Designing Mu Robust Controller in Wind Turbine in Cold Weather Conditions

Due to wind turbine is in class of complex nonlinear system so the precise model of this plant is not accessible, therefore it can be categorized as an uncertain model. So, controlling of this system is a demanding topic. Many of schemes which presented for controlling of wind turbines investigate these systems in a good weather condition. However, many turbines work in severe weather condition. In this study, wind turbine is suggested in cold weather, and in ice on turbine blades which they are considered as uncertainties in the model. A robust controller is designed for the wind turbine, to control the pitch angle

A COMPLIANT ANKLE-FOOT ORTHOSIS (AFO) BASED ON MULTI-AXIAL LOADING OF SUPERELASTIC SHAPE MEMORY ALLOYS

ABSTRACT This paper presents a novel actuation solution to address the drop foot disorder. The proposed actuator consists of a superelastic Nitinol rod with a variable torsional stiffness that is adjusted by the controlled application of an axial load. The superelastic SMA element enables the AFO to provide sufficient torque during dorsiflexion to raise the foot. The provided torque at the ankle joint assists the patient in walking more naturally and subsequently prevents further issues such as muscle atrophy. By appraising experimental data of the human gait, ankle stiffness is assessed in order to compare ankle behavior for various walking speeds during the swing phase. The adjustable compliance concept for the AFO is then explained, followed by a description of the actuation mechanism and complex loading configuration. Numerical modeling is also presented for the superelastic element of the AFO under specified multiaxial torsion-tension loading. Simulations are performed in MATLAB and variable stiffness results are compared with experimental data for verification

The development of TiNi-based negative poisson's ratio structure using selective laser melting

AbstractThere is a growing interest in using additive manufacturing to produce smart structures, which have the capability to respond to thermal and mechanical stimuli. In this report, Selective Laser Melting (SLM) is used to build a Negative Poisson's Ratio (NPR) TiNi-based Shape Memory Alloy (SMA) structure, creating a multi-functional structure that could be used as reusable armour. The study assesses the influence of SLM process parameters (laser power, scan speed, and track spacing) on the microstructural and structural integrity development in a Ti-rich TiNi alloy, as well as the impact of the post-process homogenisation treatment on the microstructure and phase transformations. The builds generally shows stress-induced cracks and residual porosity, which could be minimised through process optimisation. Nonetheless, the homogenisation treatment is essential to reduce the fraction of Ti2Ni intermetallics, which are known to disturb the B19′-chemistry, and hence the required phase transformation temperatures. The optimum process parameters are finally used to fabricate NPR structures, which were mechanically tested to validate the Poisson's ratio predictions. A higher ductility was observed in the structures that have undergone the homogenisation treatment

In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion

Porosity and high surface roughness can be detrimental to the mechanical performance of laser powder bed fusion (LPBF) additive manufactured components, potentially resulting in reduced component life. However, the link between powder layer thickness on pore formation and surface undulations in the LPBF parts remains unclear. In this paper, the influence of processing parameters on Ti-6Al-4 V additive manufactured thin-wall components are investigated for multilayer builds, using a custom-built process replicator and in situ high-speed synchrotron X-ray imaging. In addition to the formation of initial keyhole pores, the results reveal three pore phenomena in multilayer builds resulting from keyhole melting: (i) healing of the previous layers' pores via liquid filling during remelting; (ii) insufficient laser penetration depth to remelt and heal pores; and (iii) pores formed by keyholing which merge with existing pores, increasing the pore size. The results also show that the variation of powder layer thickness influences which pore formation mechanisms take place in multilayer builds. High-resolution microcomputed tomography images reveal that clusters of pores form at the ends of tracks, and variations in the layer thickness and melt flow cause irregular remelting and track height undulations. Extreme variations in height were found to lead to lack of fusion pores in the trough regions. It is hypothesised that the end of track pores were augmented by soluble gas which is partitioned into the melt pool and swept to track ends, supersaturating during end of track solidification and diffusing into pores increasing their size

Future of additive manufacturing: Overview of 4D and 3D printed smart and advanced materials and their applications

© 2020 Elsevier B.V. 4D printing is an emerging field in additive manufacturing of time responsive programmable materials. The combination of 3D printing technologies with materials that can transform and possess shape memory and self-healing capabilities means the potential to manufacture dynamic structures readily for a myriad of applications. The benefits of using multifunctional materials in 4D printing create opportunities for solutions in demanding environments including outer space, and extreme weather conditions where human intervention is not possible. The current progress of 4D printable smart materials and their stimuli-responsive capabilities are overviewed in this paper, including the discussion of shape-memory materials, metamaterials, and self-healing materials and their responses to thermal, pH, moisture, light, magnetic and electrical exposures. Potential applications of such systems have been explored to include advancements in health monitoring, electrical devices, deployable structures, soft robotics and tuneable metamaterials

