Semi-coupled Model Research Articles

Switching Longitudinal and Lateral Semi-decoupled Active Disturbance Rejection Control for Unmanned Ground Vehicles

In this paper, a switching longitudinal and lateral semi-decoupled active disturbance rejection control (ADRC) strategy is proposed for motion control of unmanned ground vehicles (UGVs). To characterize the coupling property between longitudinal and lateral dynamics, a switching longitudinal and lateral semi-coupled model is first developed. By utilizing the switching method, a so-called “two-stage ADRC” strategy is presented. It has two forms before and after the transition instant such that the boundedness premise for the derivative of the total disturbance can be removed. With the designed two-stage ADRC, a longitudinal and lateral semi-decoupled controller is then suggested to solve the motion control problem of UGVs. Finally, both stability analysis and comparison results are given to demonstrate the effectiveness and robustness of the proposed control strategy.

Numerical Simulations of Scour around Vertical Wall Abutments with Varying Aspect Ratios under Combined Waves and Current Flows

The present study employs numerical simulations to investigate vertical wall abutment scour with different aspect ratios (B/L, where B is the abutment length in the flow direction, and L is the abutment length transverse to the flow direction) under the combined effect of waves and current. The numerical model solves the Reynolds-averaged Navier–Stokes (RANS) equations and incorporates the Exner formulation to account for bed-level changes. The utilization of the Level Set Method (LSM) in the present numerical model enhances the accurate tracking of free surface and sediment bed. The numerical model validation was performed using a truncated numerical wave tank. The validated model was utilized to examine scour around vertical wall abutments with varying aspect ratios under different wave-current flows. The highest and lowest abutment scour depths were observed for aspect ratios of 0.5 and 2, respectively, in both steady current and the combined effects of waves and current. The vertical wall abutment of aspect ratio 0.5 had a maximum normalized equilibrium scour depth (S/B, where S is equilibrium scour depth), primarily attributed to a sharp edge, leading to increased turbulence and forming a strong primary vortex. The results suggest that the increase in the aspect ratio of the vertical wall abutment decreases the normalized equilibrium scour depth (S/B). According to the authors’ knowledge, this study is the first of its kind that utilizes a three-dimensional, semi-coupled model to examine combined wave- and current-flow-induced scour at vertical wall abutments with varying aspect ratios.

Proposal of fully-coupled actuated disk model for wind turbine operation modeling in turbulent flow field due to complex topography

The wind speed and direction of flow fields in the time and space domains are complicated owing to topographic relief, and it is not yet known how time-varying incoming wind speed and automatic windward effect interact with the wake characteristics of wind turbines. To address this, semi-coupled ADM-SR model (SR model) and a fully coupled ADM-DR model (DR model) are proposed in this study. The wakes of wind turbines located at various locations on the slant ridge were then compared. The wake velocity deficit of the wind turbines using the SR and DR models were found to be up to 40% and 20% upstream of the ridge, respectively, with large variations. Downstream, the wind turbine wakes of both models were similar. The DR model with the automatic windward orientation caused the wind turbine actuator disk to rotate by 9.24° and 7.40° perpendicular to the tangential direction of the streamline, and the accuracy of the control procedure was verified. Furthermore, the lower the turbulence intensity, the greater the difference between the predictions of the two models, and the power prediction value of the DR model was approximately 80% higher than that of the SR model.

A Semicoupled Shallow-Water Model for Vertical Velocity Distribution in an Open Channel with Submerged Flexible Vegetation

A Semicoupled Shallow-Water Model for Vertical Velocity Distribution in an Open Channel with Submerged Flexible Vegetation

Joint-Prior-Based Uneven Illumination Image Enhancement for Surface Defect Detection

