bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Shape Optimization of Hybrid Micro-Composite E-Springs for Vehicle Suspension Systems
Authors: Elmoselhy Salah A.
Published: October 2008

Hybrid Micro-composite E-springs are an optimized trend of springs first introduced to vehicle suspension systems. At first, a comparison between E-shape and other spring shapes is held theoretically. This theoretical comparison is verified numerically. The E-shape has proved to be the best shape in this comparison striking a balance between spring vertical deflection and maximum induced stress. Next, shape optimization of a hybrid micro-composite E-spring is conducted. At last, a thermoplastic-based hybrid micro-composite structure of the optimized E-spring is modified at micro-scale with additives of micrometer-sized particles of mineral clay. The proposed spring is presented in new passive and semi-active suspension mechanisms, displacing and remedying drawbacks of both the hydraulic dampers and steel springs.
Agent-Based Dynamic Manufacturing Scheduling
Authors: Shen Weiming , Hao Qi
Published: October 2008

Manufacturing enterprises are facing a major challenge to improve their production efficiency in order to survive in a globally competitive market. There is an opportunity to develop and apply intelligent scheduling software tools to improve their productivity and profitability. We have developed a distributed dynamic manufacturing scheduling technology using intelligent software agents. This technology can well address dynamic changes and disturbances in the shop floor locally without disruptions to regular production — a problem that cannot be solved by traditional planning and scheduling systems because these changes and disturbances cannot be predicted in advance. It can significantly improve equipment utilization rates thereby improving the efficiency and productivity of manufacturing enterprises. We have developed software prototype systems within our research facilities. We are collaborating with industrial partners to validate the technology in industrial settings and are looking for a software company in the manufacturing sector to commercialize the technology.
Minimum Quantity Lubrication (MQL) Machining for Complex Powertrain Components
Authors: Furness Richard , Stoll Alexander , Nordstrom George , Martini Gary , Johnson Jon , Loch Thomas , Klosinski Robert
Published: October 2008

Near Dry or Minimum Quantity Lubrication (MQL) Machining eliminates conventional flood coolant from the machining processes. In doing so, MQL reduces oil mist generation, biological contamination of coolant, waste water volume, costs for capital equipment and regulatory permitting. MQL also improves recyclables and transportation of coolant contaminated chips.
Radio Channel Characteristics of Zigbee Wireless Sensors in Machine Shop for Plant Floor Process Monitoring
Authors: Tang Lei , Wang Kuang-Ching , Huang Yong , Gu Fangming
Published: October 2008

Wireless sensors are envisioned to be useful for plant floor process monitoring with unprecedented flexibility and low costs, where data can be relayed via a wireless network formed among the sensors. Factory environments, however, are known harsh for radio communications. For sensor radios engineered with extremely low power and simple circuitry, the sensor radio channel characteristics must be identified for optimal network design and reliability assessment. In this paper, a preliminary radio channel measurement study was performed based on the wireless sensor pairs in normal communication at the 2.4 GHz Industrial, Scientific and Medical (ISM) band to assess the sensor radio channel properties in a university machine workshop. The effect of both stationary and moving (forklift) obstacles on the radio propagation in terms of the received signal power, bit error and packet error rates was studied. The effect of stationary obstacles was further analyzed against a simple path loss model to find the path loss exponent. A spectrum analyzer was also used to capture the noise backgrounds in free space and the machine shop, which shows significantly different radio activities among the investigated scenarios. The proposed channel measurement methodology through directly utilizing the sensor platforms will help future radio channel characterization studies in manufacturing plant floor environments.
Molding of Three-Dimensional Microcomponents
Authors: Hung W. N. P. , Agnihotri M. M. , Ali M. Y. , Yuan S.
Published: October 2008

Traditional micromanufacturing has been developed for semiconductor industry. Selected micro electrical mechanical systems (MEMS) have been successfully developed and implemented in industry. Since current MEMS are designed for manufacture using microelectronics processes, they are limited to two-dimensional profiles and semiconductor based materials. Such shape and material constraints would exclude many applications that require biocompatibility, dynamic stress, and high ductility. New technologies are sought to fabricate three dimensional microcomponents using robust materials for demanding applications. To be cost effective, such microdevices must be economically mass producible. Molding is one of the promising replication techniques to mass produce components from polymers and polymer-based composites. This paper presents the development of a micromolding process to produce thermoplastic microcomponents. Mold design required precision fitting and was integrated with a vacuum pump to minimize air trap in mold cavities. Nickel and aluminum mold inserts were used for the study; their cavities were fabricated by combinations of available micromachining processes like laser micromachining, micromilling, micro electrical discharge machining, and focused ion beam sputtering. High and low density polyethylene, polystyrene polymers were used for this study. The effects of polymer molecular structures, molding temperature, time, and pressure on molding results were studied. Simulation of stress in the microcomponents, plastic flow in microchannels, and mold defects was performed and compare with experimental data. The research results showed that a microcomponent can be fabricated to the minimum size of 10 ± 1μm (0.0004 inch) with surface roughness <10 nm Rt. Molding of micro-size geartrains and orthopedic meso-size fasteners was completed to illustrate the capability of this process.
An Experimental and Modeling Study on Meso/Micro End Milling Process
Authors: Dhanorker Atul , O¨zel Tugˇrul
Published: October 2008

