bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Methodology for Modeling Lift as a Modulated
Process
Authors: Longoria R. G. 
Published: February 2008

Abstract
This paper presents a methodology for using a modulated process to model the lift forces induced on circular cylinders by an oscillating flow. The generalization of the existing quasi-steady flow model leads to techniques which apply the Hilbert transform in model evaluation and parameter determination. Analysis of measured lift forces reveals clearly identifiable forms of amplitude and angle modulation, justifying the use of a modulation model. As a demonstration, a method is presented for evaluating the quasi-steady flow model and for determining model parameters using data obtained under both periodic and random flow conditions. Although empirical in nature, modulation models can reproduce critical characteristics of lift forces such as frequency content, amplitude, and zero-crossings. It is suggested that the Hilbert transform can facilitate model development and evaluation beyond the simple quasisteady form. Further, the methodology employed can be used in characterizing any physical process exhibiting amplitude and/or angle modulation.
Markov Description of Wave-Crest Statistics
Authors: Dawson T. H. , Kriebel D. L. , Wallendorf L. A. 
Published: February 2008

AbstractMarkov description of wave-crest statistics is considered for the case of severe random seas where Stokes nonlinearities require crests to rise higher than troughs fall. Of interest are the average number of consecutive high waves in runs of high waves and the average number of waves between beginnings of such runs, with high waves being defined in terms of a threshold level above mean water level. Two basic parameters are involved in the description: 1) the probability P that a high wave will occur at a fixed location, and 2) a coefficient C relating P to the probabilities associated with transitions from high to low waves and low to high waves. Comparison with laboratory measurements from scaled Bretschneider seas having a range of nonlinearities indicates that the basic Stokes nonlinearity is contained in the probability P, with no sensible dependence exhibited by the coefficient C. Additional comparison with scaled Jonswap seas illustrates the dependence of this coefficient on spectral shape. A final consideration of results from full-scale hurricane sea conditions, and from corresponding scaled laboratory data, demonstrates the general applicability of the laboratory results presented here to actual wind-driven seas.
A Study on Buckling of Offshore Pipelines
Authors: Chiou Y.-J. , Chi S.-Y. 
Published: February 2008

Abstract
The beam vertical mode of buckling and beam lateral mode of buckling of offshore pipelines were investigated. The pipeline was modeled as an elasto-plastic, infinitely long beam with localized imperfection. The seabed was modeled as a fluid-saturated, layered porous medium. The boundary element method, finite element method, and finite difference method were applied for the numerical study. The results show that the buckling behavior of beam vertical mode and beam lateral mode is essentially influenced by the buried depth, initial imperfection, and incline angle. The pipe tends to buckle in the beam lateral mode for the pipe with shallower buried depth, larger imperfection height, and smaller incline angle. The critical buried depth that separates beam vertical mode and beam lateral mode is shallower for smaller excess pore pressure.
Dynamic Response of Tubular T-Joints Under the Influence of
Propagating Cracks
Authors: Nwosu D. I. , Swamidas A. S. J. , Guigne´ J. Y. 
Published: February 2008

Abstract
This paper presents an analytical study on the vibration response of tubular T-joints for detecting the existence of cracks along their intersections. The ABAQUS finite element program was utilized for carrying out the analysis. Frequency response functions were obtained for a joint with and without cracks. The joint was modeled with 8-node degenerate shell elements having 5 degrees of freedom per node. Line spring elements were used to model the crack. The exact crack configuration (semielliptical shape, Fig. 5(b)), as observed from numerous experimental fatigue crack investigations at the critical location, has been achieved through a mapping function, that allows a crack in a planar element to be mapped on to the tube surface. The natural frequency changes with respect to crack depth show little changes, being 4.82 percent for a 83-percent crack depth for the first mode. On the other hand, significant changes have been observed for bending moment and curvature as a function of crack depth. For an 83-percent chord thickness crack, a 97-percent change in bending moment at points around the crack vicinity, and 34.15 to 78 percent change in bending moments, for those locations far away from the crack location, have been observed. Natural frequency change should be combined with other modal parameters such as “bending moment (or bending strain)” and “curvature” changes for crack detection. The presence of the crack can be detected at locations far away from the crack location using such sensors as strain gages.
Extreme Jack-Up Response: Simulation and Nonlinear Analysis
Methods
Authors: Winterstein S. R. , Torhaug R. 
Published: February 2008

