• Smart Structures and Systems
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• v.20 no.3
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• pp.273-283
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• 2017

This paper presents and compares three feedback control strategies for active control of noise inside a 3-D vibro-acoustic cavity. These are a) control strategy based on direct output feedback (DOFB) b) control strategy based on linear quadratic regulator (LQR) to reduce structural vibrations and c) LQR control strategy with a weighting scheme based on structural-acoustic coupling coefficients. The first two strategies are indirect control strategies in which noise reduction is achieved through active vibration control (AVC), termed as AVC-DOFB and AVC-LQR respectively. The third direct strategy is based on active structural-acoustic control (ASAC). This strategy is an LQR based optimal control strategy in which the coupling between the various structural and the acoustic modes is used to design the controller. The strategy is termed as ASAC-LQR. A numerical model of a 3-D rectangular box cavity with a flexible plate (glued with piezoelectric patches) and with other five surfaces treated rigid is developed using finite element (FE) method. A single pair of collocated piezoelectric patches is used for sensing the vibrations and applying control forces on the structure. A comparison of frequency response function (FRF) of structural nodal acceleration, acoustic nodal pressure, and piezoelectric actuation voltage is carried out. It is found that the AVC-DOFB control strategy gives equal importance to all the modes. The AVC-LQR control strategy tries to consume the control effort to damp all the structural modes. It is seen that the ASAC-LQR control strategy utilizes the control effort more intelligently by adding higher damping to those structural modes that matter more for reducing the interior noise.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.5
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• pp.688-699
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• 2017

Model-based test, a well-known method of the black box tests, is consisted of the following four steps : model construction using requirement, test case generation from the model, execution of a SUT (software under test) and detection failures. Among models constructed in the first step, state-based models such as UML standard State Machine are commonly used to design event-based embedded systems (e.g., weapon control systems). To generate test cases from state-based models in the next step, coverage-based techniques such as state coverage and transition coverage are used. Round-trip path coverage technique using W-Method, one of coverage-based techniques, is known as more effective method than others. However it has a limitation of low failure observability because the W-Method technique terminates a testing process when arrivals meet states already visited and it is hard to decide the current state is completely same or not with the previous in the case like the GUI environment. In other words, there can exist unrevealed faults. Therefore, this study suggests a Extended W-Method. The Extended W-Method extends the round-trip path to a final state to improve failure observability. In this paper, we compare effectiveness and efficiency with requirement-item-based technique, W-Method and our Extended W-Method. The result shows that our technique can detect five and two more faults respectively and has the performance of 28 % and 42 % higher failure detection probability than the requirement-item-based and W-Method techniques, respectively.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.26 no.4
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• pp.885-894
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• 2016

As smartphones become more common, anybody can take pictures and record videos easily nowadays. Video files taken from smartphones can be used as important clues and evidence. While you analyze video files taken from smartphones, there are some occasions where you need to prove that a video file was recorded by a specific smartphone. To do this, you can utilize various fingerprint techniques mentioned in existing research. But you might face the situation where you have to strengthen the result of fingerprinting or fingerprint technique can't be used. Therefore forensic investigation of the smartphone must be done before fingerprinting and the database of metadata of video files should be established. The artifacts in a smartphone after video recording and the database mentioned above are discussed in this paper.

• Journal of the Korea Society of Computer and Information
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• v.20 no.3
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• pp.47-56
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• 2015

Automated detection of interesting web pages could be used in many different application domains. Determining a user's interesting web pages can be performed implicitly by observing the user's behavior. The task of distinguishing interesting web pages belongs to a classification problem, and we choose white box learning methods (fixed effect logit regression and support vector machine) to test empirically. The result indicated that (1) fixed effect logit regression, fixed effect SVMs with both polynomial and radial basis kernels showed higher performance than the linear kernel model, (2) a personalization is a critical issue for improving the performance of a model, (3) when asking a user explicit grading of web pages, the scale could be as simple as yes/no answer, (4) every second the duration in a web page increases, the ratio of the probability to be interesting increased 1.004 times, but the number of scrollbar clicks (p=0.56) and the number of mouse clicks (p=0.36) did not have statistically significant relations with the interest.

• Korean Journal of Applied Biomechanics
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• v.25 no.1
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• pp.29-37
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• 2015

Objective : The purpose of this study was to investigate the biomechanical properties of shock absorption strategy and postural stability during the drop landing for each types. Methods : The motions were captured with Vicon Motion Capture System, with the fourteen infra-red cameras (100Hz) and synchronized with GRF(ground reaction force) data(1000Hz). Ten male soccer players performed a drop landing with single-leg and bi-legs on the 30cm height box. Dependent variables were the CoM trajectory and the Joint Moment. Statistical computations were performed using the paired t-test and ANOVA with Turkey HSD as post-hoc. Results : The dominant leg was confirmed to show a significant difference between the left leg and right leg as the inverted pendulum model during Drop Landing(Phase 1 & Phase 2). One-leg drop landing type had the higher CoM displacement, the peak of joint moment with the shock absorption than Bi-leg landing type. As a lower extremity joint kinetics analysis, the knee joint showed a function of shock absorption in the anterior-posterior, and the hip joint showed a function of the stability and shock absorption in the medial-lateral directions. Conclusion : These findings indicate that the instant equilibrium of posture balance(phase 1) was assessed by the passive phase as Class 1 leverage on the effect of the stability of shock absorption(phase 2) assessed by the active phase on the effect of Class 2 leverage. Application : This study shows that the cause of musculo-skeletal injuries estimated to be focused on the passive phase of landing and this findings could help the prevention of lower damage from loads involving landing related to the game of sports.

