| 1. |
- Dai, Zhiyuan, et al.
(författare)
-
Kriging-based multi-objective optimization on high-speed train aerodynamics using sequential infill criterion with gradient information
- 2024
-
Ingår i: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 36:3
-
Tidskriftsartikel (refereegranskat)abstract
- For models with large numerical simulation costs, such as high-speed trains, using as few samples as possible to construct a high-precision surrogate model during aerodynamic multi-objective optimization is critical to improving optimization efficiency. This study proposes a sequential infill criterion (SIC) appropriate for the Kriging surrogate model to address this issue. Three multi-objective functions are employed to test the feasibility of constructing a surrogate model based on SIC, and the SIC surrogate model then performs multi-objective aerodynamic optimizations on the high-speed train. The findings indicate that the expected improvement infill criterion (EIC) in the first stage can enhance the global prediction accuracy of the SIC. An infill criterion based on EIC that fuses gradient information (PGEIC) in the second stage is proposed to seek samples in the Pareto front. The PGEIC surrogate model achieves the lowest generational distance and prediction error. The performance of EIC for global search, EIC for Pareto front search, and infill criterion for Pareto front search using only gradient information is poor. The final PGEIC-SIC surrogate model of train aerodynamics has less than 1% prediction error for the three optimization objectives. The optimal solution reduces the aerodynamic drag force of the head car and the aerodynamic drag and lift force of the tail car by 4.15%, 3.21%, and 3.56%, respectively, compared with the original model. Furthermore, sensitivity analysis of key parameters revealed that the nose height v1, cab window height v3, and lower contour line have a greater impact on aerodynamic forces. Moreover, the nose and cab window heights of the optimal model have been reduced, and the lower contour line is concave. Correspondingly, the streamlined shape appears more rounded and slender.
|
|
| 2. |
- Bruni, Stefano, et al.
(författare)
-
The results of the pantograph-catenary interaction benchmark
- 2015
-
Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 0042-3114 .- 1744-5159. ; 53:3, s. 412-435
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes the results of a voluntary benchmark initiative concerning the simulation of pantograph-catenary interaction, which was proposed and coordinated by Politecnico di Milano and participated by 10 research institutions established in 9 different countries across Europe and Asia. The aims of the benchmark are to assess the dispersion of results on the same simulation study cases, to demonstrate the accuracy of numerical methodologies and simulation models and to identify the best suited modelling approaches to study pantograph-catenary interaction. One static and three dynamic simulation cases were defined for a non-existing but realistic high-speed pantograph-catenary couple. These cases were run using 10 of the major simulation codes presently in use for the study of pantograph-catenary interaction, and the results are presented and critically discussed here. All input data required to run the study cases are also provided, allowing the use of this benchmark as a term of comparison for other simulation codes.
|
|
| 3. |
- Zhang, Wei-Wei, et al.
(författare)
-
Thermodynamic Assessment of the Cu-B System Supported by Key Experiment and First-Principles Calculations
- 2009
-
Ingår i: Journal of Phase Equilibria and Diffusion. - : Springer Science and Business Media LLC. - 1547-7037 .- 1863-7345. ; 30:5, s. 480-486
-
Tidskriftsartikel (refereegranskat)abstract
- The Cu-B system was investigated via a hybrid approach of key experiment and thermodynamic modeling. Based on the critically assessed Cu-B phase diagram, seven crucial alloys were selected and prepared by arc melting the pure elements. An inductively coupled plasma-atomic emission spectrometric analysis was conducted to determine the compositions of the prepared alloys. The phase equilibria were determined by using x-ray diffraction, electron probe microanalysis, and differential thermal analysis. The temperature associated with the eutectic reaction, L double left right arrow (B) + (Cu); was measured to be 1028 +/- 2 degrees C. First-principles calculations indicate that the energy of inserting a B atom into the interstitial vacancy (Va) site of the lattice for Cu atoms is marginally lower than that of substituting for a Cu atom with a B atom. Consequently, the sublattice model (Cu)(B, Va) in which B atoms occupy the interstitial sites was employed for the fcc (Cu) phase rather than the model (Cu, B)(Va) in which B atoms substitute for Cu atoms. A thermodynamic modeling of the Cu-B system was then performed by considering the reliable literature data and the present experimental results. A good agreement between modeling and experiment was obtained.
|
|
| 4. |
|
|
| 5. |
- Liu, Weihua, et al.
(författare)
-
Characterizing the Reliability and Threshold Voltage Shifting of 3D Charge Trap NAND Flash
- 2019
-
Ingår i: 2019 DESIGN, AUTOMATION & TEST IN EUROPE CONFERENCE & EXHIBITION (DATE). - : IEEE. - 9783981926323 ; , s. 312-315
-
Konferensbidrag (refereegranskat)abstract
- 3D charge trap (CT) triple-level cell (TLC) NAND flash gradually becomes a mainstream storage component due to high storage capacity and performance, but introducing a concern about reliability. Fault tolerance and data management schemes are capable of improving reliability. Designing a more efficient solution, however, needs to understand the reliability characteristics of 3D CT TLC NAND flash. To facilitate such understanding, by exploiting a real-world testing platform, we investigate the reliability characteristics including the raw bit error rate (RBER) and the threshold voltage (Vth) shifting features after suffering from variable disturbances. We give analyses of why these characteristics exist in 3D CT TLC NAND flash. We hope these observations can guide the designers to propose high efficient solutions to the reliability problem.
|
|
| 6. |
- Liu, Weihua, et al.
