Project Icebreaker: Offshore Wind Project in Lake Erie

Wind energy is one of the most promising renewable energy resources. The Great Lakes region in the US has huge potential for offshore wind energy development. However, ice loading in winter brings a unique challenge to the foundations for wind turbines. Model tests and numerical simulation have been conducted to investigate different types of foundations and techniques to reduce the ice loading. The ultimate goal is to design a safe and economical foundation for future large-scale wind farms in the Great Lakes

Measurement of G\u3csub\u3emax\u3c/sub\u3e and K\u3csub\u3e0\u3c/sub\u3e of Saturated Clay Using Bender Elements

Recent development in the application of bender element technique has made it possible to measure Gmax, and K0 of soils under complex anisotropic loading conditions. By measuring the shear wave velocities in different shear planes, the anisotropy in Gmax, of soil induced by anisotropic loading can be determined. The shear wave velocities can also be used to calculate the horizontal earth pressure coefficient at rest K0. This paper reports an experimental setup developed at the Department of Civil Engineering, University of Kentucky, which uses bender elements to measure shear wave velocities in four shear planes in a saturated clay specimen under different consolidation pressure. The data is used to investigate the anisotropy of soil stiffness in clay due to anisotropic stress conditions. The measured Gmax is compared with the calculation by several empirical formulae. The measured Gmax on different shear planes are also used to calculate K. of clay under different consolidation pressure and compared with results of empirical theories. The applied stress condition includes loading, unloading, and reloading of up to 22 cycles, thus allowed us to study the influence of repeated loading on Gmax and K0 of clay. The study is funded by the National Science Foundation

Calculation of Excavation Force for ISRU on Lunar Surface

Accurately predicting the excavation force that will be encountered by digging tools on the lunar surface is a crucial element of in-situ resource utilization (ISRU). Based on principles of soil mechanics, this paper develops an analytical model that is relatively simple to apply and uses soil parameters that can be determined by traditional soil strength tests. The influence of important parameters on the excavation force is investigated. The results are compared with that predicted by other available theories. Results of preliminary soil tests on lunar stimulant are also reported

Three-dimensional modeling of monopiles in sand subjected to lateral loading under static and cyclic conditions

Here, the results of a three-dimensional finite element study of the complex interaction of horizontal and moment loads (HM) on offshore monopiles as failure envelope, are reported. A new design criterion is described which is based on critical length, ultimate limit states, load characteristics and Eigen-frequency to ensure stable behavior of laterally loaded monopiles. Numerical analyses were performed to examine nonlinear interaction of a soil-pile system for 10,000 load cycles. The resulting framework can predict angular rotation due to cyclic loading. According to the loading level and duration of a load, elastic strains accumulate in the vicinity of a pile. Fairly intermediate two-way cyclic loading induced the largest rotations irrespective of the analysis performed (i.e., drained versus partially drained). Based on the regression coefficients of the non-dimensional frameworks used, accumulating rocking deformations of a pile at seabed level appear to be dependent on cyclic load ratio, drainage condition, and duration of loading. For safe design, sensitivity of the natural frequency of offshore wind turbine (OWT) at a monopile critical length as well as shorter lengths were also examined. The analytical model proposed here for determining the natural frequency of an OWT considers that soil-structure interaction (SSI) can be represented by monopile head springs characterized by lateral stiffness, KL, rotational stiffness, KR, cross-coupling stiffness, KLR, and parabolic soil stiffness variation with depth

Cone penetrometer equipped with piezoelectric sensors for measurement of soil stiffness in highway pavement