In this paper, mechanistic and finite element modeling of meso/micro end milling process with predictions of forces, stresses and temperature distributions in the presence of tool edge ploughing are presented. The finite element modeling of micro end milling without considering tool-workpiece dynamics interaction is introduced to study the effects of cutting conditions on the workpiece deformations in meso/micro end milling. Model is tested and validated for temperature and force predictions in meso/micro end milling of AL 2024-T6 aluminum.
Optimal Dimensioning of Miniaturized Machine Tools
Authors: Park Hyung Wook , Liang Steven Y.
Published: October 2008

Increasing demand for micro fabrication of parts and products in the electronics, computer, and biomedical industrial sectors has created the need to minimize conventional manufacturing systems and machine tools such as milling, turning, and grinding machines corresponding to their fabrication targets. Among existing micro-machining technologies, mechanical solid tool machining with miniaturized manufacturing systems is one of the important processing methods, and has a number of inherent advantages. These advantages include: significant reduction of required space and energy consumption for machine drive and atmosphere; the improvement of machine robustness against external error sources due to increasing thermal, static, and dynamic stabilities; increased accuracy due to decreased overall machine size; and a greater freedom in the selection of workpiece materials, the complexity of the product geometry, and the cost of investment. However, the miniaturization of manufacturing machines unavoidably reduces the available work volume, so there are limits to the possible reduction of machine size per each machine tool configuration. Therefore, optimizing the configuration and size selection is important in order to address competing issues at the functionality level of machine tools. In this research, an effective design strategy to ensure good microscale machine performance and to provide the proper dimensions of the miniaturized manufacturing systems without resorting to exhaustive prototyping was proposed. This systematic design strategy includes the formulation and optimization of machine form shape function in the context of positioning accuracy, machine thermal error, static error, dynamic error, and work volume for various configuration candidates. The sensitivity of the optimal machine size to the relative weighing of penalty function parameters is discussed in the context of a case study. The results of this work can quantitatively support the design, configuration, fabrication, and utilization of microscale manufacturing systems in achieving precision and work volume specifications.
Analysis of Ultrashort Pulse Laser-Material Interaction Using the Two-Temperature Model
Authors: Lee Dongkyun , Kannatey-Asibu Elijah
Published: October 2008

Ultrafast or ultrashort pulse lasers are increasingly being used for micro and nano-manufacturing. Because of the extremely short pulsewidth, there is usually not enough time for energy equilibrium to be established between the electrons and lattice in metals. Thus, instead of the conventional heat conduction model, the two-temperature model (TTM) is used to analyze laser-matter interactions for ultrashort pulse lasers. However, currently available non-linear two-temperature models generally require high computation capacity and long calculation time. In this study, a laser-matter interaction analysis strategy for a simplified dimensionless linear two-temperature model (SDLTTM) with proper heat source terms is developed to provide a quick and effective analytical method. SDLTTM is derived from a non-linear TTM with an assumption of constant material properties. The analytical solutions of the SDLTTM for lattice and electron temperatures for selected heat sources are obtained in the form of infinite series, and compared with other non-linear TTMs and experimental results for the electron temperature. Good correlation is obtained with the experimental results. Finally, the limitations of the SDLTTM, which result from the linearization assumption, are discussed.
Integrated Solid Waste Management in Northwest Minnesota
Authors: Wilson Willard
Published: October 2008

