Icing Tests Research Articles

Simulation calculation of 3D electric field and natural flashover analysis of ice‐covered silicone rubber insulator

AbstractThe effects of uneven icing, number of icicles, inclination angle of icicle, ice pallets and arc ignition on the electric field are ignored for the two‐dimensional axisymmetric model of ice‐covered insulator. Therefore, a 3D simulation model was developed in this paper. The average electric field strength of air gap (Eav) and maximum field strength of icicle tip (Emax) were determined to characterize the influence of various factors on the electric field distortion degree. The results show that compared with the insulator without ice and with a dry ice, the supply voltage is almost entirely applied to all icicle air gaps for a wet ice‐covered insulator. Eav is independent of icicle diameter and icicle number but increases with the increment of icicle length and icicle inclination angle. Emax raises with the increase of icicle length, icicle number, icicle inclination angle and icicle diameter. As the source of electric field distortion, the ice pallets on the surface of the sheds rise the field strength of air gap. Based on the simulation analysis and natural icing test, the applied voltage is redistributed in the remaining air gaps when an arc occurs in the gap near the high‐voltage terminal, thereby causing the subsequent flashover.

Contrast Icing Wind Tunnel Tests between Normal Droplets and Supercooled Large Droplets

In order to compare and analyze the similarities and differences between normal droplet icing shapes and supercooled large droplet icing shapes, SADRI carried out normal droplet and supercooled large droplet icing wind tunnel tests in the NRC−AIWT icing wind tunnel. Taking the typical glaze ice in normal droplet icing conditions as the reference, the freezing drizzle and freezing rain icing tests under the supercooled large droplet conditions were carried out. The test results show that compared with normal droplets, the ice horn height of supercooled large droplets decreases with the increase in droplet particle size, and even the ice horn characteristics are not obvious when the icing condition is freezing rain. At the same time, the range and height of rough element ice shape after the main ice horn of supercooled large droplets are significantly larger and higher than those of the normal droplets, while the difference in the rough element in different supercooled large droplet icing conditions is small.

Pattern of Ocular Myasthenia Gravis in a Tertiary Eye Care Hospital, Bangladesh

Purpose: The purpose of this study was to evaluate pattern of ocular myasthenia gravis patients in a tertiary eye care hospital in Bangladesh.
 Methodology: This observational study was conducted in National Institute of Ophthalmology and Hospital (NIOH), Dhaka from January 2019 to December 2019. A total of 33 cases were purposively selected among ocular myasthenia gravis patients attending in the Department of neuro ophthalmology of NIOH irrespective of age, gender, residence. Study variables wereage, gender, clinical features, presence of thymoma, clinical, pharmacological and serological test findings. A proforma was prepared to record the data on particulars of the patients.
 Results: Among the cases, 45.5% were male and 54.5% were female where the mean age was 38.7 years. All patients presented with ptosis (100.0%) and most of them had fatigability(87.9%), cogan twice sign (81.8%) andorbicularis weakness (81.8%) while 63.6% had diplopia. Diabetes mellitus was observed in 18.2%patients and 15.1% had thyroid associations. Most of them had positive ice test(87.9%), 51.5% had positive serological test and 6.1% had positive neostigmine test. Thymoma was present in 6.1% cases.
 Conclusion: Ptosis was the most common clinical presentation for ocular myasthenia. Clinical diagnosis was confirmed by ice pack test and neostigmine test. Ocular myasthenia gravis patients may be have other systemic diseases.
 J. Natl. Inst. Ophthalmol. 2022;5(1):16-20

Construction of Multiphase Mixing Interface for Delay Icing Based on Microarray Surface

Slippery liquid‐infused porous surface (SLIPS) is an emerging anti‐icing method. The anti‐icing mechanism of SLIPS is to prevent the heat transfer from liquid droplets to the surface by forming an oil film on the solid surface. However, the contact area between the droplet and the surface of the specimen increases due to the existence of the oil film, which accelerates the heat transfer and emergence of ice. Herein, in order to further improve the anti‐icing performance of SLIPS, a microscale square column array is fabricated by wire cut electrical discharge machining (WEDM) technology, on which a circular hole structure is constructed by nanosecond laser. Lubricating oil is then injected into the fluorinated surface to produce SLIPS. The maximum contact angle (CA) of the surface is 150° ± 1.2° and the contact angle hysteresis (CHA) is 1.2°. The contact mode of droplets on the surface is liquid–oil and liquid–gas, which is a multiphase mixing interface. The icing test shows that the icing time of the droplet is 4785 s at a surface temperature of −10 °C, exhibiting a good icing‐delay performance.