"November 2005."; Executive summary report laid in.; Includes bibliographical references (leaves 68-70).; State job no. 134185; Harvested from the web on 3/21/06The stiffness (elastic modulus and shear modulus) and Poisson's ratio of the base and sublayers are important parameters in the design and quality assurance during construction of highway pavements. The new highway construction guide proposed by AASHTO (American Association for State Highway and Transportation Officials) recommends such measurements be conducted. A new field-testing technique has been developed to measure the stiffness and Poisson's ratio of soils using cone penetrometers equipped with piezoelectric sensors. The device using this technique includes a pair of cone penetrometers, each fitted with two piezoelectric sensors, which can be pushed into foundation soils. One set of the sensors is used as wave transmitters while the other set as wave receivers. An electrical pulse produced by a function generator is used to activate the transmitters. Vibration of the transmitters produces primary and shear waves that propagate through the soil and are captured by the receivers. Then from the measured velocities of shear and primary waves, soil stiffness and Poisson's ratio can be determined. The technique has been proven to produce reliable results in the laboratory.The stiffness (elastic modulus and shear modulus) and Poisson's ratio of the base and sublayers are important parameters in the design and quality assurance during construction of highway pavements. The new highway construction guide proposed by AASHTO (American Association for State Highway and Transportation Officials) recommends such measurements be conducted. A new field-testing technique has been developed to measure the stiffness and Poisson's ratio of soils using cone penetrometers equipped with piezoelectric sensors. The device using this technique includes a pair of cone penetrometers, each fitted with two piezoelectric sensors, which can be pushed into foundation soils. One set of the sensors is used as wave transmitters while the other set as wave receivers. An electrical pulse produced by a function generator is used to activate the transmitters. Vibration of the transmitters produces primary and shear waves that propagate through the soil and are captured by the receivers. Then from the measured velocities of shear and primary waves, soil stiffness and Poisson's ratio can be determined. The technique has been proven to produce reliable results in the laboratory

Influence of fabric anisotropy on seismic responses of foundations

Earthquakes, as one of the well-known natural disasters, are highly destructive and unpredictable. Foundation failure due to liquefaction induced by earthquakes can cause casualties as well as significant damage to the building itself. Fabric anisotropy of soil grains is considered to be an important factor in dynamic soil response based on previous researches and laboratory tests. However, the limited availability of real physical data makes it less persuasive. In this study, a shake table installed on a geotechnical centrifuge is used to provide the designed seismic motions, and therefore, to simulate the realistic earthquake motion to foundations. Important parameters in the responses such as acceleration, excess pore pressure and deformation are evaluated to investigate the influence. Implications for design are also discussed

Accuracy assessment and error analysis for diameter at breast height measurement of trees obtained using a novel backpack LiDAR system

Background The LiBackpack is a recently developed backpack light detection and ranging (LiDAR) system that combines the flexibility of human walking with the nearby measurement in all directions to provide a novel and efficient approach to LiDAR remote sensing, especially useful for forest structure inventory. However, the measurement accuracy and error sources have not been systematically explored for this system. Method In this study, we used the LiBackpack D-50 system to measure the diameter at breast height (DBH) for a Pinus sylvestris tree population in the Saihanba National Forest Park of China, and estimated the accuracy of LiBackpack measurements of DBH based on comparisons with manually measured DBH values in the field. We determined the optimal vertical slice thickness of the point cloud sample for achieving the most stable and accurate LiBackpack measurements of DBH for this tree species, and explored the effects of different factors on the measurement error. Result 1) A vertical thickness of 30 cm for the point cloud sample slice provided the highest fitting accuracy (adjusted R-2 = 0.89, Root Mean Squared Error (RMSE) = 20.85 mm); 2) the point cloud density had a significant negative, logarithmic relationship with measurement error of DBH and it explained 35.1% of the measurement error; 3) the LiBackpack measurements of DBH were generally smaller than the manually measured values, and the corresponding measurement errors increased for larger trees; and 4) by considering the effect of the point cloud density correction, a transitional model can be fitted to approximate field measured DBH using LiBackpack- scanned value with satisfactory accuracy (adjusted R-2 = 0.920; RMSE = 14.77 mm), and decrease the predicting error by 29.2%. Our study confirmed the reliability of the novel LiBackpack system in accurate forestry inventory, set up a useful transitional model between scanning data and the traditional manual-measured data specifically for P. sylvestris, and implied the applicable substitution of this new approach for more species, with necessary parameter calibration

Virtual Synchronous Motor Based-Control of a Three-Phase Electric Vehicle Off-Board Charger for Providing Fast-Charging Service

This study introduces a three-phase virtual synchronous motor (VSM) control and its possible application for providing fast-charging service from off-board chargers of electric vehicles (EVs). The main circuit of the off-board charger consists of a three-phase voltage source PWM rectifier (VSR) and a resonant LLC zero-voltage-switching converter. In the proposed control approach, VSM-controlled pre-stage VSR emulates the external characteristics of a synchronous motor (SM), simultaneously, droop control based on charging mode in the VSM can satisfy the demand of the EVs constant-current fast-charging; The post-stage DC–DC converter is responsible for stabilizing the DC bus voltage. The feature of this control strategy is that VSM and fast charging control are implemented by the pre-stage converter, which has better coordination. In the MATLAB, the equivalent synchronous grid of the distribution network supplies to the power battery through the off-board charger, and the effectiveness of the presented control is demonstrated by typical working conditions