Snow Accretion Research Articles

Assessing the potential for simplification in global climate model cloud microphysics

Abstract. Cloud properties and their evolution influence Earth's radiative balance. The cloud microphysical (CMP) processes that shape these properties are therefore important to represent in global climate models. Historically, parameterizations in these models have grown more detailed and complex. However, a simpler formulation of CMP processes may leave the model results mostly unchanged while enabling an easier interpretation of model results and helping to increase process understanding. This study employs sensitivity analysis of an emulated perturbed parameter ensemble of the global aerosol–climate model ECHAM-HAM to illuminate the impact of selected CMP cloud ice processes on model output. The response to the perturbation of a process serves as a proxy for the effect of a simplification. Autoconversion of ice crystals is found to be the dominant CMP process in influencing key variables such as the ice water path and cloud radiative effects, while riming of cloud droplets on snow has the most influence on the liquid phase. Accretion of ice and snow and self-collection of ice crystals have a negligible influence on model output and are therefore identified as suitable candidates for future simplifications. In turn, the dominating role of autoconversion suggests that this process has the greatest need to be represented correctly. A seasonal and spatially resolved analysis employing a spherical harmonics expansion of the data corroborates the results. This study introduces a new application for the combination of statistical emulation and sensitivity analysis to evaluate the sensitivity of a complex numerical model to a specific parameterized process. It paves the way for simplifications of CMP processes leading to more interpretable climate model results.

Wind tunnel tests on effect of relative humidity on the phenomenon of snow accretion

Wind tunnel tests on effect of relative humidity on the phenomenon of snow accretion

Natural Snow Accretion and Flashover Performance of Composite Insulators

Natural Snow Accretion and Flashover Performance of Composite Insulators

Angle of repose of snow: An experimental study on cohesive properties

The angle of repose is a measure reflecting the internal friction and cohesion properties of a granular material. In this paper, we present an experimental setup and measurements for the angle of repose of snow for seven different snow samples over a large range of temperatures. The results show that the angle of repose is dependent on the fall height, the temperature, and the grain size of the snow. These variables are quantified, and their interdependencies are separately studied. With increased snow temperature, the angle of repose increases, and this can be explained by the presence of a liquid layer on ice that can be thermodynamically stable at temperatures below the melting point of water. With decreasing grain size the angle of repose also increases which is expected since the cohesive energy decreases more slowly than the grain mass. For increasing fall height, the snow grains generally accelerate to larger collisional velocities, yielding a smaller angle of repose. In general, the dimensionless cohesion number was found to largely reflect the dependencies of the variables and is therefore useful for understanding what affects the angle of repose. The results demonstrate that the drag force and collision dynamics of ice grains are important for understanding how snow accumulates on a surface, for example if one desires predicting snow accretion by simulating a dispersed cloud of snow.

Influence of bogie fairing configurations on the snow accretion around bogie regions of a high-speed train under crosswind conditions

In this paper, the unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) was coupled with the Discrete Phase Model (DPM) to study snow accretion on the bogies of a high-speed train under crosswind conditions. The influence of bogie fairing configurations on the snow particles’ movement, accumulation and flow characteristics around bogie regions are assessed. The results show that the larger bogie fairings have a positive effect on snow reduction around the main components of bogies under crosswind conditions. Compared to currently used bogie fairings, the total snow accretion of a head car increases by 41.5% by removing the fairings, while it decreases by 24.9% with the installation of full bogie fairings. The larger bogie fairings can lower the velocity of underbody flow and prevent high-speed airflows from entering the bogie regions from the windward side of bogie cavities. Moreover, the larger bogie fairings reduce the snow concentration around the heat-producing components of the bogies and attenuate the amount of snow particles near the rear plates of the cavities. Thus, the larger fairings can provide better anti-snow performance of train bogies under crosswind conditions.

