• Smart Structures and Systems
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• v.21 no.6
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• pp.715-725
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• 2018

Truss-Z (TZ) is an Extremely Modular System (EMS). Such systems allow for creation of structurally sound free-form structures, are comprised of as few types of modules as possible, and are not constrained by a regular tessellation of space. Their objective is to create spatial structures in given environments connecting given terminals without self-intersections and obstacle-intersections. TZ is a skeletal modular system for creating free-form pedestrian ramps and ramp networks. The previous research on TZ focused on global discrete geometric optimization of the spatial configuration of modules. This paper reports on the first attempts at structural optimization of the module for a single-branch TZ. The internal topology and the sizing of module beams are subject to optimization. An important challenge is that the module is to be universal: it must be designed for the worst case scenario, as defined by the module position within a TZ branch and the geometric configuration of the branch itself. There are four variations of each module, and the number of unique TZ configurations grows exponentially with the branch length. The aim is to obtain minimum-mass modules with the von Mises equivalent stress constrained under certain design load. The resulting modules are further evaluated also in terms of the typical structural criterion of compliance.

• Earthquakes and Structures
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• v.23 no.1
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• pp.87-100
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• 2022

Limiting the displacement of seismic isolators causes a pounding phenomenon under severe earthquakes. Therefore, the ASCE 7-16 has provided minimum criteria for the design of the isolated building. In this research the seismic response of isolated buildings by Triple Friction Pendulum Isolator (TFPI) under the impact, expected, and unexpected mass eccentricity was evaluated. Also, the effect of different design parameters on the seismic behavior of structural and nonstructural elements was found. For this, a special steel moment frame structure with a surrounding moat wall was designed according to the criteria, by considering different response modification coefficients (RI), and 20% mass eccentricity in one direction. Then, different values of these parameters and the damping of the base isolation were evaluated. The results show that the structural elements have acceptable behavior after impact, but the nonstructural components are placed in a moderate damage range after impact and the used improved methods could not ameliorate the level of damage. The reduction in the RI and the enhancement of the isolator's damping are beneficial up to a certain point for improving the seismic response after impact. The moat wall reduces torque and maximum absolute acceleration (MAA) due to unexpected enhancement of mass eccentricity. However, drifts of some stories increase. Also, the difference between the response of story drift by expected and unexpected mass eccentricity is less. This indicates that the minimum requirement displacement according to ASCE 7-16 criteria lead to acceptable results under the unexpected enhancement of mass eccentricity.

• Journal of Aerospace System Engineering
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• v.8 no.1
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• pp.12-17
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• 2014

In this paper, optimal design of composite rotor blade cross-section to consider manufacturability was performed. Skin thickness, torsion box thickness and skin lay-up angle were adopted as discrete design variables and The position and width of a torsion box were considered as continuous variables. An object function of optimal design is to minimize the mass of a rotor blade, and various constraints such as failure index, center mass, shear center, natural frequency and blade minimum mass per unit length were adopted. Finally, design variables such as the thickness and lay-up angles of a skin, and the thickness, position and width of a torsion box were determined by using an in-house program developed for the optimal design of rotor blade cross-section.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.2
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• pp.7-14
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• 2013

In this paper, the optimal design of composite rotor blade cross-section is performed using a genetic algorithm. Skin thickness, torsion box thickness and skin lay-up angle are adopted as discrete design variables. The position and width of a torsion box are considered as continuous variables. An object function of optimal design is to minimize the mass of a rotor blade, and constraints are failure index, center mass, natural frequency and blade minimum mass per unit length. Finally, design variables such as the thickness and lay-up angles of a skin, and the thickness, position and width of a torsion box are determined by using an in-house program developed for the optimal design of rotor blade cross-section.

• Structural Engineering and Mechanics
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• v.62 no.1
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• pp.55-64
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• 2017

An effective design approach for Multiple Tuned Mass Dampers (MTMDs) in pedestrian bridges was proposed by utilizing the transfer function to obtain each TMD's optimum stiffness and damping. A systematic simulation of pedestrian excitations was described. The motion equation of a typical MTMD system attached to a Multi-degree-of-freedom (MDOF) system was presented, and the transfer function from the input pedestrian excitations to the output acceleration responses was defined. By solving the minimum norm of the transfer function, the parameters of the MTMD which resulted in the minimum overall responses can be obtained. Two applications of lightly damped pedestrian bridges attached with MTMD showed that MTMDs designed through this method can significantly reduce the structural responses when subjected to pedestrian excitations, and the vibration control effects were better than the MTMD when it was considered as being composed of equal number and mass ratios of TMDs designed by classical Den Hartog method.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.39-45
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• 2022