Images in real surface defect detection scenes often suffer from uneven illumination. Retinex-based image enhancement methods can effectively eliminate the interference caused by uneven illumination and improve the visual quality of such images. However, these methods suffer from the loss of defect-discriminative information and a high computational burden. To address the above issues, we propose a joint-prior-based uneven illumination enhancement (JPUIE) method. Specifically, a semi-coupled retinex model is first constructed to accurately and effectively eliminate uneven illumination. Furthermore, a multiscale Gaussian-difference-based background prior is proposed to reweight the data consistency term, thereby avoiding the loss of defect information in the enhanced image. Last, by using the powerful nonlinear fitting ability of deep neural networks, a deep denoised prior is proposed to replace existing physics priors, effectively reducing the time consumption. Various experiments are carried out on public and private datasets, which are used to compare the defect images and enhanced results in a symmetric way. The experimental results demonstrate that our method is more conducive to downstream visual inspection tasks than other methods.

Parameter identification method of the semi-coupled fracture model for 6061 aluminium alloy sheet based on machine learning assistance

The ability to describe the fracture behaviour of materials and the difficulty of parameter calibration are important factors for evaluating the ductile fracture criterion. To find a ductile fracture criterion that can balance both these factors, in this study, the fracture behaviour of 6061 aluminium alloy was characterized based on a semi-coupled damage mechanics framework, and a parameter identification method based on machine learning assistance was proposed. Using this method, the calibration method of the damage initiation model was improved to fully consider the non-linearity of the loading path. Moreover, the calibration process of the fracture and damage evolution models was replaced by the neural network model. The results indicated that the semi-coupled fracture model can accurately predict the damage initiation, accumulation, and fracture of the 6061 aluminium alloy during the forming process. The parameter identification method based on machine learning assistance can circumvent the process of extracting the stress state evolution from the numerical models of calibrated specimens; a set of reliable parameters can be extracted from the force–displacement response using only one specimen. The combination of the semi-coupled fracture model and parameter identification method provides a new approach to balance the difficulty of parameter calibration and the description ability of the ductile fracture criterion.

A semi-coupled model for determining the distribution of two-dimensional coherent structures in open channel flow

A semi-coupled model for determining the distribution of two-dimensional coherent structures in open channel flow

Failure analysis for concrete gravity dam subjected to underwater explosion: A comparative study

The failure analysis of concrete gravity dams subjected to noncontact underwater explosions (UNDEXs) plays a significant role in evaluating the safety of dams. In this paper, two types of numerical models were developed to predict the failure behavior of a typical concrete gravity dam, i.e., the fully-coupled and semi-coupled model, which can provide a cross validation of the analysis results. The two models were verified by the experimental data and then adopted for the failure analysis. The results show that the shock wave can produce peak value in the blast responses and concentrated damage directly opposite to the explosive source. Even after the energy transmission at the fluid–structure interface, the UNDEX load still had influence on the failure behavior of the dam and can induce a total swelling in the velocity response.

An unstructured finite-volume semi-coupled projection model for bed load sediment transport in shallow-water flows

The aim of this work is to develop an original semi-coupled approach for solving the Saint-Venant and Exner equation system. The shallow-water equations are solved first to calculate the full evolution of flow fields, and then the Exner equation is solved to model the morphodynamic response. The numerical method is based on a projection method, which consists in combining the momentum and continuity equations in order to establish a Poisson-type equation for water surface levels. The present formulation is identified as a semi-coupled approach because the projection method incorporates the change in the bed evolution in its approximation. A second-order numerical scheme has been proposed using an unstructured finite-volume technique and an implicit time integration method. Several benchmarks are used to demonstrate the capabilities, accuracy and performance of the model.

