Numerical studies for the thermal regime of a high-speed railway tunnel considering piston action on seasonally frozen regions

piston action describes the phenomenon that air at the train nose is pushed forward by the increased pressure and air at the train rear is drawn forward by the decreased pressure when a train passes through a tunnel. The changes of pressure can affect the thermal environment inside the tunnel, and further cause frost damage. In this paper, a fluid-thermal-solid coupled numerical model considering piston action is developed. A high-speed railway tunnel in the northeast of China is taken as an example to explore the temperature distribution laws with computational fluid dynamic (CFD). Afterwards, the effects of air temperature and train velocity on temperature distribution are analyzed. The results show that the piston action can enhance the heat transfer between cold air outside the tunnel and tunnel structure, and can cause more serious frost damage especially at the entrance and exit. The temperature distribution is characterized by three zones, including disturbed zones at two sides of tunnel and undisturbed zone at tunnel middle. The freezing length is closely related to air temperature and train velocity. And also, the lengths are different at vault and rail of tunnel portal, which indicates that the anti-freezing measure should be different at these positions considering the cost. This paper can provide some reference for determining the anti-freezing fortified length of tunnels in cold regions.

Influence of Steel Fiber on Durability Performance of Concrete under Freeze-Thaw Cycles

To verify the steel fiber effect on durability properties of the concrete in cold regions, four types of steel fiber reinforced concrete were prepared, and the fiber dosage were 0, 20 kg, 40 kg, and 60 kg, respectively. The rapid freeze-thaw test was adopted to evaluate the frost resistance durability, and the evaluation indexes of the mass loss and the residual dynamic modulus of elasticity (RDME) the samples were compared, respectively. The frost damage of the matrix regarding the different freeze-thaw cycles (FTCs) was evaluated using the Weibull distribution. The capillary water absorption (CWA) experiments were also conducted corresponding to different freeze-thaw cycles (FTCs). The results revealed that the mass loss was not an effective index for frost damage evaluation of macro-steel fiber reinforced concrete. The FTCs corresponding to the loss of RDME to 60% were enhanced noticeably with the increase of fiber content. The relationship between the frost damage and the FTCs can be evaluated using the Weibull distribution. Compared with the PC, the frost resistance grade of the reinforced concrete with fiber dosage of 60 kg/m3 increased by 125%. After the frost action, the CWA capacity of concrete improved significantly, while, under the same FTCs, the CWA of the matrix decreased with the increment of macro-steel fiber dosage. The steel fiber showed a strong positive influence on enhancing the durability performance of concrete in cold region.

Meteoroloģisko faktoru un stādmateriāla ietekme uz papeļu augšanu = Effect of meteorological factors and planting material on poplar growth

Forestry is challenged by the global demand for sustainable renewable resources. Fast-growing tree species are highly productive and pose the potential to increase roundwood and energy wood production. In Northern Europe, poplars (Populus spp.) and their hybrids are among the most productive tree species. The productivity of poplar plantations is mainly determined by selected clones. Northern European countries lack wide and systematic poplar breeding programs, therefore mainly uses clones that are imported from other European regions. Clones that are transferred northward from their parental species origin should be suitable to an altered length of the vegetation period and low temperatures during the winter season. Clonal testing before recommendation for their commercial use is topical also in Latvia. The thesis aims to characterize the growth of the poplar clones in Latvia and the factors affecting it. This thesis summarizes six thematically linked scientific publications, and their results indicate the significant effect of climatic factors on poplar growth. The radial growth of Populus clones is negatively affected by drought-related stress during the growing season and increased temperature range during the dormancy. Height growth is determined by clone and length of the cuttings, and faster-growing clones are more robust to the negative effect of meteorological factors during the growing season. The faster-growing clones are more likely to have damaged leading shoots by early autumn frost. Trees that have withered aboveground shoots by autumn frost are sprouting during the next growing season, but the regrowth is delayed. Winter frost damage is more likely for weakly growing clones. Overall, fast-growing clones with sufficient autumn and winter frost resistance and survival could be selected.

Effect of Spring Frost Damage on Apple Fruit (Malus domestica Borkh.) Inner Quality at Harvest

In the last few years, spring frosts have become more of a rule than an exception. There are several prevention measures available for growers and numerous are being tested; however, fruitlets are often affected to some extent. One of the more common phenomena is the development of frost rings. The aim of our study was to evaluate how the occurrence of frost rings affects sugar, organic acid, and phenol content in the flesh and phenol content in the peel of cv. ‘Gala’ apples. The results show that the frost damage from spring frost affects compounds in the peel, as well as in the flesh of ripe apples. The flesh of fruits with frost rings contained higher content of fructose and in the flesh directly under the rings there was higher sorbitol and malic acid content. Additionally, the hydroxycinnamic acid and dihydrochalcone content in apple flesh was also altered by frost. The frost-affected peel had a completely different ratio of phenolic compounds content in comparison to healthy apples. While there was a significantly higher content of hydroxycinnamic acids and dihydrochalcones in the corky peel in comparison to the unaffected peel, the flavonol and anthocyanin content was considerably lower.