In the early 1980’s Polk County and four other partner counties in rural Northwest Minnesota made the decision to incorporate a waste to energy (WTE) plant into their solid waste management program. This decision was made to comply with the Minnesota hierarchy for solid waste management, to extend the life of the Polk County landfill, and to recover valuable energy from the waste. The plant was constructed in 1987 and began burning MSW in 1988. The processing technology consisted of two starved air mass burn municipal solid waste combustors each with a combustion capacity of 40 tons of MSW per day, and produced energy in the form of saturated steam for customers in the adjacent industrial park. Initially each train utilized a two field electrostatic precipitator (ESP) as the air pollution control (APC) device. In 1996, a materials recovery system (MRF) was constructed in front of the waste combustors to remove problem/objectionable items most of which are recyclable. This facility has been a tremendous success providing many benefits including reduced stack emissions, lower O & M costs for the WTE units, and revenues from the sales of extracted recyclables. In 1998 Polk began injecting powdered activated carbon (PAC) into the flue gas of each unit upstream of the ESP to attain compliance with new State limits for dioxin/furans and mercury. Then in 2000 Polk County proceeded with an APC retrofit project designed to meet revised EPA emission guidelines which set more stringent limits for pollutants currently regulated and added limits for several other pollutants previously unregulated. In 2001 and 2004 Polk County performed research demonstration projects substituting screened WTE combined ash for a portion of natural aggregate in two asphalt road construction projects. Both projects passed stringent environmental testing and demonstrated superior strength and flexibility performance compared to conventional asphalt. Polk County is now proceeding with the installation of a turbine/generator to produce renewable electricity with excess steam. The electricity produced will be used to reduce the demand for incoming power from the local utility. Initially this may be only a twenty-five percent reduction but has the potential to be more in the event one or more of the steam customers reduces their dependence on steam from the WTE plant. All of these projects received funding assistance from the State of Minnesota in the form of Capital Assistance Grants. In 2003 the WTE plant and MRF became debt free and Polk County lowered the tip fee resulting in a disposal rate that is fairly competitive with that of most out of state landfills. This paper will discuss the development, success, and benefits of this completely integrated solid waste management system for these five counties located in Northwest Minnesota.
Comparison of Air Emissions From Waste-to-Energy Facilities to Fossil Fuel Power Plants
Authors: O’Brien Jeremy K.
Published: October 2008

The SWANA Applied Research Foundation’s FY2005 Waste-to-Energy Group identified the need for a public information document that compares the air emissions from waste-to-energy facilities to those of conventional fossil fuel power plants. This paper is based on a research report that was prepared by SWANA in the course of developing the public information document.
Pyrolysis in Waste to Energy Conversion (WEC)
Authors: Green Alex E. S. , Bell Sean M.
Published: October 2008

Solid waste (SW), mostly now wasted biomass, could fuel approximately ten times more of USA’s increasing energy needs than it currently does. At the same time it would create good non-exportable jobs, and local industries. Twenty four examples of wasted or under-utilized solids that contain appreciable organic matter are listed. Estimates of their sustainable tonnage lead to a total SW exceeding 2 billion dry tons. Now usually disposal problems, most of these SW’s, can be pyrolyzed into substitutes for or supplements to expensive natural gas. The large proportion of biomass (carbon dioxide neutral plant matter) in the list reduces Greenhouse problems. Pyrolysis converts such solid waste into a medium heating value gaseous fuel usually with a small energy expenditure. With advanced gas cleaning technologies the pyrogas can be used in high efficiency gas turbines or fuel cells systems. This approach has important environmental and efficiency advantages with respect to direct combustion in boilers and even air blown or oxygen blown partial combustion gasifiers. Since pyrolysis is still not a predictive science the CCTL has used an analytical semi-empirical model (ASEM) to organize experimental measurements of the yields of various product {CaHbOc} yields vs temperature (T) for r dry ash, nitrogen and sulfur free (DANSF) feedstock having various weight % of oxygen [O] and hydrogen [H]. With this ASEM each product is assigned 5 parameters (W, T0, D, p, q) in a robust analytical Y(T) expression to represent yields vs. temperature of any specific product from any specified feedstock. Patterns in the dependence of these parameters upon [O], [H], a, b, and c suggest that there is some order in pyrolysis yields that might be useful in optimize the throughput of particular pyrolysis systems used for waste to energy conversion (WEC). An analytical cost estimation (ACE) model is used to calculate the cost of electricity (COE) vs the cost of fuel (COF) for a SW pyrogas fired combined cycle (CC) system for comparison with the COE vs COF for a natural gas fired CC system. It shows that high natural gas prices solid waste can be changed from a disposal cost item to a valuable asset. Comparing COEs when using other SW capable technologies are also facilitated by the ACE method. Implications of this work for programs that combine conservation with waste to energy conversion in efforts to reach Zero Waste are discussed.
Preliminary Tank Testing of VIV Suppression of Helical Grooves
Authors: Huang Shan
Published: October 2008

Two rigid cylinders attached to a vertically cantilevered supporting rod are towed in a towing tank. The two cylinders are otherwise identical, apart from that one has a smooth surface while the other has triple-start helical grooves cut into its surface. The cross flow VIV responses are compared and it becomes clear that the grooves are useful in suppressing the VIV response with the peak amplitude reduced by close to 70%.
Characterization of the Wave Profile in the Edinburgh Curved Tank
Authors: Cruz Joa˜o M. B. P. , Pascal Remy R. C. , Taylor Jamie R. M.
Published: October 2008

A novel wave tank has been in use at the University of Edinburgh since 2003. Its main innovation is in the layout of the absorbing/wave-maker paddles, which are arranged in a 90-degree arc in an attempt to improve the angular spread of the generated three-dimensional sea states, and to minimise cross-tank seiches. This paper reports on current studies that aim to assess the quality of the waves in the tank. Directional regular and irregular wave analysis is conducted using data from two arrays of wave elevation probes. Comparisons with the expected wave patterns are made. Emphasis is given to the description of the experimental methodology. The study should prove particularly relevant in the design of a future circular combined wave and current tank.
Horizontal Pullout Capacity of Embedded Suction Anchors in Sand
Authors: Bang S. , Jones K. , Kim Y. S. , Kim K. O. , Cho Y.
Published: October 2008

