Ai-Kah Soh

KBase: a customizable tool for building Dbase-compatible knowledge-based systems

Abstract KBase is a customizable development tool for building knowledge-based systems that are compatible with DBase III tables. Currently, most tools for developing knowledge-based systems do not integrate well with databases. DBase III is the most common database system used in the personal computer environment. KBase is built such that all DBase III commands and functions are supported. Furthermore, customizing and extending KBase is as easy as programming in DBase. This flexibility arises because KBase is built using the “C” programming language and Clipper, a DBase compiler. Using Clipper also allows KBase to use many functions in the Clipper library. In this paper, we describe how KBases design is conceived. At the end, we also give a brief tour of the program with an implemented example to illustrate its application.

A parametric stress analysis of T/Y and K square-to-square tubular joints

Abstract A parametric stress analysis of T/Y and K square-to-square tubular joints subjected to axial loads, in-plane and out-of-plane bending moments has been performed using the finite element technique. Twenty-two and 26 sets of geometric parameters were used for the study of T/Y and K joints respectively. This study was carried out with the purpose of providing a sound basis for using square tubular sections in the alternative design of conductor guides which are important items of a drilling platform. The results of this analysis are presented as a set of 21 equations expressing the stress concentration factor as a function of the relevant geometric parameters for various loading conditions. The present results for square-to-square tubular joints are compared with others obtained for round-to-round and square-to-round tubular joints. In general, the stress concentration factors obtained from round-to-round and square-to-round tubular joints are closer, compared with those of the corresponding square-to-square tubular joints.

Behaviour of tubular T-joints subjected to combined loadings

Abstract A large-scale test rig was specially designed and built to study the behaviour of tubular joints subject to combined loadings. A round-to-round tubular T-joint was subjected to axial load, in-plane bending, out-of-plane bending and combinations of the three load cases. The study reveals that the peak hot spot position on the T-joint under combined loads shifts in location from that of the basic load cases. The study also shows that the peak hot spot stress under combined loads was underpredicted by superposition of basic load cases in some instances. Comparison with existing combined hot spot procedures reveals that some existing procedures are inadequate for predicting the peak hot spot stress of tubular T-joints.

Stress analysis of axially loaded T tubular joints reinforced with doubler plates

Abstract Reinforcing tubular joints using doubler plates has been a common industrial practice as a last minute solution to resolve punching shear problems due to axial compression. However, such reinforcements may have negative effects when the joints are subject to different loading conditions. A parametric stress analysis of T reinforced welded round-to-round tubular joints subjected to axial tension has been performed using the finite element technique. Sixteen sets of geometric parameters were used for the parametric study by varying three parameters, namely, doubler plate to chord thickness ratio, t p T , brace diameter to doubler plate length (width) ratio, d l p , and brace to doubler plate thickness ratio, t t p . The said study shows that t p T and t t p have significant effects on stress concentration factors but not d l p . The present results for T reinforced tubular joints are compared with those for the corresponding unreinforced joints obtained by the authors and other researchers. In general, the reinforced joints are as good as the corresponding unreinforced joints in withstanding axial tensioning, provided that certain criteria for the selection of doubler plates are adopted.

‘Hot spot’ stresses of K tubular joints subjected to combined loadings

Abstract An approach has been proposed to verify, and modify if necessary, the conventional method for determining the peak ‘hot spot’ stresses of various configurations of tubular joints subjected to combined loadings. A typical K tubular joint, which was subjected to various loading conditions, was employed to illustrate the proposed approach. It is found that the accuracy of the peak ‘hot spot’ stresses estimated by the conventional method for combined loadings are closely related to the types of loading condition involved. This is due to the possible change in peak stress locations and directions when various basic load types are combined. The peak ‘hot spot’ stresses of some combined loadings are significantly over estimated by the conventional method and, thus, can be reduced in order to provide accurate data for fatigue analysis.Abstract An approach has been proposed to verify, and modify if necessary, the conventional method for determining the peak ‘hot spot’ stresses of various configurations of tubular joints subjected to combined loadings. A typical K tubular joint, which was subjected to various loading conditions, was employed to illustrate the proposed approach. It is found that the accuracy of the peak ‘hot spot’ stresses estimated by the conventional method for combined loadings are closely related to the types of loading condition involved. This is due to the possible change in peak stress locations and directions when various basic load types are combined. The peak ‘hot spot’ stresses of some combined loadings are significantly over estimated by the conventional method and, thus, can be reduced in order to provide accurate data for fatigue analysis.

