•A novel prediction framework is proposed.•Three new hybrid models based on the framework are put forward.•Compared to normal methods, the proposed models yield a better prediction accuracy.
In this ...paper, a novel framework for wind speed forecasting is proposed. In the new prediction framework, wavelet transform is firstly adopted to decompose original wind speed history into several sub-series. Then, for low-frequency sub-series, recurrent neural networks are used to extract deeper features, which are fed into suitable machine learning methods for predicting, while others are still predicted by normal methods. Meanwhile, three new hybrid models are established, where support vector machine is taken as the predictor, and the standard recurrent neural network and its variant version: long short term memory neural networks and gated recurrent unit neural networks are employed to extract the deeper features. Four experiments from the real world are conducted through the proposed methods as well as normal algorithms. The results demonstrate that the three new proposed hybrid models based on the novel framework yield more accurate predictions.
Aerodynamic characteristics of long-span bridges with box girders have been investigated widely, and this paper presents a study on a cable-stayed bridge with two box girders in parallel arrangement. ...Computational fluid dynamics (CFD) numerical simulations were adopted to analyze the aerodynamic interference between the upper and the lower box girders. After checking the reliability of the numerical model, different angles of attack and different distances between the two girders were considered, and the variations of the aerodynamic characteristics were discussed, including the aerodynamic coefficients and the static pressure distributions. Then, the wind environment around the two box girders was focused, and the effect on the aerodynamic coefficients of a vehicle was also studied. The results show that the aerodynamic interference between the two box girders is strong, so the aerodynamic characteristics of the two boxes are different from those of a single box. The flow field between the boxes have higher wind velocities, which makes the aerodynamic force on the upper box and the lower box become upward and downward, respectively. Meanwhile, the aerodynamic forces on vehicles above the lower deck surface are larger due to the accelerated flow between the two boxes.
In order to decorate the night view for cities, installing lighting fixtures on stay cables of existing cable-stayed bridges is an effective choice, but the aerodynamic characteristics of the stay ...cables will change significantly. This paper presents a study on the galloping stability of the stay cables equipped with lighting fixtures. The static aerodynamic coefficients were computed using computational fluid dynamics (CFD) simulations, and the reason for the negative slope of the lift coefficient was discussed based on the changes in pressure distributions and flow field characteristics. Wind tunnel tests were further carried out to verify the numerical results. The possible galloping instability intervals for the stay cables with lighting fixtures were calculated. The results show that the existence of lighting fixtures has significant effects on the aerodynamic performance of stay cables. The slope of the lift coefficient becomes negative within several intervals of angles of attack, which indicates the possible galloping instability. The sudden decrease in the lift coefficient is mainly related to the vortex which covers the concave between the lighting fixture and the stay cable and makes the separated flow cannot reattach.
Osteosarcoma is a malignant tumor derived from primitive osteogenic mesenchymal cells, which is extremely harmful to the human body and has a high mortality rate. Early diagnosis and treatment of ...this disease is necessary to improve the survival rate of patients, and MRI is an effective tool for detecting osteosarcoma. However, due to the complex structure and variable location of osteosarcoma, cancer cells are highly heterogeneous and prone to aggregation and overlap, making it easy for doctors to inaccurately predict the area of the lesion. In addition, in developing countries lacking professional medical systems, doctors need to examine mass of osteosarcoma MRI images of patients, which is time-consuming and inefficient, and may result in misjudgment and omission. For the sake of reducing labor cost and improve detection efficiency, this paper proposes an Attention Condenser-based MRI image segmentation system for osteosarcoma (OMSAS), which can help physicians quickly locate the lesion area and achieve accurate segmentation of the osteosarcoma tumor region. Using the idea of AttendSeg, we constructed an Attention Condenser-based residual structure network (ACRNet), which greatly reduces the complexity of the structure and enables smaller hardware requirements while ensuring the accuracy of image segmentation. The model was tested on more than 4000 samples from two hospitals in China. The experimental results demonstrate that our model has higher efficiency, higher accuracy and lighter structure for osteosarcoma MRI image segmentation compared to other existing models.
This paper presents wind tunnel tests on the wake characteristics of a three-blade horizontal axis wind turbine and the wake effect on the performance of a downstream turbine. For a single turbine ...model, the performance was determined and this was followed by measurement of the wind characteristics including velocities, turbulence intensities, and correlation in the wake flow field. Subsequently, taking two horizontal axis wind turbines in a tandem arrangement into account, their performance was tested and the aerodynamic mechanism was discussed. The results showed that the upstream turbine with blades set at a small pitch angle provided smaller disturbance to the flow, but as the blade turned faster, larger changes in the velocity and the turbulence intensity occurred in its wake due to the more frequent disturbance of the wind turbine. The correlation of wake velocities in the turbine swept area also obviously decreased from the free-stream situation. For the downstream turbine, the output power loss largely depended on the wake characteristics of the upstream turbine, which was closely related to lower wind velocities or higher turbulence intensities. The decrease in correlation of the streamwise velocity within the blade swept area is accompanied by the increased correlation of the tangential velocity, which may be beneficial to the downstream turbine’s performance.