Trends in the Phenology of Climber Roses under Changing Climate Conditions in Mazovia Lowland in Central Europe

The genetic pool of valuable old ornamental cultivars and their in situ maintenance may be threated by climate change. Meanwhile, the ornamental plants like roses make up an important share of both gardens and urban green spaces, where they are particularly vulnerable to multistress growth conditions. The aim of this research was to evaluate the effect of changing climatic conditions on growth and flowering of 11 historic climber roses through long-term studies (2000-2017) conducted in Central Europe. The evaluation of plants consisted of assessment of frost damage and the timing of early phenological stages (starting of bud break, leaf unfolding) as well as gathering data on beginning, fullness and end of flowering and its abundance. Frost damage was not recorded in any year only in ‘Mme Plantier’, and did not occur for any cultivar after the winter in the years 2007, 2008, and 2014. Only a little damage to one-year shoots was recorded after the winter in the years 2015-2017. Frost damage to ‘Alberic Barbier’, ‘Albertine’, ‘Chaplin's Pink Climber’, ‘Orange Triumph clg’ and ‘Venusta Pendula’ led to pruning to ground level in every year excluding those listed above. Frost damage of once blooming roses limited their flowering; however, the many-year data-sets showed a trend for decreased frost damage and improved abundance of flowering, and these results can be interpreted as a response to the increase of average air temperature. The timing of bud breaking and leaf development in all climber roses was strictly correlated with average air temperature in the dormancy period. The reactions of climber roses to weather conditions confirmed the influence of climatic changes on ornamental crop plants in Central Europe, introducing the potential possibility for the wider application of climber roses, but without certainty of flowering every year.

Snow-Disaster Risk Zoning and Assessment in Heilongjiang Province

Heilongjiang Province is located in the northeast region of China, with the country’s highest latitude. It has long and cold winters, and a temperate monsoon climate. Its unique geographic location and climatic conditions make it the second largest stable snow-covered region in China. The winter snow period starts in October and ends in April of the following year. Therefore, the long-term accumulation of snow causes road obstructions and low-temperature frost damage, which seriously affects local economic development and human safety. This study adopts snow parameters (e.g., snow depth and snow-cover period), natural environmental factors (e.g., elevation and slope), and socioeconomic factors (e.g., gross domestic product and light index). On the basis of the disaster risk assessment theory, we constructed a disaster risk index from four aspects (i.e., disaster risk, susceptibility, vulnerability, and disaster prevention and mitigation). Then, we performed snow-disaster risk zoning and an assessment in Heilongjiang Province. The main findings are as follows: the snow-disaster risk in the northern and eastern regions of Heilongjiang Province was high; the central and northern regions were highly sensitive to disasters; the main urban areas were highly vulnerable; and the economically developed regions had strong disaster prevention and mitigation capabilities. Overall, the spatial distribution of the snow-disaster risk followed a decreasing trend from east to west. High-risk areas were distributed in the east and northwest (covering 34.3% of the entire Heilongjiang Province area); medium-risk areas were distributed in the north and center (accounting for 45.2% of the entire Heilongjiang Province area); and low-risk areas were concentrated in the west (constituting 20.5% of the entire Heilongjiang Province area).

Winter frost damage and its link to early growth and survival in a poplar clone collection

The Northern European countries largely rely on poplars and their hybrids that are transferred northward from more southern regions, therefore, facing a trade-off between the use of full growth potential and sufficient tolerance of low temperatures. We characterized frost damage and its link to early growth and survival of 33 poplar genotypes at the age of one, three, and four years in a clonal collection on agricultural land. The survival after the first season varied from 42% to 99%. Half of the clones had autumn frost injuries with a maximum of 20% of trees damaged. The autumn frost-damaged trees were significantly (p < 0.001) higher before the injury than the undamaged trees with site mean 105.3 ± 7.9 and 72.0 ± 2.5 cm, respectively, but, at the clone mean level, the proportion of autumn frost-damaged trees had no link to survival (rho = 0.53, p < 0.001). The observed winter frost damage showed no relation (p < 0.05) regarding the proportion of trees with autumn frost damage. Trees with winter frost damage tended to be shorter than undamaged trees (p < 0.001) and had lower survival (rho = 0.47, p < 0.01). The maximum height difference of the clones among the studied years was in a magnitude from 2.4 to 2.9, and the stability of a clonal ranking increased with the age. The results emphasize the need for further monitoring of the clone performance under the local climatic conditions before recommendations of commercial use of particular clones in Latvia.