Collision Characteristics of Water Droplets in Icing process of Insulators

Icing on the insulators of transmission lines threats the power system security. The flashover properties of ice-covered insulators have been widely studied while there is a lack of research on the icing properties of insulators. In this paper, the collision process of supercooled water droplets on insulators is studied. Based on the boundary element method (BEM), a mathematical model of airflow and water droplet motion outside insulators is established. Taking advantage of vector calculation and array tracking, the 3D distribution of collision droplets on insulators is obtained. The results show that the droplets mainly collide with windward shed edge and steel cap of insulators. With the increase of wind velocity and median volume diameter of droplets, the number of captured droplets increases and the collision area expands from the shed edge and steel cap centre to the inner surface and two sides, leading to the increase of icing rate and icing area. Moreover, the related icing tests of insulator LXY-120 were conducted on Xuefeng Mountain, the recorded icing mass and shape are compared with the simulation results, and it is found that the model in this paper has a relative error of 13.5%.

Study of a new method for the instant preparation of ice particles in ice abrasive air jet

The ice abrasive air jet is a clean surface treatment technology, which currently has limitations such as high energy consumption, uncontrollable particle size and hardness. Realizing the instant preparation and utilization of ice particles are crucial for solving the energy consumption problem. This paper based on the icing principle of heterogeneous nucleation, proposed a new method of ice making, the heat transfer mechanism of low temperature droplets was studied, and the method was proved to be feasible. Using the FLUENT solidification and melting model combined with the VOF model to calculate the freezing process of droplets, the effects of droplet particle size, initial temperature, and wall temperature on the freezing time were analyzed, and the calculation equation of the freezing time was determined, which was corrected by the icing test results. The results showed that the outside of the droplet freezes first, the liquid–solid boundary is parabolic, and the parabolic concavity increases with time and droplet size. In the freezing process, the larger the droplet size, the longer the droplet phase transition time; the higher the droplet initial temperature, the longer it took to reach the phase transition; the higher the wall temperature, the longer the ice formation time.

An investigation on the speed dependence of ice resistance using an advanced CFD+DEM approach based on pre-sawn ice tests

Over the past decades, the underlying mechanism of level ice resistance changing with ship speed has not been fully understood, particularly the resistance component due to ship interactions with broken ice pieces. Pre-sawn ice test can negate icebreaking component from the whole resistance of a ship in level ice, providing an effective approach to decompose ship-ice interactions and investigate the speed-dependent resistance from broken ice pieces. This work has built a computational model that can realistically simulate a ship advancing in a pre-sawn ice channel. The model applies Computational Fluid Dynamics (CFD) to solve the flow around an advancing ship, which is coupled with an enhanced Discrete Element Method (DEM) to model pre-sawn ice pieces. Model-scale experiments have also been conducted at the Aalto Ice Tank to validate the simulations, which shows the computational model can provide a reasonable estimation of the pre-sawn ice's resistance and movement around the ship. Upon validation, the dependence of ice resistance on ship speed was analysed. The simulations enable underwater monitoring of the ice motions, indicating that the speed dependence results from the mass of ice submerged underneath the ship and the displacement of broken ice induced by the ship. The identified relationships are more complex than the widely-used assumption that ice resistance linearly changes with ship speed in all cases, which provides a deeper understanding of ice resistance. As such, the findings from this study can potentially facilitate improvements in relevant empirical equations, useful for ship design, operational strategies and maritime management in polar regions.

