Simulation of thermal behavior of glass fiber/phenolic composites exposed to heat flux on one side

A 3D thermal response model is developed to evaluate the thermal behavior of glass fiber/phenolic composite exposed to heat flux on one side. The model is built upon heat transfer and energy conservation equations in which the heat transfer is in the form of anisotropic heat conduction, absorption by matrix decomposition, and diffusion of gas. Arrhenius equation is used to characterize the pyrolysis reaction of the materials. The diffusion equation for the decomposition gas is included for mass conservation. The temperature, density, decomposition degree, and rate are extracted to analyze the process of material decomposition, which is implemented by using the UMATHT (User subroutine to define a material’s thermal behavior) and USDFLD (User subroutine to redefine field variables) subroutines via ABAQUS code. By comparing the analysis results with experimental data, it is found that the model is valid to simulate the evolution of a glass fiber/phenolic composite exposed to heat flux from one side. The comparison also shows that longer time is taken to complete the pyrolysis reaction with increasing depth for materials from the numerical simulation, and the char region and the pyrolysis reaction region enlarge further with increasing time. Furthermore, the decomposition degree and temperature are correlated with depths, as well as the peak value of decomposition rate and the time to reach the peak value

Thermal response study of carbon epoxy laminates exposed to fire

In this article, a three‐dimensional thermal response model is developed to investigate the thermal behavior of carbon epoxy composite impacted directly by propane flame. The model is established in consideration of heat transfer and energy conservation in which the heat transfer is in the form of anisotropic heat conduction, absorption by matrix decomposition, and diffusion of gas. Arrhenius equation is utilized to present the decomposition process of the materials. The diffusion equation for the decomposition gas is included for mass conservation. The thermal response model is implemented with the UMATHT and USDFLD subroutines via ABAQUS code, from which the temperature, density, decomposition degree, and decomposition rate can be extracted to analysis the process of material decomposition by finite element simulation. The model shows its capability to analysis the evolution of a carbon epoxy composite in fire by the comparison between the numerical and experimental results. Furthermore, the numerical results show that thermal conductivities in different directions of fiber have a significant influence on the heat transfer. In addition, the relationship between the decomposition degree and temperature is correlated with depths, as well as the peak value of decomposition rate and the time to reach tha

Numerical Study on Entropy Generation of the Multi-Stage Centrifugal Pump

The energy loss of the multi-stage centrifugal pump was investigated by numerical analysis using the entropy generation method with the RNG k-ε turbulence model. Entropy generation due to time-averaged motion and velocity fluctuation was mainly considered. It was found that the entropy generation of guide vanes and impellers account for 71.2% and 23.3% of the total entropy generation under the designed flow condition. The guide vanes are the main hydraulic loss domains and their entropy generation is about 9 W/K, followed by impellers. There are vortices at the tongue of the guide vane inlet as well as flow separations in the impellers, which lead to entropy generation. The fluid impacts the outer surface of the guide vanes, resulting in the increase in entropy generation. There are refluxes near the guide vane tongues which also increase the entropy generation of this part. The entropy generation distribution of the guide vanes and impellers was investigated, which found that the positive guide vane has more entropy generation compared with the reverse guide. The entropy generation of the blade suction surface is higher compared with the pressure surface. This study indicated that the entropy generation method has distinct advantages in the assessment of hydraulic loss

Damage evaluation of concrete column under impact load using a piezoelectric-based EMI technique

One of the major causes of damage to column-supported concrete structures, such as bridges and highways, are collisions from moving vehicles, such as cars and ships. It is essential to quantify the collision damage of the column so that appropriate actions can be taken to prevent catastrophic events. A widely used method to assess structural damage is through the root-mean-square deviation (RMSD) damage index established by the collected data; however, the RMSD index does not truly provide quantitative information about the structure. Conversely, the damage volume ratio that can only be obtained via simulation provides better detail about the level of damage in a structure. Furthermore, as simulation can also provide the RMSD index relating to that particular damage volume ratio, the empirically obtained RMSD index can thus be related to the structural damage degree through comparison of the empirically obtained RMSD index to numerically-obtained RMSD. Thus, this paper presents a novel method in which the impact-induced damage to a structure is simulated in order to obtain the relationship between the damage volume ratio to the RMSD index, and the relationship can be used to predict the true damage degree by comparison to the empirical RMSD index. In this paper, the collision damage of a bridge column by moving vehicles was simulated by using a concrete beam model subjected to continuous impact loadings by a freefalling steel ball. The variation in admittance signals measured by the surface attached lead zirconate titanate (PZT) patches was used to establish the RMSD index. The results demonstrate that the RMSD index and the damage ratio of concrete have a linear relationship for the particular simulation model

The Sustainability of Online Concert and Live Concert

As environmental awareness grows, the world is increasingly focused on living a low-carbon, energy-sustainable lifestyle. At the same time, with the global outbreak of the COVID-19 in 2020, online concerts are growing rapidly to maintain social distance between people and keep isolated lives rich. Therefore, in this survey, we focus on the online music scene, which has flourished during the epidemic, and compares various indicators to find out which of the two forms of music, online or offline, is more sustainable. The article will use questionnaires, literature surveys, and three indicators - carbon footprint, water footprint, and economy -to discuss how much energy is consumed by both online and offline concerts. The energy consumption of a single person at an online concert is less than that of an offline concert. This research study will demonstrate to society the superiority of online concerts in terms of sustainability through a scientific and rigorous approach, which will be beneficial to reducing global energy consumption

BIONIC ROBOT FISH GRADIENT RELIABILITY OPTIMIZATION DESIGN BASED ON IMPROVED QUANTUM EVOLUTIONARY ALGORITHM

In order to improve the working reliability of the biomimetic robotic fish, put forward a gradient reliability robust optimization design method method which is applied to the biomimetic robotic fish.Taken the bionic killer whale as the research object, based on the flapping wing motion theory, the dynamic load of the bionic killer whale was obtained by using MATLAB.Based on the theory of reliability sensitivity design, robust design theory and the theory of performance degradation, established optimization evaluation function of bionic killer whale, obtained the influence of the bionic killer whale’s design variables to reliability sensitivity gradient.The improved quantum evolutionary algorithm was used to optimize the design, the optimal solution of caudal fin propulsion mechanism was obtained.The results show that the absolute value of sensitivity of the design variables is decreased, the reliability is improved and the structure is more robust. This paper combine the flapping wing movement theory, the reliability sensitivity design theory, the reliability-based robust design theory, the theory of performance degradation and improved quantum evolutionary algorithm were combined, put forward a gradient reliability robust optimization design method method which is applied to the biomimetic robotic fish, it provides theoretical method and data support for the reliability analysis and design of bionic robot fish

NUMERICAL SIMULATION AND RELIABILITY SENSITIVITY ANALYSIS OF BIONIC KILLER WHALES’S LOAD CHARACTERISTIC

As a kind of bionic robot fish,bionic killer whale played an important role in ocean development and scientific investigation. Based on the flapping wing movement theory,the bionic killer whale’s mechanism was analyzed,its instantaneous load was simulated by MATLAB. Based on the stress-strength interference theory,the bionic killer’s load reliability state function was established,the reliability index and reliability of bionic killer whale was calculated,combined with the reliability sensitivity analysis theory,the dimensionless sensitivity was obtained,analyzed the influence of the bionic killer whale’s design variables to reliability sensitivity gradient. This paper provides the theoretical basis,accurate data support and an effective numerical calculation method for the design and optimization of the bionic underwater robot with flapping wing theory as the propeller,which has important practical engineering significance