A Semi-Coupled Model for Morphological Flow Simulation in River Bend

A Semi-Coupled Model for Morphological Flow Simulation in River Bend

Feedback regulation mode of gene circuits directly affects the detection range and sensitivity of lead and mercury microbial biosensors

Whole cell biosensors offer high potential for the detection of heavy metals in a manner that is simple, rapid and low-cost. However, previous researchers have paid little attention to the impacts of construction models on the performance of these biosensors, thereby limiting the achievement of rational design and the optimization of detection characteristics. Herein, for the first time, three basic models of lead and mercury detection circuits, namely feedback coupled, uncoupled and semi-coupled models, have been constructed and compared to explore the effects of uncoupling the topology of sensing circuits on the reporter signals. The results demonstrated that the uncoupled model had better sensitivity for both lead (50 nM) and mercury (1 nM), while the feedback coupled circuits had a wider detection range for mercury (10 nM - 7.5 μM). Introducing the semi-coupled model into the comparison revealed that both the type and location of promoters for regulatory protein genes were key factors for sensitivity. Moreover, the detection characteristics of the uncoupled biosensors were robust, as conditions such as induction time, the concentration of microbial cells, and the concentration of antibiotics had little interference on the performance of the microbial biosensors. This study also established a novel and simple pre-treatment method for sample detection by biosensors. When the uncoupled microbial biosensor was put into practice, the concentration levels of mercury in milk and lead in sewage were determined quickly and accurately. Our study, therefore, provides a strategy for the rational design of whole cell heavy metal biosensors and has developed the potential of their application.

Study of transient indoor temperature for a HVAC room using a modified CFD method

The change of the transient indoor temperature is crucial to evaluate electrical power consumption of a heat pump and thermal comfort of the room. Computational Fluid Dynamics (CFD) model can provide the most comprehensive information in transient indoor temperature simulations. In CFD models, the transient flow and temperature fields are fully coupled. This coupling leads to high computation cost and time, which limits the CFD application in practice. A segregated CFD model was then proposed to speed up the computation. However, such model is not very accurate during the transient analysis. In this paper, a semi-coupled CFD model combining advantages of the fully-coupled CFD model and the segregated CFD model was proposed. In this CFD model, the flow and the temperature fields are firstly solved by fully coupled simulation during the transient start up period and then the segregated CFD is used for the transient temperature rising simulation. This method can reduce the computation time without losing the simulation accuracy. The transient indoor temperature is studied using the proposed method and the results are compared with those obtained from both fully-coupled and segregated CFD models. The hot air temperature is first calculated using a lumped-parameter method, and then it is applied as an initial boundary condition in the CFD models. The comparison results show that the proposed semi-coupled CFD model shows a promising capability of capturing the critical transient thermal responses for the air-conditioning room, and it can effectively reduce the computing time with an acceptable accuracy.

Elastic and piezoelectric field around a quantum dot with interface effect

Piezoelectric field is closely related to the elastic field, so it is important for the calculation of piezoelectric field to include the size-dependent interface effect for the interface in nanostructures. This work adopts the semi-coupled model to find the elastic and piezoelectric field for weakly electromechanical coupled materials (GaAs) with the consideration of interface effect. Close-form solutions are derived and numerical results are also provided to show that the piezoelectric potential in the matrix depends on the interface elasticity, the radius and stiffness of the quantum dot. Especially, it is demonstrated that the piezoelectric potentials with different interface elasticity parameters are distinct compared with the classical solution near the interface. When the interface elasticity parameter is positive, the interface effect weakens the piezoelectric effect in the material by decreasing the value of the piezoelectric potential and vice versa. The piezoelectric potential concentration ratio calculated by this work with the consideration of interface elasticity is close to 10% different from the classical solution. Such amount of difference is appreciable in the design and fabrication of nanostructures and the effect due to interface elasticity should not be neglected.

Subsidence estimation of breakwater built on loosely deposited sandy seabed foundation: Elastic model or elasto-plastic model

