查看更多>>摘要：Pump dynamic operational conditions result in extreme transient events that can enhance the response of piping networks. The predominant transients during rapid startup and shutdown are mainly studied for centrifugal pumps and are scarce for reciprocating pumps. Our study extends the conventional steady-state analysis to include the effect of reciprocating pump dynamic loading on pulsatile flow-induced acoustics and vibrations in a complex piping network. The forced response resulting from acoustical–structural coupling is assessed by utilising the one-dimensional multiphysics piping acoustic model and beam structural model. The network responses to pulsatile flows during dynamic pump loading (rapid start-up-shutdown events) are compared to the responses due to pulsatile flows during steady-state pump loading. With pump startup–shutdowns operations accompanied by pulsatile flows, the network response is the result of the combination of the transient and steady-state characteristics of plane acoustic waves and structural vibrations. The dynamic pump loading excites the fundamental, low-frequency acoustic eigenmode that causes transient loading of pipeline similar to reservoir–pipe–valve (RPV) systems.
查看更多>>摘要：Ultrasonic Machining (UM) is extensively used in processing of difficult to cut materials due to its superior performance. However, the mechanics of this process is still not fully understood when superimposed on other machining operations. In this paper, Longitudinal-Torsional Ultrasonic Assisted Milling (LTUAM) is introduced for machining of a high strength titanium alloy Ti-6Al-4V. The separation geometrical characteristics between the tool and workpiece are studied analytically. Moreover, the texturing generation mechanism of LTUAM is analyzed through a theoretical model. The proposed method considers the influence of 3D tool topography, which can accurately simulate the ultrasonic surface topography. Related experiments of the generated cutting force and the surface topography were conducted to investigate the machining characteristics. The results showed that compared with Conventional Milling (CM), a noticeable decrease of the cutting force was observed in LTUAM. This can be explained from the perspective of tool workpiece contact rate model. Micro dimpled surface textures were successfully fabricated on Ti-Al6-4V using LTUAM technique. The surface test results indicated that the surface micro-hardness was enhanced between 6.34% and 13.22% compared with CM. This research provides guidance for applications of ultrasonic machining to textured surfaces.
查看更多>>摘要：This paper presents the original incorporation of the smeared crack band (SCB) damage model within the full layerwise theory (FLWT) framework, to contribute to the increase of the computational efficiency of the progressive failure analysis of open-hole laminar composites loaded in tension, simultaneously preserving the accuracy of the conventional 3D finite element models. The developed FLWT-SCB prediction model was implemented into an original FLWTFEM framework allowing for the accurate 3D stress fields and excellent visualisation capacity. The response of damaged lamina, in both fiber and matrix directions, was described by distinct bilinear strain-softening curves. The mesh dependency problem was minimized by scaling the fracture energy using a characteristic element length. Both the failure initiation and failure modes were determined using the Hashin failure criterion. To verify the model effectiveness, the obtained results were compared against the experimental and benchmark data from the literature. Mesh dependency was analysed to confirm the benefits of suggested model, as well. The obtained results agreed with the experimental ones and those from the literature. According to the numerical results, FLWT-SCB allows for coarser meshes than those used in the standard finite element models, leading to improved computational efficiency without compromising the accuracy. The model also demonstrated the weak dependency between the size of the structure and the mesh. The advantages of using FLWT-SCB damage model in achieving significant improvements in computational efficiency are highlighted.
查看更多>>摘要：Cardiovascular system diseases, as aortic valve stenosis, are the main cause of mortality and morbidity among patients. There is still a room for enhancement of the diagnostic and therapeutic procedures, which will lead to improvement of the treatment. One of the remedies are the computer tools to support the medical diagnoses and prostheses design. The development of a procedure for modeling the aortic valves: anatomical tricuspid valve and artificial bileaflet valve, still is a very challenging task. In presented work, the application of the novel, advanced moving mesh model, that consists of the coupling of the dynamic mesh smoothing and the overset mesh technique, to speed up the computation and improve the convergence and stability was shown. The real 2D and 3D vasculature and valve geometries were created based on the echocardiography images available in literature. The calculations of anatomical and artificial valve models were performed for the various severity of the atherosclerosis — not previously published for the bileaflet mechanical valve. The impact of calcification process onto natural and artificial aortic valves was assessed and compared.
查看更多>>摘要：Modifying epoxy resin molecules using phosphorus-containing functional groups can enhance the liquid oxygen compatibility (LOC) of polymeric matrix composites, but will significantly change the mechanical and fracture properties of the functionalized thermosets due to the increased complexity of the molecular architecture. The underlying mechanisms responsible for these property changes are not well understood. In this work, we unveiled the molecular-scale fracture mechanisms of epoxy resins modified by 10-(2,5-dihydroxyphenyl) -10-hydrogen-9-oxa1-phenanthroline-10-oxide (ODOPB) using molecular dynamics (MD) simulations. We adopted a two-step reaction scheme to prepare the modified cross-linked networks of the epoxy thermosets. Then, a fracture simulation approach was developed based on hybrid use of non-reactive and reactive force field parameters, which enables accurate and efficient bond scission representation during tensile deformation. Efforts were made to explore the impact of varying the P content (proportional to ODOPB amount) on the molecular architectures and mechanical performance. It was found that the chain length distribution was a crucial determinant of the mechanical and fracture properties. More intriguingly, the simulation results showed that at a fixed P content, properties such as the fracture energy could be enhanced by regulating the chain length. This study offers valuable insights into the design and fabrication of high-performance aerospace composites with remarkable tolerance to harsh engineering environments.