Medical image analysis methods have been applied to clinical scenarios of tumor diagnosis and treatment. Many studies have attempted to optimize the effectiveness of tumor MRI image segmentation by ...deep learning, but they do not consider the optimization of local details and the interaction of global semantic information. Second, although medical image pattern recognition can learn representative semantic features, it is challenging to ignore useless features in order to learn generalizable embeddings. Thus, a tumor-assisted segmentation method is proposed to detect tumor lesion regions and boundaries with complex shapes. Specifically, we introduce a denoising convolutional autoencoder (DCAE) for MRI image noise reduction. Furthermore, we design a novel tumor MRI image segmentation framework (NFSR-U-Net) based on class-correlation pattern aggregation, which first aggregates class-correlation patterns in MRI images to form a class-correlational representation. Then the relationship of similar class features is identified to closely correlate the dense representations of local features for classification, which is conducive to identifying image data with high heterogeneity. Meanwhile, the model uses a spatial attention mechanism and residual structure to extract effective information of the spatial dimension and enhance statistical information in MRI images, which bridges the semantic gap in skip connections. In the study, over 4000 MRI images from the Monash University Research Center for Artificial Intelligence are analyzed. The results show that the method achieves segmentation accuracy of up to 96% for tumor MRI images with low resource consumption.
Box girders are aerodynamically favorable, and the paper presents a study on the vortex-induced vibration (VIV) of this girder type at large angles of attack. Taking a box girder as an example, the ...form of the guardrails and the position of the maintenance tracks were improved to increase the VIV performance. The aerodynamic mechanism was further investigated according to the change in flow field around the girder. Results showed that the VIV performance of the box girder at positive angles of attack is worse. Improving secondary elements is an effective way to increase the VIV performance. Adding four rectangle bars above the original guardrails could achieve the target by preventing the generation of the vortex and blocking its movement. Moving the maintenance tracks inwards with a reasonable distance could also achieve the target as the flow passes through the girder more smoothly. With the combination of the optimal form of the guardrails and the optimal position of the maintenance tracks, the VIV performance of the bridge is higher. The countermeasures provide reference for the inhibition of the VIV of box girders.
An increasing number of double-main-span suspension bridges with three towers are now constructed. For this bridge type, close modes exhibits similar characteristics due to the participation of two ...main and side spans, which is more prominent during girder erection as different spans are disconnected. It is important but hard to accurately determine the modal combination for flutter analyses. In this paper, full-order modal flutter analyses were performed to study the flutter performance of a double-main-span suspension bridge during erection. The dominating modal branches for the anti-symmetrical and symmetrical flutter instability were determined, respectively. After that, temporary pier constraints on the side spans and temporary connections between girder segments were set, respectively, to study the flutter suppression. The results show that the anti-symmetrical flutter instability of the bridge during erection is prior to the symmetrical one except for the first two stages. Reinforcing the connections between girder segments in the lateral direction could significantly improve the anti-symmetrical flutter stability. Meanwhile, the symmetrical flutter instability of the bridge during erection is more complicated as it is associated with the girder torsion, cable swing, and girder lateral bending. The set of temporary pier constraints or proper temporary connections is favorable.
•Symmetrical girder torsion is associated with the cable swing and girder lateral bending.•Symmetrical flutter instability is affected by the lateral flutter derivatives.•Anti-Symmetrical flutter instability is improved by reinforcing the lateral girder stiffness.•The set of proper temporary connections is favorable to the flutter performance.
As long-span cross-sea bridges extend to deeper sea areas, the bridge pile tends to increase in its slenderness ratio and becomes more susceptible to waves. To improve the structural stability at the ...construction stage, this study analyses wave-induced response of foundations. The wave theory and the method used for computing wave forces on foundations are first introduced. Then, a pile group foundation is taken as the research object, and different pile lengths ranging from 16 m to 46 m are considered. The wave-induced response of the piles and the cap is calculated. After understanding the effect of the pile length, three optimized foundations are proposed with the aim of reducing the free length of the pile, and the corresponding finite element models are established to compare their wave-induced response. The results show that the displacement at the top of the foundation increases with the increase in the pile length until the cap partly emerges from water and so does the internal force at the bottom. Setting a constraint in the middle of the piles can reduce their free lengths and is favourable to the wave-induced response of the foundation except for the shearing force. A stronger constraint shows better effects on improvement of the stability of the foundation. The conclusions provide reference for optimization on pile foundations of deepwater bridges.
•Installation of cross cables improves flutter stability of the bridge during erection.•Modal characteristics between two main spans are determined for different stages.•Suppression mechanism of ...cross cables changes with the increasing girder length.•Effects of static and dynamic wind loads on cross cables are further revealed.
Long-span suspension bridges during erection show more flexible dynamic characteristics and worse flutter performance. The aerodynamic optimization may make the flutter performance meet the requirement, but some countermeasures are costly or difficult to realize. Therefore, it is necessary to design some practicable structural countermeasures which could improve the dynamic characteristics of long-span suspension bridges during erection and so does their flutter stability. This paper takes a long-span suspension bridge with two main spans as the example. The effect of cross cables on the structural dynamic characteristics is studied, and the critical flutter state of the bridge is accurately determined by the most unfavorable modal combination. The reason why the flutter stability could be improved is revealed by changing the stiffness of the cross cables. The wind-induced static and dynamic response of the bridge is further discussed, and the effectiveness of the cross cables at high wind speeds is evaluated. The results show that the installation of the cross cables on the free ends of the girders is favorable to the flutter performance of the bridge during erection. When the bridge is equipped with the cross cables, the association between the girder lateral bending and torsion will be enhanced for later erection stages with longer suspender girder lengths, which should be taken into account in the flutter analysis. With the static wind loads, the cross cables on one side are in compression and lose the effectiveness, but the cross cables on the other side could still improve the flutter performance of the bridge. As the internal force fluctuates significantly, the cross cables and the temporary connections should have enough strength.
PDF
