• Title/Summary/Keyword: initial theory

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Domain decomposition technique to simulate crack in nonlinear analysis of initially imperfect laminates

  • Ghannadpour, S. Amir M.;Karimi, Mona
    • Structural Engineering and Mechanics
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    • v.68 no.5
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    • pp.603-619
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    • 2018
  • In this research, an effective computational technique is carried out for nonlinear and post-buckling analyses of cracked imperfect composite plates. The laminated plates are assumed to be moderately thick so that the analysis can be carried out based on the first-order shear deformation theory. Geometric non-linearity is introduced in the way of von-Karman assumptions for the strain-displacement equations. The Ritz technique is applied using Legendre polynomials for the primary variable approximations. The crack is modeled by partitioning the entire domain of the plates into several sub-plates and therefore the plate decomposition technique is implemented in this research. The penalty technique is used for imposing the interface continuity between the sub-plates. Different out-of-plane essential boundary conditions such as clamp, simply support or free conditions will be assumed in this research by defining the relevant displacement functions. For in-plane boundary conditions, lateral expansions of the unloaded edges are completely free while the loaded edges are assumed to move straight but restricted to move laterally. With the formulation presented here, the plates can be subjected to biaxial compressive loads, therefore a sensitivity analysis is performed with respect to the applied load direction, along the parallel or perpendicular to the crack axis. The integrals of potential energy are numerically computed using Gauss-Lobatto quadrature formulas to get adequate accuracy. Then, the obtained non-linear system of equations is solved by the Newton-Raphson method. Finally, the results are presented to show the influence of crack length, various locations of crack, load direction, boundary conditions and different values of initial imperfection on nonlinear and post-buckling behavior of laminates.

Analytical investigation on lateral load responses of self-centering walls with distributed vertical dampers

  • Huang, Xiaogang;Zhou, Zhen;Zhu, Dongping
    • Structural Engineering and Mechanics
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    • v.72 no.3
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    • pp.355-366
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    • 2019
  • Self-centering wall (SCW) is a resilient and sustainable structural system which incorporates unbonded posttensioning (PT) tendons to provide self-centering (SC) capacity along with supplementary dissipators to dissipate seismic energy. Hysteretic energy dissipators are usually placed at two sides of SCWs to facilitate ease of postearthquake examination and convenient replacement. To achieve a good prediction for the skeleton curve of the wall, this paper firstly developed an analytical investigation on lateral load responses of self-centering walls with distributed vertical dampers (VD-SCWs) using the concept of elastic theory. A simplified method for the calculation of limit state points is developed and validated by experimental results and can be used in the design of the system. Based on the analytical results, parametric analysis is conducted to investigate the influence of damper and tendon parameters on the performance of VD-SCWs. The results show that the proposed approach has a better prediction accuracy with less computational effects than the Perez method. As compared with previous experimental results, the proposed method achieves up to 60.1% additional accuracy at the effective linear limit (DLL) of SCWs. The base shear at point DLL is increased by 62.5% when the damper force is increased from 0kN to 80kN. The wall stiffness after point ELL is reduced by 69.5% when the tendon stiffness is reduced by 75.0%. The roof deformation at point LLP is reduced by 74.1% when the initial tendon stress is increased from $0.45f_{pu}$ to $0.65f_{pu}$.

A Predictive Model on Patient-Centered Care of Hospital Nurses in Korea (상급종합병원 간호사의 환자중심간호 예측모형)

  • Jeong, Hyun;Park, Myonghwa
    • Journal of Korean Academy of Nursing
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    • v.49 no.2
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    • pp.191-202
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    • 2019
  • Purpose: Patient-centered care is a widely utilized concept in nursing and health care. However, the key components of patient-centered nursing have not yet been reported. Moreover, previous studies on patient-centered care have mostly focused on components of nursing rather than organizational factors. Therefore, a comprehensive understanding of influential factors of patient-centered care is required. Methods: The purpose of this study was to develop a theoretical model based on person-centered care theory, and the relevant literature and to test the developed model with covariance structure analysis in order to determine the causal paths among the variables. Results: The model fit indices for the hypothetical model were suitable for the recommended level (goodness of fit index=.87, standardized root mean residual=.01, root mean square error of approximation=.06, Tucker-Lewis index=.90, comparative fit index=.92, parsimonious normed fit index=.75). In this study, five of the six paths established in the initial hypothetical model were supported. The variables of teamwork, self-leadership, and empathy accounted for 56.4% of hospital nurses' patient-centered care. Among these, empathy was the strongest predictor of patient-centered care. Conclusion: These results suggest that it is necessary to use strategies to improve self-leadership and empathy. In addition to enhancing the personal factors of nurses, nursing organizations should strive for effective multidisciplinary cooperation with active support for patient-centered care and openness to change.