Abstract
The nonlinear dynamic response of a jack-up structure under random wave loads is considered. For a simplified jack-up model, average behavior and variability in extreme forces and responses are found from simulation over many 6-h seastates. Weibull and Hermite analytical models of response extremes are also presented and evaluated. These models use shorter, less expensive simulations to estimate a limited number of response statistics, such as moments or parameters of the response peak distribution, and fit analytical models to estimate global extremes. Necessary simulation lengths are established both for direct simulation of extremes, and for analytical extreme models.
The Influence of Alternative Wave Loading and Support Modeling
Assumptions on Jack-Up Rig Response Extremes
Authors: Manuel L. , Cornell C. A. 
Published: February 2008

Abstract
A study is conducted of the response of a jack-up rig to random wave loading. Steady current and wind load effects are also included. The effects of varying the relative motion assumption (in the Morison equation) and of varying the bottom fixity assumptions are investigated. One “fixity” model employs nonlinear soil springs. Time domain simulations are performed using linearized as well as fully nonlinear models for the jack-up rig. Comparisons of response statistics are made for two seastates. Hydrodynamic damping causes the rms response to be lower in the relative Morison case. The absence of this source of damping in the absolute Morison force model gives rise to larger resonance/dynamic effects—this tends to “Gaussianize” the response. Hence, the relative Morison model leads to stronger non-Gaussian behavior than the absolute Morison model. This is reflected in moments as well as extremes. The different support conditions studied are seen to significantly influence extreme response estimates. In general, stiffer models predict smaller rms response estimates, but also exhibit stronger non-Gaussian behavior. The choice of the Morison force modeling assumption (i.e., the relative versus the absolute motion formulation) is seen to have at least a secondary role in influencing response moments and extremes.
Strain Rate Effects on Fracture Toughness of Ship Plate Steels
Authors: Pussegoda L. N. , Malik L. , Bouchard R. , Tyson W. R. 
Published: February 2008

AbstractFull thickness fracture toughness of conventional ship plate grades, including modern high-strength steels, was determined at loading rates representing quasi-static, intermediate, and impact conditions. For testing at impact strain rates (ε˙ = 5 s−1), customized equipment was designed and developed for a drop tower. It was shown from the CTOD transition temperature curves that the transition temperature increase from quasi-static to intermediate rate (a three-order rate increase) is much greater than the increase from intermediate to impact (a two-order rate increase). Comparison of the dynamic CTOD, CVN, and NDTT indicated that the correlation between the CVN and 0.1-mm dynamic CTOD transition temperature does not hold for the TMCP steels, for which the CVN transition temperature is much lower. By contrast, the results display a very good correlation between the NDTT and 0.1-mm dynamic CTOD transition temperature for all of the steels tested in this program.
The Effect of Springing Response of a TLP on Tether
Fatigue
Authors: Naess A. 
Published: February 2008

Abstract
The purpose of this paper is to investigate the effect on estimated fatigue damage of TLP tethers of the method used to model the springing response. In particular, the goal has been to look into the consequence for long-term fatigue calculation of modeling the springing response as a second-order, sum-frequency process as opposed to assuming that the springing response is Gaussian. It is shown that with a standard engineering approach to the calculation of long-term fatigue damage, this effect is in fact marginal. However, the deviation between the numerical estimates of the quadratic transfer function describing the springing response as provided by different computer codes is found to produce estimates of the long-term fatigue that exhibit substantial variability.
Comparisons of Two Different Mixed Eulerian-Lagrangian Schemes Based
on a Study of Flare-Slamming Hydrodynamics
Authors: Wang M. L. , Troesch A. W. , Maskew B. 
Published: February 2008

