• Tribology and Lubricants
• /
• v.30 no.1
• /
• pp.9-14
• /
• 2014

In this Part II study, rotordynamic stability analyses were carried out to confirm improvements to the stability of a process high-speed lightweight centrifugal compressor, depending on the effects of tilting pad journal bearing designs. The bearing design variables considered were the clearances, LBPs, LOPs, and preloads. The results showed that the rotordynamic stability of the subject compressor rotor-bearing system improves exactly in accordance with the effects of the bearing design variables, which were determined in the preceding Part I study, owing to reduced bearing stiffnesses. Specifically, it was confirmed that the stability of the rotor system can be greatly improved by increasing both the machined and assembled bearing clearances, but there were no stability improvements by simply changing from an LBP to an LOP design. In addition, it was confirmed that for given fixed machined bearing clearances, the stability can be additionally improved by decreasing the preloads, i.e., by increasing the assembled clearances. In conclusion, it may be necessary to improve the designs of the original tilting pad bearings to obtain a sufficient margin of rotordynamic stability against a possible aerodynamic cross-coupled stiffness in a process high-speed centrifugal compressor. Thus, increasing the machined and assembled bearing clearances and decreasing the preload could be effective solutions.

• Steel and Composite Structures
• /
• v.18 no.1
• /
• pp.273-288
• /
• 2015

As one of the most common failure types of arch bridges, stability is one of the critical aspects for the design of arch bridges. Using 3D finite element model in ABAQUS, this paper has studied the stability performance of an arch bridge with inclined arch ribs and hangers, and the analysis also took the effects of geometrical and material nonlinearity into account. The impact of local buckling and residual stress of steel plates on global stability and the applicability of fiber model in stability analysis for steel arch bridges were also investigated. The results demonstrate an excellent stability of the arch bridge because of the transverse constraint provided by transversely-inclined hangers. The distortion of cross section, local buckling and residual stress of ribs has an insignificant effect on the stability of the structure, and the accurate ultimate strength may be obtained from a fiber model analysis. This study also shows that the yielding of the arch ribs has a significant impact on the ultimate capacity of the structure, and the bearing capacity may also be approximately estimated by the initial yield strength of the arch rib.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.5 no.4
• /
• pp.598-613
• /
• 2013

This paper deals with the dynamic effect of pipeline installation and embedment for the on-bottom stability design of offshore pipelines on soft clay. On-bottom stability analysis of offshore pipelines on soft clay by DNV-RP-F109 (DNV, 2010) results in very unreasonable pipe embedment and concrete coating thickness. Thus, a new procedure of the on-bottom stability analysis was established considering dynamic effects of pipeline installation and pipe-soil interaction at touchdown point (TDP). This analysis procedure is composed of three steps: global pipeline installation analysis, local analysis at TDP, modified on-bottom stability analysis using DNV-RP-F109. Data obtained from the dynamic pipeline installation analysis were utilized for the finite element analysis (FEA) of the pipeline embedment using the non-linear soil property. From the analysis results of the proposed procedure, an optimum design of on-bottom stability of offshore pipeline on soft clay can be achieved. This procedure and result will be useful to assess the on-bottom stability analysis of offshore pipelines on soft clay. The analysis results were justified by an offshore field inspection.

• Geomechanics and Engineering
• /
• v.17 no.2
• /
• pp.181-194
• /
• 2019

Due to the seepage of groundwater, the resisting force of slopes decreases and the sliding force increases, resulting in significantly reduced slope stability. The instability of most natural slopes is closely related to the influence of groundwater. Therefore, it is important to study slope stability under groundwater seepage conditions. Thus, using a simplified seepage model of groundwater combined with the analysis of stresses on the slip surface, the limit equilibrium (LE) analytical solutions for two- and three-dimensional slope stability under groundwater seepage are deduced in this work. Meanwhile, the general nonlinear Mohr-Coulomb (M-C) strength criterion is adopted to describe the shear failure of a slope. By comparing the results with the traditional LE methods on slope examples, the feasibility of the proposed method is verified. In contrast to traditional LE methods, the proposed method is more suitable for analyzing slope stability under complex conditions. In addition, to facilitate the optimization of drainage design in the slope, stability charts are drawn for slopes with different groundwater tables. Furthermore, the study concluded that: (1) when the hydraulic gradient of groundwater is small, the effect on slope stability is also small for a change in the groundwater table; and (2) compared with a slope without a groundwater table, a slope with a groundwater table has a larger failure range under groundwater seepage.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.5
• /
• pp.157-170
• /
• 1999

