• Advances in aircraft and spacecraft science
• /
• 제4권4호
• /
• pp.449-465
• /
• 2017

The aim of the present work is to present a computational study of the non-linear aero-elastic behavior of a multi-layered Thermal Protection System (TPS). The severity of atmospheric re-entry conditions is due to the combination of high temperatures, high pressures and high velocities, and thus the aero-elastic behavior of flexible structures can be difficult to assess. In order to validate the specific computational model and the overall strategy for structural and aerodynamics analyses of flexible structures, the simplified TPS sample tested in the 8' High Temperature Tunnel (HTT) at NASA LaRC has been selected as a baseline for the validation of the present work. The von $K{\acute{a}}rm{\acute{a}}n^{\prime}s$ three dimensional large deflection theory for the structure and a hybrid Raleigh-Ritz-Galerkin approach, combined with the first order Piston Theory to describe the aerodynamic flow, have been used to derive the equations of motion. The paper shows that a good description of the physical behavior of the fabric is possible with the proposed approach. The model is further applied to investigate structural and aero-elastic influence of the number of the layers and the stitching pattern.

• Smart Structures and Systems
• /
• 제18권5호
• /
• pp.1029-1062
• /
• 2016

In this research, the nonlinear free vibration analysis of boron-nitride micro ribbon (BNMR) on the Pasternak elastic foundation under electrical, mechanical and thermal loadings using modified strain gradient theory (MSGT) is studied. Employing the von $K{\acute{a}}rm{\acute{a}}n$ nonlinear geometry theory, the nonlinear equations of motion for the graphene micro ribbon (GMR) using Euler-Bernoulli beam model with considering attached mass and size effects based on Hamilton's principle is obtained. These equations are converted into the nonlinear ordinary differential equations by elimination of the time variable using Kantorovich time-averaging method. To determine nonlinear frequency of GMR under various boundary conditions, and considering mass effect, differential quadrature element method (DQEM) is used. Based on modified strain MSGT, the results of the current model are compared with the obtained results by classical and modified couple stress theories (CT and MCST). Furthermore, the effect of various parameters such as material length scale parameter, attached mass, temperature change, piezoelectric coefficient, two parameters of elastic foundations on the natural frequencies of BNMR is investigated. The results show that for all boundary conditions, by increasing the mass intensity in a fixed position, the linear and nonlinear natural frequency of the GMR reduces. In addition, with increasing of material length scale parameter, the frequency ratio decreases. This results can be used to design and control nano/micro devices and nano electronics to avoid resonance phenomenon.

• Steel and Composite Structures
• /
• 제23권1호
• /
• pp.53-66
• /
• 2017

Structures submitted to Fire-After-Earthquake loading situations, are first experiencing inelastic deformations due to the seismic action and are then submitted to the thermal loading. This means that in the case of steel framed structures, at the starting point of the fire, plastic hinges have already been formed at the ends of the beams. The basic objective of this paper is the evaluation of the rotational capacity of steel I-section beams damaged due to prior earthquake loading, at increased temperatures. The study is conducted numerically and three-dimensional models are used in order to capture accurately the nonlinear behaviour of the steel beams. Different levels of earthquake-induced damage are examined in order to study the effect of the initial state of damage to the temperature-evolution of the rotational capacity. The study starts with the reference case where the beam is undamaged and in the sequel cyclic loading patterns are taken into account, which represent earthquakes loads of increasing magnitude. Additionally, the study extends to the evaluation of the ultimate plastic rotation of the steel beams which corresponds to the point where the rotational capacity of the beam is exhausted. The aforementioned value of rotation can be used as a criterion for the determination of the fire-resistance time of the structure in case of Fire-After-Earthquake situations.

• Structural Engineering and Mechanics
• /
• 제64권4호
• /
• pp.515-526
• /
• 2017

Dynamic response of functionally graded Carbon nanotubes (FG-CNT) reinforced pipes conveying viscous fluid under accelerated moving load is presented. The mixture rule is used for obtaining the material properties of nano-composite pipe. The radial force induced by viscous fluid is calculated by Navier-Stokes equation. The material properties of pipe are considered temperature-dependent. The structure is simulated by Reddy higher-order shear deformation shell theory and the corresponding motion equations are derived by Hamilton's principal. Differential quadrature (DQ) method and the Integral Quadrature (IQ) are applied for analogizing the motion equations and then the Newmark time integration scheme is used for obtaining the dynamic response of structure. The effects of different parameters such as boundary conditions, geometrical parameters, velocity and acceleration of moving load, CNT volume percent and distribution type are shown on the dynamic response of pipe. Results indicate that increasing CNTs leads to decrease in transient deflection of structure. In accelerated motion of the moving load, the maximum displacement is occurred later with respect to decelerated motion of moving load.

• 한국정밀공학회지
• /
• 제27권12호
• /
• pp.84-91
• /
• 2010

The bonding process of LCD panel is attaching an inner lead to an outer lead in the production line of LCD panel module. It is composed of an OLB process and a PCB bonding process. Since bonding tool assembly is one of the core parts of the bonding equipment that determines the durability and performance of the final product, much design efforts to enhance uniformity and efficiency of the process have been made. In this paper, FE analyses have been employed to determine the bonding tool size. Bonding tool of long bar shape has been simplified as a piece with same heater pitch, and appropriate boundary conditions such as convection and radiation are considered. Thermal analysis results by the FEM have been validated by the experiments. With the use of FE analysis varies design parameters and the corresponding effects have been evaluated. It was observed that the approach presented in this paper could be employed for the design of LCD module bonding tool.