Abstract
A comparative study of two different mixed Eulerian-Lagrangian methods is presented. Representative numerical simulations of oscillatory flare-slamming flows are given. Computations based on these two different numerical schemes, i.e., a desingularized method using Rankine ring sources and a source-doublet panel method (e.g., USAERO/FSP©), are compared with experiments. Fourier coefficients of the simulated time histories and experimentally measured forces are given for detailed error comparisons. The numerical simulations demonstrate the ranges of applicability of these two methods. Both are shown to be efficient and robust time-stepping schemes for the fully nonlinear free-surface problem studied here.
Full-Scale Experiments and Analyses of Cellular Hull Sections in
Compression
Authors: Dexter R. J. , Ricles J. M. , Lu L.-W. , Pang A. A.-K. , Beach J. E. 
Published: February 2008

Abstract
Compression tests were conducted on high-strength single-cell and multiple-cell box sections with plate width-to-thickness (b/t) ratios ranging from 48 to 96. Local plate buckling occurred at stresses as low as 5 percent of the yield stress, whereas the ultimate compression stress ranged from 38 to 72 percent of the yield stress. These critical stresses were not significantly affected by the length of the specimen, the number of cells, the boundary conditions, or lateral load. Simple empirical design equations based only on b/t gave estimates of the collapse strength within five percent in all cases. Finite-element analyses were able to predict the significant reserve load-carrying capacity and ductility after ultimate load, which was dependent on the length of the specimen as well as the b/t ratio.
Capacities of Template-Type Platforms in the Gulf of Mexico During
Hurricane Andrew
Authors: Bea R. G. , Loch K. J. , Young P. L. 
Published: February 2008

Abstract
This paper details results from nonlinear analyses of the ultimate limit state performance characteristics of four Gulf of Mexico (GOM) platforms subjected to intense loadings from hurricane Andrew. These four platforms were located to the east of the track of hurricane Andrew, and were thus in the most intense portion of the storm (Smith, 1993). The nonlinear analyses are able to replicate details of the observed behavior of the four structures. This replication is very dependent on realistic characterization of the performance characteristics of the pile foundations and on accurate information on the “as is” condition of the platforms before the storm.
Directional Wave Navigation Radar Measurements Compared With
Pitch-Roll Buoy Data
Authors: A.-Muñoyerro M. Alfonso , Nieto Borge J. C. 
Published: February 2008

Abstract
The knowledge of the spectral behavior of a specific sea region is complete when we know surface elevations and directional wave movements. Usually, sea directional descriptions have been made using pitch-roll buoys, which can provide us with several wave characteristic time series. Alternatively, there are other measure systems, which belong to remote sensing technics, such as shipboard navigation radars. The aim of the present work is to compare results obtained from pitch-roll data and ship radar wave measurements obtained during a campaign in the Cantabric Sea.
Polynomial Approximation of Morison Wave Loading
Authors: Bouyssy V. , Rackwitz R. 
Published: February 2008

Abstract
For offshore structures with slender elements, the modeling of random wave loads by the Morison equation yields an equation of motion which has no analytical solution for response moments except in a few limiting cases. If polynomial approximations of the Morison drag loads are introduced, some procedures are available to obtain the stationary moments of the approximate response. If the response process is fitted by non-Gaussian models such as proposed by Winterstein (1988), the first four statistical moments of the response are necessary. The paper investigates how many terms should be included in the polynomial approximation of the Morison drag loading to accurately estimate the first four response moments. It is shown that a cubic approximation of the drag loading is necessary to accurately predict the response variance for any excitation. For the fit of the first four response moments, at least a fifth-order approximation appears necessary.
Human and Organization Errors in Reliability of Offshore
Structures
Authors: Bea R. G. 
Published: February 2008