A model scaling approach for fracture and size effect simulations in solids: Cohesive zone, smeared crack band and phase-field models

Despite many noteworthy contributions, the computational modeling of arbitrary fracture configurations and in particular, the quantification of size effect in quasi-brittle solids, still remains a challenging issue. In this work we proposed a model scaling approach for fracture and size effect simulations in solids. It employs only the geometric transformation relations and thus applies to any material model for fracture. Those popular models, i.e., the cohesive zone model, the smeared crack model and the phase-field cohesive zone model, are considered. With the geometric scaling factor intrinsically incorporated in the formulation, the resulting scaled models are able to predict the energetic size effect of a series of geometrically similar structures by parametric numerical simulations of the reference one. The 1-D analytical results of all the three scaled models are coincident with those from the underlying unscaled counterparts, validating the proposed model scaling approach. As it is independent of the mesh discretization and insensitive to the length scale, the scaled phase-field cohesive zone model (PF-CZM) is adopted for application to several representative benchmark tests of concrete and ice with mode-I and mixed I+II failure modes. The numerical results demonstrate that, owing to the strength-based crack nucleation criterion, the energy-based crack propagation criterion and the variational principle based path chooser, as well as the geometric scaling factor, are all incorporated into a standalone framework, the scaled PF-CZM is able to predict both the type II size effect law of pre-cracked quasi-brittle structures and the type I size effect law of intact ones. Moreover, those laborious manual manipulations in the numerical modeling of a large size range of geometrically similar structures, e.g., spatial discretization, enforcement of loading and boundary conditions, postprocessing of output data, etc., need to be done only once on the reference structure. These advantages make the scaled PF-CZM rather promising in the quantification of size effect in quasi-brittle structures.

Ice accretion, shedding, and melting on cable-stayed bridges: A laboratory performance assessment

Ice accretion on cable-stayed bridge surfaces increases loading, affects the structures' aerodynamic behavior, and heightens the risk of ice pieces detaching and falling onto bridge traffic. Here we propose a comprehensive laboratory-based procedure for evaluating materials to reduce ice accretion and prevent ice shedding on cable-stayed bridge. We then assess our laboratory-based procedure by testing four high-density polyethylene sheath configurations for cable-stayed bridges. These sheaths differ in their surface finishes, chemistry, and surface roughness. We present a three-step controlled-environment procedure involving (i) the physical characterization of the surface; (ii) an evaluation of surface behavior under laboratory icing tests; and (iii) an assessment of ice accretion at −10 °C under freezing rain conditions, followed by shedding and melting phases. This testing procedure provides a simple means of evaluating geometric changes and surface modifications, including icephobicity, under repeatable and comparable conditions. Our approach could serve in the design and optimization of materials prior to their deployment under actual operational conditions.

Numerical modelling of ice: Mechanical behaviour of ice under high strain rates

Ice impact is quite common and may become critical especially if it involves the transportation sector. Simulation tools may help in the structural design phase to increase the ability to withstand this kind of impact and/or to analyse the effect under extreme weather conditions. Such tools require an accurate description of the mechanical behaviour and therefore a detailed investigation about the dynamic mechanical properties of ice is of great interest. In the present work, material characterizations of ice, including tensile and compressive tests, were carried out under different strain rates. Two different material models (i.e., the modified Johnson-Cook model and Johnson-Holmquist II model) were calibrated. Then, impact tests using ice as a projectile with aluminium panels as a target were conducted to validate the material models of ice under impact loading. Furthermore, the replication effect of ice projectiles was investigated under different impact energies based on the mechanical responses and damage phenomena of ice for both models. Results showed that while both models are able to provide reliable predictions of the impact behaviour of ice projectiles, the Johnson-Holmquist II model presents a better performance as impact energy increases.

