diameter. Besides, the splitter length has little influence on the separation angle around the cylinder.

Simulation of the overtaking maneuver between two ships using the non-linear maneuvering model

The overtaking maneuver of two Esso Bernicia 1.9×10^5 DWT tankers was investigated using the system-based maneuvering method. The Brix model was incorporated to account for the overtaking interactions. Forces/moment acting on the ship hulls and maneuvering motions were analyzed for both ships during the overtaking. The influences of the speed ratio and the passing distance were specially studied. Two fitting formulas for the minimum distance during the overtaking were finally established as functions of the two factors respectively. They can be used to predict the minimum distance during an overtaking maneuver under similar conditions to avoid marine accidents.

Ship maneuvering prediction based on virtual captive model test and system dynamics approaches

The maneuvering simulation is carried out through the continuous captive model test and the system dynamics approach.The mathematical maneuvering group(MMG)model is implemented in the virtual captive model tests by using the computational fluid dynamics(CFD)techniques.The oblique towing test(OTT),the circular motion test(CMT),the rudder force test and the open water test are performed to obtain the hydrodynamic derivatives of the hull,the rudder and the propeller,and the results are validated by experimental data.By designing the tests,the number of cases is reduced to a low level,to allow us to evaluate the maneuverability with a low cost and in a short time.Using these obtained coefficients,the system-based maneuvering simulations are conducted to calculate the position and the attitude of the ship,with results in agreement with the free running test results.This procedure can also be used for other hull forms,with reduced workload and with convenience for maneuvering simulation tasks.

TE Mode Mixing Dynamics in Curved Multimode OpticalWaveguides

Propagation of light through curved graded index optical waveguides supporting an arbitrary high number of modes is investigated.The discussion is restricted to optical wave fields which are well confined within the core region and losses through radiation are neglected.Using coupled mode theory formalism,two new forms for the propagation kernel for the transverse electric(TE)wave as it travels along a curved two-dimensional waveguide are presented.One form,involving the notion of“bend”modes,is shown to be attractive from a computational point of view as it allows an efficient numerical evaluation of the optical field for sharply bent waveguides.