• Smart Structures and Systems
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• v.4 no.3
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• pp.343-365
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• 2008

In this study, the frequency domain method which utilizes the evaluation of changes in the structural mode shape is adopted to identify regions which contain localized damages. Frequency response function (FRF) values corresponding to the modal frequency, analogous to the mode shape coefficients, are used since change in natural frequency of the system is usually insignificant for localized damage. This method requires only few sensors to obtain the dynamic response of the structure at specific locations to determine the FRF via fast-Fourier transform (FFT). Numerical examples of an aluminum plate, which includes damages of varying severity, locations and combinations of multiple locations, are presented to demonstrate the feasibility of the method. An experimental verification of the method is also done using an aluminum plate with two different degrees of damage, namely a half-through notch and a through notch. The inconsistency in attaining the FRF values for practical applications due to varying impact load may be overcome via statistical averaging, although large variations in the loading in terms of the contact duration should still be avoided. Nonetheless, this method needs special attention when the damages induce notable changes in the modal frequency, such as when the damages are of high severity or cover more extensive area or near the boundary where the support condition is modified. This is largely due to the significant decrease in the frequency term compared to the increase in the vibration amplitude. For practical reasons such as the use of limited number of sensors and to facilitate automation, extending the resolution of this method of identification may not be efficient. Hence, methods based on wave propagation can be employed as a complement on the isolated region to provide an accurate localization as well as to trace the geometry of the damage.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.3
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• pp.183-197
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• 2004

The introduction of geodetic methods of absolute displacement monitoring in tunnels has significantly improved the value of the measurements. Structurally controlled behavior and influences of an anisotropic rock mass can be determined, and the excavation and support adjusted accordingly. Three-dimensional finite element simulations of different weakness zone properties, thicknesses, and orientations relative to the tunnel axis were carried out and the function parameters were evaluated from the results. The results were compared to monitoring results from Alpine tunnels in heterogeneous rock. The good qualitative correlation between trends observed on site and numerical results gives hope that by a routine determination of the function parameters during excavation the prediction of rock mass conditions ahead of the tunnel face can be improved. Implementing the rules developed from experience and simulations into the monitoring data evaluation program allows to automatically issuing information on the expected rock mass quality ahead of the tunnel.

• Structural Engineering and Mechanics
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• v.75 no.4
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• pp.415-424
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• 2020

Recently, many structural damage detection (SDD) methods have been proposed to monitor the safety of structures. As an important modal parameter, mode shape has been widely used in SDD, and the difference of vectors was adopted based on sensitivity analysis and mode shapes in the existing studies. However, amplitudes of mode shapes in different measured points are relative values. Therefore, the difference of mode shapes will be influenced by their amplitudes, and the SDD results may be inaccurate. Focus on this deficiency, a multi-strategy SDD method is proposed based on the included angle of vectors and sparse regularization in this study. Firstly, inspired by modal assurance criterion (MAC), a relationship between mode shapes and changes in damage coefficients is established based on the included angle of vectors. Then, frequencies are introduced for multi-strategy SDD by a weighted coefficient. Meanwhile, sparse regularization is applied to improve the ill-posedness of the SDD problem. As a result, a novel convex optimization problem is proposed for effective SDD. To evaluate the effectiveness of the proposed method, numerical simulations in a planar truss and experimental studies in a six-story aluminum alloy frame in laboratory are conducted. The identified results indicate that the proposed method can effectively reduce the influence of noises, and it has good ability in locating structural damages and quantifying damage degrees.

• The Korean Journal of Pain
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• v.11 no.1
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• pp.41-46
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• 1998

Background: Preoperative analgesia may prevent nociceptive inputs generated during surgery from sensitizing central neurons and therefore may preempt postoperative pain. Although preemptive analgesia has shown to decrease postinjury pain in animals, studies in human are not consistent. We studied whether epidural morphine injection before surgical incision could affect postoperative pain and analgesic demands, compared with injection after removal of specimen. Methods: Forty patients scheduled for radical subtotal gastrectomy were randomly assigned to one of two groups for prospective study in a double-blind manner. Group 1 received an epidural injection of 3 mg of morphine in 8 ml of 0.9% saline before surgical incision, and Group 2 after removal of specimen. Postoperative pain relief was provided with I.V. patient controlled analgesia (PCA) system. Numerical rating scales for pain and mood, Prince Henry Hospital scores for pain, cumulative PCA analgesic consumptions, and incidence of side effects were assessed at 2, 6, 12, 24, 48 hours after operation. Results: Cumulative PCA analgesic consumption in group 1 was significantly less than in group 2 at 2, 6 hours after surgery. Pain scores and the incidence of side effects were similar in both groups. Conclusions: Preoperative analgesia with epidural morphine showed little difference in patient controlled analgesic consumption after upper abdominal surgery compaired to intraoperative morphine.