Anti-icing and anti-frost properties of structured superhydrophobic coatings based on aluminum honeycombs

Superhydrophobic coatings have many potential applications in prevention of ice, frost, condensation, and corrosion due to their strong hydrophobicity and self-cleaning function. However, superhydrophobic coatings do not have ideal mechanical stability in engineering applications, and the coatings lose their superhydrophobic properties with wear. We propose an innovative combination of a macroscopic aluminum honeycomb structure with a superhydrophobic coating to prepare a mechanically stable, structured coating by a simple spraying process. The coating showed excellent performance in laboratory ice, frosting, and outdoor ice tests. Compared with common superhydrophobic coatings, the total ice-up time of single droplet was prolonged by 190 s on a platform at −15 °C because of the reduced heat transfer between the macro-honeycomb wall and the droplets. After 300 wear tests, the frosting amount increased by only 0.03 g when the platform was tilted to 60% at −20 °C and 75 ± 5% humidity. In the outdoor ice test, no large area of ice was observed on the surface. Our findings provide a new strategy for industrialization of superhydrophobic coating, and our strategy has potential applications in anti-icing and anti-condensation for electrical equipment, drag reduction, and anti-corrosion.

Novel thermally insulated ultra‐lightweight fireproof and high impact resistance advanced hybrid composite

AbstractThis work investigates the development of ultra‐lightweight, hybrid fireproof composite material. The composite panels are made of 2,5‐polybenizimidazole (ABPBI) a thermally stable high‐performance fiber and poly ether ketone (PEK) a high‐performance film. The surface of ABPBI fiber and PEK film were treated by nitrogen plasma to increase the adhesion characteristics. The composite was fabricated through the stacking method. The hybrid composite was developed by sandwiching silicone rubber foam between surface‐treated ABPBI/PEK composite. The entire sample was covered with surface‐treated ABPBI fiber using silicone adhesive. The hybrid composite was tested in exposure to dry ice, fire and compression tests. After exposure to fire for 10 min, negligible loss of material was noticed. The Scanning Electron Microscopy (SEM) analysis at the interface indicated strong interfacial adhesion between the PEK matrix and the ABPBI fiber. Limiting oxygen index (LOI) of ABPBI fiber and PEK film appear to be promising in terms of fire resistivity and hence the hybrid composite of PEK/ABPBI sandwiched by silicone foam results one of the best fireproof composite. This composite also shows significant improvement of impact and compressive strength. Analysis under Ansys Fluent software also shows similar results.

Isolated Unilateral Ptosis Caused by Orbital Myositis Involving the Superior Rectus-Levator Muscle

Purpose: To present a case of orbital myositis involving the levator palpebrae superioris/superior rectus muscle (LPS/SR) complex with isolated unilateral ptosis and preserved extraocular muscle function and to review of the literature.Case summary: A healthy, 54-year old man presented with acute right upper ptosis detected 3 hours before. His best-corrected visual acuity was 20/20 in both eyes. His margin-reflex distance 1 was -2 mm and +4 mm, and levator function was 11 mm and 14 mm in the right and left eyes respectively. There was no proptosis. He had full extraocular motility with no strabismus, and normal pupillary function. There was no improvement in ptosis with the ice test and 0.5% apraclonidine test. Orbital magnetic resonance imaging demonstrated thickening and enhancement of right LPS/SR complex. Consequently, we diagnosed him with orbital myositis involving the LPS/SR complex. We started treatment with corticosteroid and ptosis completely resolved after 1 month since onset.Conclusions: We report a case of orbital myositis who showed inflammation of the LPS/SR complex early in the disease course and allowed the preservation of normal SR function. Inflammation of the LPS/SR complex might affect the function of these muscles differently due to the differences in muscle mechanics. Although orbital myositis involving LPS/SR complex is rare, it should be considered as a differential diagnosis in patients with acute unilateral ptosis.

Predicting compressive strength and behavior of ice and analyzing feature importance with explainable machine learning models

Building and using ice-related models is challenging due to the complexity of the material. A common issue, shared by both material models and (semi-)empirical approaches, is estimating unknown input parameters such as compressive strength. This is often done with additional empirical formulas which have drawbacks, e.g., they are based on a limited amount of data. Regarding material modeling, a strongly related problem is the prioritization of effects to include in the model. This is mostly done based on a subjective mix of knowledge, model purpose, and experimental studies limited to that purpose, which risks overlooking effects or interaction of effects, and limits transferability of material models to other scenarios.To tackle these issues, a hybrid approach of domain knowledge and explainable machine learning was used. A large ice test database was compiled to train machine learning models to predict compressive strength and behavior type. The machine learning models’ predictions were more accurate than existing empirical or analytical approaches and can thus be used as an alternative, though less straightforward, tool for such predictions. Further, the SHAP explainable AI method was applied to the predictions. Impact rankings of experimental parameters and interaction effects between parameters were analyzed and discussed in terms of ice mechanics. Top features were strain rate, triaxial stress state, temperature, and loading direction, but impact rankings were highly dependent on prediction target and type of ice. Few interaction effects were found. The approach adds objectivity to the prioritization of effects for material modeling and generated further insights into ice mechanics. It is also considered useful for other natural materials or generally when there is more data than knowledge.

