The prediction of ductile fracture is highly related to the stress and strain states in the plastic stage. For steel plates in the engineering structure, despite many stress-strain equations based on ...the von Mises criterion developed, it is found that the finite element (FE) analysis using true stress-strain relation calibrated by the uniaxial tensile tests cannot properly describe the shear behaviour of steel plates. In this paper, the combined linear and power stress-strain law with a shear plastic factor is proposed to characterize the mechanical behaviour of steel plates under shear dominated state. Then, Bao-Wierzbicki (BW) criterion, an uncoupled damage model, is adopted to predict the tensile and shear dominated fracture of steel plates. The uniaxial tensile and shear tests of steel plates are carried out to calibrate relevant parameters in the true stress-strain relation and ductile fracture model. Furthermore, single-bolt connections subjected to tensile and shear dominated states are designed and tested. Parallel FE simulations are performed to validate the ductile fracture model with the calibrated stress-strain relations. FE results regarding these specimens show a good agreement with the corresponding experimental results. The uncoupled damage model integrated with the proposed stress-strain relation is verified to be suitable to simulate the ductile fracture of steel plates under tensile and shear dominated states.
•The shear true stress-strain relation is proposed.•The uncoupled damage model with the corresponding true stress-strain relation is calibrated.•Single-bolt connections fractured by tensile and shear dominated states are tested.•Numerical simulations considering ductile fracture are performed.•Ductile fracture deformation and ultimate resistance of single-bolt connections are discussed.
Electronic beam steering with greater efficiency is a vibrant feature of a phased array antenna, but for all the range cells, it is fixed at a specific angle. To mitigate this problem, frequency ...diverse array (FDA) antenna was proposed. This study presents a review on the development of FDA technology in radar and navigation applications. FDA is different from a conventional phased array antenna radar in a sense that it uses a small frequency offset across the array, which helps to generate a range, angle and time-dependent beam pattern. This pattern assures the energy transmission towards the desired angle and range cell. In addition, this study also focuses the research on getting range-angle uncoupled beam patterns along with diverse hybrid cognitive FDA design, available in the literature, for improved radar performance.
The present work focuses on the design of an interval multiobserver for nonlinear systems with internal and external disturbances. The structure of the developed interval multiobserver is based on a ...discrete uncoupled multimodel. The used multimodel is known for its flexibility in the modeling step, since the state variables of the partial models can evolve in state spaces with different dimensions. Sufficient stability conditions are formulated in terms of linear matrix inequalities (LMIs), and nonnegativity constraints are imposed to ensure the cooperativity dynamic of the observation errors. A numerical example and an experimental validation on an esterification reactor are given to prove the significance of the proposed interval multiobserver.
•This paper deal with the design of an interval multiobserver for nonlinear systems with internal and external disturbances.•The structure of the developed interval multiobserver is based on a discrete uncoupled multimodel.•Sufficient stability conditions are formulated in terms of linear matrix inequalities (LMIs), and nonnegativity constraints are imposed in order to ensure the cooperativity dynamic of the observation errors.
•Uncoupled carbon and nitrogen feeding enhances the biomass PHA storage response.•The OLR has a strong impact on storage response and PHA volumetric productivity.•The MMC selected with uncoupled ...feeding reached more than 70 % g PHA/g VSS.•High OLR and uncoupled C-N feeding make the accumulation stage unnecessary.•Polymer composition is strongly affected by the OLR applied.
The selection and enrichment of a mixed microbial culture (MMC) for polyhydroxyalkanoates (PHA) production is a well-known technology, typically carried out in sequencing batch reactors (SBR) operated under a feast-famine regime. With a nitrogen-deficient carbon source to be used as feedstock for PHA synthesis, a nutrient supply in the SBR is required for efficient microbial growth. In this study, an uncoupled carbon (C) and nitrogen (N) feeding strategy was adopted by dosing the C-source at the beginning of the feast and the N-source at the beginning of the famine, at a fixed C/N ratio of 33.4 g COD/g N and 12 h cycle length. The applied organic loading rate (OLR) was increased from 4.25 to 8.5 and finally to 12.725 g COD/L d. A more efficient selective pressure was maintained at lower and intermediate OLR, where the feast phase length was shorter (around 20 % of the whole cycle length). However, at the higher OLR investigated, the PHA content in the biomass reached a value of 0.53 g PHA/g VSS at the end of the feast phase, as a consequence of the increased C-source loaded per cycle. Moreover, 2nd stage PHA productivity was 2.4 g PHA/L d, 1.5 and 3.0-fold higher than those obtained at lower OLR. The results highlight the possibility of simplifying the process by withdrawing the biomass at the end of the feast phase directly to downstream processing, without a need for the intermediate accumulation step.
Due to unphysical coupling induced by the material inhomogeneity, FG (functionally graded) nanobeam problems were formulated in a very complex way so that they cannot be analytically solved. In this ...paper, an uncoupled theory is proposed for FG nanobeams considering their small size effects. First, with the aid of the neutral axis, the axial displacement is expressed in terms of generalized displacements for FG nanobeams. Based on the nonlocal strain gradient theory, the generalized stresses and strains are accordingly defined and uncoupled constitutive relations are derived. Based on the principle of virtual work, an uncoupled theory is eventually established, including governing equations and boundary conditions. Within the present framework, analytical solutions to FG nanobeams are obtained for the first time for general boundary conditions. These solutions not only re-evaluate the previous results but shed light on the small size effects of FG nanobeams.
