Discrete Element Analysis of High-Pressure Zones of Sea Ice on Vertical Structures

In cold regions, ice pressure poses a serious threat to the safe operation of ship hulls and fixed offshore platforms. In this study, a discrete element method (DEM) with bonded particles was adapted to simulate the generation and distribution of local ice pressures during the interaction between level ice and vertical structures. The strength and failure mode of simulated sea ice under uniaxial compression were consistent with the experimental results, which verifies the accuracy of the discrete element parameters. The crushing process of sea ice acting on the vertical structure simulated by the DEM was compared with the field test. The distribution of ice pressure on the contact surface was calculated, and it was found that the local ice pressure was much greater than the global ice pressure. The high-pressure zones in sea ice are mainly caused by its simultaneous destruction, and these zones are primarily distributed near the midline of the contact area of sea ice and the structure. The contact area and loading rate are the two main factors affecting the high-pressure zones. The maximum local and global ice pressures decrease with an increase in the contact area. The influence of the loading rate on the local ice pressure is caused by the change in the sea ice failure mode. When the loading rate is low, ductile failure of sea ice occurs, and the ice pressure increases with the increase in the loading rate. When the loading rate is high, brittle failure of sea ice occurs, and the ice pressure decreases with an increase in the loading rate. This DEM study of sea ice can reasonably predict the distribution of high-pressure zones on marine structures and provide a reference for the anti-ice performance design of marine structures.

Failure Analysis and Research of Wing Anti-ice Pressure Release on Civil Aircraft

CAS alert message ‘PSW FAIL’ shows up frequently during civil aircraft test flights. This thesis provides an in-depth study of the problem by describing the fault phenomena and analyzing the fault based on historical data, system principles, and fault tree analysis. For the AT version after IASC 2nd stage software upgrade, pressure release response is triggered on the wing anti-ice valve when unilateral throttle lever is pushed over 40 degrees with both PACKs off and both WAIVs closed. Test flight data will be analyzed and verified. With respect to the flaws of pressure release response, this study optimizes the logic of ECS IASC software by analyzing trigger mechanism, adding pressure release response pre-requisites such as both PRSOV shut and signals off, with no APR mode initiated, and not under single engine startup. The study of the thesis helps to essentially improve the software, avoiding frequent occurrence of the pressure release response, enabling an accelerated production test flight and delivery test flight of Civil aircrafts.

The impact of temperature and unwanted impurities on slow compression of ice

For slowly compressed hexagonal ice pressure-induced amorphisation to high-density amorphous ice (HDA) takes place below and at 130 K, but polymorphic transformation to ice IX at 140–170 K. Stable ice...

Static Ice Pressure Measuring System Based on Fiber Loop Ring-Down Spectroscopy and FPGA

Hydraulic engineering built in the cold region, such as reservoirs and hydropower stations, is often threatened by static ice pressure from nature. Therefore, it is of vital significance to research the pressure variation in the growth and melting processes of the ice layer for the design and protection of hydraulic structures in cold regions. This paper introduces an optical fiber sensor system based on the fiber loop ring-down spectroscopy technology and field-programmable gate array (FPGA) pulse modulation technology. An electro-optic modulation scheme that relied on FPGA to generate optical pulses with adjustable pulse width and period is proposed, which is more suitable for the in-situ observation. In addition, the temperature stability and repeatability of the system are also discussed. This system was applied to the real-time detection of static ice pressure on the sidewall and bottom of the polyvinyl chloride (PVC) pipe during the ice growth and melting processes. The results indicate that the system has favorable stability and sensitivity, and the relationship obtained between the static ice pressure and temperature could provide some references for the field application in the future.

Toward a method for downscaling sea ice pressure for navigation purposes

Sea ice pressure poses great risk for navigation; it can lead to ship besetting and damages. Contemporary large-scale sea ice forecasting systems can predict the evolution of sea ice pressure. There is, however, a mismatch between the spatial resolution of these systems (a few kilometres) and the typical dimensions of ships (a few tens of metres) navigating in ice-covered regions. In this paper, the downscaling of sea ice pressure from the kilometre-scale to scales relevant for ships is investigated by conducting high-resolution idealized numerical experiments with a viscous-plastic sea ice model. Results show that sub-grid-scale pressure values can be significantly larger than the large-scale pressure (up to ∼ 4 times larger in our numerical experiments). High pressure at the sub-grid scale is associated with the presence of defects (e.g. a lead). Numerical experiments show significant stress concentration on both sides of a ship beset in sea ice, especially at the back. The magnitude of the stress concentration increases with the length of the lead (or channel) behind the ship and decreases as sea ice consolidates by either thermodynamical growth or mechanical closing. These results also highlight the difficulty of forecasting, for navigation applications, the small-scale distribution of pressure, and especially the largest values as the important parameters (i.e. the length of the lead behind the ship and the thickness of the refrozen ice) are not well constrained.

Should Sea-Ice Modeling Tools Designed for Climate Research Be Used for Short-Term Forecasting?

In theory, the same sea-ice models could be used for both research and operations, but in practice, differences in scientific and software requirements and computational and human resources complicate the matter. Although sea-ice modeling tools developed for climate studies and other research applications produce output of interest to operational forecast users, such as ice motion, convergence, and internal ice pressure, the relevant spatial and temporal scales may not be sufficiently resolved. For instance, sea-ice research codes are typically run with horizontal resolution of more than 3 km, while mariners need information on scales less than 300 m. Certain sea-ice processes and coupled feedbacks that are critical to simulating the Earth system may not be relevant on these scales; and therefore, the most important model upgrades for improving sea-ice predictions might be made in the atmosphere and ocean components of coupled models or in their coupling mechanisms, rather than in the sea-ice model itself. This paper discusses some of the challenges in applying sea-ice modeling tools developed for research purposes for operational forecasting on short time scales, and highlights promising new directions in sea-ice modeling.

Numerical Study of Large Pendulum Ice Impact Loads

The large pendulum ice impact experiments performed at the Memorial University of Newfoundland recorded pressure distributions using a novel high-fidelity measurement device, the Impact Module, which is capable of fine spatial and temporal resolutions — effectively 2 cm2 at 500 Hz. These experiments achieved impact energies approaching 29 kJ, velocities of 4.7 m/s, and loads reaching 620 kN. The data obtained by the device are unique, as the Impact Module is capable of recording ice pressure data with both high spatial and high temporal resolution over a large contact area. Until recently, there was no ice load measurement technique capable of excelling in all these aspects. This work aims to study the simulation of a numerical test panel model under the action of the loads measured during the ice impact experiments. This is done by using a non-linear numerical model with explicit time integration capable of simulating the dynamic transient ice loads and comparing their effects to a quasi-static approach.