| 1. |
- Fenstermacher, M.E., et al.
(författare)
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DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.
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| 2. |
- Chen, H., et al.
(författare)
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Unprecedented non-hysteretic superelasticity of [001]-oriented NiCoFeGa single crystals
- 2020
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Ingår i: Nature Materials. - : Nature Research. - 1476-1122 .- 1476-4660.
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Tidskriftsartikel (refereegranskat)abstract
- Superelasticity associated with the martensitic transformation has found a broad range of engineering applications1,2. However, the intrinsic hysteresis3 and temperature sensitivity4 of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. Here, we report a large superelasticity up to 15.2% strain in [001]-oriented NiCoFeGa single crystals, exhibiting non-hysteretic mechanical responses, a small temperature dependence and high-energy-storage capability and cyclic stability over a wide temperature and composition range. In situ synchrotron X-ray diffraction measurements show that the superelasticity is correlated with a stress-induced continuous variation of lattice parameter accompanied by structural fluctuation. Neutron diffraction and electron microscopy observations reveal an unprecedented microstructure consisting of atomic-level entanglement of ordered and disordered crystal structures, which can be manipulated to tune the superelasticity. The discovery of the large elasticity related to the entangled structure paves the way for exploiting elastic strain engineering and development of related functional materials.
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| 3. |
- Calabuig, D., et al.
(författare)
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Resource and Mobility Management in the Network Layer of 5G Cellular Ultra-Dense Networks
- 2017
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Ingår i: IEEE Communications Magazine. - 0163-6804 .- 1558-1896. ; 55:6, s. 162-169
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Tidskriftsartikel (refereegranskat)abstract
- The provision of very high capacity is one of the big challenges of the 5G cellular technology. This challenge will not be met using traditional approaches like increasing spectral efficiency and bandwidth, as witnessed in previous technology generations. Cell densification will play a major role thanks to its ability to increase the spatial reuse of the available resources. However, this solution is accompanied by some additional management challenges. In this article, we analyze and present the most promising solutions identified in the METIS project for the most relevant network layer challenges of cell densification: resource, interference and mobility management.
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| 4. |
- Ren, Guorui, et al.
(författare)
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Analysis of wind power intermittency based on historical wind power data
- 2018
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 150, s. 482-492
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Tidskriftsartikel (refereegranskat)abstract
- As wind power provides an increasingly larger share of electricity supply, the challenges caused by wind power intermittency have become more and more prominent. A better understanding of wind power intermittency would contribute to mitigate it effectively. In the present study, the definition of wind power intermittency is given firstly. Based on the definition, wind power intermittency is quantified by duty ratio of wind power ramp (DRWPR). This index provides system operators quantitative insights into wind power intermittency. Furthermore, some characteristics of wind power intermittency can be extracted by the index, such as the differences between wind speed intermittency and wind power intermittency, the differences of wind power intermittency between different scales and so on. The wind power intermittency of a Chinese wind farm is studied in detail based on the proposed index and historical data.
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| 5. |
- Ren, G. R., et al.
(författare)
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Prediction of the Standard Deviation of Wind Speed Turbulence
- 2018
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Ingår i: JOURNAL OF ENVIRONMENTAL INFORMATICS. - : INT SOC ENVIRON INFORM SCI. - 1726-2135 .- 1684-8799. ; 32:1, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Turbulent wind speed is a vital component of wind speed, corresponding to the small-scale uncertainty of wind speed. The wind power output and aerodynamic loads are significantly influenced by turbulent wind speed. The present paper concentrates on the study of turbulent wind speed prediction, which is hardly addressed in previous studies and is a novel approach to understand turbulent wind speed in advance. In the present study, turbulent wind speed is measured by turbulence standard deviation. Although turbulent wind speed itself is unpredictable, the correlation analysis proves that the turbulence standard deviation is predictable within a proper time horizon. As a result, the turbulent wind speed can be understood ahead of time by predicting turbulence standard deviation. The 10-min ahead, 30-min ahead and 60-min ahead predictions of turbulence standard deviation are provided by Support Vector Regression and Kernel Ridge Regression. Furthermore, the average wind speed is fused into the forecasting model to improve the prediction accuracy of turbulence standard deviation.
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| 6. |
- Ren, Guorui, et al.
(författare)
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The analysis of turbulence intensity based on wind speed data in onshore wind farms
- 2018
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Ingår i: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 123, s. 756-766
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Tidskriftsartikel (refereegranskat)abstract
- Wind speed turbulence intensity is crucial for wind turbine structure design and aerodynamic loads calculation. In the study, the actual turbulence intensity observations are compared with the Normal Turbulence Model defined by IEC standard. The results show that the Normal Turbulence Model overestimates the turbulence intensity. A new turbulence intensity model is proposed based on the actual observations, which shows better performance than the Normal Turbulence Model. Then the variation pattern of turbulence intensity during a day is analyzed. The turbulence intensity exhibits obvious daily periodicity in two wind farms. Furthermore, the causes of daily periodicity are discussed and verified by the wind speed dataset 3. Finally, an improved time-varying turbulence intensity model is developed according to the daily periodicity.
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| 7. |
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| 8. |
- Yang, D., et al.
(författare)
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Fault Diagnosis of Transformer Based on Capsule Network
- 2021
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Ingår i: Gaodianya Jishu. - : Science Press. - 1003-6520. ; 47:2, s. 415-424
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Tidskriftsartikel (refereegranskat)abstract
- Traditional methods for transformer fault diagnosis are difficult to fit the complex nonlinear relationship between dissolved gas and fault type accurately, and their diagnosis accuracy is limited. To improve the accuracy of transformer fault diagnosis, a method of transformer fault diagnosis based on capsule network (CapsNet) is proposed. The convolutional layers with strong feature extraction ability are used to map the dissolved gas data into the feature space to realize the automatic extraction of key features. Furthermore, the mapping relationship between feature and fault type is established by primary capsule layers and digital capsule layers. Dynamic routing algorithm and back propagation algorithm are used to complete the training process of CapsNet. The simulation results show that the fault diagnosis performance of CapsNet is better than that of the traditional methods such as convolutional neural network, multi-layer perceptron, support vector machine, extreme gradient boosting tree, and light gradient lifting machine in different input characteristics and data scales, which can effectively meet the needs of diagnosis accuracy and provide guidance for the operation pattern of relay. The research can provide references for the fault diagnosis of the transformer.
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| 9. |
- Zhang, Y., et al.
(författare)
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Inverse design of compact digital nanophotonic power dividers with arbitrary power ratios using modified adjoint method
- 2019
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Ingår i: Optics InfoBase Conference Papers. - : OSA - The Optical Society.
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Konferensbidrag (refereegranskat)abstract
- Inverse-designed digital nanophotonic devices have been widely and successfully used due to their simple brute-force design methods, compact footprint, flexibly-designed functions and high performance in various applications. Unfortunately, the number of 3D FDTD simulations in brute-force methods will increase exponentially with the “pixel” number in a digital pattern, which may drastically limit the inverse design capability of digital nanophotonic devices. In this work, we propose and demonstrate a modified adjoint method for efficient inverse design of compact digital nanophotonic power dividers with arbitrary power ratios.
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