Ocular Myasthenia: Clinical Course and the Diagnostic Utility of Assaying Acetylcholine Receptor Antibodies

ABSTRACT Myasthenia gravis (MG) is an autoimmune disease that causes neuromuscular junction transmission defect and has a predilection for the with neuromuscular junction transmission defect and predilection for extra-ocular and eyelid muscles. Most cases of ocular MG (OMG) convert later to generalised MG (GMG). Assaying acetylcholine receptor antibodies (AchRA) has been used to diagnose MG, but the reported sensitivity in OMG is lower (50%) than in GMG. We report the clinical course and the diagnostic yield of assaying AchRA in a Kuwaiti cohort of patients with OMG. We carried out a retrospective review of 47 patients diagnosed with OMG who were tested for AchRA. Ancillary tests included the ice test, single-fibre electromyography (SFMEG), and repetitive nerve stimulation electromyography (RNS). Progression to GMG occurred in 51% of OMG patients with a mean time to progression of 12.1 months (range 4 to 20 months). AchRAs were positive in 46 of 47 cases (98%), while SFEMG was positive in 31 of 34 cases (91.1%). Older age (44.25 years versus 38 years, p < .05) and higher AchRA titre (2.0 nmol/L versus 1.27 nmol/L, p < .05) were significantly associated with conversion to GMG. We have found a high rate of AchRA seropositivity in relatively younger subjects of OMG. Higher AchRA titres and older age were associated with conversion to GMG, usually within the first 2 years.

An improved Bessel beam-based method for processing curved/tilted surface with anti-icing property

Icing is a serious threat to the flight safety of aircraft. In order to reduce the accumulation of ice on the surface and improve the anti-icing ability, various anti-icing methods have been developed. Among them, laser-induced anti-icing surface has advantages of low energy-cost as it does not need extra energy to de-ice by heat or vibration. However, conventional laser preparation approaches of anti-icing surfaces are only suitable for processing planar structures due to the limitation of the focus length. Meanwhile, aircrafts are composed by many curved/tilted structures. How to quickly fabricate anti-icing curved/tilted surfaces is an urgently issue. In this paper, an approach for preparing anti-icing curved/tilted surface based on Bessel beam is proposed. By utilizing the long focal depth of Bessel beam, curved/tilted surfaces can be fabricated in one-step. Moreover, the fabrication parameters have been quantitatively investigated to process surface with anti-icing property. The processed anti-icing surface has undergone a simulated icing test and showed anti-icing characteristics.

An Experimental Apparatus for Icing Tests of Low Altitude Hovering Drones

The icing facilities of the Anti-Icing Materials International Laboratory AMIL have been adapted to reproduce icing conditions on a Bell APT70 drone rotor, typical of small-to-medium UAV models. As part of an extensive icing test campaign, this paper presents the design and preliminary testing of the experimental setup and representative icing conditions calibration in the laboratory’s cold chamber. The drone rotor used has four blades with a diameter of 0.66 m and a maximum tip speed of 208 m/s. For the icing conditions, freezing rain and freezing drizzle were selected. A Liquid Water Content (LWC) calculation methodology for a rotor in hover was developed, and procedures to determine experimental LWC in the facility are presented in this paper. For the test setup, the cold chamber test section was adapted to fit the rotor and to control its ground clearance. Testing was aimed at studying the effect of rotor height h on aerodynamic performance, both with and without icing conditions. Results show no significant effect on the ground effect between h = 2 m and h = 4 m in dry runs, while the icing behavior can be largely influenced for certain conditions by the proximity of the precipitation source, which depend on the height of the rotor in these experiments.

