• Structural Engineering and Mechanics
• /
• 제88권4호
• /
• pp.355-368
• /
• 2023

Employing the non-local strain gradient theory (NSGT), this paper investigates the nonlinear resonance characteristics of functionally graded material (FGM) nanoshells with initial geometric imperfection for the first time. The effective material properties of the porous FGM nanoshells with even distribution of porosities are estimated by a modified power-law model. With the guidance of Love's thin shell theory and considering initial geometric imperfection, the strain equations of the shells are obtained. In order to characterize the small-scale effect of the nanoshells, the nonlocal parameter and strain gradient parameter are introduced. Subsequently, the Euler-Lagrange principle was used to derive the motion equations. Considering three boundary conditions, the Galerkin principle combined with the modified Lindstedt Poincare (MLP) method are employed to discretize and solve the motion equations. Finally, the effects of initial geometric imperfection, functional gradient index, strain gradient parameters, non-local parameters and porosity volume fraction on the nonlinear resonance of the porous FGM nanoshells are examined.

• Advances in aircraft and spacecraft science
• /
• 제10권6호
• /
• pp.545-554
• /
• 2023

The widespread introduction of unmanned aircrafts has led to the understanding of the need to organize a common information space for manned and unmanned aircrafts, which is reflected in the Russian Unmanned aircraft system Traffic Management (RUTM) project. The present article deals with the issues of spatial information database (DB) organization, which is the core of RUTM and provides storage of various data types (spatial, aeronautical, topographical, meteorological, vector, etc.) required for flight safety management. Based on the analysis of functional capabilities and types of work which it needs to ensure, the architecture of spatial information DB, including the base of source information, base of display settings, base of vector objects, base of tile packages and also a number of special software packages was proposed. The issues of organization of these DB, types and formats of data and ways of their display are considered in detail. Based on the analysis it was concluded that the optimal construction of the spatial DB for RUTM system requires a combination of different model variants and ways of organizing data structures.

• 한국산학기술학회논문지
• /
• 제13권7호
• /
• pp.3057-3064
• /
• 2012

본 연구에서는 뇌졸중 환자의 건강신념과 환자의 운동기능 재활 이행 및 일상생활동작 수행능력의 관계를 파악하고 뇌졸중 환자의 성공적인 재활 프로그램에 대한 기초 자료를 제공함으로써 임상에서 뇌졸중 환자의 재활시 근거자료로 활용하고자 시도되었다. 전라북도 J시에 소재하고 있는 D병원에 뇌졸중으로 진단 받고 입원 치료중인 뇌졸중 환자들을 대상으로 본 연구목적을 이해하고 연구 참여에 동의한 환자에게 총 150부의 설문지를 배부한 후 132부를 회수하였고 그 중 자료가 불충분한 11부를 제외한 총 121부를 자료 분석하고, 평가를 실시하였다. 수집된 자료는 SPSS for Window(ver.12.0) 프로그램을 사용하여 대상자 일반적 특성을 파악하기 위해 빈도분석을 하였으며, 건강신념과 운동기능 재활 이행 및 일상생활동작 수행능력 사이의 상관관계를 알아보기 위하여 이변량 상관분석과 회귀분석을 실시하였다. 본 연구결과 지각된 민감성, 지각된 유익성, 지각된 심각성이 높아질수록 운동기능 재활 이행이 높았으며, 지각된 장애성 낮을수록 운동기능 재활 이행이 높아지는 것을 확인하였다.

