• Geomechanics and Engineering
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• v.36 no.3
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• pp.277-293
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• 2024

Shored Mechanically Stabilized Earth (SMSE) walls are types of soil retaining structures that increase soil stability under static and dynamic loads. The damage caused by an earthquake can be determined by evaluating the probabilistic seismic response of SMSE walls. This study aimed to assess the seismic performance of SMSE walls and provide fragility curves for evaluating failure levels. The generated fragility curves can help to improve the seismic performance of these walls through assessing and controlling variables like backfill surface settlement, lateral deformation of facing, and permanent relocation of the wall. A parametric study was performed based on a non-linear elastoplastic constitutive model known as the hardening soil model with small-strain stiffness, HSsmall. The analyses were conducted using PLAXIS 2D, a Finite Element Method (FEM) program, under plane-strain conditions to study the effect of the number of geogrid layers and the axial stiffness of geogrids on the performance of SMSE walls. In this study, three areas of damage (minor, moderate, and severe) were observed and, in all cases, the wall has not completely entered the stage of destruction. For the base model (Model A), at the highest ground acceleration coefficient (1 g), in the moderate damage state, the fragility probability was 76%. These values were 62%, and 54%, respectively, by increasing the number of geogrids (Model B) and increasing the geogrid stiffness (Model C). Meanwhile, the fragility values were 99%, 98%, and 97%, respectively in the case of minor damage. Notably, the probability of complete destruction was zero percent in all models.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.5
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• pp.388-399
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• 2016

A motion analysis of an underwater towed cable is a complex task due to its nonlinear nature of the problem. The major source of the nonlinearity of the underwater cable analysis is that the motion of the cable involves large rigid-body motion. This large rigid-body motion makes difficult to use standard displacement-based finite element method. In this paper, the authors apply recently developed nodal position-based finite element method which can deal with the geometric nonlinearity due to the large rigid-body motion. In order to enhance the stability of the large-scale nonlinear cable motion simulation, an efficient time-integration scheme is proposed, namely predictor/multi-corrector Newmark scheme. Three different predictors are introduced, and the best predictor in terms of stability and robustness for impulsive cable motion analysis is proposed. As a result, the nonlinear motion of underwater cable is predicted in a very efficient manner compared to the classical finite element of finite difference methods. The efficacy of the method is demonstrated with several test cases, involving static and dynamic motion of a single cable element, and also under water towed cable composed of multiple cable elements.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.351-361
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• 2019

Present article deals with the static stability analysis of compositionally graded nanocomposite beams reinforced with graphene oxide powder (GOP) is undertaken once the beam is subjected to an induced force caused by nonuniform magnetic field. The homogenized material properties of the constituent material are approximated through Halpin-Tsai micromechanical scheme. Three distribution types of GOPs are considered, namely uniform, X and O. Also, a higher-order refined beam model is incorporated with the dynamic form of the virtual work's principle to derive the partial differential motion equations of the problem. The governing equations are solved via Galerkin's method. The introduced mathematical model is numerically validated presenting a comparison between the results of present work with responses obtained from previous articles. New results for the buckling load of GOP reinforced nanocomposites are presented regarding for different values of magnetic field intensity. Besides, other investigations are performed to show the impacts of other variants, such as slenderness ratio, boundary condition, distribution type and so on, on the critical stability limit of beams made from nanocomposites.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1505-1514
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• 2019

The permanent magnet synchronous motor (PMSM) is widely used in various fields and the proportional-integral (PI) controller is popular in PMSM control systems. However, the motor parameters are usually unknown, which can lead to a complicated PI controller design and poor performance. In order to design a PI controller with good performance when the motor parameters are unknown, a control algorithm based on stability margin is proposed in this paper. First of all, based on the mathematical model of the PMSM and the least squares (LS) method, motor parameters are estimated offline. Then based on the estimation values of the motor parameters, natural angular frequency and phase margin, a PI controller is designed. Performance indices including the natural angular frequency and the phase margin are used directly to design the PI controller in this paper. Scalar functions of the d-loop and the q-loop are selected. It can be seen that the designed controller parameters satisfy Lyapunov large scale asymptotic stability theory if the natural angular frequencies of the d-loop and the q-loop are large than 0. Experimental results show that the parameter estimation method has good accuracy and the designed PI controller proposed in this paper has good static and dynamic performances.

• International Journal of Highway Engineering
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• v.11 no.1
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• pp.233-245
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• 2009

Availability of pressuremeter test for evaluation of geotechnical properties of foundation soil into which guardrail post is to be installed is investigated in this study. First, an analysis method of the post based on the pressuremeter test is proposed that can obtain bending moment and load-deformation profiles of the post. Then static horizontal load test onto a small scale guardrail post is performed in order to get bearing capacity and load-deformation pattern of the model post. The obtained results are compared with the load-deformation curves and bearing capacity of the post obtained from the pressuremeter method. In addition horizontal impact test to the post is performed using a model bogie car in order to check failure pattern around the model foundation and to investigate dynamic bearing capacity due to deceleration and inertia force of the soil. It is verified that the pressuremeter test is so useful and reasonal technique to analyze road foundation-post interaction.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.27 no.4
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• pp.803-810
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• 2017

Recently, social security problems have been caused by the development of the software industry, and a variety of automation techniques have been used to verify software stability. In this paper, we propose a method of automatically detecting a use-after-free vulnerability on Windows system calls using dynamic symbolic execution, one of the software testing methods. First, a static analysis based pattern search is performed to select a target point. Based on the detected pattern points, we apply an induced path search technique that blocks branching to areas outside of interest. Through this, we overcome limitations of existing dynamic symbolic performance technology and verify whether vulnerability exists at actual target point. As a result of applying the proposed method to the Windows system call, it is confirmed that the use-after-free vulnerability, which had previously to be manually analyzed, can be detected by the proposed automation technique.

