• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.7
• /
• pp.723-731
• /
• 2016

A core technological base to provide enhanced data rates required by 5G mobile wireless communications is the improved bandwidth efficiency using massive multiple-input multiple-output (MIMO) transmission. MIMO transmission requires the channel estimation using the channel state information reference signaling (CSI-RS) and appropriate beamforming, thus the design of the codebook defining proper beamforming vectors is an important issue. In this paper, we propose a multi-rank codebook based on the discrete Fourier transform (DFT) matrix, by utilizing statistical properties of the channel generated by the spatial channel model (SCM). The proposed method includes a structural change of the precoding matrix indicator (PMI) by considering the phase difference distributions between adjacent antenna elements, as well as the selected codevector characteristics of each transmission layer. Performance gain of the proposed method is evaluated and verified by making the performance comparison to the 3GPP standard codebooks adopted by Long-Term Evolution (LTE) systems.

• Tunnel and Underground Space
• /
• v.25 no.2
• /
• pp.115-124
• /
• 2015

Thermal energy storage (TES) is a technology that stores surplus thermal energy at high or low temperatures for later use when the customer needs it, not just when it is available. TES systems can help balance energy demand and supply and thus improve the overall efficiency of energy systems. Furthermore, the conversion and storage of intermittent renewable resources in the form of thermal energy can help increase the share of renewable resources in the energy mix which refers to the distribution of energy consumption from different sources, and to achieve this, it is essential to combine renewable resources with TES systems. Underground TES using rock caverns, known as cavern thermal energy storage (CTES), is a viable option for large-scale, long-term TES utilization although its applications are limited because of the high construction costs. Furthermore, the heat loss in CTES can significantly be reduced due to the heating of the surrounding rock occurred during long-term TES, which is a distinctive advantage over aboveground TES, in which the heat loss to the surroundings is significantly influenced by climate conditions. In this paper, we introduced important factors that should be considered in the shape and multiple layout design of TES caverns, and proposed guidelines for storage space design.

• Smart Structures and Systems
• /
• v.17 no.6
• /
• pp.981-994
• /
• 2016

Two field research stations based upon atmospheric corrosivity monitoring combined with reinforced concrete corrosion rate sensors have been established in Kuwait. This was established for the purpose of remote monitoring of building materials performance for concrete under Kuwait atmospheric environment. The two field research sites for concrete have been based upon an outcome from a research investigation intended for monitoring the atmospheric corrosivity from weathering station distributed in eight areas, and in different regions in Kuwait. Data on corrosivity measurements are essential for the development of specification of an optimized corrosion resistance system for reinforced concrete manufactured products. This study aims to optimize, characterize, and utilize long-term concrete structural health monitoring through on line corrosion measurement and to determine the feasibility and viability of the integrated anode ladder corrosion sensors embedded in concrete. The atmospheric corrosivity categories supported with GSM remote data acquisition system from eight corrosion monitoring stations at different regions in Kuwait are being classified according to standard ISO 9223. The two nominated field sites where based upon time of wetness and bimetallic corrosion rate from atmospheric data where metals and rebar's concrete are likely to be used. Eight concrete blocks with embeddable anodic ladder corrosion sensors were placed in the atmospheric zone adjacent to the sea shore at KISR site. The anodic ladder corrosion rate sensors for concrete were installed to provide an early warning system on prediction of the corrosion propagation and on developing new insights on the long-term durability performance and repair of concrete structures to lower labor cost. The results show the atmospheric corrosivity data of the environment and the feasibility of data retrieval of the corrosion potential of concrete from the embeddable sets of anodic ladder corrosion sensors.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.4
• /
• pp.27-36
• /
• 2018

Although the current evaluation system has been revised four times since it was revised in 1996, it is insufficient to utilize it as a basis for predicting the performance degradation from the long-term viewpoint and prioritization decision for the budget input due to the evaluation system limited to securing the structural safety. Therefore, this study proposes a new evaluation system suitable for the performance evaluation of conventional (ASSM) tunnels among the various types of existing road tunnels using Delphi technique and AHP technique. Since the existing evaluation systems and evaluation items in domestic and overseas are limited in scope of evaluation criteria, the survey was conducted in conjunction with closed questionnaires on existing items and open questionnaires for eliciting new items. The validity of the questionnaire results were verified and the performance evaluation factors suitable for conventional (ASSM) tunnels were derived. After calculating weighted value of the derived evaluation item using AHP technique, a new evaluation system is proposed to meet the characteristics of the ASSM tunnel, so that they can be used as reference materials for revising and supplementing detailed guidelines of performance evaluation in the future.

• Smart Structures and Systems
• /
• v.5 no.4
• /
• pp.317-328
• /
• 2009

Current maintenance operations and integrity checks on a wide array of structures require personnel entry into normally-inaccessible or hazardous areas to perform necessary nondestructive inspections. To gain access for these inspections, structure must be disassembled and removed or personnel must be transported to remote locations. The use of in-situ sensors, coupled with remote interrogation, can be employed to overcome a myriad of inspection impediments stemming from accessibility limitations, complex geometries, the location and depth of hidden damage, and the isolated location of the structure. Furthermore, prevention of unexpected flaw growth and structural failure could be improved if on-board health monitoring systems were used to more regularly assess structural integrity. A research program has been completed to develop and validate Comparative Vacuum Monitoring (CVM) Sensors for surface crack detection. Statistical methods using one-sided tolerance intervals were employed to derive Probability of Detection (POD) levels for a wide array of application scenarios. Multi-year field tests were also conducted to study the deployment and long-term operation of CVM sensors on aircraft. This paper presents the quantitative crack detection capabilities of the CVM sensor, its performance in actual flight environments, and the prospects for structural health monitoring applications on aircraft and other civil structures.

