Rorik Peterson

Bedrock Fracture by Ice Segregation in Cold Regions

The volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions. Data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation. Fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model. The depth and geometry of fractures match those in Arctic permafrost and ice-age weathering profiles. This agreement supports a conceptual model in which ice segregation in near-surface permafrost leads progressively to rock fracture and heave, whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement.

A mechanism for differential frost heave and its implications for patterned-ground formation

The genesis of some types of patterned ground, including hummocks, frost boils and sorted stone circles, has been attributed to differential frost heave (DFH). However, atheoretical modelthat adequatelydescribes DFHhasyettobe developedand validated. In this paper, we present a mathematical model for the initiation of DFH, and discuss how variations inphysical (i.e. soil/vegetationproperties) andenvironmental (i.e. ground/air temperatures) properties affect its occurrence and length scale. Using the Fowler and Krantz multidimensional frost-heave equations, a linear stability analysis anda quasi-steady-statereal-timeanalysisareperformed.Resultsindicatethatthefollow- ing conditions positively affect the spontaneous initiationof DFH: silty soil, smallYoungs modulus, small non-uniform surface heat transfer or cold uniform surface temperatures, and small freezing depths.The initiating mechanism for DFH is multidimensional heat transfer within the freezing soil. Numerical integration of the linear growth rates indi- catesthatexpressionof surfacepatternscanbecomeevidentonthe10^100yeartime-scale.

Volcanic ash transport and dispersion models

A volcanic eruption is an amazing event. The associated earthquakes, lava flows, and ash clouds are both intriguing yet potentially dangerous features that can cause enormous changes to the landscape, damage to infrastructure, and even loss of life. Obviously, the ability to predict the occurrence and dynamics of an eruption is both desirable and necessary for public safety. Despite many advances in the understanding of what leads to volcanic eruptions, predicting the commencement of an eruption remains difficult. Once an eruption has begun, predicting its behavior is equally if not more important in order to minimize the potential financial and human costs.

DEVELOPMENT OF A FULL-SCALE-LAB-VALIDATED DYNAMIC SIMULINK © MODEL FOR A STAND-ALONE WIND-POWERED MICROGRID

Isolated hybrid wind microgrids operate within three distinct modes, depending on the wind resources and the consumer grid demand: diesel-only (DO), wind-diesel (WD) and windonly (WO). Few successful systems have been shown to consistently and smoothly transition between wind-diesel and wind-only modes. The University of Alaska – Fairbanks Alaska Center for Energy and Power (ACEP) has constructed a full scale test bed of such a system in order to evaluate technologies that facilitate this transition. The test bed is similar in design to the NREL Power Systems Integration Laboratory (PSIL) and sized to represent a typical off-grid community. The objective of the present work is to model the ACEP test bed in DO and WD modes using MATLAB™ SIMULINK

Distributed self-sensing secondary loads for frequency regulation in wind-powered islanded microgrids

Frequency regulation in wind-powered islanded microgrids (WPIM) is critical for system stability given unpredictable dynamics from variations in wind generation and demand. Traditional methods of frequency regulation in WPIM have used classical secondary load controllers (CSLC) in a centralized approach to buffer wind generation and demand events. This study investigates the feasibility of using a network of self-sensing distributed secondary loads (SSDSL) consisting of electric-thermal storage (ETS) to assist in frequency regulation in WPIM. Individual SSDSL sense the local grid frequency and activate resistive load elements in order to absorb surplus energy during high wind events. Four major parameters: 1) zero-order hold time 2) full response point 3) network capacity ratio, and 4) coordination mode, are used in a dynamic model to explore the effect of SSDSL on frequency regulation. SSDSL are shown to assist with frequency regulation in WPIM.

Improved frequency regulation on hybrid wind-diesel microgrids using self-sensing electric thermal storage devices

Frequency regulation is central to the successful operation of remote wind-diesel powered electrical grids. Use of secondary or “dump” loads are necessary to allow instantaneous wind generation to exceed grid demand. The present study investigates the feasibility of using a network of Electric Thermal Storage (ETS) units without centralized control as an effective secondary load. Individual ETS units respond to changes in grid frequency by activating an appropriate number of heating elements in order to absorb energy surplus during high wind events. It is shown through numerical modelling that there are four major parameters that affect the response of the system: 1) zero-order hold time 2) full response point 3) number of units per phase, and 4) switching method. The effect of these parameters on frequency and voltage regulation is explored. When properly tuned, the ETS network can improve frequency and voltage regulation in wind-diesel mode.