• The Korean Journal of Pain
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• v.22 no.3
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• pp.234-240
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• 2009

Background: The purpose of this study was to compare the analgesic effect of 0.25% and 0.5% levobupivacaine for real time ultrasound guided single-injection femoral nerve block for the patients who are undergoing bilateral total knee arthroplasty (TKA). Methods: Femoral nerve block was done to all patients with 20 ml of 0.9% normal saline on one leg and 20 ml of 0.25% levobupivacaine on the other leg for group I (n = 16) and 0.5% levobupivacaine for group II (n = 15) with 1:200,000 epinephrine and using real-time ultrasound and a nerve stimulator. The data concerning the verbal numerical rating scale (VNRS) for each leg, the consumption of the intravenous patient-controlled analgesia (IV PCA) and the demands for the additional analgesics was collected at 0, 1, 6, 12, 24 and 48 hours after the operation. Results: The legs on which femoral nerve block was done with levobupivacaine showed a lower VNRS score than the legs with normal saline in either group I or group II. The VNRS scores between the two legs, the consumption of the IV PCA and the demand for additional analgesics showed no significant differences between the groups. Conclusions: Our results demonstrate that single-injection femoral nerve block using real-time ultrasound with either 0.25% levobupivacaine or 0.5% levobupivacaine 20 ml provides a good effect for the postoperative pain control after TKA.

• Journal of Biosystems Engineering
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• v.39 no.4
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• pp.310-317
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• 2014

Purpose: This study was conducted to analyze the air flow characteristics in a plant factory with different inlet and outlet locations using computational fluid dynamics (CFD). Methods: In this study, the flow was assumed to be a steady-state, incompressible, and three-dimensional turbulent flow. A realizable k-${\varepsilon}$ turbulent model was applied to show more reasonable results than the standard model. A CFD software was used to perform the numerical simulation. For validation of the simulation model, a prototype plant factory ($5,900mm{\times}2,800mm{\times}2,400mm$) was constructed with two inlets (${\Phi}250mm$) and one outlet ($710mm{\times}290mm$), located on the top side wall. For the simulation model, the average air current speed at the inlet was $5.11m{\cdot}s^{-1}$. Five cases were simulated to predict the airflow pattern in the plant factory with different inlet and outlet locations. Results: The root mean square error of measured and simulated air current speeds was 13%. The error was attributed to the assumptions applied to mathematical modelling and to the magnitude of the air current speed measured at the inlet. However, the measured and predicted airflow distributions of the plant factory exhibited similar patterns. When the inlets were located at the center of the side wall, the average air current speed in the plant factory was increased but the spatial uniformity was lowered. In contrast, if the inlets were located on the ceiling, the average air current speed was lowered but the uniformity was improved. Conclusions: Based on the results of this study, it was concluded that the airflow pattern in the plant factory with multilayer cultivation shelves was greatly affected by the locations of the inlet and the outlet.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.290-299
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• 2017

Reconfigurable flight control using various kinds of adaptive control methods has been studied since the 1970s to enhance the survivability of aircraft in case of severe in-flight failure. Early studies were mainly focused on the failure of actuators. Recently, studies of reconfigurable flight controls that can accommodate complex damage (partial wing and tail loss) in conventional aircraft were reported. However, the partial wing loss effects on the aerodynamics of conventional type aircraft are quite different to those of BWB(blended wing body) aircraft. In this paper, a reconfigurable flight control algorithm was designed using a direct model reference adaptive method to overcome the instability caused by a complex damage of a BWB aircraft. A model reference adaptive control was incorporated into the inner loop rate control system enhancing the performance of the baseline control to cope with abrupt loss of stability. Gains of the model reference adaptive control were polled out using the Liapunov's stability theorem. Outer loop attitude autopilot was designed to manage roll and pitch of the BWB UAV as well. A 6-DOF dynamic model was built-up, where the normal flight can be made to switch to the damaged state abruptly reflecting the possible real flight situation. 22% of right wing loss as well as 25% loss for both vertical tail and rudder control surface were considered in this study. Static aerodynamic coefficients were obtained via wind tunnel test. Numerical simulations were conducted to demonstrate the performance of the reconfigurable flight control system.

• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.481-495
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• 2015

Many hydropower stations in southwest China are located in regions of brittle rock mass with high geo-stresses. Under these conditions deep fractured zones often occur in the sidewalls of the underground caverns of a power station. The theory and methods of fracture and damage mechanics are therefore adopted to study the phenomena. First a flexibility matrix is developed to describe initial geometric imperfections of a jointed rock mass. This model takes into account the area and orientation of the fractured surfaces of multiple joint sets, as well as spacing and density of joints. Using the assumption of the equivalent strain principle, a damage constitutive model is established based on the brittle fracture criterion. In addition the theory of fracture mechanics is applied to analyze the occurrence of secondary cracks during a cavern excavation. The failure criterion, for rock bridge coalescence and the damage evolution equation, has been derived and a new sub-program integrated into the FLAC-3D software. The model has then been applied to the stability analysis of an underground cavern group of a hydropower station in Sichuan province, China. The results of this method are compared with those obtained by using a conventional elasto-plastic model and splitting depth calculated by the splitting failure criterion proposed in a previous study. The results are also compared with the depth of the relaxation and fracture zone in the surrounding rock measured by field monitoring. The distribution of the splitting zone obtained both by the proposed model and by the field monitoring measurements are consistent to the validity of the theory developed herein.

• Structural Engineering and Mechanics
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• v.66 no.6
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• pp.677-691
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• 2018

Reliability assessment of complex structures using simulation methods is time-consuming. Thus, surrogate models are usually employed to reduce computational cost. AK-MCS is a surrogate-based Active learning method combining Kriging and Monte-Carlo Simulation for structural reliability analysis. This paper proposes three modifications of the AK-MCS method to reduce the number of calls to the performance function. The first modification is related to the definition of an initial Design of Experiments (DoE). In the original AK-MCS method, an initial DoE is created by a random selection of samples among the Monte Carlo population. Therefore, samples in the failure region have fewer chances to be selected, because a small number of samples are usually located in the failure region compared to the safe region. The proposed method in this paper is based on a uniform selection of samples in the predefined domain, so more samples may be selected from the failure region. Another important parameter in the AK-MCS method is the size of the initial DoE. The algorithm may not predict the exact limit state surface with an insufficient number of initial samples. Thus, the second modification of the AK-MCS method is proposed to overcome this problem. The third modification is relevant to the type of regression trend in the AK-MCS method. The original AK-MCS method uses an ordinary Kriging model, so the regression part of Kriging model is an unknown constant value. In this paper, the effect of regression trend in the AK-MCS method is investigated for a benchmark problem, and it is shown that the appropriate choice of regression type could reduce the number of calls to the performance function. A stepwise approach is also presented to select a suitable trend of the Kriging model. The numerical results show the effectiveness of the proposed modifications.

• The Korean Journal of Pain
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• v.30 no.3
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• pp.220-228
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• 2017

Background: The transforaminal (TF) epidural steroid injection (ESI) is suggested as more effective than the interlaminar (IL) route due to higher delivery of medication at the anterior epidural space. However, serious complications such as spinal cord injury and permanent neural injury have been reported. The purpose of this study is to evaluate and compare the clinical effectiveness, technical ease, and safety of the TF and parasagittal IL (PIL) ESI. Methods: A total of 72 patients were randomized to either the PIL group (n = 41) or the TF group (n = 31) under fluoroscopic guidance. Patients were evaluated for effective pain relief by the numerical rating scale (NRS) and Oswestry Disability Index (ODI) (%) before and 2 weeks after the ESI. The presence of concordant paresthesia, anterior epidural spread, total procedure time, and exposed radiation dose were also evaluated. Results: Both the PIL and TF approach produced similar clinically significant improvements in pain and level of disability. Among the 72 patients, 27 PIL (66%) and 20 TF (64%) patients showed concordant paresthesia while 14 (34%) and 11 (36%) patients in the same respective order showed disconcordant or no paresthesia. Radiation dose and total procedure time required were compared; the PIL group showed a significantly lower radiation dose ($30.2{\pm}12$ vs. $80.8{\pm}26.8$ [$Cgy/cm^2$]) and shorter procedure time ($96.2{\pm}31$ vs. $141.6{\pm}30$ seconds). Conclusions: ESI under fluoroscopic guidance with PIL or TF approach were effective in reducing the NRS and ODI. PIL ESI was a technically easier and simple method compared to TF ESI.