Virtual real mapping method of marine condensate feedwater system based on multi-domain modeling

ObjectiveIt is difficult to carry out effective online monitoring and condition evaluation using traditional modeling and analysis methods. Therefore, it is imperative to research an accurate and effective virtual real mapping method for the whole life cycle of a marine condensate feedwater system.MethodsOn the basis of multi-domain modeling, this paper combines the mechanism model with multi-source data, uses the multi-domain physical modeling language Modelica/MWorks system simulation platform to build a digital twin model of the condensate feedwater system, and integrates online and offline data, numerical calculation, simulation analysis and other methods to evaluate the operating state characteristics of the condensate feedwater system.Results The established model can analyze the dynamic characteristics of the condensate feedwater system under all working conditions with a static analysis error lower than 2%. The dynamic response trend is consistent with the actual operation. ConclusionsThis study shows that the proposed method can realize virtual real mapping between the physical entity and the digital twin model of the marine condensate feedwater system, thereby laying a foundation for the health management of shipborne thermal equipment

Research on the Vanishing Point Detection Method Based on an Improved Lightweight AlexNet Network for Narrow Waterway Scenarios

When an unmanned surface vehicle (USV) navigates in narrow waterway scenarios, its ability to detect vanishing points accurately and quickly is highly important for safeguarding its navigation safety and realizing automated navigation. We propose a novel approach for detecting vanishing points based on an improved lightweight AlexNet. First, a similarity evaluation calculation method based on image texture features is proposed, by which some scenarios are selected from the filtered Google Street Road Dataset (GSRD). These filtered scenarios, together with the USV Inland Dataset (USVID), compose the training dataset, which is manually labeled according to a non-uniformly distributed grid level. Next, the classical AlexNet was adjusted and optimized by constructing sequential connections of four convolutional layers and four pooling layers and incorporating the Inception A and Inception C structures in the first two convolutional layers. During model training, we formulate vanishing point detection as a classification problem using an output layer with 225 discrete possible vanishing point locations. Finally, we compare and analyze the labeled vanishing point with the detected vanishing point. The experimental results show that the accuracy of our method and the state-of-the-art algorithmic vanishing point detector improves, indicating that our improved lightweight AlexNet can be applied in narrow waterway navigation scenarios and can provide a technical reference for autonomous navigation of USVs

Hot deformation behavior and processing map of a superlight dual-phase Mg–Li alloy

Hot deformation behavior of a superlight dual phase Mg-9Li-3Al-2Y alloy was investigated by developing constitutive equations and constructing processing maps. Constitutive relationship was established by the prediction of materials constants (α β n, Q and lnA) based on true stress-strain curves. Processing maps were constructed for Mg-9Li-3Al-2Y alloy based on dynamic materials model (DMM). The instability domains occurred over a narrow temperature range of 423–450 K and strain rate range of 0.01–1s−1, and over a temperature range of 560–573 K and close to strain rate of 1s−1. The twinning in ɑ-Mg phase and cracks in the matrix were observed in the instability domains, the refined dynamic recrystallization (DRX) grains were formed in the regions with high efficiency values. It is undesirable to deform at high strain rates for mechanical properties because of the instability. Dynamic recrystallization occurs first in β-Li phases, and the Al2Y particles were conducive to the DRX process with particle stimulated nucleation effect. The DRX process of ɑ-Mg phase was retarded by β-Li phase. The DRXed grains of β-Li phase showed a random texture, while the basal poles of ɑ-Mg phase rotated towards the normal direction, which can enhance the further deformation. Based on constitutive relationship, processing map and texture evolution, the Mg-9Li-3Al-2Y alloy is easy to suffer from deformation at a wide range of temperatures and strain rates

Dynamic Recrystallization Behavior and Corrosion Resistance of a Dual-Phase Mg-Li Alloy

The hot deformation and dynamic recrystallization behavior of the dual-phase Mg-9Li-3Al-2Sr-2Y alloy had been investigated using a compression test. The typical dual-phase structure was observed, and average of grain size of as-homogenized alloy is about 110 µm. It mainly contains β-Li, α-Mg, Al4Sr and Al2Y phases. The dynamic recrystallization (DRX) kinetic was established based on an Avrami type equation. The onset of the DRX process occurred before the peak of the stress–strain flow curves. It shows that the DRX volume fraction increases with increasing deformation temperature or decreasing strain rate. The microstructure evolution during the hot compression at various temperatures and strain rates had been investigated. The DRX grain size became larger with the increasing testing temperature or decreasing strain rate because the higher temperature or lower strain rate can improve the migration of DRX grain boundaries. The fully recrystallized microstructure can be achieved in a small strain due to the dispersed island-shape α-Mg phases, continuous the Al4Sr phases and spheroidal Al2Y particles, which can accelerate the nucleation. The continuous Al4Sr phases along the grain boundaries are very helpful for enhancing the corrosion resistance of the duplex structured Mg-Li alloy, which can prevent the pitting corrosion and filiform corrosion

Risk Assessment Method for Ship Based on Improved Fuzzy Multicriteria Decision-Making

