• Structural Engineering and Mechanics
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• v.39 no.1
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• pp.147-168
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• 2011

To ensure safety and long term performance, structural control has rapidly matured over the past decade into a viable means of limiting structural responses to strong winds and earthquakes. Nonlinear response history analysis requires rigorous procedure to compute seismic demands. Therefore the simplified nonlinear analysis procedures are useful to determine performance of the structure. In this investigation, application of improved capacity demand diagram method in the control of structural system is presented for the first time. Developed pole assignment method (DPAM) in structural systems control is introduced. Genetic algorithm (GA) is employed as an optimization tool for minimizing a target function that defines values of coefficient matrices providing the placement of actuators and optimal control forces. The ground acceleration is modified under induced control forces. Due to this, performance of structure based on improved nonlinear demand diagram is selected to threshold of nonlinear behavior of structure. With small energy consumption characteristics, semi-active devices are especially attractive solutions for limiting earthquake effects. To illustrate the efficiency of DPAM, a 30-story steel moment frame structure employing the semi-active control devices is applied. In comparison to the widely used linear quadratic regulation (LQR), the DPAM controller was shown to be just as effective and better in the reduction of structural responses during large earthquakes.

• Journal of Industrial Technology
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• v.17
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• pp.323-330
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• 1997

In this paper, a new approach to modeling of nonlinear systems using fuzzy theory is presented. To express the various and complex behavior of nonlinear system, we combine multiple model method with hierachical prioritized structure, and the mountain clustering technique is used in partitioning of system. TSK rule structure is adopted to form the fuzzy rules, and Back propagation algorithm is used for learning parameters in consequent parts of the rules. Also we soften the paradigm of Mamdani's inference mechanism by using Yager's S-OWA operators. Computer simulations are performed to verify the effectiveness of the proposed method.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1996.10a
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• pp.302-305
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• 1996

In this paper, an optimal identification method using fuzzy-neural networks is proposed for modeling of nonlinear complex systems. The proposed fuzzy-neural modeling implements system structure and parameter identification using the intelligent schemes together with optimization theory, linguistic fuzzy implication rules, and neural networks(NNs) from input and output data of processes. Inference type for this fuzzy-neural modeling is presented as simplified inference. To obtain optimal model, the learning rates and momentum coefficients of fuzz-neural networks(FNNs) and parameters of membership function are tuned using genetic algorithm(GAs). For the purpose of its application to nonlinear processes, data for route choice of traffic problems and those for activated sludge process of sewage treatment system are used for the purpose of evaluating the performance of the proposed fuzzy-neural network modeling. The show that the proposed method can produce the intelligence model w th higher accuracy than other works achieved previously.

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.356-358
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• 1994

In this paper, to alleviate the effect of approximation error and discontinuous variation of the controller parameters, the variable structure control scheme using neural networks is presented. In the proposed method, the variable structure control rules for each local linear models are designed to reject the effect of linearization error caused by linearization of the nonlinear system. And neural network infer approximate controller gains from combination of local linear control gains. The proposed control methods can be used to control nonlinear systems and it has robust characteristic against system parameter variations and external disturbances.

• Earthquakes and Structures
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• v.14 no.5
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• pp.459-465
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• 2018

Reducing response of buildings during earthquakes by mass dampers, has been examined in many articles and books. Nowadays, many researchers are trying to realistically examine this type of dampers by new methods of performance. In this paper, for the better study of tuned mass damper (TMD), two schematic models are presented for a passive TMD with softening stiffness (softening TMD) and a passive TMD with hardening stiffness (hardening TMD). Then by modeling and analysis of the damper on a single degree of freedom (SDOF) structure and an 11-story steel building, the dampers performance was evaluated. State space was used for damper and structure modeling and to solve nonlinear equations, the Newton-Raphson method was used. The results show that when the structure is subjected to the Chi-Chi earthquake, response of the sixth floor in the system without TMD reduces 54.0% in comparison to the structure with softening TMD. This percentage of reduction for hardening TMD is 55.0%. Also for the Tabas earthquake, reduction in the RMS acceleration of the sixth floor in the system with hardening TMD is 96.2% more than the structure without TMD. This percentage of reduction for hardening TMD is 96.3%.