• International conference on construction engineering and project management
• /
• 2022.06a
• /
• pp.814-822
• /
• 2022

The deployment of sensors for Structural Health Monitoring requires a complicated network arrangement, ground truthing, and calibration for validating sensor performance periodically. Any conventional sensor on a structural element is also subjected to static and dynamic vertical loadings in conjunction with other environmental factors, such as brightness, noise, temperature, and humidity. A structural model with strain gauges was built and tested to get realistic sensory information. This paper investigates different deep learning architectures and algorithms, including unsupervised, autoencoder, and supervised methods, to benchmark blind drift calibration methods using deep learning. It involves a fully connected neural network (FCNN), a long short-term memory (LSTM), and a gated recurrent unit (GRU) to address the blind drift calibration problem (i.e., performing calibrations of installed sensors when ground truth is not available). The results show that the supervised methods perform much better than unsupervised methods, such as an autoencoder, when ground truths are available. Furthermore, taking advantage of time-series information, the GRU model generates the most precise predictions to remove the drift overall.

• Journal of the Korean Society of Safety
• /
• v.29 no.6
• /
• pp.81-86
• /
• 2014

Composite materials have high specific stiffness, specific strength than existing concrete or steel materials. It has superior dynamic properties when utilizing advantages of material such as Non-corrosive, light weight, non-conducting and it has superior mold ability which can make variable shapes. Thus, in the construction, for using composite materials as construction materials, the study carried out static strength of fiber right angle direction and fatigue performance of FRP deck member. The study is going to deduct S-N curve by analyzing the results comparatively and estimate long-term durability. From now on, the study is going to provide interpretation of FRP member and basic data of design basis, furthermore providing foundation technique of composite materials' application of structural frame is the goal of this study.

• Structural Monitoring and Maintenance
• /
• v.2 no.1
• /
• pp.49-64
• /
• 2015

This paper presents a method for assessing the risk of wave run-up and overtopping of existing coastal defences and for analysing the probability of failure of the structures under future hydraulic conditions. The recent UK climate projections are employed in the investigations of the influence of changing environments on the long-term performance of sea defences. In order to reduce the risk of wave run-up and overtopping caused by rising sea level and to maintain the present-day allowances for wave run-up height and overtopping discharge, the future necessary increase in crest level of existing structures is investigated. Various critical failure mechanisms are considered for reliability analysis, i.e., erosion of crest by wave overtopping, failure of seaside revetment, and internal erosions within earth sea dykes. The time-dependent reliability of sea dykes is analysed to give probability of failure with time. The results for an example earth dyke section show that the necessary increase in crest level is approximately double of sea level rise to maintain the current allowances. The probability of failure for various failure modes of the earth dyke has a significant increase with time under future hydraulic conditions.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.6
• /
• pp.699-706
• /
• 2015

This paper presents results of one-year monitoring on prestressing force of a 7-wire steel post-tensioning strand which is installed in a UHPC(ultra high performance concrete) bridge with 11.0 m long, 5.0 m wide, and 0.6 m high by using a FBG-encapsulated 7-wire steel strand. The initial prestressing forces and the prestress changes during a vehicle load test were measured using the FBG-encapsulated strand. The results show that the FBG-encapsulated 7-wire strand is very effective for monitoring the prestress forces even the change in the tension force is very small. Additionally, it was indicated that selection of the thermal expansion coefficient which is used for the temperature correction shall be carefully carried out.

• Smart Structures and Systems
• /
• v.25 no.1
• /
• pp.111-122
• /
• 2020

Researchers up to date have introduced several Structural Health Monitoring (SHM) techniques with varying advantages and drawbacks for each. Satellite positioning systems (GPS, GLONASS and GALILEO) based techniques proved to be promising, especially for high natural period structures. Particularly, the GPS has proved sufficient performance and reasonable accuracy in tracking real time dynamic displacements of flexible structures independent of atmospheric conditions, temperature variations and visibility of the monitored object. Tall structures are particularly sensitive to oscillations produced by different sources of dynamic actions; such as typhoons. Wind forces induce in the structure both longitudinal and perpendicular displacements with respect to the wind direction, resulting in torsional effects, which are usually more complex to be detected. To efficiently track the horizontal rotations of the in-plane sections of such flexible structures, two main issues have to be considered: a suitable sensor topology (i.e., location, installation, and combination of sensors), and the methodology used to process the data recorded by sensors. This paper reports the contributions of the measurements recorded from dual frequency GPS receivers and uni-axial accelerometers in a full-scale experimental campaign. The Canton tower in Guangzhou-China is the case study of this research, which is instrumented with a long-term structural health monitoring system deploying both accelerometers and GPS receivers. The elaboration of combining the obtained rather long records provided by these two types of sensors in detecting the torsional behavior of the tower under ambient vibration condition and during strong wind events is discussed in this paper. Results confirmed the reliability of GPS receivers in obtaining the dynamic characteristics of the system, and its ability to capture the torsional response of the tower when used alone or when they are combined with accelerometers integrated data.