In offshore area, newly deposited Quaternary loose seabed soils are widely distributed. There are a great number of offshore structures has been built on them in the past, or will be built on them in the future due to the fact that there would be no very dense seabed soil foundation could be chosen at planed sites sometimes. However, loosely deposited seabed foundation would bring great risk to the service ability of offshore structures after construction. Currently, the understanding on wave-induced liquefaction mechanism in loose seabed foundation has been greatly improved; however, the recognition on the consolidation characteristics and settlement estimation of loose seabed foundation under offshore structures is still limited. In this study, taking a semi-coupled numerical model FSSI-CAS 2D as the tool, the consolidation and settlement of loosely deposited sandy seabed foundation under an offshore breakwater is investigated. The advanced soil constitutive model Pastor-Zienkiewics Mark III (PZIII) is used to describe the quasi-static behavior of loose sandy seabed soil. The computational results show that PZIII model is capable of being used for settlement estimation problem of loosely deposited sandy seabed foundation. For loose sandy seabed foundation, elastic deformation is the dominant component in consolidation process. It is suggested that general elastic model is acceptable for subsidence estimation of offshore structures on loose seabed foundation; however, Young's modulus E must be dependent on the confining effective stress, rather than a constant in computation.

Long-term performance of cast-iron tunnel cross passage in London clay

A series of 3D soil–fluid coupled finite element analyses was conducted to examine the long-term tunnel behaviour of an old cast-iron cross passage in stiff London clay. In the proposed geotechnical FE model, an advanced critical state constitutive model was employed to simulate complex soil behaviour, whereas the details of the tunnel linings was simplified using shell elements. The computed time-dependent soil load derived from the geotechnical model was then applied to a structural finite element model where the details of the cross passage structure such as bolted-joints and tunnel segments were explicitly modelled. This proposed semi-coupled soil-structure model shows agreement against field observations and it was found in this particular case that the structural condition evaluated from the FE model is more critical than that of the conventional bedded ring method. Results show that the surface ground settlement is governed mainly by the twin tunnel construction and the presence of the cross passage does not increase the settlement. On the other hand, the construction of a cross passage affects the structural performance of the adjacent running tunnel in both short term (undrained) and long term (soil consolidation). In particular, the critical location is identified to be the tunnel segment adjacent to the opening at the axis level and its stresses and deformation increase with consolidation time.

Nonlinear interaction between wave, breakwater and its loose seabed foundation: A small-scale case

In offshore environment, newly deposited quaternary loose sediments widely exist in the world. Sometimes, coastal engineers cannot avoid choosing these natural loose sediments as the foundation of marine structures. Under this situation, the interaction between ocean wave, marine structures and their loose sand foundation, and the wave-induced pore pressure built-up in loose seabed foundation are the key factors in which coastal engineers would most concern. In this study, the nonlinear interaction mechanism between ocean wave, a composite breakwater and its loose elasto-plastic sand bed foundation is investigated by utilizing a semi-coupled numerical model FSSI-CAS 2D. In the coupled numerical model FSSI-CAS 2D, VARANS equation for wave model, and dynamic Biot׳s equation for soil model are used for the governing equations. The advanced and excellent elasto-plastic constitutive model PZIII proposed by Pastor et al. (1990) is adopted to describe the nonlinear dynamic behavior of loose sand soil under cyclic wave loading. Taking the parameters of Neveda sand determined in the VELACS project funded by NSF as the property parameters for the loose sand bed, a small-scale computational case like the experimental set-up in Mostafa et al. (1999) is taken as a representative case to investigate the wave-structure-loose seabed foundation interaction mechanism. The numerical results indicate that the pore pressure in loose seabed foundation builts up significantly, and the marine structure subsides and tilts under wave loading. The loose sand bed becomes denser and denser due to soil compaction. Parametric studies show that both the wave characteristics and the soil properties can affect the built-up of residual pore pressure in loose seabed foundation.