Aimed at the uncertainties and relevance issues during the risk factor identification in multicriteria decision-making, this paper presents a ship risk assessment model based on the improved fuzzy multicriteria decision-making. First, on the basis of safety assessment and importance judgment of risk sources conducted by experts, the peer-to-peer consensus model is employed to integrate the relative importance of risk sources and obtain the weight of experts; the weight of risk factors is then determined by nonlinear programming model according to the experts’ preference for risk sources; finally, the risk assessment is carried out using the MULTIMOORA method and the final ranking of the alternatives is determined by means of the fuzzy number quantitative calculation method. Analysis and research are conducted on specific causes of ship engine room fires, and the results are compared with outcomes of the traditional MULTIMOORA method and the fuzzy analytic hierarchy process based on Monte Carlo simulation. It is concluded that the calculated ranking results are more reasonable, hence verifying the superiority of this model

Microstructure and Mechanical Behavior of Mg-10Li-3Al-2.5Sr Alloy

As-cast Mg-10Li-3Al-2.5Sr alloy was prepared and extruded at 340°C using double change channel pressing (DCCAP) with an extrusion ratio of 4.5. The microstructure and mechanical response of the as-cast and the extruded alloy are reported and discussed. The present results show that Mg-10Li-3Al-2.5Sr alloy contains bcc β-Li, hcp α-Mg and Al4Sr phases, and that the matrix primarily consists of the β-Li phase. The microstructure in the as-cast alloy shows ultrafine primary regions and coarse eutectic structures with an average grain size of 450nm, attributable to the solidification conditions. Dynamic recrystallization (DRX) is reported to occur during the DCCAP process and DRX lead to grain refinement in coarse eutectic regions and a concomitant increase of grain size in ultrafine primary regions. As a result of DRX, the microstructure in the extruded alloy, with an average grain size of 501nm, is more homogeneous than that in the as-cast one. Moreover, the dislocation density in the DCCAP-processed alloy is lower than that in the as-cast alloy as a result of DRX. The tensile strength of the as-cast alloy (172±7MPa) is slightly higher than that of the extruded one (165±6MPa), whereas the ductility of the extruded alloy (42.2±3.0%) is significantly higher than that of the as-cast one (13.6±1.0%)

Constitutive modeling of Mg-9Li-3Al-2Sr-2Y at elevated temperatures

Abstract Constitutive modeling of Hot deformation behavior of Mg-9Li-3Al-2Sr-2Y alloy was studied via hot compression tests in the temperature range of 423-573 K with different strain rates ranging from 0.001 to 1.0 s-1 using the Gleeble® 3500 thermal-mechanical simulation testing system at the University of Waterloo. A number of constitutive equation models including the Ludwik, Zener-Hollomon and modified Hensel-Spittel models were used to evaluate the correct material parameters for this alloy and assessed in terms of their ability to accurately predict the constitutive behavior. The analysis of the experimental data by the three constitutive models resulted in an excellent description of the flow curves. The results showed that the Ludwik and Zener-Hollomon models lead to a good agreement between the calculated and measured flow stresses during work softening. Whereas, the modified Hensel-Spittel equation was able to describe the entire deformation process for the deformation temperatures studied. The developed models were then applied to predict the stress strain behavior of this alloy under different thermomechanical behavior paths and showed good accuracy

Microstructural evolution and enhanced mechanical properties of Mg–Gd–Y–Zn–Zr alloy via centrifugal casting, ring-rolling and aging

A ring-shaped Mg–8.5Gd–4Y–1Zn–0.4Zr (wt%) alloy was manufactured via centrifugal casting and ring-rolling process. The effects of accumulative ring-rolling reduction amount on the microstructure, texture, and tensile properties of the alloy were investigated. The results indicate that the microstructure of centrifugal cast alloy consists of equiaxed grains and network-like eutectic structure present at grain boundaries. The ring-rolled alloy exhibits a characteristic bimodal microstructure composed of fine dynamic recrystallized (DRXed) grains with weak basal texture and coarse un-DRXed grains with strong basal texture, along with the presence of LPSO phase. With increasing amount of accumulative ring-rolling reduction, the coarse un-DRXed grains are refined via the formation of increasing amount of fine DRXed grains. Meanwhile, the dynamic precipitation of Mg5RE phase occurs, generating a dispersion strengthening effect. A superior combination of strength and ductility is achieved in the ring-rolled alloy after an accumulative rolling reduction of 80%. The tensile strength of this ring-rolled alloy after peak aging is further enhanced, reaching 511 MPa, while keeping a reasonable ductility. The salient strengthening mechanisms identified include the grain boundary strengthening of fine DRXed grains, dispersion strengthening of dynamic precipitated Mg5RE phase, short fiber strengthening of LPSO lamellae/rods, and precipitation strengthening of nano-sized prismatic β′ precipitates and basal γ′ precipitates

Microstructure evolution and simulation study of a duplex Mg-Li alloy during Double Change Channel Angular Pressing

The dual-phase Mg-9Li-3Al-2Sr-2Y alloy was extruded at 553. K using Double Change Channel Angular Pressing (DCCAP) with an extrusion ratio of 17. The commercial code DEFORM-3D was used to develop a numerical model for deformation of the investigated material and the strain distribution, damage and grain shape evolution were predicted. The accurate computation of the material flow and deformation was performed, of which the results showed good agreement with microscope observations and micro-hardness measurements on the deformed billet and extrudate. Results suggest that dynamic recrystallization (DRX) occurs during the deformation and leads to grain refinement during the DCCAP process. The tensile strength and elongation after fracture in middle part of the extrudate show optimum values of 246.6. MPa and 19.9%, respectively