• Steel and Composite Structures
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• v.18 no.4
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• pp.985-1000
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• 2015

The method of cross-section analysis for different sections in a structural frame has been widely investigated since the 1960s for determination of sectional capacities of beam-columns. Many hand-calculated equations and design graphs were proposed for the specific shape and type of sections in pre-computer age decades ago. In design of many practical sections, these equations may be uneconomical and inapplicable for sections with irregular shapes, leading to the high construction cost or inadequate safety. This paper not only proposes a versatile numerical procedure for sectional analysis of beam-columns, but also suggests a method to account for residual stress and geometric imperfections separately and the approach is applied to design of high strength steels requiring axial force-moment interaction for advanced analysis or direct analysis. A cross-section analysis technique that provides interaction curves of arbitrary welded sections with consideration of the effects of residual stress by meshing the entire section into small triangular fibers is formulated. In this study, two doubly symmetric sections (box-section and H-section) fabricated by high-strength steel is utilized to validate the accuracy and efficiency of the proposed method against a hand-calculation procedure. The effects of residual stress are mostly not considered explicitly in previous works and they are considered in an explicit manner in this paper which further discusses the basis of the yield surface theory for design of structures made of high strength steels.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.1
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• pp.139-146
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• 2017

The ISDB-T(Integrated Service Digital Broadcasting Terrestrial) can be used in the multipath and impulsive noise, also it provide good performance over mobile reception environment since it use the OFDM(Orthogonal Frequency Division Multiplexing) based transmission technology and time interleaving technology. One segment and full segment are divided according to the number of the assigned segment. And one-segment broadcasting receiver can design and implement without high levels of technology than the full-segment broadcasting receiver using 64QAM(64 Quadrature Amplitude Modulation) since it uses QPSK(Quadrature Phase Shift Keying) modulation/demodulation. However, it has a constraint in the display size and resolution due to data-rate limits. In this paper, we design and implementation of full-segment ISDB-T receiver module which support HD resolution for set-top box, digital TV, navigation. In experimental results, the implemented full-segment ISDB-T receiver module was satisfactory for all of the desired functions.

• Journal of the Ergonomics Society of Korea
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• v.36 no.1
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• pp.37-52
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• 2017

Objective: The present study developed a user-centered 3D virtual liver surgery planning (VLSP) system called Dr. Liver to provide preoperative information for safe and rational surgery. Background: Preoperative 3D VLSP is needed for patients' safety in liver surgery. Existing systems either do not provide functions specialized for liver surgery planning or do not provide functions for cross-check of the accuracy of analysis results. Method: Use scenarios of Dr. Liver were developed through literature review, benchmarking, and interviews with surgeons. User interfaces of Dr. Liver with various user-friendly features (e.g., context-sensitive hotkey menu and 3D view navigation box) was designed. Novel image processing algorithms (e.g., hybrid semi-automatic algorithm for liver extraction and customized region growing algorithm for vessel extraction) were developed for accurate and efficient liver surgery planning. Usability problems of a preliminary version of Dr. Liver were identified by surgeons and system developers and then design changes were made to resolve the identified usability problems. Results: A usability testing showed that the revised version of Dr. Liver achieved a high level of satisfaction ($6.1{\pm}0.8$ out of 7) and an acceptable time efficiency ($26.7{\pm}0.9 min$) in liver surgery planning. Conclusion: Involvement of usability testing in system development process from the beginning is useful to identify potential usability problems to improve for shortening system development period and cost. Application: The development and evaluation process of Dr. Liver in this study can be referred in designing a user-centered system.

• Composites Research
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• v.30 no.2
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• pp.126-131
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• 2017

For structural health monitoring of a complex shaped structure a new sensor that can compensate for the drawbacks of the current sensors such as brittleness is needed and the sensor should be highly flexible and durable. In this study a textile sensor made of polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) which is a type of electroactive polymer was fabricated. And the textile sensors were applied to a complex shaped structure (an egg-box panel made of carbon/epoxy composite) for checking their feasibility of structural health monitoring. To correlate the collapse response with failure mechanisms of the structure the multiply-interrupted compressive test was carried out. During the test, the textile sensors succeeded to prove their applicability for damage detection (crack initiation) by generating electric voltages (0.05 V-0.25 V) in the real time.

• Journal of the Korean Society for Railway
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• v.19 no.6
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• pp.755-764
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• 2016

In this paper, to verify the field application of a displacement estimation technique based on the relationship between displacement and strain, static and dynamic field load test are performed on three-span continuous real bridge structures. The superstructure types of the test bridges are IPC girder highway bridge and steel box girder AGT bridge. LVDTs and strain gauges are attached to them; then, the responses due to test vehicle are measured. To obtain the displacement-strain relationship of the test bridges, the bridges are modeled as grillage system with 6 DOFs for the purpose of structural analyses. Static and dynamic displacements, which are estimated using both the calculated displacement-strain relationship and the measured strain signal, agree well with the values measured by LVDT. This study demonstrates that the displacement estimation technique using the strain signal can be effectively applied to the displacement measurement of bridge structures that cross rivers/roads/railways or have high clearance.