Validation of a 2-D semi-coupled numerical model for fluid–structure–seabed interaction

A 2-D semi-coupled model PORO-WSSI 2D (also be referred as FSSI-CAS 2D) for the Fluid-Structure-Seabed Interaction (FSSI) has been developed by employing RANS equations for wave motion in fluid domain, VARANS equations for porous flow in porous structures; and taking the dynamic Biot's equations (known as "u − p" approximation) for soil as the governing equations. The finite difference two-step projection method and the forward time difference method are adopted to solve the RANS, VARANS equations; and the finite element method is adopted to solve the "u − p" approximation. A data exchange port is developed to couple the RANS, VARANS equations and the dynamic Biot's equations together. The analytical solution proposed by Hsu and Jeng (1994) and some experiments conducted in wave flume or geotechnical centrifuge in which various waves involved are used to validate the developed semi-coupled numerical model. The sandy bed involved in these experiments is poro-elastic or poro-elastoplastic. The inclusion of the interaction between fluid, marine structures and poro-elastoplastic seabed foundation is a special point and highlight in this paper, which is essentially different with other previous coupled models The excellent agreement between the numerical results and the experiment data indicates that the developed coupled model is highly reliablefor the FSSI problem.

Crystal orientation effects on wurtzite quantum well electromechanical fields

A one-dimensional continuum model for calculating strain and electric field in wurtzite semiconductor heterostructures with arbitrary crystal orientation is presented and applied to GaN/AlGaN and ZnO/MgZnO heterostructure combinations. The model is self-consistent involving feedback couplings of spontaneous polarization, strain, and electric field. Significant differences between fully coupled and semicoupled models are found for the longitudinal and shear-strain components as a function of the crystal-growth direction. In particular, we find that the semicoupled model, typically used in the literature for semiconductors, is inaccurate for ZnO/MgZnO heterostructures where shear-strain components play an important role. An interesting observation is that a growth direction apart from $[\overline{1}2\overline{1}0]$ exists for which the electric field in the quantum well region becomes zero. This is important for, e.g., optimization of light-emitting-diode quantum efficiency.

Fully coupled and semi-coupled piezoelectric models on the optical properties of InGaN quantum dots

This paper investigates the differences between the fully coupled and the semi-coupled piezoelectric models for determining strain fields, piezoelectric potentials and optical properties of wurtzite InGaN quantum dots (QDs) in three different shapes. Through the calculations, we show that the relative difference of the x-component strain inside the dot remains almost unchanged regardless of the shapes and the sizes of the dot. On the other hand, a large relative difference for the z-component strain is obtained with the use of the semi-coupled model. We also find that the semi-coupled model clearly overestimates the piezoelectric potential, and the transition energy difference increased with increases in the dot size and indium composition. Consequently, the semi-coupled model causes a great amount of distortion in predicting the optical properties of InGaN QDs. It is thus evident that the fully coupled model for calculating the electromechanical fields and optical properties of InGaN QDs may be more appropriate according to our numerical examples.

Elastic and piezoelectric fields around a quantum dot: Fully coupled or semicoupled model?

In the study of elastic and piezoelectric fields in semiconductors due to buried quantum dots (QDs), the semicoupled piezoelectric model is commonly adopted. However, its accuracy and suitability have never been studied. In this article, by developing a fully coupled piezoelectric model and deriving the analytical elastic and piezoelectric fields based on this and the semicoupled models, we are able to verify that when the piezoelectric coupling is weak, like GaAs with the electromechanical coupling factor g=0.04, the semicoupled model predicts very accurate results as compared to those based on the fully coupled model. However, if the piezoelectric coupling is relatively strong, like AlN with g=0.32, we have shown that the semicoupled model gives very serious errors or even totally wrong results. Applying these two models to a uniformly strained AlN layer grown along the polar axis has also confirmed our observation. Therefore, for semiconductors like AlN, the fully coupled model presented in this article must be employed in order to give a reliable and accurate prediction for the elastic and piezoelectric fields. Also presented in this article is the distribution of the piezoelectric field on the surface of a half-space GaAs due to a buried QD located at 2 nm below the surface with a volume 4π/3 (nm)3. It is observed that the horizontal electric field on the traction-free and insulating surface shows some special features and its maximum magnitude can be as high as 3.5×107 V/m when the uniform mismatch eigenstrain is 0.07. Furthermore, the piezoelectric field on the traction-free and conducting surface exhibits different characters as compared to the traction-free and insulating case.