• 대한환경공학회지
• /
• 제31권5호
• /
• pp.332-340
• /
• 2009

20종의 아미노산 성분들에서의 염소 소독부산물 생성 특성을 조사한 결과, 단위 DOC당 THM 생성능은 Br 첨가 유무에 관계없이 tryptophan과 tyrosine에서 높게 나타났고 나머지 18종에서는 매우 낮은 생성능을 나타내었다. 단위 DOC당 HAA 생성능 조사결과, tryptophan, tyrosine, asparagine, aspartic acid 및 histidine에서 Br 첨가 유무에 관계없이 높은 생성능을 보였으며, asparagine, aspartic acid 및 histidine은 DCAA 생성능 조사결과, aspartic acid, histidine, asparagine, tyrosine 및 tryptophan에서 Br 첨가 유무에 관계없이 높은 생성능을 나타내었으며, aspartic acid는 660.2 ${\mu}$g/mg으로 나타나 다른 아미노산 성분들에 비해 월등히 높은 HAN 생성능을 나타내었으며, 반응성이 높은 6종의 아미노산 성분에서 생성되는 HAN 구성종의 대부분은 DCAN으로 나타났다. 단위 DOC당 chloral hydrate 와 chloropicrin의 생성능을 조사결과에서 chloral hydrate는 asparagine, aspartic acid, histidine, methionine, tryptophan 및 tyrosine에서 생성능이 높은 것으로 나타났고, chloropicrin의 경우는 20종의 아미노산에서 전체적으로 1${\mu}$g/mg 이하의 아주 낮은 생성능을 보였다. 아미노산의 작용기별 소독부산물 생성 특성은 THM의 경우 방향족(aromatic) 화합물인 tryptophan과 tyrosine에 반응성이 높았고, HAA는 aromatic, neutral, acidic, basic 순으로 반응성을 보였으며, HAN은 acidic, basic, neutral, aromatic 순으로 반응성을 나타내어 방향족 화합물보다 지방족 화합물이며 친수성인 물질에서 반응성이 더 높은 것으로 나타났다.

• Smart Structures and Systems
• /
• 제22권3호
• /
• pp.341-358
• /
• 2018

This present study investigates Love-type wave propagation in composite structure consists of a loosely bonded functionally graded piezoelectric material (FGPM) stratum lying over a functionally graded initially-stressed fibre-reinforced material (FGIFM) substrate. The closed-form expressions of the dispersion relation have been obtained analytically for both the cases of electrically open and electrically short conditions. Some special cases of the problem have also been studied and the obtained results are found in well-agreement with the classical Love wave equation. The emphatic influence of wave number, bonding parameter associated with bonding of stratum with substrate of the composite structure, piezoelectric coefficient as well as dielectric constant of the piezoelectric stratum, horizontal initial stresses, and functional gradedness of the composite structure on the phase velocity of Love-type wave has been reported and illustrated through numerical computation along with graphical demonstration in both the cases of electrically open and electrically short condition for the reinforced and reinforced-free composite structure. Comparative study has been carried out to analyze the distinct cases associated with functional gradedness of the composite structure and also various cases which reveals the influence of piezoelectricity, reinforcement and horizontal initial stress acting in the composite structure, and bonding of the stratum and substrate of the composite structure in context of the present problem which serves as one of the major highlights of the study.

• Advances in Computational Design
• /
• 제5권4호
• /
• pp.363-380
• /
• 2020

In this paper, a cylindrical shell is immersed in a non-viscous fluid using first order shell theory of Sander. These equations are partial differential equations which are solved by approximate technique. Robust and efficient techniques are favored to get precise results. Employment of the Rayleigh-Ritz procedure gives birth to the shell frequency equation. Use of acoustic wave equation is done to incorporate the sound pressure produced in a fluid. Hankel's functions of second kind designate the fluid influence. Mathematically the integral form of the Lagrange energy functional is converted into a set of three partial differential equations. Throughout the computation, simply supported edge condition is used. Expressions for modal displacement functions, the three unknown functions are supposed in such way that the axial, circumferential and time variables are separated by the product method. Comparison is made for empty and fluid-filled cylindrical shell with circumferential wave number, length- and height-radius ratios, it is found that the fluid-filled frequencies are lower than that of without fluid. To generate the fundamental natural frequencies and for better accuracy and effectiveness, the computer software MATLAB is used.

• Smart Structures and Systems
• /
• 제7권5호
• /
• pp.379-392
• /
• 2011

This paper presents a multi-functional system, consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) device, and its applications in stay cables. The proposed system is capable of offering multiple functions: (1) mitigating excessive vibrations of cables, (2) estimating cable tension, and (3) harvesting energy for wireless sensors used health monitoring of cable-stayed bridges. In the proposed system, the EMI device, consisting of permanent magnets and a solenoid coil, can converts vibration energy into electrical energy (i.e., induced emf); hence, it acts as an energy harvesting system. Moreover, the cable tension can be estimated by using the emf signals obtained from the EMI device. In addition, the MR damper, whose damping property is controlled by the harvested energy from the EMI device, can effectively reduce excessive cable vibrations. In this study, the multi-functionality of the proposed system is experimentally evaluated by conducting a shaking table test as well as a full-scale stay cable in a laboratory setting. In the shaking table experiment, the energy harvesting capability of the EMI device for wireless sensor nodes is investigated. The performance on the cable tension estimation and the vibration mitigation are evaluated using the full-scale cable test setup. The test results show that the proposed system can sufficiently generate and store the electricity for operating a wireless sensor node twice per day, significantly alleviate vibration of a stay cable (by providing about 20% larger damping compared to the passive optimal case), and estimate the cable tension accurately within a 2.5% error.

