• The Journal of the Acoustical Society of Korea
• /
• v.33 no.6
• /
• pp.392-399
• /
• 2014

The underwater acoustic communication is characterized by doubly spread channels, which are the delay spread due to multiple paths and the doppler spread due to environmental fluctuations or a moving platform. An equalizer is used to remove the inter-symbol interferences that the delay spread causes, but an equalizer doesn't use an acoustic environment such as a multipath. However, a passive time-reversal mirror is simpler than an equalizer because a matched filter is implemented numerically at the receiver structure along with one-way propagation. In this paper, a passive time-reversal mirror is applied to remove interferences due to a multipath in sea-going experimental data in East Sea in Oct. 2010 and improved communication performance is confirmed. The performance is verified by comparing the signal-to-interference plus noise ratio before/after passive time-reversal mirror. It is also performed independently of the passive time-reversal mirror and adaptive equalizer and the bit error rate is compared to verify the performance of underwater acoustic communication.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.14 no.1
• /
• pp.1-10
• /
• 1977

The major objects of this report are to supplement data of natural frequencies of thin elastic rectangular plates to the available data, and to give an experimental verification for natural frequencies obtained by Rayleigh-Ritz method, the generation set of which are eigenfunctions of Euler beams. For the first object the following five models, for which data only for the fundamental mode or data only for square plates are available, are adopted; (1) two opposed edges are clamped and the other two opposed edges simply supported (C-C, S-S), (2) one edge is simply supported and the other three edges clamped (C-C, C-S), (3) one edge is free and the other three edges clamped (C-C, C-F), (4) two adjacent edges are clamped and the other two adjacent edges free (C-F, C-F). For the (C-C, S-S) model the frequency equation obtained with the mode shapes assumed as of a single trigonometric series is solved. And for the other four models Rayleigh-Ritz method taking eigenfunctions of Euler beams as the generating set is applied. The numerical examples are obtained up to the fourth, the fifth or the sixth order depending on the range of the aspect ratio (0.1-10.0). The number of terms in the generating set for Rayleigh-Ritz method is fifteen for all models. For the experiment three models made of 3.2mm thickness mild steel plate for general structure use were prepared in following size; $300mm{\times}600mm,\;600mm{\times}600mm\;and\;900mm{\times}600mm$. Their boundary conditions are made to fit (C-C, C-F) condition. From the experiment mechanical impedance curves based on the frequency response method were obtained together with phase relation diagrams. The experimental data are resulted in good conformity to calculated values.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.11
• /
• pp.97-108
• /
• 2016

Lunar rover plays an important role in lunar exploration. Especially, performance of rover wheel related to interaction with lunar soil is of great importance when it comes to optimization of rover's configuration. In this study, in order to investigate the motion performance of lunar rover's wheel on Korean Lunar Soil Simulant (KLS-1), a single wheel testbed was developed and used to carry out a series of experiments with two kinds of wheel with grousers and without grousers which were used to perform the experiments. Wheel traction performance was evaluated by using traction parameters such as drawbar pull, torque and sinkage correlated with slip ratio. The results showed that the single wheel testbed was suitable for evaluation of the performance of wheel and rover wheel with grousers which was likely to have higher traction performance than that without grousers in Korean Lunar soil simulant. The experimental results could be utilized in verification of the optimum wheel design and effectiveness of wheel traction for Korean lunar rover.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.22 no.1
• /
• pp.141-148
• /
• 2008

This paper presents experimental results on the safety of persons and protection of low-voltage equipments of the sub-station due to a single-phase ground fault in 22.9 kV-Y distribution system. In order to evaluate the hazard voltages and the stress voltage of the low-voltage(LV) equipment due to faults between high-voltage systems and earth based on the newly prescribed KS C IEC 60364 standard series, the verification tests in a 22.9[kV] neutral multiple grounding system were carried out. From the experimental results, we introduce serious problems causing some discomfort when applying KS C IEC 60364 standard series to the existing domestic distribution system and the effective protective measures against temporary overvoltages due to a ground fault in the common grounding which is combined the 22.9 kV-Y grounding and the customer's installation grounding are proposed. As a consequence, it was found that the equipotential bonding is an important prerequisite for the effectiveness of the protective measures for the safety of persons and LV equipment in the combined 22.9 kV-Y and low-voltage grounding system.

• Advanced Composite Materials
• /
• v.17 no.1
• /
• pp.57-73
• /
• 2008

The present paper focuses on experimental verification of the ply-by-ply basis inelastic analysis of multidirectional laminates. First of all, rate dependence of the tensile behavior of balanced symmetric cross-ply T800H/epoxy laminates with a $[0/90]_{3S}$ lay-up under off-axis loading conditions at $100^{\circ}C$ is examined. Uniaxial tension tests are performed on plain coupon specimens with various fiber orientations $[{\theta}/(90-{\theta})]_{3S}$ ($\theta$ = 0, 5, 15, 45 and $90^{\circ}C$) at two different strain rates (1.0 and 0.01%/min). The off-axis stress.strain curves exhibit marked nonlinearity for all the off-axis fiber orientations except for the on-axis fiber orientations $\theta$ = 0 and $90^{\circ}$, regardless of the strain rates. Strain rate has significant influences not only on the off-axis flow stress in the regime of nonlinear response but also on the apparent off-axis elastic modulus in the regime of initial linear response. A macromechanical constitutive model based on a ply viscoplasticity model and the classical laminated plate theory is applied to predictions of the rate-dependent off-axis nonlinear behavior of the cross-ply CFRP laminate. The material constants involved by the ply viscoplasticity model are identified on the basis of the experimental results on the unidirectional laminate of the same carbon/epoxy system. It is demonstrated that good agreements between the predicted and observed results are obtained by taking account of the fiber rotation induced by deformation as well as the rate dependence of the initial Young's moduli.