Normal strategy of structure optimization procedure has been minimum cost or weight design. Minimum weight design satisfying an allowable stress has been used for the ship and offshore structure, but minimum cost design could be used for the case of high human cost. Natural frequency analysis and forced vibration one have been used for the strength estimation of marine structures. For the case of high precision experiment facilities in marine field, the structure has normally enough margin in allowable stress aspect and sometimes needs high natural frequency of structure to obtain very high precise experiment results. It is not easy to obtain a structure design with high natural frequency, since the natural frequency depend on the stiffness to mass ratio of the structure and increase of structural stiffness ordinary accompanies the increase of mass. It is further difficult at the grillage structure design using the profiles, because the properties of profiles are not continuous but discrete, and resource of profiles are limited at the design of grillage structure. In this paper, the grillage structure design system under the constraint of high natural frequency is introduced. The design system adopted genetic algorithm to realize optimization procedure and can be used at the design of the experimental facilities of marine field such as a towing carriage, PMM, test frame, measuring frame and rotating arm.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.2
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• pp.130-134
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• 2011

This study aims at the structural safety with optimum design of automotive bumper in order to minimize the maximum stress and displacement and reduce the minimum quantity of bumper material. As the forces of X and Y direction increase, equivalent stress and displacement increase. The displacement of X direction force increases more than 20% in comparison with Y direction force. But the equivalent stress of Y direction force increases more than 60% in comparison with X direction force. The mass of inner bumper becomes minimum and the mass of outer bumper becomes maximum when the force of 4000N is applied on the direction inclined at $45^{\circ}$ toward outer bumper. In 50% range of increase and decrease at X and Y direction force, the optimum forces of X and Y component becomes 2368.8N and 1538.8N respectively. And the masses of inner and outer polypropylene bumper become $3.3227{\times}10^{-2}kg$and $3.5538{\times}10^{-2}kg$respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.275-283
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• 2013

In this paper, the structural optimum design method of composite rotor blade cross-section was investigated with the genetic algorithm. An auto-mesh generation program was developed for iterative calculations of optimum design, and stresses in the blade cross-section were analyzed by VABS (variational asymptotic beam sectional analysis) program. Minimum mass of rotor blade was defined as an object function, and stress failure index, center mass and blade minimum mass per unit length were chosen as constraints. Finally, design parameters such as the thickness and layup angles of a skin, and the thickness, position and width of a torsion box were determined through the structural optimum design method of composite rotor blade cross-section presented in this paper.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1834-1847
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• 2006

A robust minimum-time control (RMTC) strategy is addressed and it is extended to the dual-stage servo design. Rather than conventional switching type sub-optimal controls, it is a reference following control approach where the predetermined minimum-time trajectory (MTT) is tracked by the perturbation compensator based feedback controller. First, the minimum-time trajectory for a mass-damper system is derived. Then, the perturbation compensator to achieve robust tracking performance in spite of model uncertainty and external disturbance is suggested. The RMTC is also applied to the dual-stage positioner which consists of coarse actuator and fine one. To best utilize the actuation redundancy of the dual-stage mechanism, a null-motion controller to actively regulate the relative motion between the two stages is formulated. The performance of RMTC is validated through simulation and experiment.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.3
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• pp.357-363
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• 2022

In this study, in order to develop an non-slip metal grating, the stability of the grating according to the span of the grating and the gap and height of the bearing bar was evaluated. The optimal shape design of the grating was performed using the results of determining the stability of the grating. The purpose of this study is to determine the stability according to the spacing and height of the bearing bar by applying the design pressure at the design stage to develop the anti-skid grating, and to design the optimal shape for cost reduction. In the optimal design, the target variable was set as the mass, and the optimal design of the grating was performed based on about 20%. Regardless of the height of the bearing bar of the grating, the stress and deformation of the span and the grating showed a proportional tendency to each other, and it was found that the stress decreased as the height of the bearing bar increased. Based on the structural analysis results, an optimal design was performed using mass as the objective variable, and the existing 2mm thickness was changed to 1.6mm, reducing the mass by about 19%. The stress increased by about 4.4% compared to the maximum stress of the existing grating, but the minimum safety factor was 3.1, indicating that the optimally designed grating was stable.