Abstract
This paper addresses human and organization errors (HOE) in the context of quantitative reliability analyses (QRA) that are intended to help improve the quality of offshore structures. A classification of HOE is proposed that addresses individual, organization, equipment/hardware, procedures/software, and environmental considerations. A generic process to address the life-cycle quality characteristics of offshore structures incorporating HOE is discussed. Based on these developments, a probability-based risk analysis is developed that addresses HOE in addition to the structure system aspects. Alternatives for improved management of HOE are discussed including quality assurance and quality control (QA/QC), and design of error-tolerant or “robust” structures. Application of the HOE classification, generic assessment process, QRA formulation, and QA/QC measures are illustrated.
Stability-Based Design of Two-Point Mooring Systems With Hydrodynamic
Memory
Authors: Chung J.-S. 
Published: February 2008

Abstract
A systematic method of determining the design parameter values of two-point mooring (TPM) systems is presented. The conclusions of nonlinear stability analysis of horizontal plane slow motion dynamics of TPM systems with hydrodynamic memory are used to guide selection of the design variables. Specifically, within the stable regions of bifurcation diagram, a set of parameter values is chosen systematically to examine the corresponding TPM system. Then, each TPM system is simulated and the results are evaluated in terms of given criteria such as tension level of the mooring line or offset of the moored vessel. The hydrodynamic memory effect due to the oscillatory motions of moored vessel is included in the formulation. The memory effect influences the stability properties of TPM systems and alters the design chart/bifurcation diagram and particularly the static loss and dynamic loss of stability. The significance of hydrodynamic memory on several TPM systems is illustrated by comparing the statistics of the simulations. The design approach implemented in this work shows that nonlinear stability theory can be used effectively in the actual design process of mooring systems to reduce dramatically the number of simulations required. It is also shown that the often inconclusive nonlinear time simulations can be guided by theoretical nonlinear stability analysis of system dynamics to produce improved design values of system parameters of TPM systems.
Modeling the Effect of Shelter in the Modification of Waves From the
Open Sea to Near-Shore
Authors: Oliveira-Pires H. , Carvalho F. , Pontes T. 
Published: February 2008

Abstract
An efficient method has been developed to compute the wave conditions in sheltered areas from the open sea directional spectrum using a reverse tracing wave ray model with weighted spectral filtering. The results were verified for Porto Cachorro—Azores, surrounded by several islands with an intricate geometry, and for Sines, at the west coast of Portugal. The range of applicability of this type of ray model seems to lie at the transition between the open sea, well represented through large-scale wind-wave models, and the zones close to shore where shallow water wave breaking (not represented in the model) begins to play a dominant and decisive role.
On the Wind and Current Forces Acting on a Very Large Floating
Structure
Authors: Ohmatsu S. , Takai R. , Sato H. 
Published: February 2008

Abstract
This paper deals with the estimation method of wind force and current force acting on a very large floating structure. In this paper, as a very large floating structure, we consider a matlike very large platform which will be used as a floating airport. In order to estimate the fluid drag coefficient for such a huge structure, wind tunnel and towing tank model experiments were conducted paying special attention to the frictional drag coefficient. This paper shows the methods and results of these model experiments and discusses the application methods for wind and current forces on a full-scale structure.
Wave Energy-Driven Resonant Sea-Water Pump
Authors: Czitrom S. P. R. 
Published: February 2008

Abstract
A wave-driven sea-water pump which operates by resonance is described. Oscillations in the resonant and exhaust ducts perform similar to two mass-spring systems coupled by a third spring acting for the compression chamber. Performance of the pump is optimized by means of a variable volume air compression chamber (patents pending) which tunes the system to the incoming wave frequency. Wave tank experiments with an instrumented, 1:20-scale model of the pump are described. Performance was studied under various wave and tuning conditions and compared to a numerical model which was found to describe the system accurately. Successful sea trials at an energetic coastline provide evidence of the system’s viability under demanding conditions.
A Response Surface for Structural Optimization
Authors: Rule W. K. 
Published: February 2008