The Main Elements of the Field Ice-wedge Sampling Strategies for Isotope and Radiocarbon Analysis

The main purpose of the paper is to create an optimal strategy for field testing of wedge ice for isotope and radiocarbon analyses. The scientific significance of this task is the need for a detailed isotopic characterization of well-dated sections with ice wedges. The solution of this problem will allow us to obtain a complete isotopic and paleotemperature scenario for the Holocene and the late Pleistocene in the north of Western Siberia, northern and central Yakutia, Chukotka, and the Arctic islands. Reliable ranges of isotopic composition values will be obtained as a result of the application of an improved method of wedge ice sampling. It will give a complete picture of isotopic variations in ice wedges during a certain period of its formation in combination with the age setting of the obtained isotope data. The main provisions of the optimal strategy for field testing of wedge ice for isotope and radiocarbon analyses are formulated. The innovativeness of the proposed technique consists in comparing of oxygen isotope and deuterium curves obtained from two parallel and quasi-synchronous ice wedges exposed by a single outcrop in the yedoma and Holocene deposits. Previously, it was believed that the sampling from different ice wedges in the single outcrop would give the same results. The preliminary studies carried out by the author show that this is not always the case. At the same depths, both identical and noticeably different isotopic determinations were obtained from samples from neighboring ice wedges. Predominantly horizontal sampling from ice wedges in yedoma deposits should still be referred to as an insufficiently developed procedure, it should be supplemented by vertical sampling from ice wedges. It is possible to develop criteria for excluding older 14С dates due to admixture of allochthonous organic material as inversions with vertical sampling only. This is impossible using horizontal sampling.

Transparent hydrophobic, self-cleaning, anti-icing and anti-dust nano-structured silica based thin film on cover glass solar cell

Silica thin film with anti-reflective, hydrophobic and anti-icing properties was prepared on glass substrate by a sol-gel method. For this purpose, silica sol based on the TEOS and TMMS precursors were prepared. Then, different TCMS concentrations were added to the primary sol solution. Film deposition on glass substrate was performed by a dip coating method. Hydrophobicity, transparency, morphology and chemical analysis of the films were investigated. Icing tests were performed at a constant operating temperature of -12 °C. Also, the self-cleaning behavior of the samples was evaluated by iron oxide powders. The thin film stability under ultraviolet light irradiation was investigated. The results showed that with increasing TCMS, the transmittance of the glass coated substrate increased until 0.2 ml and then decreased. Also, the results of the water contact angle measurements showed that the contact angle increased with increasing the TCMS concentration until 0.33 ml (123°) and then with more increasing the TCMS concentration, it remained constant. Icing tests showed that the start time of the icing and the time required for complete icing on the thin layer of modified silica base with 0.2 mm TCMS is much longer than the uncoated glass. Also, the self-cleaning test showed that the glass coated sample has a self-cleaning behavior. After exposure to the ultraviolet light, the hydrophobicity and transparency of the glass coated sample did not disappear.

Methodology Based on Photogrammetry for Testing Ship-Block Resistance in Traditional Towing Tanks: Observations and Benchmark Data

The real resistance that a ship must face when it is navigating in ice floes is the key factor for knowing the necessary power and the required engine size. The aim of this work is to provide valuable data to help other research in which numerical frameworks will be developed to study ship navigation in broken ice. In this work, we used paraffin wax as an alternative to obtain affordable solutions, avoiding the high cost of ice tests. The experiments were carried out in a traditional basin facility and they consisted of towing tank tests with a ship model using different concentrations of blocks simulated by the use of paraffin wax. Photogrammetry was used as technique to determine the initial position of the ice blocks, which is important as starting data in the current development of numerical simulation code for studying the features of ship resistance in drift ice. These data are available for some ice concentrations in attached files. In addition, a procedure for testing in traditional towing facilities is presented and discussed. The results of the resistance obtained in the experiments in the presence of simulated floes are presented for three concentrations and three model speeds. Some findings may be applicable to ice sailing, under given circumstances.