Moment Resisting Connection with Curved Endplates: Behaviour Study

This article provides a behaviour analysis of moment resisting joints with curved endplates. This is a new type of connection that can be used for joining steel beams to the circular hollow section (CHS) columns by means of bolts. Some researchers apply the Eurocode model without considering the differences in calculation schemes and assumptions, such as by using the general model of an equivalent T-stub in tension. Consequently, many of the existing behaviour studies are somewhat misleading, thus there is a need for further research. Apart from the absence of analytical methods that are devoted to predicting the initial stiffness and strength of the curved T-stub, other technical difficulties were encountered, such as gaps between the endplate and the column, as well as the initial pre-loading force of the bolts. In the previous studies, endplates were manufactured by rolling flat plates to the precise curvature which resulted in firm contact. In contrast, in this study, endplates were manufactured from a standard CHS tube, which led to significant initial gaps. Meanwhile, in terms of preloading force, it was found that it affected the moment resistance of the joint. This paper discusses problems associated with ongoing researches and presents experimental tests of the two connections. The obtained results were further used in the parametric finite element analysis (FEA) to determine the effect of the gaps and preloading force of the bolts on the moment resistance and initial rotational stiffness of the joint. The results indicate that the behaviour of curved plated connections is exceedingly complex and that the preloading force is the key factor, therefore, it should be controlled.

Squeeze Film Damper Bearing With Double-Ended Beam Centering Springs: Part I — Design and Analysis

Squeeze film damper (SFD) bearings are widely used in industry to enhance rotor dynamic stability in super-critical applications. This study examines an SFD bearing design with double-ended beam centering springs placed external to the squeeze film and in parallel with O-ring seals. The purpose of the new SFD bearing design is to minimize the use of O-rings as a support and centering device, instead relying on compact external springs that can be independently adjusted to ensure centered operation. The new design is applicable to a wide range of bearing sizes and rotor weights with variable spring stiffness, damping value and envelope dimensions. Spring stiffness and stress coefficients were generated for 3.5-inch bearing and SFD assembly from a parametric finite element analysis (FEA). High cycle fatigue of the springs was evaluated using the Soderberg criterion with an additional safety factor. Rotor-dynamic performance of the new design was analyzed using an historical rotor applying both π-film and full-film models. To evaluate the design, the same 3.5 inch SFD bearing presented in this study was manufactured and tested in succeeding work.

Optimization-Based Multi-Attribute Decision Making for the 7th Generation Semi-Submersible Drilling Unit

The 7th generation semi-submersible drilling units (CSDU) are characteristic of deeper drilling depth, site locations and higher operational efficiency, compared with the last generation ones. Given the enormous live loads change and increasing trend of main size dimensions, considerable optimization should be deployed to achieve a balance of economy, safety and good work performance. Trial calculation and definite assessment to check whether alternative schemes meet the requirements turns out to be ineffective, for the case by case study of hydrodynamic and structure strength analysis is time consuming. In the paper, an integrated optimal design model is formulated by merging multi-objective optimization and multi-attribute decision making into one. A predesigned parametric Finite Element Analysis (FEA) structural model of CSDU is developed and validated and then coupled with detailed hydrodynamic analysis. Three mutually conflicting design objectives are arrived by hydrodynamic solutions. They are stability, hydrodynamic performance and steel consumption, which are screened to obtain Pareto optimality. The Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) is applied to incorporate these optimal attributes into decision-making process, considering all criteria in terms of quantitative stability, hydrodynamic performance and qualitative economy. The objective entropy coefficient measuring the importance of different attributes is introduced into weight selection for the purpose of avoiding non-determinacy and optional judgements. The optimal solutions are further verified with main dimensions of CSDUs in service and also could give predictive suggestion for the new CSDUs. The study provides a more objective way of benchmarking different structural schemes of CSDU by considering multiple criteria simultaneously. It is demonstrated that the proposed structural optimization model is capable of effectively and accurately determining the optimal design of CSDU.