Best Practices for Developing the Engineer\u27s Estimate

The research project \u27Best Practices for Developing the Engineering Estimate\u27 was executed by Clemson University on behalf of the South Carolina Department of Transportation (SCDOT). The primary objective of this research project was to investigate the strengths and weaknesses of two types of estimating methods being utilized today by state department of transportations (DOT) nationwide. These two types of estimating methods are the unit cost line item approach, which the SCDOT utilizes, and the cost-based estimating approach. This research report identifies accuracy obtained, resources expended, and methodologies utilized when implementing either type of estimating approach. This was done so the research team could gather enough evidence to suggest if a change was needed in the SCDOT estimating methodology. There is no compelling evidence to suggest that SCDOT adopt a cost-based/combination estimating approach when preparing the engineer\u27s estimate

OMAE2002-28536 COUPLED DYNAMIC ANALYSIS OF A MINI TLP: COMPARISON WITH MEASUREMENTS

ABSTRACT A numerical code (COUPLE) was recently developed for computing 6 Degree-Of-Freedom (DOF) motions of a moored floating structure dynamically interacting with its mooring/riser/tendon system. The computation of hydrodynamic forces on the moored structure can be conducted based on a diffraction wave theory model, e.g. WAMIT, and/or the Morison Equation based upon a slender body assumption. Wave kinematics up to the free surface, used in the Morison Equation, is computed using nonlinear deterministic Hybrid Wave Models, and is accurate up to second order in wave steepness. Experimental data from the model tests of a mini TLP was used as the basis for investigation of the numerical computation. Using COUPLE and its alternatives, coupled as well as quasi-static analyses were conducted for the mini TLP model that incorporates four risers and four tendons. Two different methods for computing hydrodynamic loads, namely, WAMIT and Morison Equation, were used, respectively. Through the comparison between the numerical results and the corresponding measurements, dynamic interactions between the riser/tendon system and the hull were examined. Findings made in this study, though based upon a mini TLP may have valuable applications to the design and simulation of a wide range of compliant deep-water structures

Nearshore regional behavior of lightning interaction with wind turbines

The severity of lightning strikes on offshore wind turbines built along coastal and nearshore regions can pose safety concerns that are often overlooked. In this research study the behavior of electrical discharges for wind turbines that might be located in the nearshore regions along the East Coast of China and Sea of Japan were characterized using a physics-based model that accounted for a total of eleven different geometrical and lightning parameters. Utilizing the electrical potential field predicted using this model it was then possible to estimate the frequency of lightning strikes and the distribution of electrical loads utilizing established semi-empirical relationships and available data. The total number of annual lightning strikes on an offshore wind turbine was found to vary with hub elevation, extent of cloud cover, season and geographical location. The annual lightning strike rate on a wind turbine along the nearshore region on the Sea of Japan during the winter season was shown to be moderately larger compared to the lightning strike frequency on a turbine structure on the East Coast of China. Short duration electrical discharges, represented using marginal probability functions, were found to vary with season and geographical location, exhibiting trends consistent with the distribution of the electrical peak current. It was demonstrated that electrical discharges of moderately long duration typically occur in the winter months on the East Coast of China and the summer season along the Sea of Japan. In contrast, severe electrical discharges are typical of summer thunderstorms on the East Coast of China and winter frontal storm systems along the West Coast of Japan. The electrical charge and specific energy dissipated during lightning discharges on an offshore wind turbine was found to vary stochastically, with severe electrical discharges corresponding to large electrical currents of long duration

On the.Design of Mooring Lines for Deep Water Applications

As ocean engineers begin to extend their analytical and design capabilities from the shallow regions of the oceans to the deep regions it becomes necessary to examine the e

An inverse-reliability approach to generating composite seismic response spectra

This study presents an Inverse-First Order Reliability Method (FORM) approach to generating site-specific composite seismic response spectra. The proposed technique searches the surfaces of Inverse-FORM generated contours for the earthquake statistically most likely to produce the target spectral acceleration at the desired structural period, as modelled by the appropriate attenuation relation. Identification of this spectral acceleration level over a range of periods produces a composite design response spectrum consisting of spectral acceleration levels most likely to occur and all lying on the surface of the n-year contour, hence possessing the desired n-year return period. This composite seismic response spectrum can be used in design and analysis of structural systems having variable levels of complexity. The result is an n-year composite, seismic design response spectrum, found using Inverse-FORM generated contours that are generated in a discrete four-dimensional space. The random variables associated with this four-dimensional space are earthquake magnitude, site-to-source distance, attenuation relation uncertainty, and fault of origin. This study outlines the technique and presents a hypothetical example for a region threatened by three behaviorally different earthquake source mechanisms. An illustrative example is presented for target spectral accelerations of 0.1g and 0.4g, having two different return periods. The number of different earthquakes contributing to each spectrum varied between three and nine, depending on the specifics