• Journal of Sensor Science and Technology
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• v.5 no.6
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• pp.51-59
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• 1996

A flow sensor has been fabricated by preparing thin film Pt-heater and Bi-Sb thermocouples array on 150 nm-$Si_{3}N_{4}$/300 nm-$SiO_{2}$/150 nm-$Si_{3}N_{4}$ dielectric diaphragm which has low thermal conductivity and balanced stress with silicon substrate for the purpose of improving the thermal isolation between heater and silicon substrate. Pt-heater showed nonlinear I-V characteristics due to the thermal isolation effect of the diaphragm. Its temperature coefficient of resistance was about $0.00378\;/^{\circ}C$ and Seebeck coefficient of Bi-Sb thermocouple was about $97\;{\mu}V/K$. The sensor showed that thermoelectric voltage decreased as thermal conductivity of gas increased, and flow sensitivity increased as heater voltage increased or as the distance between heater and thermocouple decreased. When heater voltage was about 2.5 V, $N_{2}$-flow sensitivity and thermal response time of the sensor were about $1.27\;mV{\cdot}(sccm)^{-1/2}$ and 0.13 sec., respectively.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.4
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• pp.51-63
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• 2002

This paper presents a hybrid control strategy for seismic protection of a benchmark cable-stayed bridge, which is provided as a testbed structure for the development of strategies for the control of cable-stayed bridges. This benchmark problem considers the cable-stayed bridge that is scheduled for completion in Cape Girardeau, Missouri, USA in 2003. Seismic considerations were strongly considered in the design of this bridge due to the location of the bridge in the New Madrid seismic zone and its critical role as a principal crossing of the Mississippi river. Based on detailed drawings of this cable-stayed bridge, a three-dimensional linearlized evaluation model has been developed to represent the complex behavior of the bridge. A set of eighteen evaluation criteria has been developed to evaluate the capabilities of each control strategy. In this study, a hybrid control system is composed of a passive control system to reduce the earthquake-induced forces in the structure and an active control system to further reduce the bridge responses, especially deck displacements. Conventional base isolation devices such as lead rubber bearings are used for the passive control design and Bouc-Wen model is used to simulate the nonlinear behavior of these devices For the active control design, ideal hydraulic actuators are used and on $H_2$/LQG control algorithm is adopted. Numerical simulation results show that the performance of the proposed hybrid control strategy is quite effective compared to that of the passive control strategy and slightly better than that of the active control strategy. The hybrid control method is also more reliable than the fully active control method due to the passive control part. Therefore, the proposed hybrid control strategy can effectively be used to seismically excited cable-stayed bridges.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.2
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• pp.73-87
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• 2019

Ocean waves are the driving force for the sediment transport and the beach process. However, wave actions are nonlinear and non-stationary, and the response of the beach is inconsistent in terms of reaction rate and magnitude. Therefore, the beach process is difficult to predict accurately. The purpose of this study is to identify the correlations between the shoreline change and ocean waves observed in the east coast of Korea. The relation of the beach width obtained from video monitoring at five sandy beaches and the wave data obtained from nearby wave monitoring at three points was analyzed. Although the correlations estimated over the whole data sets was not significant, the correlations estimated based on the seasonal period or wave conditions provided more noteworthy information. When the non-exceedance probability of the wave height was greater than 0.99, the wave period and beach width showed strong negative correlations. In case the non-exceedance probability of the wave period was greater than 0.99, the wave height and beach width showed strong negative correlations as well. Furthermore, the erosion rate of the beach width increased when the primary wave direction was close to normal to the coastline. Little significant seasonal or monthly change was found between the beach width and the wave, but it was greatly affected by intensive events such as typhoons. Thus, it is necessary to analyze in detail the wave height or period level explaining the change of beach width for more relevant and practical information.

• Journal of the Korean GEO-environmental Society
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• v.24 no.9
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• pp.15-24
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• 2023

The behavior of buried pipes is directly influenced by the nonlinearity and complex characteristics of the surrounding soil. However, the simplified beam-spring model, which ignores the nonlinearity and complex behavior of soil, is commonly used in practice. In response, several studies have employed continuum analysis methods to account for the nonlinear and complex behavior of the soil. This paper presents various numerical continuum analysis techniques and verifies their comparison with full-scale tests. The study found that reaction force results close to the full-scale test could be obtained by applying contact surface characteristics that take into account the interaction between the ground and the buried pipe. In the case of sharing pipe and soil node method and ignoring the interaction between pipe and soil, excessive reaction force was derived, and the failure shapes were different. In addition, this study applied the dynamic explicit analysis method, ALE method, and CEL method. It was confirmed that the displacement-reaction relationship and failure shape are similar to those of the static analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.49-56
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• 2024