Time accurate implicit methods for unsteady turbulent flows are proposed based on the energy conservative finite difference method of the incompressible Navier-Stokes equations with convection ...linearization. The standard and Runge-Kutta type high-order temporal linearizations are introduced for the convective term. The time increment independent solution of turbulence is explored for the linearized coupled governing equations. Coupled and uncoupled (splitting) algorithms are then considered to isolate the effect of splitting error. The simulation examples are periodic inviscid, Taylor-Green vortex, and DNS of turbulent plane channel flows. These are test cases for the energy conservation property, the order of accuracy, and the time increment independence of turbulence statistics, respectively. The second order accurate two-stage convection linearized semi-implicit Runge-Kutta (SIRK2L) method works very well and has almost the same conservation property as the fully (spatio-temporally) conservative nonlinear method based on the implicit midpoint (IM) time marching. The second place is the standard third order convection linearization (IM3L) method. The second order convection linearization method (IM2L) is not recommended, although it may be preferred by the point of view of formal accuracy. The effect of splitting error is significant, and the numbers of coupling iteration of 5 and 10 are required for SIRK2L and IM3L methods with the uncoupled (splitting) algorithm, respectively, for the turbulent plane channel flow simulation. Finally, the DNS of forward-facing step flow is carried out as an example of practical problems.
•The second order accurate two-stage convection linearized Runge-Kutta (SIRK2L) method works very well.•In the standard convection linearization methods, the third order convection linearization method (IM3L) works well.•The standard second order convection linearization method (IM2L) is not recommended.•The splitting methods of SIRK2L and IM_3L are also constructed as SIRK2L/SP(ic) and IM_3L/SP(ic).
The response of a structure subjected to a moving load can be obtained using coupled or uncoupled methods. The uncoupled method is often preferred since modal superposition is applicable, which ...implies computational efficiency and ease of implementation. However, the uncoupled method ignores the changes in the dynamic features of the combined structural system due to the time-varying location of the load. This paper analyses the extent to which the accuracy of the uncoupled method is affected by these changes. First, a parametric study is conducted on two discretized beam models traversed by a sprung mass at a constant speed. The error associated with the uncoupled method is calculated using the coupled solution as a reference. The influence of the load to structure mass and frequency ratios and the speed of the vehicle on the error is quantified. Heavier loads travelling at higher speeds are found to increase the inaccuracy of the uncoupled method. Then, the analysis is extended to a half-car travelling on a rough profile. Although errors from the uncoupled simulation remain low for the range of parameters under investigation, they may not be acceptable in some applications, i.e., the training of an algorithm for early damage detection.
This paper reviews the characteristics of coupled and uncoupled multicore fibers for enhancing the capacity of optical fiber communication system by utilizing both the space and mode division ...multiplexing technologies. Various limitations in realizing efficient few mode multicore fiber (FM-MCF) design are analyzed in this paper. For both types of fibers, achievable spatial channel count, crosstalk and dispersion behavior, nonlinear effects and overhead at the receiver side are discussed. Some of the reported coupled MCF and uncoupled MCF designs are also summarized from the view point of mechanical reliability and transmission characteristics of the fiber. The constraints of the state of the art fiber designs are discussed. Also the advantages and drawbacks of both types of the fibers were reviewed. It has been observed from the existing MCF designs that, improvement in one transmission characteristics costs the other required characteristics to degrade. Finally it is outlined in this paper that, in order to make the space and mode division multiplexing more efficient and realistic in all aspects simultaneously, still better optimization in the MCF system design is required and the same can be achieved with the development of novel FM-MCF fibers, active and passive devices, data modulation techniques and signal processing algorithms.
This paper is devoted to sensor fault detection for nonlinear systems using an interval multiobserver based on uncoupled multimodel. This proposed interval multiobserver is used to detect the faults ...through residual intervals multigenerator. The Formula: see text performance technique is introduced to improve the accuracy of the sensor fault detection. The stability analysis of the fault detection system is carried out using Lyapunov approach under LMI(s) formulation. A numerical simulation example is used to highlight the efficiency of the proposed residual intervals multigenerator and the robustness of the fault detection strategy.
Multiview clustering plays an important part in unsupervised learning. Although the existing methods have shown promising clustering performances, most of them assume that the data is completely ...coupled between different views, which is unfortunately not always ensured in real-world applications. The clustering performance of these methods drops dramatically when handling the uncoupled data. The main reason is that: 1) cross-view correlation of uncoupled data is unclear, which limits the existing multiview clustering methods to explore the complementary information between views and 2) features from different views are uncoupled with each other, which may mislead the multiview clustering methods to partition data into wrong clusters. To address these limitations, we propose a tensor approach for uncoupled multiview clustering (T-UMC) in this article. Instead of pairwise correlation, T-UMC chooses a most reliable view by view-specific silhouette coefficient (VSSC) at first, and then couples the self-representation matrix of each view with it by pairwise cross-view coupling learning. After that, by integrating recoupled self-representation matrices into a third-order tensor, the high-order correlations of all views are explored with tensor singular value decomposition (t-SVD)-based tensor nuclear norm (TNN). And the view-specific local structures of each individual view are also preserved with the local structure learning scheme with manifold learning. Besides, the physical meaning of view-specific coupling matrix is also discussed in this article. Extensive experiments on six commonly used benchmark datasets have demonstrated the superiority of the proposed method compared with the state-of-the-art multiview clustering methods.
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