An analytical solution has been developed to estimate the horizontal pullout capacity of embedded suction anchors. Validation has been made through comparisons with the centrifuge model test results. The results indicate that the horizontal pullout capacity of the embedded suction anchor in sand increases, reaches its peak and then starts to decrease as the point of the load application moves downward. The effect of flanges on the horizontal pullout capacity is also found to be significant.
Mechanical Fatigue Simulation by Unconventional Plasticity Model
Authors: Tsutsumi Seiichiro , Toyosada Masahiro , Yajima Daiki , Gotoh Koji , Hashiguchi Koichi
Published: October 2008

The deformation behavior of a structure under cyclic loading condition is simulated by using FEM analysis in which a cyclic plasticity model, so-called extended subloading surface model, is incorporated. The adopted cyclic plasticity model is categorized in the framework of the unconventional plasticity model premising that the interior of the yield surface is not a purely elastic domain. The developed FEM program does not include algorithms for both the yielding-judgment and the control of stress so as to lie on the yield surface, since the subloading surface model has the stress controlling function so that a stress approaches the yield surface automatically. In this study, several examples of FEM analysis on the cyclic deformation behaviors are presented to show the potential of the developed FEM program and an incorporated cyclic plasticity model.
Maximum Crest Heights Over an Area and the Air Gap Problem
Authors: Forristall George Z.
Published: October 2008

Ocean waves are dispersive and directionally spread, changing size and shape as they propagate. Therefore the maximum crest height over an area in a given length of time will be larger than the maximum crest at a single point. Extreme crest heights are usually calculated from single point statistics, but the designer of a platform is really interested in the probability of a wave crest reaching any part of the deck area. Statistics for the maximum crest over an area have been developed using a combination of analytic theory and numerical simulations. The resulting crest heights are significantly higher than given by point statistics even for relatively small areas. On the other hand, only a small fraction of the deck may be inundated. That fraction can be estimated by a applying a two dimensional version of the NewWave method that finds the most probable shape of an extreme wave.
Manned Evaluation of a Prototype Cold Water Diving Garment Using Superinsulation Aerogel Materials
Authors: Nuckols Marshall , Henkener Jerry , Chao Jeffrey , Shaffer Chris , Swiergosz Matthew
Published: October 2008

During January 2005, the U. S. Navy Experimental Diving Unit (NEDU) in Panama City, Florida conducted a repeated measures series of twelve test dives, each up to three hours in duration, to compare the thermal performance of a prototype diving garment using a superinsulation aerogel fabric with that of a commercially-available Thinsulate garment worn beneath a commercial dry suit. The thermal benefit of the experimental aerogel garment was determined by statistics describing psychological and physical thermal status data from the aerogel and the commercial Thinsulate garments. All tests were conducted to simulate long-duration cold water conditions in the NEDU test pool, where water temperature was maintained between 1.7 and 4.4 °C (35 and 40 °F). Divers remained immobile while either lying or sitting in chairs on the bottom of the test pool, and they subjectively reported their thermal comfort at 30-minute intervals during each dive. Mean dive durations were found to be approximately 43% longer when divers wore the prototype aerogel garment than when they wore an M400 Thinsulate liner. The prototype aerogel garment also enhanced thermal protection to the fingers and toes, although thermal stress to these body regions still remained the most frequent reason for aborting dives. Future research should include work on localized active heating of the hands and feet to augment the thermal insulation of the prototype aerogel garment.
Design and Optimization of an Ice Class Propeller Under Shallow Water, Semi-Tunnel Hull and Heavy Load Conditions
Authors: Liu Pengfei , Islam Mohammed Fakhrul , Searle Shawn , MacNeil Andrew , Prior Andrew
Published: October 2008

A design and optimization procedure developed and used for a propeller installed on a twin-semi-tunnel-hull ship navigating in very shallow and icy water under heavy load conditions is presented. The base propeller was first determined using classical design routines under open water condition utilizing existing model test data. In the optimization process, a panel method code (PROPELLA) was used to vary the pitch values and distributions and take into account the inflow wake distribution, tunnel gap and cavitation effects. The optimized propeller was able to numerically achieve a ship speed 0.02 knots higher than the desired speed and 0.06 knots higher than the classical B-series propeller. The analysis of the effect of inflow wake, hull tunnel, cavitation and blade rake angle on propulsive performance will be the focus of this paper.
A Stereoscopic Endoscopic Optical System for Measurement of the 3D Weld Geometry of Pipes: Concepts and Preliminary Results
Authors: Hofmann Allan , Albertazzi Armando , Castilho Santos Joa˜o , Valim Eduardo , Gondo Ricardo , Freitas Thiago
Published: October 2008

