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The population of countries with high altitudes accounts for about 20.4% of the world's population, but the annual electricity consumption is still at a low level, which significantly slows down the development of these regions. Wind energy is suggested as the solution, but the progress is very slow due to challenges in operations from the relatively harsh environment. To overcome this challenge while considering Qinghai-Tibet plateau is one of most representative high altitude regions in the world, we recently developed a 22 MW wind farm at an altitude of over 5000 m in Tibet, China, and conducted a one-year field-test campaign using direct-drive permanent-magnet generators (DDPMGs) and doubly fed induction generators (DFIGs) as a case study. In this paper, we report some main results. During resource assessment, it is found that the wind speeds is between 11 m/s and 22 m/s for most winter time with abundant energy production but relatively significant daily fluctuation due to temperature change. From a technology perspective, we found that both DDPMGs and DFIGs can adapt to the ultra-high-altitude environment. Wind turbines with DDPMGs are reliable because of their gearless design, and turbines with DFIGs have a lower cut-in wind speed, which enables them to generate power in regions with low wind speeds. This wind farm generates nearly 60 million kWh of electricity to support 8410 local households per year. It can also eliminate the need to burn 50.24 million kg of cow dung, thereby effectively reducing the local residents' dependence on burning organic matter for energy. This study is expected to provide guidance to technology developers and governmental policymakers to plan future wind farms in the high altitude area. • Field study of the world first wind farm over 5000 m was systematically conducted. • Wind speed is found as 11–22 m/s with significant fluctuation in winter. • Performance and reliability of different turbine designs are extensively discussed. • The 22 MW farm can provide 60 m kWh electricity to support 8410 households. [ABSTRACT FROM AUTHOR]

This paper investigated the freezing processes of Qinghai-Tibet silty clay within an added quartz sand layer (QSL) under different one-dimensional freezing temperature gradients by using computed tomography scanning and image acquisition technologies in an open system. The heat transfer, cryostructure formation and water migration processes and mechanisms were discussed. The results reveal that the temperature of the samples was essentially steady within 12 h, and the addition of the QSL has a significant impact on the temperature distribution in the samples. The moisture content of the QSL and the frozen part of the sample increased, while the moisture content of the unfrozen zone decreased significantly after being frozen for 120 h. The QSL was able to effectively limit liquid water migration, however, there was still vapor migration in the samples. Ladder-like and net -like cryostructures formed in the vertical sections of the sample while polygon cracks formed in the horizontal sections, which providing pathways for moisture migration. The saturated vapor pressure difference which calculated by the Antony Equation can be used as the driving force for vapor migration from the unfrozen zone to the frozen zone. From both an experimental and theoretical standpoint, this work is intended to aid research into the physical process and mechanism of sand interbedded stratum and foundation freezing. • The image acquisition and computed tomography scanning method were used to study the cryostructure of freezing soil. • Ladder-like and net-like cryostructures were formed due to the freezing temperature gradient. • The added quartz sand layer was able to effectively limit liquid water migration but there still vapor migration exists. • The polygon cracks formed in the horizontal sections of the soil samples, providing pathways for moisture migration. • The saturated vapor pressure difference provides the driving factor for vapor migration in the freezing soil. [ABSTRACT FROM AUTHOR]

The bimodal structure in expansive soils that refers to the bimodality of the pore size distribution significantly affects the soil freezing characteristic curve (SFCC). In this paper, the artificial samples with different bimodal structures are prepared by mixing Qinghai-Tibet silty clay and bentonite in different proportions. The influence of the bimodal structure on the SFCC of the samples was studied by the mercury intrusion porosimetry test, the nuclear magnetic resonance (NMR) test and the freezing-point test. The results show that the freezing stage of the SFCC in bimodal soils consists of a rapid-drop part related to freezing of macropore water and a slow-drop part related to freezing of micropore water. As the specific surface area increases, the proportion of the rapid-drop part decreases whereas the slow-drop part increases. On the temperature-time curve, the duration of the isothermal stage and the freezing point decrease with the rising specific surface area. Based on the experimental results, we established a novel SFCC function derived from the theory of pore size distribution by extending the lognormal distribution to consider bimodality. The SFCC function can fit the measured data of the SFCC well. • The influence of the bimodal structure on SFCC is experimentally investigated. • The freezing stage of SFCC comprises a rapid-drop part and a slow-drop part. • The freezing point decreases with rising amounts of micropores. • A new SFCC function with bimodality is proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Provenance is defined for the lakeshore dunes around Co Nag Lake on Tibet Plateau. • The combination of MixSIAR and end-member model can reliably infer the provenance. • Lacustrine and fluvial deposits on the eastern bank are main sources of dune sands. • The coupling of fluvial and aeolian systems promotes the development of sandy land. • Enhanced sand-control project should be taken to protect the Qinghai-Tibet railway. Studies of the provenance of aeolian dunes are crucial for providing knowledge of landscape evolution and developing management strategies to control aeolian desertification. The lakeshore dune is a typical aeolian landform that is widely distributed around the world. However, there has been little work on the provenance and formation mechanism of lakeshore dunes. By comparing the elemental and grain-size compositions of lakeshore dunes and potential sources around Co Nag Lake, this paper combines sediment fingerprinting analysis and end-member modeling. The results identify the provenance of aeolian sands on the eastern bank of Co Nag Lake and draw the following conclusions. (1) The combined use of fingerprinting analysis and grain-size analysis can yield a comprehensive and reliable provenance assessment. (2) The lakeshore dunes on the eastern bank of the lake are primarily derived from lacustrine deposits and fluvial deposits on the eastern bank. The coupling of fluvial and aeolian systems promotes the development of eastern sandy land. (3) Sand-control projects in the Co Nag Lake region should be carried out according to the sources of aeolian sands. It is necessary to strengthen efforts to control lacustrine deposits and sands in gullies. [ABSTRACT FROM AUTHOR]