• Structural Engineering and Mechanics
• /
• v.74 no.1
• /
• pp.1-18
• /
• 2020

For the large deformation of shear walls under vertical and horizontal loads, there are difficulties in obtaining accurate simulation results using the response analysis method, even with fine mesh elements. Furthermore, concrete material nonlinearity, stiffness degradation, concrete cracking and crushing, and steel bar damage may occur during the large deformation of reinforced concrete (RC) shear walls. Matrix operations that are involved in nonlinear analysis using the traditional finite-element method (FEM) may also result in flaws, and may thus lead to serious errors. To solve these problems, a planar four-node element was developed based on vector mechanics. Owing to particle-based formulation along the path element, the method does not require repeated constructions of a global stiffness matrix for the nonlinear behavior of the structure. The nonlinear concrete constitutive model and bilinear steel material model are integrated with the developed element, to ensure that large deformation and damage behavior can be addressed. For verification, simulation analyses were performed to obtain experimental results on an RC shear wall subjected to a monotonically increasing lateral load with a constant vertical load. To appropriately evaluate the parameters, investigations were conducted on the loading speed, meshing dimension, and the damping factor, because vector mechanics is based on the equation of motion. The static problem was then verified to obtain a stable solution by employing a balanced equation of motion. Using the parameters obtained, the simulated pushover response, including the bearing capacity, deformation ability, curvature development, and energy dissipation, were found to be in accordance with the experimental observation. This study demonstrated the potential of the developed planar element for simulating the entire process of large deformation and damage behavior in RC shear walls.

• Journal of Fisheries and Marine Sciences Education
• /
• v.24 no.1
• /
• pp.56-78
• /
• 2012

This study which is an alternative exploration for improving the quality level of instruction considering the perception of the teachers in early childhood education field on instructional design is to develop Differentiated Instructional Design Model coincides with the purpose of differentiated instruction curricula and with instructional design principles, and to find out whether the model has significant effect on development of teacher's professionalism. With these purposes, the perception of 343 teachers from early childhood education institutions are investigated, and after component variables are set by drawing the instructional design model available in early childhood education field and reviewing the literature of differentiated instruction model, the Differentiated Instructional design Model for Early Childhood are developed based on FGI(Focus Group Interview) expert evaluation. The experimental study of 88 teachers working in childcare facilities was implemented for effectiveness verification. As a result, first, most teachers consider the priority on making the lesson plans as the development of early childhood and Kindergarten Educational Subjects, and they realize the development of instructional design model which contributes on lesson planning and implementation is much needed. Second, the Differentiated Instructional design Model for Early Childhood are developed, which consists of the cyclic process - pre-lesson phase, lesson implementation phase, and assessment phase -based on development characteristics of early childhood. Third, the experiment of the developed model showed that the scores of experimental group is significantly higher than those of comparative group in knowledge and technique development aspect, and self-understanding development aspect among the aspects of development of teacher's professionalism.

• Journal of Digital Convergence
• /
• v.13 no.1
• /
• pp.11-23
• /
• 2015

Recently the military is improving the policies of military culture for soldiers to lead a better military life. In this effect, 'division A' introduced 'goal-directed self development program'. This program is guiding the soldiers to set up personal mission in life not only in the military but also linked to the future, after being discharged from military service. Therefore the purpose of this research is to test the effect of this program on soldier's objective management, self esteem and satisfaction and to propose political strategies for creating healthier military culture. The research method was to compare and analyze the difference between two groups, 'division A'(experimental group), which operated the program, and 'division B'(controlled group) which did not operated the program. research targets were 488 soldiers in total, 257 soldiers in experimental group and 231 in controlled group. T-test(verification) and analysis of covariance was done with SPSS WIN 11.5 program with collected information. The result showed that the program has meaningful effect in every aspect mentioned above to the soldiers.

• Journal of Digital Convergence
• /
• v.15 no.7
• /
• pp.213-222
• /
• 2017

This paper proposes a new service design which is deep learning-based image retrieval system for product search on O2O shopping mall platform. We have implemented deep learning technology that provides more convenient retrieval service for diverse images of many products that are sold in the internet shopping malls. In order to implement this retrieval system, real data used by shopping mall companies were used as experimental data. However, result from several experiments have confirmed deterioration of retrieval performance due to data components. In order to improve the performance, the learning data that interferes with the retrieval is revised several times, and then the values of experimental result are quantified with the verification data. Using the numerical values of these experiments, we have applied them to the new service design in this system.

• Journal of Ocean Engineering and Technology
• /
• v.19 no.1 s.62
• /
• pp.64-70
• /
• 2005

Target Strength(TS) is an important factor for the detection of the target in an active sonar system: thus the numerical model for the prediction of TS is widely being developed. For the frequency range of several kHz, the most important scattering mechanism is known to be specular reflection, which is largely affected by the geometrical shape of the target. In this paper, a numerical algorithm to predict TS is developed based on the Kirchhoff approximation which is computationally efficient. The developed algorithm is applied to the canonical targets of simple shapes, for which the analytical solutions exist. The numerical results show good agreement with the analytical solutions. Also, the algorithm is applied to more complex scatterers, and is compared with the experimental data obtained in the water tank experiment for the purpose of verifying the developed numerical model. Discussions on the effect of spatial sampling and other aspects of numerical m odeling are presented.