(författare)
-
Modeling of Threshold Voltage Distribution in 3D NAND Flash Memory
- 2021
-
Ingår i: PROCEEDINGS OF THE 2021 DESIGN, AUTOMATION & TEST IN EUROPE CONFERENCE & EXHIBITION (DATE 2021). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1729-1732
-
Konferensbidrag (refereegranskat)abstract
- 3D NAND flash memory faces unprecedented complicated interference than planar NAND flash memory, resulting in more concern regarding reliability and performance. Stronger error correction code (ECC) and adaptive reading strategies are proposed to improve the reliability and performance taking a threshold voltage (Vth) distribution model as the backbone. However, the existing modeling methods are challenged to develop such a Vth distribution model for 3D NAND flash memory. To facilitate it, in this paper, we propose a machine learning-based modeling method. It employs a neural network taking advantage of the existing modeling methods and fully considers multiple interferences and variations in 3D NAND flash memory. Compared with state-of-the-art models, evaluations demonstrate it is more accurate and efficient for predicting Vth distribution.
|
|
| 7. |
- Ren, Shan, et al.
(författare)
-
A personalised operation and maintenance approach for complex products based on equipment portrait of product-service system
- 2023
-
Ingår i: Robotics and Computer-Integrated Manufacturing. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0736-5845 .- 1879-2537. ; 80
-
Tidskriftsartikel (refereegranskat)abstract
- Based on the holistic data of product-service system (PSS) delivery processes, equipment portrait can be used to describe personalised user requirements and conduct targeted analysis on the performance of complex products. Therefore, a promising application combining PSS and equipment portrait is to establish a more refined portrait model to improve the accuracy and applicability of operation and maintenance (OM) schemes for industrial products. However, studies in the above field are facing many challenges. For example, the research on equip-ment portrait in the industrial field is still in its infancy. PSS and equipment portrait are studied separately, and the overall solution that integrates PSS and equipment portrait for complex products OM service is almost vacant. A personalised OM approach for complex products (POMA-CP) is proposed to address these challenges. First, a framework of POMA-CP is developed to show how the processes of refined OM can be implemented. Then, a solution of POMA-CP based on the framework is designed. A multi-level case library, dynamic equipment portrait model, and case-pushing mechanism are established and developed. Active pushing of the best similar cases and automatic generation of service schemes are realised. Finally, an application scenario for a high-speed electric multiple units (EMU) bogie is presented to illustrate the feasibility and effectiveness of the proposed approach. Higher accuracy and applicability for service schemes are achieved, resulting in the efficient reusing of OM knowledge, proactive implementation of refined maintenance, and reducing maintenance cost and resource consumption.
|
|
| 8. |
|
|
| 9. |
- Xu, Yan, et al.
(författare)
-
Long-Term High-Speed Train–Track Dynamic Interaction Analysis Using a Moving Train–Track Interaction Model
- 2022
-
Ingår i: IAVSD 2021: Advances in Dynamics of Vehicles on Roads and Tracks II. - Cham : Springer Nature. ; , s. 272-281
-
Konferensbidrag (refereegranskat)abstract
- A new moving train–track interaction model is shown in the paper to accurately and efficiently determine long-term high-speed train–track interaction dynamic response. In this model, the rail is represented with a reduced beam model (RBM) and the slabs mainly affected by the train–track interaction are modeled with four-node Kirchhoff-Love plate elements. The fastenings are modeled with spring-damper elements and the Concrete Asphalt (CA) layer is modeled with a Winkler foundation. Since only a small part of the rail and a few slabs from the whole slab track are included, the present model has fewer degrees of freedom than the traditional model using the modal superposition method and the simulation time is significantly decreased. The present model is validated by a long-term train–track interaction case where the results are compared with those from the traditional method. The simulation results show that the present model is accurate and efficient and has great advantages in solving high-speed train–track interaction problems.
|
|
| 10. |
- Xu, Yan, et al.
(författare)
-
Reduced-order modeling of train-curved-slab-track dynamics with the effects of fastening failures
- 2022
-
Ingår i: Acta Mechanica Sinica. - : Springer Nature. - 0567-7718 .- 0459-1879 .- 1614-3116. ; 38
-
Tidskriftsartikel (refereegranskat)abstract
- Fastening failures have frequently been found on China high-speed railway curved tracks in recent years. Thus the influence of fastening failures on high-speed train-track interaction in curved track needs to be analyzed. A train-curved slab track interaction model is built, in which the real shape of the curved rail is considered and modeled with reduced beam model (RBM) and curved beam theory, and the slabs are modeled with four-nodes Kirchhoff-Love plate elements. The present model is validated at first with different traditional models. Then the influence of fastening failure in curved slab track on train-track interaction dynamics is studied. A different number of failed fastenings is assumed to occur at the curved track, and different types of fastening failure including the fatigue fracture of the clip structure and failure of the rail pad are considered. Based on the calculation results, the fatigue fracture of the clip structure has little influence on train-track interaction dynamics. But when rail pad failure happens and its equivalent vertical stiffness and damping are less than one-tenth of its original, the fastening failure seriously affects the high-speed train operation safety, and it must be prevented
|
|