<b>Method for Estimating Snow Accretion on Shinkansen Bogies using Weather Data</b>

Shinkansen trains operating in snowy areas accumulate snow on their bogies, which can sometimes lead to damage to ground facilities. To prevent this type of damage, snow is removed from trains in stations. We developed a method to estimate the amount of snow accretion on bogies: first, snow density on the railway track is estimated using weather data, then, flying up snow flux is estimated. This is then used to predict the accumulated snow amount under the bogies. Our research confirmed that snow accretion under a bogie upon arrival at a station can be estimated to within 3 cm.

Numerical study of dry snow accretion characteristics on the bogie surfaces of a high-speed train based on the snow deposition model

ABSTRACT To investigate the distribution of dry snow particles deposited on the bogie surfaces of a high-speed train, a snow particle deposition model based on the critical capture velocity and the critical wind friction speed was established. The suspension motion behaviour of snow particles in the air was simulated by the unsteady Reynolds-averaged Navier–Stokes (uRANS) simulations, based on the Realizable k–ε turbulence model and the Discrete Phase Model (DPM). The results show that the crossbeam of the bogie frame, the anti-snake movement dampers, the middle brake shoes of the rear brake rigging, the traction rods and the anti-rolling torsion bars are prone to accumulating snow. Furthermore, the critical capture velocity has a significant effect on the distribution of snow accretion. When the critical capture velocity is changed from 1.0 m/s to 3.0 m/s, the total snow accumulation on the bogie will increases by 20%.

Predicting ice accretion from freezing rain on bridge stay cables

An morphogenetic model that simulates ice accretion on arbitrarily oriented cables exposed to freezing rain has been developed at the National Research Council Canada (NRC). This predictive numerical model has been validated experimentally for a limited number of conditions in the NRC Climatic Testing Facility. The facility is 6 m wide, 6 m high and 30 m long, and can generate a range of freezing precipitation environments. Inclined stay cable models with a diameter of 0.218 m and a length of 2.4 m were exposed to simulated freezing rain. The final experimental ice accretion shapes were scanned and digitized using a handheld laser scanner. These three-dimensional experimental ice shapes were used to partially validate the NRC morphogenetic model. The successfully validated model was used to examine ice accretion on stay cable geometry in an environment representative of freezing rain conditions in Eastern Canada. Prediction of wet snow accretion on already ice covered stay cables has also been undertaken.

Numerical Study on the Effects of Anti-Snow Deflector on the Wind-Snow Flow Underneath a High-Speed Train

In order to study the effect of the anti-snow deflector on the wind-snow flow underneath a high-speed train, Detached Eddy Simulation (DES) approach and discrete phase model (DPM) are used to simulate the windsnow flow around the train. The distribution of snow particles underneath the train body is analyzed. Meanwhile, the influence of deflectors on the movement of snow particles around the train is investigated. The results show that lots of vortices shed from the bogie, and the entrainment vortices near the ground actuates the movement of the snow particles on the snow-covered track, which forms a wind-snow flow. The snow smoke around the train develops gradually from the bottom of the first bogie to the end of the tail car. The deflector installed in the front of the bogie will guide the vortices off the bogie region to the ground, which results in flying up more downstream snow particles and correspondingly the number of snow particles accumulated in the bottom of the rear car and around the rear skirt plate is increased. The installation position for the deflector has a certain effect on the snow accretion in the bogie region. When the deflector is installed in the front of the 2nd and 4th bogies, the snow particles captured in the bogie region are reduced by 42.3% and 15.6%, respectively.

Verification of reduction effect of snow accretion using numerical simulator

Verification of reduction effect of snow accretion using numerical simulator

Development of snow accretion simulator for railway vehicles (Part 2)

Development of snow accretion simulator for railway vehicles (Part 2)

Development of snow accretion simulator for railway vehicles (Part 1)

Development of snow accretion simulator for railway vehicles (Part 1)

雪庇・着雪現象を考慮した吹雪数値シミュレーションの検討 -その3，建築物雪庇形成の予測に関する吹雪シミュレーションの適用性について-

雪庇・着雪現象を考慮した吹雪数値シミュレーションの検討 -その3，建築物雪庇形成の予測に関する吹雪シミュレーションの適用性について-

山形蔵王における雪氷現象の観測(2019/2020冬季)