An automated dynamic structural analysis module stands as a crucial element within a structural integrated mitigation system. This module must deliver prompt real-time responses to enable timely actions, such as evacuation or warnings, in response to the severity posed by the structural system. The finite element method, a widely adopted approximate structural analysis approach globally, owes its popularity in part to its user-friendly nature. However, the computational efficiency and accuracy of results depend on the user-provided finite element mesh, with the number of elements and their quality playing pivotal roles. This paper introduces a computationally efficient adaptive mesh generation scheme that optimally combines the h-method of node movement and the r-method of element division for mesh refinement. Adaptive mesh generation schemes automatically create finite element meshes, and in this case, representative strain values for a given mesh are employed for error estimates. When applied to dynamic problems analyzed in the time domain, meshes need to be modified at each time step, considering a few hundred or thousand steps. The algorithm's specifics are demonstrated through a standard cantilever beam example subjected to a concentrated load at the free end. Additionally, a portal frame example showcases the generation of various robust meshes. These examples illustrate the adaptive algorithm's capability to produce robust meshes, ensuring reasonable accuracy and efficient computing time. Moreover, the study highlights the potential for the scheme's effective application in complex structural dynamic problems, such as those subjected to seismic or erratic wind loads. It also emphasizes its suitability for general nonlinear analysis problems, establishing the versatility and reliability of the proposed adaptive mesh generation scheme.

• Structural Engineering and Mechanics
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• v.90 no.6
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• pp.611-633
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• 2024

This study intends to investigate the response of multi-cell (MC) beams to flexural loads in which the primary reinforcement is composed of both metallic and non-metallic materials. "Multi-cell" describes beam sections with multiple longitudinal voids separated by thin webs. Seven reinforced concrete MC beams measuring 300×200×1800 mm were tested under flexural loadings until failure. Two series of beams are formed, depending on the type of main reinforcement that is being used. A control RC beam with no openings and six MC beams are found in these two series. Series one and two are reinforced with metallic and non-metallic main reinforcement, respectively, in order to maintain a constant reinforcement ratio. The first crack, ultimate load, deflection, ductility index, energy absorption, strain characteristics, crack pattern, and failure mode were among the structural parameters of the beams under investigation that were documented. The primary variables that vary are the kind of reinforcing materials that are utilized, as well as the kind and quantity of mesh layers. The outcomes of this study that looked at the experimental and numerical performance of ferrocement reinforced concrete MC beams are presented in this article. Nonlinear finite element analysis (NLFEA) was performed with ANSYS-16.0 software to demonstrate the behavior of composite MC beams with holes. A parametric study is also carried out to investigate the factors, such as opening size, that can most strongly affect the mechanical behavior of the suggested model. The experimental and numerical results obtained demonstrate that the FE simulations generated an acceptable degree of experimental value estimation. It's also important to demonstrate that, when compared to the control beam, the MC beam reinforced with geogrid mesh (MCGB) decreases its strength capacity by a maximum of 73.33%. In contrast, the minimum strength reduction value of 16.71% is observed in the MC beams reinforced with carbon reinforcing bars (MCCR). The findings of the experiments on MC beams with openings demonstrate that the presence of openings has a significant impact on the behavior of the beams, as there is a decrease in both the ultimate load and maximum deflection.

• Journal of Biomedical Engineering Research
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• v.19 no.1
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• pp.59-68
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• 1998

Digital hearing aids offer many advantages over conventional analog hearing aids. With the advent of high speed digital signal processing chips, new digital techniques have been introduced to digital hearing aids. In addition, the evaluation of new ideas in hearing aids is necessarily accompanied by intensive subject-based clinical tests which requires much time and cost. In this paper, we present an objective method to evaluate and predict the performance of hearing aid systems without the help of such subject-based tests. In the hearing impairment simulation(HIS) algorithm, a sensorineural hearing impairment medel is established from auditory test data of the impaired subject being simulated. Also, the nonlinear behavior of the loudness recruitment is defined using hearing loss functions generated from the measurements. To transform the natural input sound into the impaired one, a frequency sampling filter is designed. The filter is continuously refreshed with the level-dependent frequency response function provided by the impairment model. To assess the performance, the HIS algorithm was implemented in real-time using a floating-point DSP. Signals processed with the real-time system were presented to normal subjects and their auditory data modified by the system was measured. The sensorineural hearing impairment was simulated and tested. The threshold of hearing and the speech discrimination tests exhibited the efficiency of the system in its use for the hearing impairment simulation. Using the HIS system we evaluated three typical hearing aid algorithms.

