Modelling vortex-induced fluid-structure interaction

The principal goal of this research is developing physics-based, reduced-order, analytical models of nonlinear fluid-structure interactions associated with offshore structures. Our primary focus is to generalize the Hamilton's variational framework so that systems of flow-oscillator equations can be derived from first principles. This is an extension of earlier work that led to a single energy equation describing the fluid-structure interaction. It is demonstrated here that flow-oscillator models are a subclass of the general, physical-based framework. A flow-oscillator model is a reduced-order mechanical model, generally comprising two mechanical oscillators, one modelling the structural oscillation and the other a nonlinear oscillator representing the fluid behaviour coupled to the structural motion.Reduced-order analytical model development continues to be carried out using a Hamilton's principle-based variational approach. This provides flexibility in the long run for generalizing the modelling paradigm to complex, three-dimensional problems with multiple degrees of freedom, although such extension is very difficult. As both experimental and analytical capabilities advance, the critical research path to developing and implementing fluid-structure interaction models entails-formulating generalized equations of motion, as a superset of the flow-oscillator models; and-developing experimentally derived, semi-analytical functions to describe key terms in the governing equations of motion.The developed variational approach yields a system of governing equations. This will allow modelling of multiple d.f. systems. The extensions derived generalize the Hamilton's variational formulation for such problems. The Navier-Stokes equations are derived and coupled to the structural oscillator. This general model has been shown to be a superset of the flow-oscillator model. Based on different assumptions, one can derive a variety of flow-oscillator models.     

Structural Design of a Lunar Habitat

A lunar base is an essential part of all the new space exploration programs because the Moon is the most logical first destination in space. Its hazardous environment will pose challenges for all engineering disciplines involved. A structural engineer’s approach is outlined in this paper, discussing possible materials and structural concepts for second-generation construction on the Moon. Several different concepts are evaluated and the most reasonable is chosen for a detailed design. During the design process, different solutions—for example, for the connections—were found. Although lunar construction is difficult, the proposed design offers a relatively simple structural frame for erection. A habitat on the Moon can be built with a reasonable factor of safety and existing technology. Even so, we recognize the very significant difficulties that await our return to the Moon.     

Space Structures: Issues in Dynamics and Control

A selective technical overview is presented on the vibration and control of large space structures, the analysis, design, and construction of which will require major technical contributions from the civil∕structural, mechanical, and extended engineering communities. The immediacy of the U.S. space station makes the particular emphasis placed on large space structures and their control appropriate. The space station is but one part of the space program, and includes the lunar base, which the space station is to service. This paper attempts to summarize some of the key technical issues and hence provide a starting point for further involvement. The first half of this paper provides an introduction and overview of large space structures and their dynamics; the latter half discusses structural control, including control‐system design and nonlinearities. A crucial aspect of the large space structures problem is that dynamics and control must be considered simultaneously; the problems cannot be addressed individually and coupled as an afterthought.     

Risk factors in ulcerative colitis

In 504 Jewish patients with ulcerative colitis the following risk factors were evaluated: sex, age at onset of disease, community group, extent of disease, and duration of disease. The disease was more severe in females. Severe attacks, weight loss, iron deficiency, liver disease and arthritis were significantly more frequent in females than in mles. Mortality was higher in patients who contracted the disease above age 50. The disease appeared to be more severe in patiets of Ashkenazi origin as compared to Orientals. The difference failed to reach statistical signifcance except for mortality. We confirmed the well-known adverse effect of extensive colonic involvement. Severe attacks, a severe course of the disease and extensive colonic involvement are more frequent with increasing duration of the disease.     

The Neumann series/Born approximation applied to parametrically excited stochastic systems

Intensive efforts have been expended to understand and apply the theory of the Neumann series and the Born approximation. We are able to discuss, to the best of our knowledge for the first time, the method in a more complete manner, presenting not only the theory, but also its analytical and simulation aspects, and its application to a simple structure.     

Engineering, Design and Construction of Lunar Bases

How do we begin to expand our civilization to the Moon? What are the technical issues that infrastructural engineers, in particular, must address? This paper has the goal of introducing this fascinating area of structural mechanics, design, and construction. Published work of the past several decades about lunar bases is summarized. Additional emphasis is placed on issues related to regolith mechanics and robotic construction. Although many hundreds of papers have been written on these subjects, and only a few tens of these have been referred to here, it is believed that a representative view has been created. This summary includes environmental issues, a classification of structural types being considered for the Moon, and some possible usage of in situ resources for lunar construction. An appendix provides, in tabular form, an overview of structural types and their lunar applications and technology drivers.     

Design and Construction Considerations for Lunar Outpost

Engineers utilize various codes in the process of design, whether structural, mechanical, or otherwise. Reliance on a code for design is based on the knowledge that a tremendous amount of time and effort was spent by experienced engineers to codify theories and good practice in a particular design discipline. Good practice in structural design implies cognizance of materials, structural behavior, environmental loadings, assumptions made in analysis and behavior, and the uncertainties inherent in all of these. The American Institute of Steel Construction's (AISC) Manual of Steel Construction is such a codification for the design and construction of steel structures. It includes information, some tabular and the rest in the form of specifications and commentaries, necessary to design and provide for the safe erection of steel‐framed structures. The design equations are generally semiempirical, that is, they are based on a mix of theoretical analysis, experimental data, and factors of safety. Each of these components has associated implicit assumptions. Some of these assumptions were explored to understand how and if the Earth‐based design code could be used for the design of a lunar outpost. Topics discussed come from the AISC Code of Standard Practice and the commentaries, and issues such as scaling of loads and strength in the 1∕6 g lunar environment, thermal cycling effects and fatigue, stiffening and buckling are briefly discussed. Important topics for further detailed study include: (1) The relationships between severe lunar temperature cycles and fatigue; (2) very low temperature effects and the possibility of brittle fractures; (3) outgassing for exposed steels and other effects of high vacuum on steel∕alloys; (4) factors of safety originally developed to account for uncertainties in the Earth design∕construction process undoubtedly need adjustment for the lunar environment; (5) dead loads∕live loads under lunar gravity; (6) buckling∕stiffening and bracing requirements for lunar structures that will be internally pressurized; and (7) consideration of new failure modes such as high‐velocity micrometeorite impacts.     

Development and Operation of a Prototype Superconducting Linac for Heavy-Ion Acceleration

A prototype superconducting-helix accelerator is described and design considerations are discussed. The results obtained during 120 hours of beam acceleration are given. These include a wealth of practical engineering experience, the demonstration of stable operation with external phase control, and measurements of various kinds of accelerator-physics data.