Steel catenary risers (SCRs) have been considered a strong candidate in future sub sea developments at Campos Basin (Brazil). So there is an enormous effort to guarantee the structural integrity along its lifetime. In this context, inspection activities become significantly important in the manufacturing process. The welding is considered a critical process so it is the inspection focus. Studies and analysis have demonstrated that fatigue performance of one sided girth weld is considered a critical issue, mainly in the touch down point (TDP) area. In this context, control the girth weld misalignment would improve fatigue performance during fabrication. This paper presents an optical system developed to inspect the root region of the weld during fabrication. A pair of stereoscopic images is obtained when two images of the same scene are taken from slightly different viewing angles. Both images can be combined to give information about the 3D nature of the scene. This is naturally done by the brain of most animals and humans. It is also already a very well established computer vision technique to extract 3D information from objects. The authors developed an alternative endoscopic configuration to extract and analyze stereoscopic images from the inside of pipes is presented. Two cameras are coupled with conical optics to produce a pair of endoscopic stereoscopic images of a 360° measurement ring. A light projector is used to illuminate the inner surface and, alternatively, to generate a random pattern of dots that is projected into the inner surface of a pipe to make it easier to correlate the images. Both images are analyzed by cross-correlation technique. The corresponding position of the spots in each image are found and combined to compute the 3D coordinates of points laying on the inner surface of the pipe. As a result, a dense cloud of points of the inner surface is obtained and used to extract geometrical features of the pipe. The software is capable to represent the measured surface from different angles and through different cuts. A prototype using this principle was built and tested in laboratory. Some practical considerations and early measurement results are here presented. The aim is to measure and quantify the misalignment between the pipes and to detect common welding defects like lack and excess of penetration.
The Motion of Floating Systems: Nonlinear Dynamics in Periodic and Random Waves
Authors: Ellermann Katrin
Published: October 2008

Floating systems, such as ships, barges or semi-submersibles, show a dynamical behavior which is determined by their internal structure and the operating conditions caused by external forces e.g. due to waves and wind. Due to the complexity of the system which commonly includes coupling of multiple components or nonlinear restoring forces, the response can exhibit inherently nonlinear characteristics. In this paper different models of floating systems are considered. For the idealized case of purely harmonic forcing they all show nonlinear behavior such as subharmonic motion or different steady state responses at constant operating conditions. The introduction of random disturbances leads to deviations from the idealized case which may change the overall response significantly. Advantages and limitations of the different mathematical models and the applied numerical techniques are discussed.
Three-Dimensional Numerical Simulations of Circular Cylinders Undergoing Two Degree-of-Freedom Vortex-Induced Vibrations
Authors: Pontaza Juan P. , Chen Hamn-Ching
Published: October 2008

In an effort to gain a better understanding of the VIV phenomena, we present three-dimensional numerical simulations of VIV of circular cylinders. We consider operating conditions that correspond to high Reynolds number flow, low structural damping, and allow for two-degree of freedom motion. The numerical implementation makes use of overset (Chimera) grids, in a multiple block environment where the workload associated with the blocks is distributed among multiple processors working in parallel. The three-dimensional grids around the cylinder are allowed to undergo arbitrary motions with respect to fixed background grids, eliminating the need for tedious grid regeneration at every time step.
Fatigue Mitigation Design of Deepwater Steel Catenary Risers
Authors: Yao Xiongliang , Sun Liping
Published: October 2008

With the development of deepwater offshore industries, Steel Catenary Riser (SCR) concept offers great advantages over others and has been widely deployed worldwide. More than 100 SCRs have been installed in the deepwater fields including West of Africa, Gulf of Mexico, and Offshore Brazil. Fatigue is still the number one governing design criterion of the deepwater SCR regardless the floater types (SPAR, TLP, SEMI, and FPSO). Typical SCR fatigue damages include vortex induced vibration (VIV), host floater motion induced, floater vortex induced motion (VIM) fatigue, floater vertical motion induced VIV, installation, and other kinds of dynamic loading imposed to SCR. The success of the SCR design depends primarily upon the fatigue design and its mitigation methods. This paper summaries the viable fatigue mitigation design for deepwater SCR. Detailed discussion is given to different kind of fatigue damages of SCR. Focus of fatigue design of each type of deepwater floater is pointed out. Detailed discussion is given to the selection of design methods, SN curves, stress concentration factors, influence of sweet and sour service, and post-processing of fatigue sensitive welds. Different potential and practical fatigue design mitigations have been evaluated and discussion. The most viable options have been pointed out. Some examples based on actual projects experience are given to demonstrate the design principles and fatigue mitigation methods.
A Study of Dynamic Responses and Wave Loads on Ships by 3-D Green Function Method
Authors: Inoue Yoshiyuki , Kamruzzaman Md.
Published: October 2008