• Structural Engineering and Mechanics
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• v.24 no.6
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• pp.709-725
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• 2006

In this paper the buckling and post-buckling behavior of slender bars under self-weight are studied. In order to study the post-buckling behavior of the bar, a geometrically exact formulation for the non-linear analysis of uni-directional structural elements is presented, considering arbitrary load distribution and boundary conditions. From this formulation one obtains a set of first-order coupled nonlinear equations which, together with the boundary conditions at the bar ends, form a two-point boundary value problem. This problem is solved by the simultaneous use of the Runge-Kutta integration scheme and the Newton-Raphson method. By virtue of a continuation algorithm, accurate solutions can be obtained for a variety of stability problems exhibiting either limit point or bifurcational-type buckling. Using this formulation, a detailed parametric analysis is conducted in order to study the buckling and post-buckling behavior of slender bars under self-weight, including the influence of boundary conditions on the stability and large deflection behavior of the bar. In order to evaluate the quality and accuracy of the results, an experimental analysis was conducted considering a clamped-free thin-walled metal bar. As this kind of structure presents a high index of slenderness, its answers could be affected by the introduction of conventional sensors. In this paper, an experimental methodology was developed, allowing the measurement of static or dynamic displacements without making contact with the structure, using digital image processing techniques. The proposed experimental procedure can be used to a wide class of problems involving large deflections and deformations. The experimental buckling and post-buckling behavior compared favorably with the theoretical and numerical results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.10
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• pp.809-819
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• 2020

In this study, the twist angle and wing planform shapes were selected as design variables and optimized to secure the stability of the flying-wing type UAV. Flying-wing aircraft has no separated fuselage and tails, which has advantages in aerodynamic characteristics and stealth performance, but it is difficult to secure the flight stability. In this paper, the sweep back angle and twist angle were optimized to obtain the lateral stability, the static margin and wing planform shapes were optimized to improve the longitudinal stability of the flying-wing, then effect of the twist angle was confirmed by comparing the stability of the shape with the winglet and the shape with the twist angle. In the optimization formulation, focusing on improving stability, constraints were established, objective functions and design variables were set, then design variable sensitivity analysis was performed using the Sobol method. AVL was used for aerodynamic analysis and stability analysis, and SQP was used for optimization. The CFD analysis of the optimized shape and the simulation of the dynamic stability proved that the twist angle can be applied to the improvement of the lateral stability as well as the stealth performance in the flying-wing instead of the winglet.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.9
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• pp.3258-3273
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• 2021

Malware is a severe threat to the computing system and there's a long history of the battle between malware detection and anti-detection. Most traditional detection methods are based on static analysis with signature matching and dynamic analysis methods that are focused on sensitive behaviors. However, the usual detections have only limited effect when meeting the development of malware, so that the manual update for feature sets is essential. Besides, most of these methods match target samples with the usual feature database, which ignored the characteristics of the sample itself. In this paper, we propose a new malware detection method that could combine the features of a single sample and the general features of malware. Firstly, a structure of Directed Cyclic Graph (DCG) is adopted to extract features from samples. Then the sensitivity of each API call is computed with Markov Chain. Afterward, the graph is merged with the chain to get the final features. Finally, the detectors based on machine learning or deep learning are devised for identification. To evaluate the effect and robustness of our approach, several experiments were adopted. The results showed that the proposed method had a good performance in most tests, and the approach also had stability with the development and growth of malware.

• PNF and Movement
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• v.22 no.2
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• pp.275-288
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• 2024

Purpose: The purpose of this study was to assess the effects of breathing techniques on trunk muscle activity and balance during Pilates reformer footwork exercises, comparing results both within and between groups before and after the intervention. Methods: Thirty-one adult women over the age of 20 were selected as subjects for this study. They were divided into a Pilates breathing group (n = 15) and a general breathing group (n = 16) using a randomized control group study design. A surface electromyogram was used to measure muscle activity within and between the groups before and after the reformer footwork exercise. Static balance measurements were taken while standing on two legs, and dynamic balance measurements were taken while standing on one leg. All measurements were taken three times, and the average values were used for analysis. Results: The results of the study showed that muscle activity increased with significant differences in the external oblique and transverse abdominal muscles after exercise in the pre-post comparison within the Pilates breathing group (p < 0.05). In the between-group comparison, there was a significant difference in the increase in muscle activity of the external oblique and transverse abdominal muscles in the Pilates breathing group (p < 0.05). In the pre-post comparison of static and dynamic balance within the Pilates breathing group, there was a significant increase (p < 0.05) after exercise. The Pilates breathing group also showed a significant increase even in the between-group comparison (p < 0.05). Conclusion: This study confirmed that reformer footwork exercise accompanied by Pilates breathing has positive effects on muscle activity and static balance ability of trunk muscles in adult women. Therefore, reformer footwork exercise accompanied by Pilates breathing can be presented as an effective exercise method to increase trunk stability and balance ability through the simultaneous activity of the trunk muscles.