山形蔵王における雪氷現象の観測(2019/2020冬季)

The attenuation characteristics of millimeter-wave by snow accretion

The attenuation characteristics of millimeter-wave by snow accretion

Influence of snow accretion on arc flashover gradient for various types of insulators

Atmospheric snow accretion along the insulators can eventually bridge adjacent shed spacing, which pose severe risks to the security of power networks. Aiming to investigate the influence of snow accumulation on the electrical performance of various types of insulators, the flashover tests of snow-accreted insulators were conducted. The effects of various factors on the electrical characteristics of insulators were analysed based on the experimental data. Results show that AC arc flashover gradient of the insulator covered with nonuniform snow accumulation is lower than that of the uniform snow-covered insulator. The former is as low as 22.5% lower than the latter. Moreover, the AC arc flashover gradient of the porcelain and glass insulators is 0.27–6.27% higher than that of the DC. For a silicone rubber insulator, this gap is greater than 20%. The flashover gradient of the glass insulator is the minimum at the snow thickness of 10 mm. The flashover process of snow-covered insulator is neither similar to that of the contaminated insulator nor different from that of the iced insulator but a combination of the two. The presented work helps to better understand the flashover mechanism of snow-covered insulators, and take efforts to mitigate its effects.

Numerical and experimental investigation on snow accumulation on bogies of high-speed trains

This paper reviews the current status of investigation on snow accumulation on the bogies of high-speed trains (HSTs) running in snowy region. First, the background of the snow issue occurring to the HST and the contra-measures for the snow issue proposed in the past decades are provided by reviewing previous studies. Next, the methodology for investigating the snow issue developed by High-Speed Train Research Center of Central South University is introduced, including the numerical simulation research platform and the experimental devices for two-phase flow wind tunnel tests. Then, effective anti-snow flow control schemes for guiding the underbody airflow and their impact on the motion and accretion of snow in the installation region of the bogies are presented. Finally, the remaining investigating challenge for the snow issue of HST and the future research with respect to the challenge are provided from an engineering application viewpoint.

Evaluation for characteristics of wet snow accretion on transmission lines - Establishment of an experimental method using a vertical plate

It is of primary importance to decrease risks of snow damages on electric transmission lines to ensure a stable supply of electricity. For the acquisition of reliable data to clarify characteristics of snow accreted on a transmission line, it is effective to conduct an indoor experiment. The present report describes an experimental method for snow accretion on a vertical plate by using a wind tunnel including measurements of snow properties such as snow density and liquid water content, which can be extended to measure a shear adhesive stress of accreted snow. These measurements are systematically applied to different conditions of the wind speed, the air temperature, as well as the snow flux particularly focusing on wet snow accretion. Based on measurement data, the influence of the wind speed, the air temperature, and the snow flux on the snow density and the liquid water content is investigated. The analysis is further extended to include a parametric evaluation of the snow density and the liquid water content to examine their dependency on atmospheric parameters. As a result of analytical considerations of the consolidation effect by wind and melting of snow by heat exchanges, equations to estimate the snow density and the liquid water content by the wind speed, the air temperature, as well as the accreted snow mass are derived. The experimental results validate these equations, which enable the acquisition of desired snow properties by adjusting experimental parameters. The successful evaluation of snow properties in the presented experiments can substantially contribute to the establishment of practical data-set for further investigations to characterize wet snow accretion.