• 환경생물
• /
• 제17권3호
• /
• pp.249-255
• /
• 1999

Poly(3-hydroxybutyrate)의 표면 형태가 생분해성에 미치는 영향을 조사하였다. 용융 상태의 PHB를 서냉 ($-0.5^{\circ}C$/min)시켰을 때 PHB의 결정화도는 액체질소 속으로 급냉한 후 $90^{\circ}C$에서 2시간 동안 숙성한 PHB의 결정화도보다 높게 나타났으나 전자의 PHB 시료는 미세 균열의 존재로 인하여 후자의 PHB 시료보다 더 빠르게 생분해되었다. 거친 표면을 가진 평판 위에서 hot press하여 표면을 거칠게 만든 PHB film의 생분해는 표면이 평활한 film보다 훨씬 더 빠르게 진행되었다.

• Steel and Composite Structures
• /
• 제22권3호
• /
• pp.567-587
• /
• 2016

The present investigation is to study the plane wave propagation and reflection of plane waves in a homogeneous transversely isotropic magnetothermoelastic medium with two temperature and rotation in the context of GN Type-II and Type-III (1993) theory of thermoelasticity. It is found that, for two dimensional assumed model, there exist three types of coupled longitudinal waves, namely quasi-longitudinal wave (QL), quasi-transverse wave (QTS) and quasi-thermal waves (QT). The different characteristics of waves like phase velocity, attenuation coefficients, specific loss and penetration depth are computed numerically and depicted graphically. The phenomenon of reflection coefficients due to quasi-waves at a plane stress free with thermally insulated boundary is investigated. The ratios of the linear algebraic equations. These amplitude ratios are used further to calculate the shares of different scattered waves in the energy of incident wave. The modulus of the amplitude and energy ratios with the angle of incidence are computed for a particular numerical model. The conservation of energy at the free surface is verified. The effect of energy dissipation and two temperatures on the energy ratios are depicted graphically and discussed. Some special cases of interest are also discussed.

• Membrane and Water Treatment
• /
• 제3권4호
• /
• pp.253-266
• /
• 2012

In this work, the effect of hybrid salts precipitation-nanofiltration (SP-NF) process on the scale deposits in thermal and membrane desalination processes has been studied. The analysis was carried out to study the scale formation from the Arabian Gulf seawater in MSF and RO reference processes by changing the percentage of pretreatment from 0 to 100%. Four different SP-NF configurations were suggested. A targeted Top Brine Temperature (TBT) of $130^{\circ}C$ may be achieved if 30% portion is pretreated by SP and/or NF processes. As a rule of thumb, each 1% pretreatment portion increases the reference TBT of $115^{\circ}C$ by $0.6^{\circ}C$. For both MSF and RO, parallel pretreatment of certain percentage of the feed by SP and the rest by NF, showed the lowest scale values. The case showed the best values for sulfate scale prevention and the highest values of increasing the monovalent ions relative to the divalent scale forming ions. Sulfate scale is significant in MSF process while carbonate scale is significant in RO. Salt precipitation was suggested because it is less costly than nanofiltration, but nanofiltration was used here because it is efficient in sulfate ions removal.

• Structural Engineering and Mechanics
• /
• 제12권5호
• /
• pp.559-572
• /
• 2001

A numerical model, in the form of a computer program, for evaluating the fire resistance of insulated wide-flange steel columns is presented. The three stages associated with the thermal and structural analysis in the calculation of fire resistance of columns is explained. The use of the computer program for tracing the response of an insulated steel column from the initial pre-loading stage to collapse, due to fire, is demonstrated. The validity of the numerical model used in the program is established by comparing the predictions from the computer program with results from full-scale fire tests. Details of fire tests carried out on wide-flange steel columns protected with ceramic fibre insulation, together with results, are presented. The computer program can be used to evaluate the fire resistance of protected wide-flange steel columns for any value of the significant parameters, such as load, section dimensions, column length, type of insulation, and thickness of insulation without the necessity of testing.

• Steel and Composite Structures
• /
• 제12권4호
• /
• pp.325-350
• /
• 2012

Concrete filled steel hollow structural sections (CFSs) are an efficient, sustainable, and attractive option for both ambient temperature and fire resistance design of columns in multi-storey buildings and are becoming increasingly common in modern construction practice around the world. Whilst the design of these sections at ambient temperatures is reasonably well understood, and models to predict the strength and failure modes of these elements at ambient temperatures correlate well with observations from tests, this appears not to be true in the case of fire resistant design. This paper reviews available data from furnace tests on CFS columns and assesses the statistical confidence in available fire resistance design models/approaches used in North America and Europe. This is done using a meta-analysis comparing the available experimental data from large-scale standard fire tests performed around the world against fire resistance predictions from design codes. It is shown that available design approaches carry a very large uncertainty of prediction, suggesting that they fail to properly account for fundamental aspects of the underlying thermal response and/or structural mechanics during fire. Current North American fire resistance design approaches for CFS columns are shown to be considerably less conservative, on average, than those used in Europe.