The dynamic wave loads are the most significant factor for the hull design of a ship. But experimental works for the motion responses of a ship and sea loads on her are expensive and time consuming for individual ship design. Therefore, the development of theoretical and numerical methods for predicting ship motions and dynamic loads on a ship in waves is very important for rational ship design procedure. In general, though 3-D Green function techniques with forward speed need long computation time, however it should be more accurate assumption of the flow field problem on an advancing ship in waves. Nowadays the availability of much faster computer makes the 3-D Green function techniques with forward speed more familiar than before. In this paper, numerical analyses on ship motions and wave loads are presented for ships with forward speed advancing in regular waves. 3-D Green function techniques have been used to carry out the numerical computations for the radiation problem and wave loads for a moving ship. Based on the 3–D linearized potential theory, dynamic wave loads have been computed of a bulk carrier in regular waves where experimental measurements are available. The computations are carried out for various heading angles between head sea and following sea and various ranges of frequencies. The results for motions, and vertical and horizontal bending moments are presented in this paper. Computed results are compared with the experimental data. The results calculated by the present method are found in fairly good agreement with the experimental results and those calculated by the other researchers. Using developed computer code, some parametric studies are also carried out for the ship design criteria and the discussions are made.
Reliability Calculation of RC Monopod Structures Under Extreme Wave Loading
Authors: Karadeniz H.
Published: October 2008

In this paper, a general formulation of section-capacities of a circular RC tubular cross-section is first presented. It is assumed that the strain-stress relation of the concrete in the compression zone is simply modelled as bilinear function with ultimate values given in Eurocode 2, and the concrete works only in the compression zone. Tension stresses of the cross-section are carried by the reinforcement. Having presented a general formulation of extreme bending moment and axial force of a RC monopod offshore tower under wave loading, uncertainties in both section capacities and loading terms are presented. Then, a reliability calculation of the cross-section is performed. In this calculation, the balance of the axial force is used to determine concrete compression zone during the reliability iteration and the failure function is defined on the basis of the section capacity- and applied bending moments. Variation of the reliability index with various parameters is investigated and most sensitive uncertainty variables are identified.
Response Reduction of Motion and Steady Wave Drifting Forces of Floating Bodies Supported by Aircushions in Regular Waves
Authors: Ikoma Tomoki , Masuda Koichi , Rheem Chang-Kyu , Maeda Hisaaki
Published: October 2008

This paper describes the response characteristics and reduction effect of motion and tether tension of two test models that float in water waves by using buoyancy of aircushions. The experimental basic model is 3m long. The basic model has a large mono-aircushion. The second model has three aircushions. Objectives of this study are to examine responses of vertical motion and the wave drifting force and to prove that aircushion supporting system is available in order to reduce vertical motion and the wave drifting force simultaneously using model experiments in a wave tank. Motion response and tether tension of a linear spring are measured. Not only linear responses of them but also steady responses due to the wave drifting force are measured and analyzed. The result of the model tests has proved that draft of skirt like walls has much influence to air-pressure in the aircushion and motion response when the mono-aircushion is compartmentalized to three aircushions. It is found that nonlinearity of response of the air-pressure is strong. Finally we can confirm that reduction of vertical motion and the wave drifting force simultaneously is possible experimentally.
Unit-Tests Based Validation and Verification of Numerical Procedure to Predict Vortex-Induced Motion
Authors: Schowalter David , Ghosh Indradeep , Kim Sung-Eun , Haidari Ahmad
Published: October 2008

Vortex-induced vibration of a circular cylinder with two degrees-of-freedom (2-DOF) is numerically studied using a mixed Lagrangian-Eulerian approach at several Reynolds numbers. The computations were carried out using a parallelized finite-volume Navier-Stokes solver based on a multidimensional linear reconstruction scheme that allows use of unstructured meshes. The effects of turbulence are modeled using an approach based on unsteady Reynolds-averaged Navier-Stokes (URANS) equations and a hybrid approach often referred to as detached eddy simulation (DES). In order to better understand the potential sources of the prediction error, a systematic verification and validation of the numerics and the physical models is attempted in this study with problems of progressively increasing complexity.
The Effect of Wind and Wave Misalignment on the Response of a Wind Turbine at Bockstigen
Authors: Trumars Jenny M. V. , Jonsson Johan O. , Bergdahl Lars
Published: October 2008

The aim of this work is to evaluate data from the offshore wind farm Bockstigen in order to study the effect of directional spreading of waves and wind wave misalignment on the response of the structure. The development of offshore wind energy has led to wind farms at sites with water depths ranging from approximately 6 to 30 m. The change of location from land to sea changes the design requirements of wind energy converters. In addition to wind loads, the wave load on the structure has to be taken into account. Since a wind turbine is highly damped in the inline direction as compared to the crosswise direction, the effect of directional spreading of waves on the response is studied. Depending on the dynamics of the structure the crosswise force could give a larger response than the corresponding inline force. In this study the influence of the directional spreading of the waves on the response is not clear, however the effect of wind and wave misalignment is clear.
Modelling Strength Degradation Phenomena and Inspections Used for Reliability Assessment Based on Maintenance Planning
Authors: Garbatov Y. , Guedes Soares C. , Ok D. , Pu Y. , Rizzo C. M. , Rizzuto E. , Rouhan A. , Parmentier G.
Published: October 2008