A new design technique is presented to stabilize cut slopes in cohesive soils by use of piles. The design method can consider systematically factors such as the gradient and height of slope, the number and position of pile's rows, the interval and stiffness of piles, etc. The design method is established on the basis of the stability analysis of slope with rows of piles. The basic concept applied in the stability analysis is that the soil across the open space between piles can be retained by the arching action of the soil, when a row of piles is installed in soil undergoing lateral movement such as landslides. To obtain the whole stability of slope containing piles, two kinds of analyses for the pile-stability and the slope- stability must be performed simultaneously. An instrumentation system has been installed at a cut slope in cohesive soil, which has been designed according to the presented design process. The behavior of both the piles and the soil across the open space between piles is observed precisely. The result of instrumentation shows that the cut slope has been stabilized by the contribution of stabilizing effect of piles on the slope stability in cohesive soil.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.7 no.3
• /
• pp.72-80
• /
• 1997

A new design method for Takagi-Sugeno (T-S in short) fuzzy controller which guarantees global asymptotic stability and satisfies a desired performance is proposed in this paper. The method uses LMI(Linear Matrix Inequality) approach to find the common symmetric positive definite matrix P and feedback fains K/sub i/, i= 1, 2,..., r, numerically. The LMIs for stability criterion which treats P and K'/sub i/s as matrix variables is derived from Wang et al.'s stability criterion. Wang et al.'s stability criterion is nonlinear MIs since P and K'/sub i/s are coupled together. The desired performance is represented as $ LMIs which place the closed-loop poles of $ local subsystems within the desired region in s-plane. By solving the stability LMIs and pole placement constraint LMIs simultaneously, the feedback gains K'/sub i/s which gurarntee global asymptotic stability and satisfy the desired performance are determined. The design method is verified by designing a T-S fuzzy controller for an inverted pendulum with a cart using the proposed method.

• Journal of Ocean Engineering and Technology
• /
• v.17 no.6
• /
• pp.23-31
• /
• 2003

As there are so many uncertainties associated with using the determinism analysis method in the design of rubble mound breakwater, it is impossible for a designed construction to provide ultimate stability. First of all, due to the uncertainty of Load and Resistance, a safety level concerning the destruction mode of construction must be given. Then, the optimization design should be processed. After all, we can say that it is a more reasonable design method than the design used by the stability rate. In this study, an established design process is accomplished using Hudson's equation and an economic analysis with the breakwater's section is also conducted. Hudson's equation is compared to Van der Meer's equation. These results are utilized to drop a damage rate, increase the stability of construction, and determine the optimization section of the breakwater.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1425-1429
• /
• 2003

In this study, when structure which is combined by welding is receiving internal pressure, finite element analysis to confirm stability of structure and reliability of welding part is achieved. And we analyze the results. Also, if stability of the structure and reliability of the welding part are not defined, research that look for method to change design to receive stability and reliability is achieved.

• Journal of Korean Society of Steel Construction
• /
• v.18 no.2
• /
• pp.225-237
• /
• 2006

Based on the study conducted by Kim et al. (205a, b), an improved stability design method for evaluating the effective buckling lengths of beam-column members is proposed herein, using system elastic/inelastic buckling analysis and second-order elastic analysis. For this purpose, the stress-strain relationship of a column is inversely formulated from the reference load-carrying capacity proposed in design codes, so as to derive the tangent modulus of a column as a function of the slenderness ratio. The tangent stiffness matrix of a beam-column element is formulated using the so-called "stability functions," and elastic/inelastic buckling analysis Effective buckling lengths are then evaluated by extending the basic concept of a single simply-supported column to the individual members as one component of a whole frame structure. Through numerical examples of several structural systems and loading conditions, the possibilities of enhancement in stability design for frame structures are addressed by comparing their numerical results obtained when the present design method is used with those obtained when conventional stability design methods are used.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.8 no.2
• /
• pp.165-172
• /
• 2003

In this paper, the new robust current control scheme is proposed for an Induction motor. The proposed design scheme of current controller tan obtain a specified stability margin through electrical parameter variation by using Kharitonov robust stability theory. The characteristics of the proposed design scheme are compared with those of a conventional scheme by computer simulation and its effectiveness and usefulness is verified by experiments on the 0.75kW induction motor drive.