• Smart Structures and Systems
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• v.30 no.3
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• pp.273-286
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• 2022

In recent years, vision-based monitoring has received great attention. However, structural identification using vision-based displacement measurements is far less established. Especially, simultaneous identification of structural systems and unknown excitation using vision-based displacement measurements is still a challenging task since the unknown excitations do not appear directly in the observation equations. Moreover, measurement accuracy deteriorates over a wider field of view by vision-based monitoring, so, only a portion of the structure is measured instead of targeting a whole structure when using monocular vision. In this paper, the identification of structural system and excitations using vision-based displacement measurements is investigated. It is based on substructure identification approach to treat of problem of limited field of view of vision-based monitoring. For the identification of a target substructure, substructure interaction forces are treated as unknown inputs. A smoothing extended Kalman filter with unknown inputs without direct feedthrough is proposed for the simultaneous identification of substructure and unknown inputs using vision-based displacement measurements. The smoothing makes the identification robust to measurement noises. The proposed algorithm is first validated by the identification of a three-span continuous beam bridge under an impact load. Then, it is investigated by the more difficult identification of a frame and unknown wind excitation. Both examples validate the good performances of the proposed method.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.330-336
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• 2022

This paper proposes a method to calibrate the electrode misplacement in underwater electric field sensor arrays (EFSAs) for accurate measurements of underwater electric field signatures. The electrode misplacement of an EFSA was estimated by measuring the electric field signatures generated by a known electric source and by comparing the measurements with the theoretical calculations under similar measurement conditions. When the EFSA measured the electric field signatures induced by an unknown electric source, the electric properties of the unknown electric source were approximated by considering the optimized estimation of the electrode misplacement of the EFSA. Finally, the measured electric field signatures were calibrated by calculating the theoretical electric field signatures to be measured with an ideally installed EFSA without electrode misplacement; the approximated electric properties of the unknown electric source were also taken into account. Simulations were conducted to test the proposed calibration method. The results showed that the electrode misplacement could be estimated. Further, the electric field measurements and the electric field-based localization of underwater vessels became more accurate after the application of the proposed calibration method. The proposed method will contribute to applications such as the detection and localization of underwater electric sources, which require accurate measurements of underwater electric field signatures.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.3
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• pp.38-44
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• 1995

The scattered electric field from a multilayered circular dielectric cylinder is caculated. Approximate boundary condition used in on-surface radiation boundary condition(OSRC) method has been applied to all the boundary surface of N-layered dielectric cylinder. It was assumed that scattered electric field at inner boundary surface in one region transmitted to the adjacent region at outer boundary surface. In the whole region, the unknown coefficients of electric field are acquired by the given incident electric field with ease. Electric field distribution at each boundary surface and the scattered electric field in free space are taken with the calculated unknown coefficients. the results obtainted were compared with those results that were used by regular surface boundary condition.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2000.11a
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• pp.269-273
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• 2000

This paper proposes a algorithm for several mobile robots navigation. There are three parts in this algorithm. First part generates robots turning angle and moving distance for goal approaching, sencond part generates robots avoiding angle and avoiding distance for static obstacles or other robots and third part adjust between robots moving distance and avoiding distance. Most simulation results of this algorithm are very effective for several mobile robots traveling in unknown field.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1E
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• pp.11-18
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• 2003

Non-singular boundary element method (BEM) codes are developed in acoustics application. The BEM code is then used to calculate unknown boundary surface normal displacements and surface pressures from known exterior near field pressures. And then the calculated surface normal displacements and surface pressures are again applied to the BEM in forward in order to calculate reconstructed field pressures. The initial exterior near field pressures are very well agreed with the later reconstructed field pressures. Only the same number of boundary surface nodes (1178) are used for the initial exterior pressures which are at first calculated by Finite Element Method (FEM) and BEM. Pseudo-inverse technique is, used for the calculation of the unknown boundary surface normal displacements. The structural object is a tuning fork with 128.4 ㎐ resonant. The boundary element is a quadratic hexahedral element (eight nodes per element).

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.3
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• pp.275-284
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• 2006

This paper deals with problems of safe and efficient navigation algorithm for autonomous mobile robots in unknown environments. Since the obstacle avoidance algorithms are very important in mobile robot navigation, two obstacle avoidance algorithms: VFH(vector field histogram) algorithm and a fuzzy algorithm are combined to have optimal performance in various environments. And a upper-level supervisor is to select the proper one from VFH algorithm and the fuzzy algorithm according to the situations the robot faces. Computer simulation results show the effectiveness of the proposed navigation algorithm for autonomous mobile robots.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2003.09a
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• pp.500-503
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• 2003

The navigation problem of robot is one of the main themes to deal with conficts or interferences between obstacles and the robot itself In this case, while the robot avoids obstacles on the space, the passage route should be determined efficiently. In order to solve problems above, we have come up with the distance field space medel (DFM) and then, under known environment, we have presented the distance field A algorithm for passage route path search. In this research, the method of performing the 3-dimensional passage route path search of robot under unknown environment is proposed. It is shown that the authors can build the distance search model the does not need space division by taking into account of sensor information to a distance field space model, and constructing this information as virtual obstacle information.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.306-311
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• 2002

Non-singular boundary element method (BEM) codes are developed in acoustics application. The BEM code is then used to calculate unknown boundary surface normal displacements and surface pressures from known exterior near Held pressures. And then the calculated surface normal displacements and surface pressures are again applied to the BEM in forward in order to calculate reconstructed field pressures. The initial exterior near field pressures are very well agreed with the later reconstructed field pressures. Only the same number of boundary surface nodes (1178) are used far the initial exterior pressures which are initially calculated by Finite Element Method (FEM) and BEM. Pseudo-inverse technique is used for the calculation of the unknown boundary surface normal displacements. The structural object is a tuning fork with 128.4 Hz resonant. The boundary element is a quadratic hexahedral element (eight nodes per element).

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.378-380
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• 2009

For the autonomous movement, the optimal pat]1 planning connecting between current and target positions is essential, and the optimal path of mobile robot means obstacle-free and the shortest length path to a target position. Many actual mobile robots should move without any information of surrounded obstacles. This paper suggests a new method of obstacle avoidment which is suitable in unknown environments. This method of obstacle avoidance is designed with a distributed fuzzy control system, and imitates a Potential Field method. A simulation confirms the performance and correctness of the obstacle avoidance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.2
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• pp.161-167
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• 1999

There is an increasing need for the estimation of foundation piles whose depths are unknown. Especially in repair and reinforcement works or in safety inspection and assessment to the big structures whose foundations are piles, the accurate information about the depth of foundation piles is one of the most important factors. A borehole magnetic tool has been developed and tested to meet this object. The fundamental base is that there usually exist many re-bars inside the foundation structure such as piles, and these re-bars are ferromagnetic materials which cause strong induced magnetic field comparable to the earth magnetic field. It utilizes flux-gate type magnetometer which measures 3-components of the magnetic field. Taking vertical derivatives of vertical component of the measured magnetic field, we can expect the error limit of estimating the depth of the pile end less than 20 cm in favorable condition. The maximum measurable distance is about 3 m to the pile from the borehole. The field data show that borehole magnetics is one of the most accurate, fast, and reliable methods for this object so far, as long as there is no magnetic materials such as deep located steel pipe or power cables close to the foundation piles.