The work reviews different probabilistic models of strength degradation of steel ship hull structures considering time dependent corrosion phenomena. Different models of time variation of the degradation phenomena are analyzed as well as the probability of detection and different inspection methods associated with each phenomenon is discussed.
Determination of Weight Functions for Cracks Under Mode-II Loading
Authors: Li H. L. , Wang X. , Bell R.
Published: October 2008

For cracks under mode-I loading, it has been demonstrated that a general weight function expression with three unknown parameters can be used to approximate a variety of crack configurations under mode-I loading. For a given crack geometry, the unknown parameters can be determined from reference stress intensity factors (SIFs) together with characteristic properties of the weight functions. It is demonstrated in this paper that a general weight function expression also exists for cracks under mode II loading. The determination of weight functions for cracks in mode II can then also be conducted using reference stress intensity factors (SIFs) together with characteristic properties of the weight functions. This method is used to obtain the mode II weight functions for test specimens including single edge cracked plate, internal center cracked plate and double edge cracked plate. These derived weight functions were further used to calculate the SIFs for the above cracks subjected to several linear and non-linear shear loads and were compared to available SIF solutions.
Hydrodynamic and Control Analysis of a Self-Controllable Underwater Towed Vehicle
Authors: Wu Jiaming , Xiong Xiaohui
Published: October 2008

The hydrodynamic and control performances of a self-stable controllable underwater towed vehicle developed by South China University of Technology under different depth trajectory control operations are analyzed by means of a proposed hydrodynamic numerical model. The model is established based on LMBP algorithm of neural network theory. Training samples for the neural network model are provided from the experimental data of the vehicle prototype towing experiments conducted in a large-scale ship model towing tank under the manipulation of a depressing wing installed in the vehicle. After the LMBP model is established, a depth trajectory control system for the towed vehicle is designed in order to accomplish vehicle trajectory control. This system is mainly composed of tow parts: a neural network identifier based on genetic algorithm and a fuzzy neural network controller based on genetic algorithm simulated annealing. Hydrodynamic performances of the vehicle under various control operations can then be numerically simulated with the proposed LMBP model and the depth trajectory control system of the towed vehicle. In numerical simulation of trajectory control to the towed vehicle, deflection of the vehicle’s depressing wing is adjusted at every time step by the proposed control system to match the trajectory of the vehicle with a pre-designated one. The value of the deflection is taken as input parameter for the LMBP neural network model, trajectory and attitude behavior of the towed vehicle under the control manipulations can then be predicted by the LMBP model.
Effective and Efficient Breakwater Design for Trading Vessels and FPSOs
Authors: Varyani Kamlesh , Hodgson Trevor , Pham Xuan
Published: October 2008

Breakwaters obviously need to fulfil their function (protecting sensitive structures or cargo) while at the same time remaining intact and imposing manageable loads onto supporting structure. It goes without saying that such breakwaters should be cost effective, so that complex designs with extensive welding may not be preferable. In this paper the authors will discuss green water loading on breakwaters for trading vessels like container ships which have forward speed and FPSOs which have zero speed. Different generic designs of V shape, vane type, double skin with and without holes and forward sloping forecastle (whaleback deck) breakwaters applied to trading vessels will be discussed. Guidelines for modelling green water horizontal loading on breakwaters of FPSOs and trading vessels using CFD techniques will be provided. The paper will also include a review of breakwater design criteria in rules and regulations.
An Efficient Method for Hydrodynamic Analysis of a Floating Vertical Sided Structure in Shallow Water
Authors: Drobyshevski Y.
Published: October 2008

Vertical sided objects with a flat bottom represent a broad class of marine structures, which include barges, pontoons, floating docks, breakwaters and some offshore platforms. When such structures are towed or operated in shallow water, accurate prediction of wave induced motions is required to design the mooring system and to determine the dynamic under-keel clearance. The hydrodynamic analysis may be difficult when the gap between the structure bottom and the sea floor is small, calling for a large number of panels to be used on the bottom and near the edges, to capture the singular behaviour of the flow in these regions. The paper presents a method for hydrodynamic analysis, which is intended to avoid these difficulties and to provide good accuracy for any small value of the under bottom clearance. Following the method of matched asymptotic expansions, the linear wave-body interaction problem is solved by matching the two “outer” flows with the “inner” flow near the structure edge. The three-dimensional hydrodynamic problem is reduced to an integral equation in two dimensions formulated on the water line (footprint) of the structure, simplifying the numerical implementation and reducing the number of subdivisions elements. Because the singular behaviour of the flow near the edge and under the bottom is effectively extracted from the solution, the method enables to use the same number of subdivisions for any small under-keel clearance, providing improving accuracy as the under-keel clearance shrinks to zero. Numerical results are presented and discussed for typical geometries, which compare well with those obtained by other methods.
New Design Code for Interference Between Trawl Gear and Pipelines: DNV RP-F111
Authors: Askheim Dag O̸. , Fyrileiv Olav
Published: October 2008