Abstract
Structural optimization is computationally intensive. Typically, a finite element model must be solved repeatedly during the process. Accordingly, various approximation schemes have been developed to reduce the cost of solves or to eliminate solves entirely during portions of the optimization process. In this paper, a new type of approximation or interpolation function in the form of a global response surface is described. With this function, approximations can be made with a limited amount of calibrating data points. The response surface requires no matrix inversions for coefficient evaluation, and therefore it is relatively efficient and stable. The new response surface is used in conjunction with a modified zero-order Powell search algorithm. The effectiveness of the response surface is evaluated for a reasonably realistic offshore structure application. This planar truss structure is subjected to a deck load, a lateral wave load (considered quasi-static), and member self-weight loads. The objective for this test case was to minimize the structural cost. Nodal coordinates were considered to be the explicit design variables. Response surface results are compared with those obtained by the common optimization algorithms: steepest descent, conjugate directions, and a conventional implementation of Powell’s method. The response surface appears to be effective for the test case considered.
A Reliability-Based Calibration Study for Upheaval Buckling of
Pipelines
Authors: Mørk K. J. , Bjørnsen T. , Venås A. , Thorkildsen F. 
Published: February 2008

Abstract
The present paper describes a reliability-based design procedure against upheaval buckling of rock or soil-covered pipelines. The failure mode considered is “snap-through” buckling. The study is performed using state-of-the-art design methodologies, including an assessment of all known uncertainties related to the load and capacity, measurements, surveys, and confidence in the applied models. A response surface technique is applied within the level III reliability analysis. Target safety levels are discussed for both SLS and ULS conditions, and a case-specific reliability-based calibration study is performed in order to derive a consistent design format.
Thermal EHL Analysis of Circular Contacts With Measured Surface
Roughness
Authors: Xu Gang , Sadeghi Farshid 
Published: February 2008

Abstract
Time dependent thermal EHL circular contact results with measured surface roughness were obtained to analyze the effects of roughness on pressure, film thickness, temperature, and coefficient of friction. Both contact surfaces are considered to be rough. Multilevel multigrid techniques (with multigrid integration) were used to solve the system of two dimensional Reynolds, elasticity and three dimensional energy equations simultaneously. The effects of surface roughness under various loads, speeds, and slip conditions have been studied. Surface roughness causes pressure and temperature spikes and increases the coefficient of friction, and surface roughness flattens due to the high pressure in EHL contact. The higher the load, speed and slide to roll ratio, the more significant the effect of the surface roughness. A comparison between rough EHL and smooth EHL results indicates that surface roughness cannot be ignored in EHL analysis.
Effects of Wall Flexibility on the Rotordynamic Coefficients of
Turbulent Cryogenic Annular Seals
Authors: Venkataraman B. , Palazzolo A. B. 
Published: February 2008

Abstract
A theory for analyzing the effects of elastic deformations of the seal wall on the dynamic characteristics of high pressure cryogenic annular seals under concentric operation is presented. The bulk flow continuity, axial and circumferential momentum, and the energy transport equations are utilized to determine the pressure distribution in the seal. Thermophysical properties of the cryogenic fluid are assumed to be functions of the local pressure and temperature. The wall deformations are obtained using an iso-parametric, axi-symmetric Finite Element formulation of the seal wall. A perturbation analysis is employed to arrive at the first order solution which yields the rotordynamic coefficients. Results obtained for the case of Space Shuttle Main Engine Oxygen Turbopump (SSME-HPOTP) Preburner Seal show a significant impact of seal flexibility on the dynamic coefficients.