Investigating Microstructural Effects on Hall-Petch Relationship of Mg-4Al Alloy

Grain size strengthening, referred to as the Hall-Petch effect, is a common strategy to improve the yield strength of magnesium (Mg) alloys. Several theoretical studies have reported that the geometry and structure of grain boundaries in polycrystalline materials could impose a significant effect on the Hall-Petch slope. However, experimental observations are primarily limited by the ability of the techniques to accurately quantify the grain boundary barrier strength to dislocation glide and validate these theoretical models. Using high-resolution electron backscatter diffraction (HR-EBSD), the local stress tensor ahead of a slip band blocked by a grain boundary was quantified and coupled with a continuum dislocation pile-up model to assess the barrier strength of specific grain boundaries to specific slip systems, referred to as micro-Hall-Petch coefficient. For basal slip system in a deformed Mg-4Al alloy, the micro-Hall-Petch coefficient (PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/172590/1/mtaheri_1.pd

Prediction of the Elastic Response of TPMS Cellular Lattice Structures Using Finite Element Method

Cellular lattice structures are a group of porous materials in which the cells are regularly distributed. Since the morphology of the cells is complicated, the fabrication of them is challenging using conventional methods. However, with the advent of additive manufacturing technology, more attention is focused on these classes of materials because the regular geometry makes it possible to tailor the mechanical response of the structure. Among all kinds of cellular lattice structures, those based on triply periodic minimal surfaces are of great importance due to mechanical and biological properties. Since the fabrication of such structures is challenging and expensive, it is desirable to predict their mechanical response before fabrication. In this paper, finite element approach is employed to predict the elastic response of two well-known Schwarz minimal surfaces named P-Type and G-Type. To do so, first, the cloud points of the surfaces are generated using the implicit equation of the surface and are converted into solid finite element models. The results show that at the same value of porosity, the P-Type specimen provides a higher value of elastic modulus than G-Type one.Mechanical Engineerin

Novel Approach to Grain Boundary Modification in Stainless and Duplex Steel L-PBF Components through In Situ Heat Treatment

Additive manufacturing (AM) has provided new possibilities for improving the grain boundary properties of metallic components. However, effectively modifying the microstructure, particularly the grain boundary properties, of laser powder bed fusion (L-PBF) components remains a challenge. Post-processing methods have shown some success in adjusting grain boundary angles, but they have limitations when it comes to complex geometries and internal features. In this study, we propose an innovative in situ heat treatment to control the grain boundary properties of L-PBF components. A model is proposed to predict the thermal cycle at a single point, and it is validated through experiments on 2507 super duplex steel and 316L austenitic steel samples. The results demonstrate that, by applying controlled in situ heat treatment, the dynamic recovery processes can be influenced, and thereby the grain boundary properties of the manufactured parts can be controlled. This proposed method improves our understanding of the impact of in situ heat treatment on grain boundary properties and offers potential for designing and fabricating high-performance L-PBF components. The findings from this study lay the groundwork for the further exploration of grain boundary engineering in metallic components using L-PBF. By leveraging in situ heat treatment, future research can open up new avenues in additive manufacturing, facilitating the production of advanced and high-quality metallic components

An Adjustable Zero Vibration Input Shaping Control Scheme for Overhead Crane Systems

This article presents a modified zero vibration (ZV) input shaping technique to address the sensitivity and flexibility limitations of the classic ZV shapers commonly implemented in overhead crane applications. Starting with the classical ZV formulation, new parameters are introduced to optimize the control system performance according to a versatile objective function. The new shaper enhances the design flexibility and operational domain of the shaper, while it inherits the robustness properties and computational efficiency of the ZV scheme. Unlike the original ZV shaper, the proposed shaper allows for the point-to-point maneuver time to be fixed. The sensitivity analysis of the controller confirms that the new shaper effectively reduces the ZV sensitivity to the cable length variations

A Quantitative Study of Slip Band-Grain Boundary Interactions in Mg Alloys

International audienceFundamental understanding of defect-defect interactions such as dislocations-grain boundaries (GBs), GBs-twins, GBs-solute atom, dislocations-twins, and dislocations-precipitates are essential to assess the mechanical properties of polycrystalline materials. Under an applied load, dislocation glide accommodates plastic deformation until impeded by obstacles such as grain boundaries. The pileup of dislocations at a grain boundary successively increases the stress concentration until the boundary barrier to slip transmission is exceeded, resulting in slip transmission and further deformation. Such a theory has been proposed to explain the empirical Hall-Petch equation, which predicts the flow stress of a slip system is inversely proportional to the square root of the grain size. Despite theoretical research dedicated to studying the role of GB parameters on the flow stress of a slip system, our experimental understanding of how measure the stress field induced by blocked dislocations at a GB and its subsequent effect on the flow stress is still limited. The objective of this work is to utilize high-resolution electron backscatter diffraction technique combined with a dislocation pile-up model to assess the Hall-Petch coefficients at the microscopic level for different GB types. A simple phenomenological relationship to account for grain misorientation is proposed to foster implementation of grain size effects on the critical resolved shear stresses used in crystal plasticity constitutive models. Obtaining such microstructural measurements will help to accurately calibrate the crystal plasticity finite element constitutive model to predict the mechanical response of magnesium alloys, considering both the grain size and geometrical features of grain boundaries. This research will provide new insight into understanding the GB effect in plasticity of Mg alloys