• Nonlinear Functional Analysis and Applications
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• 제28권4호
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• pp.943-956
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• 2023

Let p(z) be a polynomial of degree n and for any complex number 𝛽, let D_𝛽p(z) = np(z) + (𝛽 - z)p'(z) denote the polar derivative of the polynomial with respect to 𝛽. In this paper, we consider the class of polynomial $$p(z)=(z-z_0)^s \left(a_0+\sum\limits_{{\nu}=0}^{n-s}a_{\nu}z^{\nu}\right)$$ of degree n having a zero of order s at z₀, |z₀| < 1 and the remaining n - s zeros are outside |z| < k, k ≥ 1 and establish upper bound estimates for the maximum of |D_𝛽p(z)| as well as |p(Rz) - p(rz)|, R ≥ r ≥ 1 on the unit disk.

• 한국지진공학회논문집
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• 제19권2호
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• pp.63-74
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• 2015

This study investigated the influence of probabilistic variability in stiffness and nonlinearity of soil on response of nuclear power plant (NPP) structure subjected to seismic loads considering the soil-structure interaction (SSI). Both deterministic and probabilistic methods have been employed to evaluate the dynamic responses of the structure. For the deterministic method, $SRP_{min}$ method given in USNRC SRP 3.7.2(2013) (envelope of responses using three shear modulus profiles of lower bound($G_{LB}$), best estimate($G_{BE}$) and upper bound($G_{UB}$)) and $SRP_{max}$ method (envelope of responses by more than three ground profiles within range of $G_{LB}{\leq}G{\leq}G_{UB}$) have been considered. The probabilistic method uses the Latin Hypercube Sampling (LHS) that can capture probabilistic feature of soil stiffness defined by the median and the standard deviation. These analysis results indicated that 1) number of samples shall be larger than 60 to apply the probabilistic approach in SSI analysis and 2) in-structure response spectra using equivalent linear soil profiles considering the nonlinear behavior of soil medium can be larger than those based on low-strain soil profiles.

• Earthquakes and Structures
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• 제9권3호
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• pp.481-501
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• 2015

Current design codes and technical recommendations often provide rough indications on how to assess effective stiffness of Reinforced Concrete (R/C) frames subjected to seismic loads, which is a key factor when a linear analysis is performed. The Italian design code (NTC-2008), Eurocode 8 and ACI 318 do not take into account all the structural parameters affecting the effective stiffness and this may not be on the safe side when second-order $P-{\Delta}$ effects may occur. This paper presents a study on the factors influencing the effective stiffness of R/C beams, columns and walls under seismic forces. Five different approaches are adopted and analyzed in order to evaluate the effective stiffness of R/C members, in accordance with the scientific literature and the international design codes. Furthermore, the paper discusses the outcomes of a parametric analysis performed on an actual R/C building and analyses the main variables, namely reinforcement ratio, axial load ratio, concrete compressive strength, and type of shallow beams. The second-order effects are investigated and the resulting displacements related to the Damage Limit State (DLS) under seismic loads are discussed. Although the effective stiffness increases with steel ratio, the analytical results show that the limit of 50% of the initial stiffness turns out to be the upper bound for small values of axial-load ratio, rather than a lower bound as indicated by both Italian NTC-2008 and EC8. As a result, in some cases the current Italian and European provisions tend to underestimate second-order $P-{\Delta}$ effects, when the DLS is investigated under seismic loading.

• 자연과학논문집
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• 제8권2호
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• pp.63-67
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• 1996

LVCMS나 LMF와 같이 고차의 통계에 근거한 적응 신호 알고리즘들은 입력신호에 꼬리가 두툼한 확률밀도를 같는 잡음이 섞여있는 경우 현저한 성능 저하를 보여준다. 일반적인 알고리즘 분석 방법에서는 순환식에서 2차 보다 큰 power를 갖는 항들을 모두 무시하기 때문에 정확한 알고리즘의 성능을 예측하지 못할 수도 있다. 이 논문에서는 새로운 분석방법을 통하여 무시된 항들의 영향이 무엇인가를 알아본다. 분석 결과 무시된 항들은 스텝 크기의 상한선에는 영향을 미치지 못하나 misadjustment를 증가시킬 수 있는 것으로 나타났다. 그러나 그 영향은 스텝 크기의 제곱에 비례하여 감소한다.

• Steel and Composite Structures
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• 제1권4호
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• pp.411-426
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• 2001

This paper treats the failure analysis of prestressing steel wires with different kinds of localised damage in the form of a surface defect (crack or notch) or as a mechanical action (transverse loads). From the microscopical point of view, the micromechanisms of fracture are shear dimples (associated with localised plasticity) in the case of the transverse loads and cleavage-like (related to a weakest-link fracture micromechanism) in the case of cracked wires. In the notched geometries the microscopic modes of fracture range from the ductile micro-void coalescence to the brittle cleavage, depending on the stress triaxiality in the vicinity of the notch tip. From the macroscopical point of view, fracture criteria are proposed as design criteria in damage tolerance analyses. The transverse load situation is solved by using an upper bound theorem of limit analysis in plasticity. The case of the cracked wire may be treated using fracture criteria in the framework of linear elastic fracture mechanics on the basis of a previous finite element computation of the stress intensity factor in the cracked cylinder. Notched geometries require the use of elastic-plastic fracture mechanics and numerical analysis of the stress-strain state at the failure situation. A fracture criterion is formulated on the basis of the critical value of the effective or equivalent stress in the Von Mises sense.

