Static non-linear three-dimensional analysis of a riser bundle by a substructuring and incremental finite element algorithm

The problem of static, non-linear, large three-dimensional deformation of riser bundles used in offshore oil and gas production is studied within the limits of small strain theory. The mathematical model consists of the models of component-risers and connectors which hold risers together. Each riser is modelled as a thin walled, slender, extensible or inextensible tubular beam-column. It is subject to non-linear three-dimensional deformation dependent hydrodynamic loads, torsion and distributed moments, varying axial tension, and internal and external fluid forces. The problem is solved numerically by developing an algorithm which features substructuring, condensation and non-linear incremental finite elements. Substructuring is used to decompose the riser bundle problem into those of individual component-risers and equilibria of connectors. Condensation is used along with the connector equilibrium equations to produce connector forces and moments. Strong non-linearities present in the model are handled by an incremental finite element approach. Accuracy of the computer code is verified by solving simple three-dimensional cases. Two three-dimensional applications are solved for a bundle with seven component-risers and up to a total of 1267 degrees of freedom. Finally, a comparison is made with numerical results of a two-dimensional analysis code. The influence of problem size on total CPU time is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50097/1/1620281104_ftp.pd

Naval Engineering A National Naval Obligation

As part of its national obligations, ONR must ensure US world leadership in those unique technology areas that insure naval superiority. ONR accomplishes this mission through research, recruitment and education, maintaining an adequate base of talent, and sustaining critical infrastructure for research and experimentation. One critical area requiring support by ONR is the "knowledge infrastructure" in Naval Architecture and Marine Engineering. An innovative knowledge infrastructure in NA & ME consists of two main elements: • People who have the knowledge, skills and experience to perform innovative design and engineering applied to in Naval Architecture and Marine Engineering; and • An industry that employs these people and allows this innovative knowledge to be applied in the ships it designs and builds for the Navy. The universities along with industry develop the technology and educate the people who are employed by industry. In turn, the research supported primarily by the government provides direct support for the conduct of research and the education of the future faculty who perform their doctoral research in this discipline. This study examined the current situation in navy related Naval Architecture and Marine Engineering. The need for ONR support in this area is identified and recommendations made to establish long term support that will provide for the introduction of innovative technology in naval ships. The following are documented in this report to establish this need: (1) The uniqueness of "Engineering for the Marine Environment" is explained. Naval Architecture and Marine Engineering, among all engineering disciplines, studies the design of complex marine systems and their performance in the marine environment. The latter is stochastic in nature and exerts motion and vibration dependent loads. (2) The uniqueness of analysis, design, and manufacture of naval ships is presented. A key unique aspect of naval ship design is the need for new capabilities in performance such as high speed while remaining affordable. (3) A vision of the role and knowledge of the NA&ME professional of the future is presented. In a distributed simulation based environment, naval architects will lead the design effort by contributing the expertise in marine mechanics, design of complex marine systems, and design for manufacturing. Naval Architects are trained in marine mechanics and the design of complex marine systems. This breadth of skills will be even broader in the future while remaining base on experience in designing naval ships. (4) The Navy need for a solid national knowledge infrastructure in NA&ME is established. Accordingly, the need for ONR support of research and education in the few healthy NA&ME Departments remaining in top tier US universities is very strong. (5) Navy needs for breakthroughs in such areas as survivability of structures, stealth and hydrodynamic performance, and adaptive structures are identified. From those, fundamental research that naval architects are uniquely qualified to perform for ONR is specified. (6) A selective industry survey has established the areas of technical expertise needed. Naval Architecture and Integrated Ship Design and Shipbuilding and Manufacturing Technology top the list. (7) Freshmen in engineering, the few universities remaining active in teaching and research in NA&ME, ONR, and the shipbuilding industry are the parties involved in this problem. The challenges each party faces are discussed. (8) The urgency for ONR to help preserve the knowledge infrastructure in NA&ME is assessed based on current national trends in funding and student choices. (9) An educated estimate of the national need for naval architects is presented and used as a basis for establishing the level of long term funding in research and education required for a steadily healthy and competitive higher education environment. (10) An implementation plan for a vigorous knowledge infrastructure and a healthy university environment is proposed. This plan abides by the ONR mandate of supporting fundamental, high risk, innovative research needed by the Navy. It calls for: • A research program centered on National Challenge Initiatives with the intent to revolutionize the state of the art in ship analysis and design and to bring the participants, industry, government and academia, in this endeavor closer together in perspective and time for innovation. • Acknowledging NA&ME as a specialty area of basic research. This is typically done by federal research funding agencies. As an example, in NSF, mechanical, civil, electrical, chemical, etc. are established specialty areas. • Modernization of contents and methods of delivery of marine curricula. • Industrial participation in both research and education activities.Office of Naval Research Code 334 ONR Contract number N0001499WR2016

Sudden hearing loss as an early detector of multiple sclerosis: a systematic review