• Computers and Concrete
• /
• 제23권1호
• /
• pp.1-10
• /
• 2019

The use of non-linear analysis of structures in a functional way for evaluating the structural seismic behavior has attracted the attention of the engineering community in recent years. The most commonly used functional method for analysis is a non-linear static method known as the "pushover method". In this study, for the first time, a cyclic pushover analysis with different loading protocols was used for seismic investigation of curved bridges. The finite element model of 8-span curved bridges in plan created by the ZEUS-NL software was used for evaluating different pushover methods. In order to identify the optimal loading protocol for use in astatic non-linear cyclic analysis of curved bridges, four loading protocols (suggested by valid references) were used. Along with cyclic analysis, conventional analysis as well as adaptive pushover analysis, with proven capabilities in seismic evaluation of buildings and bridges, have been studied. The non-linear incremental dynamic analysis (IDA) method has been used to examine and compare the results of pushover analyses. To conduct IDA, the time history of 20 far-field earthquake records was used and the 50% fractile values of the demand given the ground motion intensity were computed. After analysis, the base shear vs displacement at the top of the piers were drawn. Obtained graphs represented the ability of a cyclic pushover analysis to estimate seismic capacity of the concrete piers of curved bridges. Based on results, the cyclic pushover method with ISO loading protocol provided better results for evaluating the seismic investigation of concrete piers of curved bridges in plan.

• Computers and Concrete
• /
• 제27권4호
• /
• pp.333-341
• /
• 2021

Steel slag, an industrial reject from the steel rolling process, has been identified as one of the suitable, environmentally friendly materials for concrete production. Given that the coarse aggregate portion represents about 70% of concrete constituents, other economic approaches have been found in the use of alternative materials such as steel slag in concrete. Unfortunately, a standard framework for its application is still lacking. Therefore, this study proposed functional model equations for the determination of strength properties (compression and splitting tensile) of steel slag aggregate concrete (SSAC), using gene expression programming (GEP). The study, in the experimental phase, utilized steel slag as a partial replacement of crushed rock, in steps 20%, 40%, 60%, 80%, and 100%, respectively. The predictor variables included in the analysis were cement, sand, granite, steel slag, water/cement ratio, and curing regime (age). For the model development, 60-75% of the dataset was used as the training set, while the remaining data was used for testing the model. Empirical results illustrate that steel aggregate could be used up to 100% replacement of conventional aggregate, while also yielding comparable results as the latter. The GEP-based functional relations were tested statistically. The minimum absolute percentage error (MAPE), and root mean square error (RMSE) for compressive strength are 6.9 and 1.4, and 12.52 and 0.91 for the train and test datasets, respectively. With the consistency of both the training and testing datasets, the model has shown a strong capacity to predict the strength properties of SSAC. The results showed that the proposed model equations are reliably suitable for estimating SSAC strength properties. The GEP-based formula is relatively simple and useful for pre-design applications.

• Geomechanics and Engineering
• /
• 제29권4호
• /
• pp.377-390
• /
• 2022

The stability of the roof rock-coal pillar-floor rock composite structure is of great significance to coal mine safety production. The cracks existing in the composite structure seriously affect the stability of the roof rock-coal pillar-floor rock composite structure. The numerical simulation tests of rock-coal-rock composite structures with different crack characteristics were carried out to reveal the composite structures' mechanical properties and failure mechanisms. The test results show that the rock-coal-rock composite structure's peak stress and elastic modulus are directly proportional to the crack angle and inversely proportional to the crack length. The smaller the crack angle, the more branch cracks produced near the main control crack in the rock-coal-rock composite structure, and the larger the angle between the main control crack and the crack. The smaller the crack length, the larger the width of the crack zone. The impact energy index of the rock-coal-rock composite structure decreases first and then increases with the increase of crack length and increases with the increase of crack angle. The functional relationships between the different crack characteristics, peak stress, and impact energy index are determined based on the sensitivity analysis. The determination of the functional relationship can fully grasp the influence of the crack angle and the crack length on the peak stress and impact energy index of the coal-rock composite structure. The research results can provide a theoretical basis and guidance for preventing the instability and failure of the coal pillar-roof composite structure.