Word Embeddings-Based Pseudo Relevance Feedback Using Deep Averaging Networks for Arabic Document Retrieval

  • Farhan, Yasir Hadi;Noah, Shahrul Azman Mohd;Mohd, Masnizah;Atwan, Jaffar
    • Journal of Information Science Theory and Practice
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    • v.9 no.2
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    • pp.1-17
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    • 2021
  • Pseudo relevance feedback (PRF) is a powerful query expansion (QE) technique that prepares queries using the top k pseudorelevant documents and choosing expansion elements. Traditional PRF frameworks have robustly handled vocabulary mismatch corresponding to user queries and pertinent documents; nevertheless, expansion elements are chosen, disregarding similarity to the original query's elements. Word embedding (WE) schemes comprise techniques of significant interest concerning QE, that falls within the information retrieval domain. Deep averaging networks (DANs) defines a framework relying on average word presence passed through multiple linear layers. The complete query is understandably represented using the average vector comprising the query terms. The vector may be employed for determining expansion elements pertinent to the entire query. In this study, we suggest a DANs-based technique that augments PRF frameworks by integrating WE similarities to facilitate Arabic information retrieval. The technique is based on the fundamental that the top pseudo-relevant document set is assessed to determine candidate element distribution and select expansion terms appropriately, considering their similarity to the average vector representing the initial query elements. The Word2Vec model is selected for executing the experiments on a standard Arabic TREC 2001/2002 set. The majority of the evaluations indicate that the PRF implementation in the present study offers a significant performance improvement compared to that of the baseline PRF frameworks.

Higher-order Spectral Method for Regular and Irregular Wave Simulations

  • Oh, Seunghoon;Jung, Jae-Hwan;Cho, Seok-Kyu
    • Journal of Ocean Engineering and Technology
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    • v.34 no.6
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    • pp.406-418
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    • 2020
  • In this study, a nonlinear wave simulation code is developed using a higher-order spectral (HOS) method. The HOS method is very efficient because it can determine the solution of the boundary value problem using fast Fourier transform (FFT) without matrix operation. Based on the HOS order, the vertical velocity of the free surface boundary was estimated and applied to the nonlinear free surface boundary condition. Time integration was carried out using the fourth order Runge-Kutta method, which is known to be stable for nonlinear free-surface problems. Numerical stability against the aliasing effect was guaranteed by using the zero-padding method. In addition to simulating the initial wave field distribution, a nonlinear adjusted region for wave generation and a damping region for wave absorption were introduced for wave generation simulation. To validate the developed simulation code, the adjusted simulation was carried out and its results were compared to the eighth order Stokes theory. Long-time simulations were carried out on the irregular wave field distribution, and nonlinear wave propagation characteristics were observed from the results of the simulations. Nonlinear adjusted and damping regions were introduced to implement a numerical wave tank that successfully generated nonlinear regular waves. According to the variation in the mean wave steepness, irregular wave simulations were carried out in the numerical wave tank. The simulation results indicated an increase in the nonlinear interaction between the wave components, which was numerically verified as the mean wave steepness. The results of this study demonstrate that the HOS method is an accurate and efficient method for predicting the nonlinear interaction between waves, which increases with wave steepness.

Investigation of continuous and discontinuous contact cases in the contact mechanics of graded materials using analytical method and FEM

  • Yaylaci, Murat;Adiyaman, Gokhan;Oner, Erdal;Birinci, Ahmet
    • Computers and Concrete
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    • v.27 no.3
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    • pp.199-210
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    • 2021
  • The aim of this paper was to examine the continuous and discontinuous contact problems between the functionally graded (FG) layer pressed with a uniformly distributed load and homogeneous half plane using an analytical method and FEM. The FG layer is made of non-homogeneous material with an isotropic stress-strain law with exponentially varying properties. It is assumed that the contact at the FG layer-half plane interface is frictionless, and only the normal tractions can be transmitted along the contacted regions. The body force of the FG layer is considered in the study. The FG layer was positioned on the homogeneous half plane without any bonds. Thus, if the external load was smaller than a certain critical value, the contact between the FG layer and half plane would be continuous. However, when the external load exceeded the critical value, there was a separation between the FG layer and half plane on the finite region, as discontinuous contact. Therefore, there have been some steps taken in this study. Firstly, an analytical solution for continuous and discontinuous contact cases of the problem has been realized using the theory of elasticity and Fourier integral transform techniques. Then, the problem modeled and two-dimensional analysis was carried out by using ANSYS package program based on FEM. Numerical results for initial separation distance and contact stress distributions between the FG layer and homogeneous half plane for continuous contact case; the start and end points of separation and contact stress distributions between the FG layer and homogeneous half plane for discontinuous contact case were provided for various dimensionless quantities including material inhomogeneity, distributed load width, the shear module ratio and load factor for both methods. The results obtained using FEM were compared with the results found using analytical formulation. It was found that the results obtained from analytical formulation were in perfect agreement with the FEM study.

