Procedia IUTAM最新文献

During machining, the use of variable helix tools can potentially improve the system's stability to regenerative chatter. However, this configuration of tool has a distributed time delay, which makes the stability analysis more complex. The analysis is further exacerbated by the time-periodic coefficients that occur during milling. The present contribution demonstrates how the Fourier transform and harmonic transfer function approach can be used to analyse the system stability. This provides new insight into the stability of these tools, based on a mathematically elegant approach that makes extensive use of the shift theorem.

The present paper aimed at experimental study for the distortion of geometrical shape of thin walled structures manufactured by stereolithography technologies. It is proposed that total distortion occurring due to layer-by-layer photopolymerisation can be estimate using experimental data about distortion caused by curing single intermediate or final layer. The experiments used a sample in the form of a hollow cube. The distortion of the cube is recorded using time-average holographic interferometry.

This study deals with the nonlinear dynamics of a uniformly heated and simply-supported rectangular thin plate in the presence of two adjacent in-plane stick-slip-stop boundaries in order to release the thermal stresses in the plate. The analysis of linear vibration of the plate shows that the natural frequency of mode (2, 1) decreases with an increase of temperature and may coincide with the natural frequency of mode (1, 1) if the assembly forces on the in-plane movable boundaries are not very strong. Hence, the study focuses on the one-to-one internal resonance of the plate subject to weak assembly forces and temperature rise. Both analysis and numerical examples show that the one-to-one internal resonance happens for different combination of excitation amplitude and assembly forces, and exhibits a great variety of periodic, quasi-periodic and chaotic vibrations.

For linear delay-differential equations, a question of ongoing interest is to determine conditions on the equation parameters that guarantee exponential stability of solutions. Recent results have shown an unexpected link between the stable manifold and the variety characterizing multiple characteristic spectral values allowing to the right-most root assignment. In this paper, such an idea is presented and exploited in the control of active vibrations.

The role of a global dynamics analysis to assess a system robustness and actual safety in operating conditions is investigated by studying the effect of different local and global control techniques on the nonlinear behavior of a noncontact AFM via dynamical integrity concepts and tools.

Study of networks with multiple agent dynamics has been a central focus in systems and control community, with numerous results. Among them is the study of how time delays in sensing and actuation could affect network stability, and/or control design for the agents. However, little is known in published work regarding how to design agents’ protocols analytically to achieve fast stability reaching. Here, an approach is developed to optimize the rightmost roots of a class of large scale LTI network dynamics via Lambert W function, in order to accomplish this. Results indicate that a delay explicitly present in the controller as a coefficient can create conditions for arbitrary rightmost root assignment. This feature is scalable, can be implemented with ease, and applied effectively for relatively large/small delays.

Accurate forecasts of extreme storm surge water levels are vital for operators of major ports. Existing regional tide-surge models perform well at the open coast but their low spatial resolution makes their forecasts less reliable for ports located in estuaries. In December 2013, a tidal surge in the North Sea with an estimated return period of 760 years partially flooded the Port of Immingham in the Humber estuary, on the UK east coast. Damage to critical infrastructure caused several weeks of disruption to vital supply chains and highlighted a need for additional forecasting tools to supplement national surge warnings. In this paper, we show that Artificial Neural Networks (ANNs) can generate better short-term forecasts of extreme water levels at estuarine ports. Using Immingham as a test case, an ANN is configured to simulate the tidal surge residual using an input vector that includes observations of surge at distant tide gauges in NW Scotland, wind and atmospheric pressure, and the predicted astronomical tide at Immingham. The forecast surge time-series, combined with the astronomical tide, provides a boundary condition for a local high-resolution 2D hydrodynamic model that predicts flood extent and damage potential across the port. Although the forecasting horizon of the ANN is limited, 6 to 24 hour forecasts at Immingham achieve an accuracy comparable to or better than the UK national tide-surge model and at far less computational cost. Use of a local rather than a larger regional hydrodynamic model means that potential inundation can be simulated very rapidly at high spatial resolution. Validation against the 2013 surge shows that the hybrid ANN-hydrodynamic model generates realistic flood extents that can inform port resilience planning.

This paper describes a model package that simulates wave transformation, overtopping and flooding in coastal reaches. The present model is extended from the non-linear shallow water equations by means of including the non-hydrostatic pressure terms in the momentum equations. The transformed vertical coordinate, i.e. the σcoordinate, is adopted to fit the free surface and the uneven bottom. When a wave is ready to break, the non-hydrostatic model is locally switched to hydrostatic model by suppressing the dispersive effects. The breaking wave front is handled as a shock, and the shock wave can be simulated by non-linear shallow water equations with conservative numerical strategy. The treatments of the wave breaking and the shoreline motion are validated by experiments. One extensive application of the model to predict flooding induced by large waves or storm surge is presented to verify the efficiency of the present model in modeling of wave transformation and flooding over complex geometry in coastal reaches.

The Ni₃Al intermetallics involve more attention because of inherent material properties especially interesting in high temperature application. In this study, the Selective Laser Melting (SLM) and Direct Laser Metal Deposition (DLMD) are used to manufacture the single-tracks and layers. The optical microscopy, SEM, XRD and EDX microelement analysis were involved for the comparison of the methods. The materials showed no significant differences but each SLM and DLMD have the target application.

Selective laser melting is a layer-by-layer technique to form a solid part from powder. The thermal cycle of this process can be as short as one millisecond and less. This is why it is favorable to obtain nanostructured materials with advanced properties. Metal matrix composite WC-Co is studied. Micron-sized Co powder was mixed with WC nanopowder in a planetary ball mill to prepare uniform composite powder. Single remelted beads and monolayers were obtained from the composite powder on the substrates of sintered WC-Co. No cracks and good adhesion to the substrate are observed. The high cooling rate up to 10⁶ K/s explains the fine microstructures. Increasing the scanning velocity is favourable because of refining the microstructure and decreasing the balling-effect. The attained values of surface roughness are as low as 1-2 μm.