The offshore petroleum and the fishing industries are often operating in the same areas. Fishing, in particular bottom trawling, is of concern to pipeline integrity. Such trawling is mainly conducted with two types of trawl gear: otter or beam trawls. The otter trawl boards are steel, more or less rectangular boards which keep the trawl bag open by hydrodynamic drag forces. While the beam trawls use a 10–20 meters long beam to keep the trawl bag open. These trawl gears are dragged along the seabed and represent a potential hazard to pipelines. This paper gives a brief description of types and dimensions of trawl gear. Further it deals with methods for calculating the pipeline response when interacting with bottom trawl gear and finally adresses acceptance criteria for pipeline design and assessment during operation. The calculation methods and acceptance criteria given in this paper are based on test results and research done during the last decades including results from the Kristin, Sno̸hvit and Ormen Lange projects. The above mentioned trawl data, analysis methodology and acceptance criteria are taken from the new DNV Recommended Practice, DNV RP-F111 (2006). This Recommended Practice is an update of the former design code DNV GL 13 (1997). The update was performed mainly due to new types of trawl gear, updated trawl gear data, various experience from application of GL 13 in projects and a general harmonizing process with the pipeline code, DNV OS-F101, and the Hotpipe project, ref Collberg et al. (2005). Large sums are often spent in pipeline projects to protect against trawl gear interaction in terms of concrete coating, trenching or burial. On the other hand the costs of not providing a sufficient protection could be extremely high, with costs related to leakages, failures, stop in production and repair/replacement. This Recommended Practice provides a rational tool to optimize the costs related to trawl gear interference and still ensure that the integrity of the pipeline becomes acceptable.
An Integrated Approach to Offshore Pile Axial Design in Sands and Clays
Authors: Morgan Neil , Finnie Ian
Published: October 2008

Most offshore pile axial design is currently carried out according to API RP 2A WSD, the recommendations of which we understand are due to change. As a result there are many new pile axial capacity calculation methods emerging which may become acceptable for use, each with its own particular site investigation requirements. For the same soil input these methods usually result in just as many different capacities and it is apparent that no single design method is applicable to all design situations and it would be unusual for a single method to be completely reliable for a single platform. We examine the sources of geotechnical uncertainty and concentrate on the transformation uncertainty which is principally due to the choice of pile design method. It would be a rational approach to use a single set of soil and pile input parameters and calculate the pile capacities according to all of the methods. This paper considers two major pile test sites that have had detailed site investigations (Pentre and Euripides) and uses the API, UWA, ICP, NGI, Fugro and Kolk pile design methods to compare the results. We examine the reliability of this combined approach with depth, which shows that our predictive ability varies between shallower (e.g. less than 20 metres) and deeper penetrations. It concludes with practical recommendations on how a rational pile design may be achieved. One such approach is to take the mean average of all the capacities calculated. Optimising pile design in this manner may help to identify and reduce unwarranted conservatism and conversely help to ensure that optimum pile capacity is achieved and to avoid installation difficulties associated with piles that are unnecessarily too long.
Comparison of Time and Frequency Domain Analysis With Full Scale Data for the Horn Mountain Spar During Hurricane Isidore
Authors: Tahar Arcandra , Halkyard John , Irani Mehernosh
Published: October 2008

The Horn Mountain Spar is located in 1,654 m of water about 135 km from Venice, Louisiana in the Gulf of Mexico. The facility was instrumented extensively to measure key spar and riser response parameters (Edwards et. al. 2003). Halkyard et. al. (2004) and Tahar et. al. (2005) have compared measured spar responses such as motion and mooring line tensions with numerical predictions. This paper extends the work done on comparison of the full scale data during hurricane Isidore. All previous numerical simulations were based on a time domain analysis procedure. One concern related to this method is that it is computationally intensive and time consuming. In the initial stages of a project, a frequency domain solution may be an effective tool compared with a fully coupled time domain analysis. The present paper compares results of time domain and frequency domain simulations with field measurements. Particular attention has been placed on the importance of the phase relationship between motion and excitation force. In the time domain analysis, nonlinear drag forces are applied at the instantaneous position. Whereas in the frequency domain analysis, nonlinear drag forces are stochastically linearized and solutions are obtained by an iterative procedure. The time domain analysis has better agreement with the field data compared to the frequency domain. Overall, however, the frequency domain method is still promising for a quick and approximate estimation of relevant statistics. With advantages in terms of CPU time, the frequency domain method can be recommended as a tool in pre-front end engineering design or in a phase where an iterative nature of design of an offshore structure takes place.