• 대한기계학회논문집A
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• 제20권11호
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• pp.3538-3548
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• 1996

In this study, as a part of basic study for developing the simulation program for the assemssment of reliability of electronic EMC packaging which covers from EMC mixing step to thermal analysis, comparison between a measured and predicted values of material properties of EMC and finitde element analysis of thermal stress are performed. For the experimental testing specimens of fifty, sixty hive and eighty percent filler($13\mu m$, spherical silica) weight fraction are fabricated using tranfer molding. Coefficient of thermal expansion, elastic modulus and thermla conductivity are measured using these specimens and then these measured values are compared with the predicted values by various equations ( such as dilute suspension method. self consistent method, generalized self consistent method, Hashin-Shtrikman's bounds. Shapery's bounds, Nielsen's method and others). Measured values are distributed within the upper and lower bounds of equations. Measured elastic modulus and coefficient of thermal expansion approaches closely the perdicted values with self consisten mehtod and upper bound of Shaperys equation respectively. However small differences of thermal conductivity between the different filler volume fraction are obserbed. FEM analysis indicates that firstly stress is concentrated at the corner section of EMC and secondly EMC with eighty percent filler weight fraction shows less thermal stress when package is cooling down and relatively high thermal stress when package is heating up.

• Journal of Welding and Joining
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• 제35권1호
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• pp.55-60
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• 2017

There are many Industry Code and Standard (ICS) for Structural Integrity Assessment (SIA) on welded structure with defect. The general ICSs, such as R6, BS 7910 and API 579-1/ASME FFS-1, provide equations to determine the upper bound residual stress profiles based on collections from many literatures. However, these residual stress profiles used in the SIA cause the conservative design for welded structures. In this study, the structural integrity assessment for girth weld in pipeline has been conducted based on fracture mechanics. In addition, thermo-elastic plastic FE analysis was performed for evaluating the residual stress of girth weld in pipeline. The weight function solution is used to determine the stress intensity factor using the residual stress profile obtained by the FE analysis. This approach can account for redistribution and relaxation of residual stress as the defects grow. In order to the evaluate quantitative comparison between BS 7910 and weight function solution, structural integrity assessment determining allowable crack size on cracked pipe was performed with failure assessment diagram.

• 한국자기공명학회논문지
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• 제21권3호
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• pp.109-113
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• 2017

The hepatitis C virus (HCV) internal ribosome entry site (IRES) is an RNA structure located in the 5'-UTR of the HCV RNA genome. The HCV IRES consists of four domains I, II, III, and IV, where domains II - IV are recognized by 40S ribosomal subunit and the domain III is bound to eukaryotic initiation factor 3 (eIF3) for translation initiation. Here, we have characterized the tertiary interaction between an L-/K- rich peptide and the HCV IRES domain IV. To probe the peptide binding interface in RNA, we synthesized $^{13}C$- and $^{15}N$-double labeled RNA and the binding site was identified by using the chemical shift perturbation (CSP) NMR methods. Our results showed that the peptide binds to the upper stem of the IRES domain IV, indicating that the tertiary interaction between the IRES domain IV and the peptide would disrupt the initiation of translation of HCV mRNA by blocking the start codon exposure. This study will provide an insight into the new peptide-based anti-viral drug design targeting HCV IRES RNA.

• Coupled systems mechanics
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• 제2권1호
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• pp.23-51
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• 2013

An analytical algorithm for the estimation of the resistance forces exerted on the dipper of a cable shovel and the specific energy consumed in the cutting-loading process is presented. Forces due to payload and to cutting of geomaterials under given initial conditions, cutting trajectory of the bucket, bucket's design, and geomaterial properties are analytically computed. The excavation process has been modeled by means of a kinematical shovel model, as well as of dynamic payload and cutting resistance models. For the calculation of the cutting forces, a logsandwich passive failure mechanism of the geomaterial is considered, as has been found by considering that a slip surface propagates like a mixed mode crack. Subsequently, the Upper-Bound theorem of Limit Analysis Theory is applied for the approximate calculation of the maximum reacting forces exerted on the dipper of the cable shovel. This algorithm has been implemented into an Excel$^{TM}$ spreadsheet to facilitate user-friendly, "transparent" calculations and built-in data analysis techniques. Its use is demonstrated with a realistic application of a medium-sized shovel. It was found, among others, that the specific energy of cutting exhibits a size effect, such that it decreases as the (-1)-power of the cutting depth for the considered example application.

• 한국소음진동공학회논문집
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• 제15권4호
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• pp.457-464
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• 2005

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of thick, complete (not truncated) conical shells of revolution, Unlike conventional shell theories, which are mathematically two-dimensional (2-D). the present method is based upon the 3-D dynamic equations of elasticity. Displacement components $u_{r},\;u_{z},\;and\;u_{\theta}$ in the radial, axial, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in , and algebraic polynomials in the r and z directions. Potential (strain) and kinetic energies of the conical shells are formulated, the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four-digit exactitude is demonstrated for the first five frequencies of theconical shells. Novel numerical results are presented for thick, complete conical shells of revolution based upon the 3-D theory. Comparisons are also made between the frequencies from the present 3-D Ritz method and a 2-D thin shell theory.