• Journal of the Society of Naval Architects of Korea
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• v.61 no.2
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• pp.115-124
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• 2024

To detect and prevent structural damage caused by various loads on marine structures and ships, structural health monitoring procedure is essential. Estimating loads acting on the structures which are measured by sensors that are mounted properly are crucial for structural health monitoring. However, attaching an excessive number of sensors to the structure without consideration can be inefficient due to the high costs involved and the potential for inducing structural instability. In this study, we introduce a method to determine the optimal number of sensors and their optimized locations for strain measurement sensors, allowing for accurate load estimation throughout the structure using model expansion method. To estimate the loads exerted on the entire structure with minimal sensors, we construct a strain-load interpolation matrix using the strain mode shapes of the finite element (FE) model and select the optimal sensor locations by applying D-Optimal Design and the row exchange algorithm. Finally, we estimate the loads exerted on the entire structure using the model expansion method. To validate the proposed method, we compare the results obtained by applying the optimal sensor placement and model expansion method to an FE model subjected to arbitrary loads with the loads exerted on the entire FE model, demonstrating efficiency and accuracy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.928-933
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• 2008

본 연구에서는 최적 빔포머 (optimal beamformer)를 이용하여, 높은 지향특성을 갖는 라우드스피커 어레이를 구성하였다. 센서 어레이 시스템에 널리 적용되는 빔포밍 방법은 상반성 (reciprocity)의 원리에 의하여 라우드스피커 시스템에도 적용이 가능하다. 음원의 개수 및 배치 간격과 같은 최적 빔포머의 설계 변수와 지향성과의 관계를 살펴보고, 잡음 증폭을 억제하기 위해 적용되는 안정화 계수 (stability factor)도 유용한 설계 변수로 활용하였다. 또한 라우드스피커 자체가 갖는 지향성과 반사와 산란 등을 고려하여 빔포머를 최적화하는 방법을 제안하였고, 이 방법을 통해 예측치와 실제 시스템과의 차이를 줄였다. 실행 예제로 실제 어레이 시스템을 구성하고, 모의 실험과 실제 측정을 수행하여 성능을 확인하였다.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.4
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• pp.341-347
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• 2011

This paper presents the performance evaluation. optimal design. and complex obstacle detection of an overlapped ultrasonic sensor ring by introducing a new concept of effective beam width. It is assumed that a set of ultrasonic sensors of the same type are arranged along a circle of nonzero radius at regular spacings with their beams overlapped. First, the global positional uncertainty of an overlapped ultrasonic sensor ring is expressed by the average value of local positional uncertainty over the entire obstacle detection range. The effective beam width of an overlapped ultrasonic sensor ring is assessed as the beam width of a single ultrasonic sensor having the same amount of global positional uncertainty, from which a normalized obstacle detection performance index is defined. Second. using the defined index, the design parameters of an overlapped ultrasonic sensor ring are optimized for minimal positional uncertainty in obstacle detection. For a given number of ultrasonic sensors, the optimal radius of an overlapped ultrasonic sensor ring is determined, and for a given radius of an overlapped ultrasonic sensor ring, the optimal number of ultrasonic sensors is determined. Third, the decision rules of positional uncertainty zone for multiple obstacle detection are provided based on the inequality relationships among obstacle distances by three adjacent ultrasonic sensors. Using the provided rules, the obstacle outline detection is performed in a rather complex environment consisting of several obstacles of different shapes.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.475-478
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• 2004

본 논문에서는 multistatic 소나망의 효과도 분석을 하였다. 특히 본 논문에서는 multistatic 소나망의 탐지 성능 분석을 통해 효용성을 알아보았다. Multistatic 소나망은 송/수신기가 분리된 일종의 다중 분산 센서 시스템으로, 최적의 탐지 성능을 갖기 위해서는 적절한 융합 규칙 및 센서 배치가 필요하다. 분산 센서 융합 기법으로 bayesian 결정 기법을 기반으로 한 융합 기법을 적용하였으며, 실제 해양 환경하에서의 탐지 성능 분석을 위해 개선된 bistatic 표적 강도 모델과 거리 종속 전송 손실 모델을 이용한 multistatic 소나망 탐지 모델을 제안하였다. 기존 소나망과의 모의 비교 실험을 통해 multistatic 소나망의 우수성을 입증하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.5
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• pp.596-603
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• 2019