A Study on the Online Perception of Chabak Using Big Data Analysis (빅데이터 분석을 통한 차박의 온라인 인식에 대한 연구)

  • Kim, Sae-Hoon;Lee, Hwan-Soo
    • The Journal of Society for e-Business Studies
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    • v.26 no.2
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    • pp.61-81
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    • 2021
  • In the era of untact, the "Chabak" using cars as accommodation spaces is attracting attention as a new form of travel. Due to the advantages, including low costs, convenience, and safety, as well as the characteristics of the vehicle enabling independent travel, the demand for Chabak is continuously increasing. Despite the rapid growth of the market and related industries, little academic has investigated this trend. To establish itself as a new type of travel culture and to sustain the growth of related industries, it is essential to understand the public perception of Chabak. Therefore, based on the marketing mix theory and big data analysis, this study analyzes the public perception of Chabak. The results showed that Chabak has established itself as a consumer-led travel culture, contributing to the aftermarket growth of the automobile industry. Additionally, consumers were found to be increasingly inclined to enjoy travel economically and wisely, and actively share information through social media. This initial study on the new travel trend of Chabak is significant in that it employs big data analysis on a theoretical basis.

Aerodynamic Model Development for Three-dimensional Scramjet Model Based on Two-dimensional CFD Analysis (스크램제트 2차원 모델의 전산해석을 이용한 3차원 비행체의 공력 모델 개발)

  • Han, Song Ee;Shin, Ho Cheol;Park, Soo Hyung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.24 no.5
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    • pp.65-76
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    • 2020
  • On the initial design process of a scramjet vehicle such as the trajectory prediction, it is inevitable to estimate the aerodynamic performance of a three-dimensional effect. Despite the necessity of intensive computing for the three-dimensional model, it is inefficient in predicting a wide range of aerodynamic performance. In this study, an engineering model for aerodynamic performance was developed based on two-dimensional computational fluid analysis and linearized supersonic inviscid flow theory. Correspondingly, the three-dimension aerodynamic performance relations are presented based on the two-dimensional results. And the additional three-dimensional computation was performed to evaluate the adequacy for the extended relations.

A Study on Improved Inspection Method of the Foundation Scouring and Establishment of 3D Underwater Surface Map (개선된 교량 기초세굴 점검방법 및 3D 하상지도 구축 연구)

  • Choi, Hyun-Chul;Ko, Jun-Young
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.26 no.5
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    • pp.161-170
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    • 2022
  • The maintenance of bridges installed in rivers is carried out through facility safety inspection and repair & reinforcement procedures according to the results. Many studies have been so far conducted on the safety check of the bridge upperstructure because of the ease of access. However as it is impossible to directly investigate whether the pier foundation installed in the river has been scoured. Management of underwater foundations has remained based on theory. In this study, the scour of the bridge foundation installed in such a river was realized in 3D form by using an echo sounder and VRS. This made it possible to predict the scour pattern through comparison and analysis with the ground height of the riverbed at the time of the bridge installation. Based on these results, if the pier foundation is used as an initial data to determine whether or not local scour is present and to predict long-term scouring, bridge collapse due to foundation scour can be prevented.

Excess Pore Pressure Induced by Cone Penetration in OC Clay (콘관입으로 인한 과압밀점토의 과잉간극수압의 분포)

  • Kim, Tai-Jun;Kim, Sang-In;Lee, Woo-Jin
    • Journal of the Korean Geotechnical Society
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    • v.22 no.11
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    • pp.75-87
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    • 2006
  • A series of calibration chamber tests are performed to investigate the spatial distribution of the excess porewater pressure due to piezocone penetration into overconsolidated clays. It was observed that the excess porewater pressure increases monotonically from the piezocone surface to the outer boundary of the shear zone and then decreases logarithmically, approaching zero at the outer boundary of the plastic zone. It was also found that the size of the shear zone decreases from approximately 2.2 to 1.5 times the cone radius with increasing OCR, while the plastic radius is about 11 times the piezocone radius, regardless of the OCR. Based on the modified Cam clay model and the cylindrical cavity expansion theory, the expressions to predict the Initial porewater pressure at the piezocone were developed, considering the effects of the strain rate and stress anisotropy. The method of predicting the spatial distribution of excess porewater pressure proposed in this study was verified by comparing it with the porewater pressure measured in overconsolidated specimens in the calibration chamber.