查看更多>>摘要：Acoustic metasurfaces (AMs) used for reflected sound wavefront manipulation are generally designed based on the generalized Snell's law (GSL) at a single frequency, suffering from inferior broadband properties. Herein, an acoustic meta-porous layer (AMPL) with periodic structures is designed to realize reflected wavefront manipulation and effective sound absorption over a wide frequency band. The AMPL is constructed by four periodically arranged units, each consisting of porous elements inserted by acoustically rigid partitions, forming a linear reflected phase-shifting within 0 to 2π maintaining in a target frequency range of [1000,3000]Hz. To predict the reflected response of the element of the AMPL, an analytical model is proposed based on the transfer matrix method and is numerically validated. The sound reflection and absorption performance of the AMPL is investigated numerically and experimentally. The scattering sound pressure fields under normally and obliquely incident sound waves at different frequencies demonstrate the broadband reflected wavefront manipulation capability, including negative reflection and surface wave conversion. Compared to a uniform porous foam, an effective absorption is achieved by the AMPL due to the surface wave excitation at an identical thickness of 40 mm, with an averaged absorption coefficient greater than 0.9 in [800,3000]Hz. The results suggest the proposed structure could be a promising candidate of broadband noise absorption metamaterial for practical applications.
查看更多>>摘要：Compressive tests are performed on hollow carbon-fibre-reinforced-plastic (CFRP)/aluminium columns (H-C), foam-filled CFRP/aluminium columns (HF-C), and the corresponding net components. The energy absorption of the H-C column is lower than the total energy absorption of the net components under loading angles of 0° and 10°. The energy absorption of the HF-C column decreases under a 0° loading angle but increases under a 10° loading angle compared with the sum of the net components. Numerical models for the net components and the multimaterial hybrid columns are developed in LS-DYNA. Simulations indicate that the energy absorption reductions of external CFRP tubes primarily decrease energy absorption of hybrid columns, whereas energy absorption improvements in internal aluminium tubes primarily increase the energy absorption of hybrid columns, and that foam fillings can significantly improve crushing behaviours of aluminium tubes. Furthermore, parametric studies indicate that the energy absorption of hybrid columns can be increased by increasing the CFRP thickness and foam density. Finally, a discrete procedure is conducted to optimise the crashworthiness of hybrid columns with structural mass and crushing force constraints under multiple loads. Results indicate that compared with the baseline design, the energy absorption is improved by 7%, whereas the cost is reduced by 1.8%.
查看更多>>摘要：A flow-induced vibration (FIV) investigation to show the transition from vortex-induced vibration (VIV) to galloping for a circular cylinder equipped with a rear rigid splitter plate was undertaken in a water tunnel at Reynolds number of 1100-7700. The length of the splitter plate is in a range of L?=0-4.0 (L? = L/D, L is the plate length, D is the cylinder diameter). The dependence of oscillation characteristics, vortex evolution, force coefficients, mean added mass and effective added mass on L? is illustrated in detail. In the investigated L?, five oscillation patterns are identified successively: VIV, combined VIV–galloping, separated weak VIV (WVIV)–galloping, WVIV and weak galloping, WVIV and desynchronized. For L? = 0.4–1.8, severe galloping is observed at high reduced velocities. The oscillation can be well suppressed when L?>3.2. The transition from VIV to galloping, indeed, is the competition of vortex shedding and free shear layers attachment. At low reduced velocities, the oscillation is always synchronized with the vortex shedding. Beyond a critical plate length (0.4D), however, galloping is found at high reduced velocities, despite of the interference of vortex shedding. Harmonic force component at three times the oscillation frequency is identified in the galloping dominated region for L? = 0.4–1.8. Although it has little energy transfer to the oscillation, considerable negative effective added mass is induced.
查看更多>>摘要：In this paper, a new analytical model of ultrasonic shot peening (USP) that can predict the impact velocity and the residual stress distribution was proposed and verified by experiments and simulations. The motion law of a single sphere during USP and effect of ultrasonic vibration on restitution coefficient are analyzed and a formula that can estimate the rebound velocity of the sphere after collision with the ultrasonic sonotrode using initial velocity, ultrasonic amplitude and frequency was proposed. Then, an analytical model to predict the impact velocity of the spheres was proposed and verified by high-speed camera observation. Besides, based on Hertz contact theory and Hill's elastic-plastic spherical shell expansion theory, the conversion between hydrostatic pressure and Hertz pressure was realized. Then, a new analytical model that can predict the deformation extent, stress variation and residual stress distribution of the ideal elastic-plastic plate impacted by a rigid sphere with a certain velocity was proposed and verified by finite element simulations. Based on the above two models and the results of two different stress superposition methods, an analytical model that can estimate the impact velocity and the residual stress distribution of the USP-treated plate surface layer with the USP process parameters and material properties of the sphere, sonotrode and treated material was proposed and experimentally verified. The calculated results are consistent with the experimental results well.
查看更多>>摘要：Using the potential theory and the mirror-image method, the three-dimensional (3D) Green's function solutions for a double-layer transversely isotropic thermoelastic plate with varying thickness were obtained for the first time. The exact 3D explicit closed analytical forms of the temperature and thermal-stress fields were expressed by simple functions. These forms can be used to accurately calculate the full-field distribution under heat source, which is suitable for plates with a wide range for thickness—particularly for ultrathin coating plates. Results for numerical examples indicated that the coating thermal parameters, coating stiffness, and coating thickness ratio significantly affect the temperature increment and stress field. The influence rules of key parameters obtained in this study can guide the design of double-layer plates in thermal environments.
NSTL
Elsevier