• Journal of Korean Association for Spatial Structures
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• v.9 no.2
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• pp.91-97
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• 2009

This study presents geometric nonlinear and material analysis of under-tension structure using Total Lagrangian and Updated Lagrangian method. In the regard, the under-tension system enables the load of upper part to carry to the end of beam by pre-tensional force in cable. The under-tension system on lower part of the structure is applied in order to reduce the deflection and size of member. This study is performed with conforming of the effect by pretension value in the cable and applying loading. Dead and Live loads are supposed to apply nodal on the top member. The member force and deflection of the structure are with MIDAS and ADINA.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.52-54
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• 1996

A number of algorithm using the VSS(Variable Structure System) for uncertain dynamic system are developed. But, in these algorithms, the assumption that the uncertainties are bounded and their bounds are available to the designer is involved. And bounds on the uncertainties are an important clue to guarantee the stability of the closed loop system. However, sometimes bounds on the uncertainties may not be easily obtained because of the complexity of the structure of the uncertainties. Therefore, a methodology by which the boundary values on the uncertainties can be easily obtained is required. The VSS proposed in this proposal employ the new adaptive VSS scheme for uncertain dynamic system being estimated on line. The resulting control law is simple and easy to apply to on line computer control. It can also suppress chattering and maintain good tracking precision even if unmodeled dynamics are considered. And, a new method using nonlinear switching surface is introduced so that the speed response is improved and the good transient response can be obtained. Simulation results are presented and show the advantage of the proposed adaptive VSS with nonlinear switching surfaces.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.1985-1996
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• 1994

A new design method of sliding hyperplanes is proposed in the synthesis of a variable structure controller for robust tracking of general nonlinear multi-input-output(MIMO) uncertain systems of relative degree higher than two. Input/ output(I/O) linearzation is firstly undertaken by employing the concept of relative degree and minimum phase followed by the construction of sliding mode controllers. Sliding hyperplanes are then derived from the inherent properties of companion matrix and ideal sliding mode characterized in I/O linearized system. Subsequently, the gradient magnitudes of the sling hyperplanes are determined in an optimal manner by considering a quadratic performance index to be evaluated at two phases; a reaching phase and a sliding phase. The proposed design methodology is relatively straightforward and systematic compared with conventional strategies such as geometric approach or pole assignment technique. A nonlinear governor and exciter control problem for a power system is adopted herein in order to demonstrate the design efficiency and also favorable and robust control performances.

• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.19-30
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• 1998

In this paper, the dynamic analysis of a dolphin system for mooring a floating structure such as barge mounted plant is studied. The characteristics of the soil-pile system are simplified by a set of equivalent spring elements at the mudline. To evaluate the equivalent spring constants, the finite difference method is used. Since the characteristics of the soil-pile system are nonlinear in case of soft foundation, the nonlinear dynamic analysis technique is needed. The Newmark $beta$ method incorporating the modified Newton-Raphson method(initial stiffness method) is used. A numerical analysis is performed on two mooring dolphin systems on soft foundation and rock foundation. In case of the rock foundation, the characteristics are found to be nearly linear, so the linear dynamic analysis may be sufficient to consider the foundation effect. But in case of soft foundation, the non-linearity of the foundation appears to be very signigicant, so the nonlinear dynamic analysis si needed.

• Smart Structures and Systems
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• v.18 no.6
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• pp.1251-1267
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• 2016

In this paper, Simple Adaptive Control (SAC) is used to enhance the seismic response of nonlinear tall buildings based on acceleration feedback. Semi-active MR dampers are employed as control actuator due to their reliability and well-known dynamic models. Acceleration feedback is used because of availability, cost-efficiency and reliable measurements of acceleration sensors. However, using acceleration feedback in the control loop causes the structure not to apparently meet some requirements of the SAC algorithm. In addition to defining an appropriate SAC reference model and using inherently stable MR dampers, a modification in the original structure of the SAC is proposed in order to improve its adaptability to the situation in which the plant does not satisfy the algorithm's stability requirements. To investigate the performance of the developed control system, a numerical study is conducted on the benchmark 20-story nonlinear building and the responses of the SAC-controlled structure are compared to an $H_2/LQG$ clipped-optimal controller under the effect of different seismic excitations. As indicated by the results, SAC controller effectively reduces the story drifts and hence the seismically-induced damage throughout the structural members despite its simplicity, independence of structural parameters and while using fewer number of dampers in contrast with the $H_2/LQG$ clipped-optimal controller.