To evaluate whether Sudden Sensorineural Hearing Loss (S-SNHL) may be an early symptom of Multiple Sclerosis (MS). A systematic review was conducted using the following keywords: "Multiple sclerosis, hearing loss, sudden hearing loss, vertigo, tinnitus, magnetic resonance imaging, otoacoustic emission, auditory brainstem responses, white matter lesions, sensorineural hearing loss, symptoms of MS and otolaryngology, nerve disease and MS". Only the articles that included results of at least one auditory test and MRI were considered. We evaluated the prevalence of SNHL in patients with MS, the presence of different forms of SNHL (S-SNHL and Progressive SNHL (P-SNHL)) and their correlation with the stage of MS, the results of electrophysiological tests, and the location (if any) of MS lesions as detected by white matter hyperintensities in the MRI. We reviewed a total of 47 articles, which included 29 case reports, 6 prospective studies, 6 cohort studies, 4 case-control studies, and 2 retrospective studies. 25% of patients suffered from SNHL. S-SNHL typically occurred in the early stage of the disease (92% of patients) and was the only presenting symptom in 43% of female subjects. Instead, P-SNHL occurred in the late stage of MS (88% of patients). Auditory Brainstem Responses (ABR) were abnormal in all MS patients with S-SNHL. When S-SNHL appeared during the early stage of the disease, MS lesions were found in the brain in 60% of patients and in the Internal Auditory Canal in 40% of patients. ABR remained abnormal after recovery. S-SNHL can be an early manifestation of MS and should always be considered in the differential diagnosis of this condition, especially in women. The pathophysiology can be explained by the involvement of microglia attacking the central and/or peripheral auditory pathways as indicated by WMHs

Structural model correlation using large admissible perturbations incognate space

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76957/1/AIAA-10863-901.pd

Nonlinear incremental inverse perturbation method for structural redesign

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76715/1/AIAA-1983-892-392.pd

Effect of fluid static pressure on the immediate postbuckling behavior of heavy tubular columns

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26654/1/0000198.pd

Low Head, Vortex Induced Vibrations River Energy Converter

Vortex Induced Vibrations Aquatic Clean Energy (VIVACE) is a novel, demonstrated approach to extracting energy from water currents. This invention is based on a phenomenon called Vortex Induced Vibrations (VIV), which was first observed by Leonardo da Vinci in 1504AD. He called it ‘Aeolian Tones.’ For decades, engineers have attempted to prevent this type of vibration from damaging structures, such as offshore platforms, nuclear fuel rods, cables, buildings, and bridges. The underlying concept of the VIVACE Converter is the following: Strengthen rather than spoil vortex shedding; enhance rather than suppress VIV; harness rather than mitigate VIV energy. By maximizing and utilizing this unique phenomenon, VIVACE takes this “problem” and successfully transforms it into a valuable resource for mankind

Admissible large perturbations in structural redesign

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76363/1/AIAA-10551-828.pd

Three-dimensional nonlinear statics of pipelaying using condensation in an incremental finite element algorithm

The problem of static, nonlinear three-dimensional deformation of pipelaying used in construction and installation of underwater pipelines is studied within the limits of small strain theory. The mathematical model consists of the pipeline model and geometric constraints imposed by the seabed and the lay vessel in stinger or J-type pipelaying. The pipeline is modeled as a thin-walled, slender, extensible or inextensible tubular beam-column. It is subject to gravity, lateral friction from the seabed, nonlinear three-dimensional deformation dependent hydrodynamic loads, torsion and distributed moments, varying axial tension, and internal and external static fluid forces. The problem is solved numerically by developing a nonlinear incremental finite element algorithm which features condensation and principles of contact mechanics. Condensation is used along with the geometric constraints to formulate a condensed problem which produces reaction forces. Strong nonlinearities present in the model are handled by an incremental finite element approach. The developed computer code is used to study stinger pipelaying for various stinger configurations, investigate the effect of water depth, and compare stinger to J-type pipelaying in deep water.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28834/1/0000669.pd

Redesign of marine structures by perturbation

Finite element (FE) methods are extensively used for analysis of static and dynamic behavior of marine structures. Often predicted response is unacceptable from the point of view of design or operation. Improvement of response then, becomes a design goal which can be achieved by redesign or reduction of operational threshold. Traditional trial and error techniques using FE methods make redesign expensive and are often inconclusive. In this paper a perturbation-based method is developed to solve redesign problems with both static and modal dynamic objectives using data only from the FE analysis of the baseline structure. Code RESTRUCT implements this method and functions as postprocessor to general or special purpose FE codes. Several simple numerical applications are used to illustrate the efficiency of this redesign method and how it can be used to resolve conflicts caused by incompatible redesign requirements. A 192-degree-of-freedom tower with repeated eigenvalues is redesigned subject to frequency and displacement constraints. Finally the impact of perturbation-based redesign on marine structural design is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27488/1/0000532.pd