SCF equations for DT/X square-to-round tubular joints

Abstract A parametric stress analysis of DT/X square-to-round tubular joints subjected to axial loads and in-plane and out-of-plane bending moments has been performed using the finite element technique in order to provide a sound basis for using such sections in the design of complex structures. The results of this analysis are presented as a set of equations expressing the stress concentration factor as a function of the relevant geometric parameters for various loading conditions. A comparison is made between the results obtained for square-to-round tubular joints and those obtained for round-to-round tubular joints by other researchers. In general, the stress concentration factors for square-to-round tubular joints are generally lower than those of the corresponding round-to-round tubular joints when the joints are subject to axial loads and out-of-plane bending moments. But the reverse is true when the joints are subject to in-plane bending moments.

ON THE COMPATIBILITY CONDITIONS FOR MODELING TUBULAR JOINTS USING DIFFERENT TYPES OF ELEMENTS

Abstract It has been a common practice to model an offshore tubular joint using three-dimensional brick elements for the brace/chord intersection region, including the weldment, and shell elements for the rest of the joint, instead of using only three-dimensional brick elements. This is to ensure that the model size is manageable for performing parametric studies. However, it is an extremely tedious procedure to implement the necessary and sufficient compatibility conditions at all nodes lying on the interface between brick and shell elements. An investigation has been carried out to examine the effects of partial relaxation of compatibility conditions on the location and magnitude of hot spot stresses at the brace/chord intersection. Results obtained have shown that, as long as the compatibility conditions at the shell loof nodes were implemented, the hot spot stresses obtained would be reasonably accurate. It was also found that using three or more rows of brick elements after the weld toe will ensure better accuracy of results.

Subassemblage with semi-rigid joint

The finite element technique is employed to analyse and perform a parametric study on cold-formed thin-walled column subassemblage with a semi-rigid joint. Besides large displacement, the analysis also considers the area of contact between the fastener, connector and the member in the vicinity of the joint. Results obtained from a series of preliminary experimental tests are used to verify and validate the accuracy of the analysis.

Elimination of self-straining in four-noded plate elements for large deflection analysis

Abstract A method has been proposed to solve the self-straining problem of four-noded plate elements by analysing large deflection problems. The results obtained by the proposed method for a test example are found to be in good agreement with those of the exact solution.

Using meta-level knowledge in the design of offshore structures

Abstract The design of offshore structures is a complex iterative process involving a very diversified range and depth of knowledge. A major portion of this knowledge is factual and algorithmic in nature. Yet, as in other engineering design, the creativity and success of design is possible only through the extensive experience of the designers, utilizing this factual and algorithmic knowledge. This generally heuristic and non-algorithmic experience forms a relatively small proportion of the knowledge used in design. A usable knowledge-based engineering system for the design of offshore structures must be able to operate quickly enough, without any deterioration in the quality of the solutions. The ‘number crunching’ involved in the factual and algorithmic knowledge quickly leads to a combinatorial explosion. We need to use the heuristic knowledge to rapidly reduce the many possibilities in design. In this way, a usable system which uses multi-level reasoning about a huge volume of diversified knowledge can be constructed. In this paper, we examine the feasibility of using meta-level knowledge to swiftly narrow the search for quality designs. We describe a system, IPDOJS ( I nteractive P reliminary D esign of O ffshore J acket S tructures), to illustrate the use of such metal-level knowledge.