A reprogramming operation is necessary to update the software code of the node to change or update the functionality of the deployed node in wireless sensor networks. This paper proposes an optimization algorithm that minimizes the transmission energy of a node for the purpose of reprogramming a node in wireless sensor networks. We also design an algorithm that keeps energy consumption of all nodes balanced in order to maintain the lifetime of the network. In this paper, we propose a Tabu search algorithm with a new neighborhood generation method for minimizing transmission energy and energy consumption in wireless sensor networks with many nodes. The proposed algorithm is designed to obtain optimal results within a reasonable execution time. The performance of the proposed Tabu search algorithm was evaluated in terms of the node's transmission energy, remaining energy, and algorithm execution time. The performance evaluation results showed better performance than the previous methods.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.35-43
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• 2016

Recently, the pipeline system for waste transportation has been increasingly constructed as new solution for the waste collection and disposal system by constantly increasing domestic waste which issued as social problem. The pipeline system is constructed through long distance, so proper long-term monitoring system is necessary which available to detect the damage location for the effective maintenance. In this paper, the experimental study is carried out to evaluate the applicability of optical strain gauge sensor based on FBG for the long-term monitoring system. Three test parameters such as pressure leaking, blockage and deformation are considered as typical damages for real-scale pipeline test specimen. In order to measure flexural and volumetric strain and temperature, three FBG sensors are installed at each monitoring sections. From the test results, this study suggested effective methods of sensor installation and arrangement. Also the sensor spacing for the design of monitoring system using FBG sensor is derived by the correlation of distances from deformation between sensor responses.

• Journal of the Korea Society of Computer and Information
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• v.19 no.11
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• pp.91-96
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• 2014

Since the sensors of Internet of Things (IOT) collect various data, the lifetime of sensor network is very important and the data should be aggregated efficiently. The contiguous collection by the certain sensors occurs an excessive battery consumption and successive transmission of same value of data should be avoided. To solve these things, we propose an weight-based cluster head replacement method that divides whole network into several grids and cluster head is selected by remaining energy, density of alive sensors and location of sensor. The aim of algorithm maximizes the lifetime of network. Our simulation results shows that the proposed method is very simple as well as balances energy consumption.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.5
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• pp.381-389
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• 2014

This study is concerned with the estimation of vibration-field of a cylindrical structure by modal expansion method(MEM). MEM is a technique that identifies modal participation factors using some of vibration signals and natural modes of the structure: The selection of sensor locations has a big influence on predicted vibration results. Therefore, this paper deals with four optimal sensor placement( OSP) methods, EFI, EFI-DPR, EVP, AutoMAC, for the estimation of vibration field. It also finds optimal sensor locations of the cylindrical structure by each OSP method and then performs MEMs. Predicted vibration results compared with reference ones obtained by forced response analysis. The standard deviations of errors between reference and predicted results were also calculated. It is utilized to select the most suitable OSP method for estimation of vibration field of the cylindrical structure.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.5
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• pp.538-547
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• 2015

The goal of this study is to develop an algorithm to propose optimal deployment of detection sensor nodes in the target area, based on a performance surface, which represents detection performance of active and passive acoustic sonar systems. The performance surface of the active detection system is calculated from the azimuthal average of maximum detection ranges, which is estimated with a transmission loss and a reverberation level predicted using ray-based theories. The performance surface of the passive system is calculated using the transmission loss model based on a parabolic equation. The optimization of deployment configurations is then performed by a hybrid method of a virtual force algorithm and a particle swarm optimization. Finally, the effectiveness of deployment configurations is analyzed and discussed with the simulation results obtained using the algorithm proposed in this paper.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.12-19
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• 2020

The clustered heterogeneous wireless sensor network is comprised of sensor nodes and cluster heads, which are hierarchically organized for different objectives. In the network, we should especially take care of managing node resources to enhance network performance based on memory and battery capacity constraints. For instances, if some interesting events occur frequently in the vicinity of particular sensor nodes, those nodes might receive massive amounts of data. Data congestion can happen due to a memory bottleneck or link disconnection at cluster heads because the remaining memory space is filled with those data. In this paper, we utilize drones as mobile sinks to resolve data congestion and model the network, sensor nodes, and cluster heads. We also design a cost function and a congestion indicator to calculate the degree of congestion. Then we propose a data congestion map index and a data congestion mapping scheme to deploy drones at optimal points. Using control variable, we explore the relationship between the degree of congestion and the number of drones to be deployed, as well as the number of drones that must be below a certain degree of congestion and within communication range. Furthermore, we show that our algorithm outperforms previous work by a minimum of 20% in terms of memory overflow.