• Korean journal of applied entomology
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• v.48 no.2
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• pp.237-243
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• 2009

This study was conducted to develop economic injury level (ElL) and economic threshold (ET) of Cabbage armyworm, Mamestra brassicae L. on cabbage (Brassica oleracea L. var). The changes of cabbage biomass and M. brassicae density were investigated after introduction of larval M. brassicae (2nd instar) at different densities: 0, 1, 2, 4, 8, and 16 larvae per plant at 40 d after planting for an open field experiment, and 0, 2, 5, 8 and 12 larvae per plant at 25 d after planting for a glass house experiment. In the field experiment, the yield loss of cabbage was not significantly different among treated-plots at 30 d after the larval introduction, showing an over-compensatory response of cabbage plants to M. brassicae attack. In the glasshouse experiment, however, the biomass of cabbage at 15 d after the larval introduction significantly decreased with increasing the initial introduced number of M. brassicae, resulting in 38.3, 36.7, 21.7, 23.3 and 16.7g in above treated-plots, respectively. The relationship between cumulative insect days (CID) and yield loss (%) of cabbage was well described by a nonlinear logistic equation. Using the estimated equation, ElL of M. brassicae on cabbage was estimated at 44 CID per plant based on the yield loss 14%, which take into account of an empirical gain threshold 5% and marketable rate 91% of cabbage. Also, ET was calculated at 80% of the EIL: 35 CID per plant. Until a more elaborate EIL-model is developed, the present result may be useful for M. brassicae management at early growth stage of cabbage.

• The Journal of the Acoustical Society of Korea
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• v.35 no.4
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• pp.261-271
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• 2016

In the prediction of response of a pile in soil, numerical approaches such as a finite element method are generally applied due to complicate nonlinear behaviors of soils. However, the numerical methods based on the finite elements require heavy efforts in pile and soil modelling and also take long computing time. So their usage is limited especially in the early design stage in which principal dimensions and properties are not specified and tend to vary. On the contrary, theoretical approaches adopting linear approximations for soils are relatively simple and easy to model and take short computing time. Therefore, if they are validated to be reliable, they would be applicable in predicting responses of a pile in soil, particularly in early design stage. In case of wind turbines regarded in this study, it is required to assess their natural frequencies in early stages, and in this simulation the supporting pile inserted in soil could be replaced with a simplified elastic boundary condition at the bottom end of the wind turbine tower. To do this, analysis for a pile in soil is performed in this study to extract the spring constants at the top end of the pile. The pile in soil can be modelled as a beam on elastic spring by assuming that the soils deform within an elastic range. In this study, it is attempted to predict pile deformations and influence factors for lateral loads by means of the beam-on-spring model. As two example supporting structures for wind turbines, mono pile and suction pile models with different diameters are examined by evaluating their influence factors and validated by comparing them with those reported in literature. In addition, the deflection profiles along the depth and spring constants at the top end of the piles are compared to assess their supporting features.

• Journal of the Korea Organic Resources Recycling Association
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• v.2 no.2
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• pp.3-17
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• 1994

The inhibitory effect of sodium ion on the anaerobic degradation of food waste was studied by an anaerobic batch toxicity assay and inhibition model. The anaerobic degradation activity of food waste spiked with over $2g\;Na^+/L$ of sodium ion was severely inhibited at the initial stage of the exposure. The inhibition response of anaerobic microorganisms on the sodium ion estimated from the methane production was differed according to the concentration of sodium ion. The relative acclimation time(RAT) and methanation rate(RMR), defined as the ratios of initial lag time and maximum methane production rate of the sample spiked with sodium ion to the control. respectively, were used to evaluate the acclimation and inhibitory effects quantitatively on the anaerobic microorganisms. When sodium ion was increased from $2g\;Na^+/L$ to $20g\;Na^+/L$, the RAT was exponentially increased from 18.9 to 90. but the RMR was linearly decreased from 0.97 to 0.02. The effects of sodium ion for the maximum methanation rate, first order kinetic constant and ultimate methane production were well evaluated by a generalized nonlinear expression model. it could be described by the uncompetitive inhibition mode. The sodium ion concentration causing 50% inhibition of methanation activity was about $11g\;Na^+/L$, and the critical sodium ion beyond to compelete inhibition was 20 to $21g\;Na^+/L$. The presented results could be used to obtain the design or operation parameters of the anaerobic process treating food waste of high salt.