Interview

Shamsodin Taheri Shamsodin Taheri, from the University of Quebec Outaouais, Canada, talks to us about his group's submission “Analysis of electrical behaviour of PV arrays covered with nonuniform snow” page 192. I am an Associate Professor of Electrical Engineering in the Department of Computer Science and Engineering at the Université du Québec en Outaouais (UQO). The expertise of my research group in the field of power energy has advanced our understanding of the performance of photovoltaic (PV) sources in cold-climate conditions. This research was inspired by the issues that PV plants in Canada experience during cold months. In recent years, we have collaborated with several industry partners, who own utility-scale PV plants, to evaluate the performance of their facilities. This ongoing research helps mitigate the technical challenges facing the integration of renewable energy sources into power grids in cold regions. PV systems have found different applications in cold areas for a long time, such as remote research facilities in the South and North Poles and space travelling. The majority of PV energy plants are presently installed in geographical cold locations with a considerable amount of snowfall every year. Furthermore, the solar energy industry is expanding competitively in cold climate regions. For example, in Canada, the installed capacity of solar PV grew from 95 MW to more than 2500 MW during 2009–2016. PV panel efficiency is not only influenced by PV technology, but environmental conditions can also influence their energy production. Accumulation of snow/ice decreases solar radiation reaching the PV panels, which results in a significant loss of power generation. Non-uniform snow accretion on PV panels often occurs due to ambient conditions such as wind, temperature variation, partial snow shedding and ground interference. This leads to power loss that is dependent on the configuration of the PV system. Owing to the increasing deployment of PV systems, there is a significant interest in optimal utilisation of PV potential in cold climate regions. A fundamental need for knowledge of the impact of nonuniform snow accretion on PV systems is therefore essential. This research has shown that the snow-covered PV panels can still produce a significant amount of energy depending on the pattern and depth of the snow accumulation. The portion of this energy that could be collected is decided by configuration of the PV array as well as the maximum power point tracking (MPPT) technique. Investigations concerning the effect of bypass diodes have shown that the PV string without bypass diodes generally experiences more power loss. In addition, the vertical and horizontal PV array layouts were tested to determine power loss due to nonuniform snow accretion. The horizontal PV array layout would be more effective in snowy climates. This work is helpful for PV system performance assessment, MPPT development and testing, power generation prediction, and proper arrangement of panels in cold regions. The accumulation of snow on PV modules weakens the intensity of incoming solar radiation and hence limits their ability to generate electricity during cold months. However, the true extent of such impact on the energy production of PV modules cannot be specified in a straightforward way, since it is not proportional to the snow-covered area. In some instances, snow covering only one cell can reduce the efficiency of a whole module by a noticeable amount. Snow is a complex phenomenon, and a quantitative characterisation of radiation transmittance through snow coverage requires knowledge of the physical properties of snow. In fact, the interaction of sunlight with snow to determine the influence of snow coverage on the PV modules is a challenge. This leads to changing the electrical characteristics of the PV array and producing multiple, local peaks on PV characteristics. Accurate modelling of the electric behaviour of PV modules and systems is a key element in improving system operation and efficiency. Hence, proper modelling approaches of the operation of PV generators under varying environmental conditions that improve their performance control and assist the design of PV converters and their MPPT controller have been achieved. Moreover, an appropriate tool has been proposed to determine the efficiency of PV farms under cold conditions. Furthermore, a high performance MPPT technique has been proposed to harvest the maximum energy of a PV array with multipeak characteristic under partial shading condition. Major progress must be made on the proper design and arrangement of PV arrays and power electronic interfaces, minimising the effects of snow on large-scale PV farms and the increasing the use of bifacial PV modules as a candidate for cold regions over the next ten years.

Analysis of electrical behaviour of PV arrays covered with non‐uniform snow

Snowfall during cold months impacts the performance of photovoltaic (PV) installations. In real field operations, different ambient conditions often cause non-uniform snow accretion on PV panels. This can have a considerable effect on PV power production depending on array configuration, the pattern of snow coverage, and bypass diodes included in a PV system. The electrical behaviour of snow-covered PV cells is experimentally characterised. Then, the true impact of non-uniform snow accretion on PV system performance is investigated. Effect of employing bypass diodes on a PV string power generation is also verified. Different PV array layouts are studied to improve the PV harvest efficiency in cold climate regions. This research may be regarded as a practical tool for the design and selection of PV modules subjected to snowfall.