A general approach to counterexamples in numerical analysis

A comprehensive experimental program of cyclic tests on 1:3-scale models of bridge piers is going to be carried out at the Laboratory of Structures and Materials of the University of Basilicata. The testing models include eight RC single shaft piers with hollow circular cross section. Four piers have been realised using corroded steel rebars. In this paper, the results of preliminary numerical simulation analyses of the cyclic behaviour of the piers, carried out with Opensees using fiber-based models, are presented. Pull-out and lap-splice effects of steel rebars have been taken into account in the numerical analyses. First, the experimental specimens and the test set up are presented. Next, the results of the numerical analyses are discussed. In the numerical analyses, different configurations and levels of corrosion have been considered. The effective stiffness and equivalent damping of the piers is reported as a function of pier ductility and pier drift.

본 연구는 강우재현장치를 제작하고, 화강암질 풍화토로 조성된 모형사면에 강우 및 사면조건에 따라 모형실험과 수치해석을 실시하였다. 모형실험에서 계측된 체적함수비와 간극수압의 변화특성을 분석하였으며 또한 수치해석 결과와 비교하였다. 체적함수비는 강우강도가 크고 사면경사가 급할수록 한계값에 도달하는데 짧은 시간이 소요되는 반면 강우강도가 작고 사면경사가 완만할수록 많은 시간이 소요되는 것으로 나타났다. 강우강도가 작고 강우지속시간이 짧을수록 더 큰 부의 간극수압을 나타내고 회복하는 시간도 짧은 것으로 나타났다. 이와 반면 강우강도가 크고 강우지속시간이 길수록 부의 간극수압을 회복하는데 오랜 시간이 소요되는 것으로 나타났다. 강우재현 모형실험과 수치해석을 수행한 결과 체적함수비와 간극수압의 분포경향이 유사하게 나타났다. 그러나 체적함수비는 최대 5% 정도, 간극수압은 최대 3kPa 정도의 차이를 보였다. This present study implemented a rainfall simulation system, and performed simulation and numerical analysis according to rainfall and slope conditions using a model slope built with weathered granite soil. Extensive analysis were conducted on the characteristics of changes in volumetric water content and pore water pressure measured in the simulation, and compared them with the results of numerical analysis. It took longer for the volumetric water content to reach the limit when rainfall intensity was high and the slope was steep and shorter when rainfall intensity was low and the slope was gentle. When rainfall intensity was low and the duration of rainfall was short, negative pore water pressure was higher and the time for restoration was shorter. On the contrary, when rainfall intensity was high and the duration of rainfall was long, it took a longer time to restore negative pore water pressure. In the results of rainfall simulation and numerical analysis, the distribution of volumetric water content and pore water pressure was similar between the two. However, the volumetric water content was different by up to 5%, and pore water pressure by up to 3kPa.

A CFPBS (Cone-type Friction Pendulum Bearing System) was developed to control the acceleration delivered to a structure to prevent the damage and degradation of critical communication equipment during earthquakes. This study evaluated the isolation performance of the CFPBS by numerical analysis. The CFPBS was manufactured in the shape of a cone differenced with the existing FPS (Friction Pendulum System), and a pattern was engraved on the friction surface. The natural frequencies of the CFPBS were evaluated from a free-vibration test with a seismic isolator system consisting of 4 CFPBS. To confirm the earthquake-resistant performance, a numerical analysis program was prepared using the equation of the CFPBS induced from the equations of motion. The equation reported by Tsai for the rolling- type seismic isolation bearings was proposed to design the equation of the CFPBS. Artificial seismic waves that satisfy the maximum earthquake scale of the Korean Building Code-Structural (KBC-2005) were created and verified to review the earthquake-resistant performance of the CFPBS by numerical analysis. The superstructural mass of the CFPBS and the skew angle of friction surface were considered for numerical analysis with El Centro NS, Kobe NS and artificial seismic waves. The CFPBS isolation performance evaluation was based on the numerical analysis results, and comparative analysis was performed between the results from numerical analysis and simplified theoretical equation under the same conditions. The validity of numerical analysis was verified from the shaking table test

This study predicts the intermetallic compound’s production through numerical analysis of a 2 mm thickness AA6061-T6 and a 2 mm thickness galvanized steel (GI steel) welded joint by AC pulse MIG welding. The intermetallic compounds are brittle to joint strength in the welded joint of dissimilar material, suggesting that the intermetallic compounds be minimized. For this study, 3D heat conduction analysis was performed, and intermetallic compounds at the joints were predicted based on the temperature history results. As a result of the experiment, the intermetallic compounds layer thickness is at each current 50, 60, 70 A as 0.8, 2.3, 2.6 μm, respectively. The result of numerical analysis is at each current 1.4, 2.08, 3.39 μm. The result shows that as the current increases, the amount of intermetallic compounds layer thickness increases. The temperature history examination result of the maximum temperature for each current is each 50, 60, 70 A as 772, 848, 916 K the numerical analysis, at each current as 1043.96, 1167.9, 1259.19 K. In order to verify the validity of the numerical analysis results, the experimental values are compared. After the comparison, it is confirmed that the measured temperature is approximately 100–130 K different from the numerical analysis of the temperature.KeywordsAC pulse MIGGalvanized steelAA6061-T6Intermetallic compoundsNumerical analysis

Recently, the importance of low-noise design on transformers has been growing. This is due to increasing requirements from customers whose substations are being installed nearby downtowns. Increasingly stringent noise emission limits are therefore being placed on transformers by both regulators and utility operators. This paper presents numerical analyses to identify the vibration characteristics based on the shape and dimensions of internal reinforcements at the tank corners and predicts the sound pressure level for load and no-load noise in large power transformers. The numerical analyses involve the vibro-acoustic finite element model of a transformer including the excitations of the forces present in a transformer’s active part. Subsequently, an optimal design solution effective in noise reduction is selected. Additionally, no-load and load vibro-acoustic analysis results indicates that the vibration and acoustic behavior of the transformer is influenced by the size, spacing, quantity, and centerline placement of the internal reinforcements. In conclusion, the optimal design of the internal reinforcement at the tank corners, selected in this paper, was validated through appropriate experimental measurements. These measurements were conducted on multiple manufactured transformers. Notably, the experimentally determined noise reduction trends in sound pressure levels showed favorable agreement with the numerical analysis results. Through this process, the numerical analysis results and the optimal design proposed in this paper have been validated.

Numerical Simulation of Temperature Effects on Mechanical Behavior of the Railway Tunnel in Tibet

<div class="section abstract"><div class="htmlview paragraph">Heat transfer optimization is a crucial aspect of the design process for Formula Student race cars, particularly for the radiator, usually housed in a side pod. For the car to operate at peak performance, a well-designed radiator-sidepod system is essential such that it can dissipate heat generated by the engine faster, for the car to run in optimal performance. Testing the car physically for various radiator-sidepod design iterations is a very difficult task, also considering the costs to manufacture the radiator-sidepod setup. The objective of this study is to develop a comprehensive methodology for analysing heat transfer through radiator setup using Computational Fluid Dynamics and to validate it through experimental investigations, to enhance performance and efficiency of the radiator setup. It further explains how to find out its heat transfer efficiency, and to choose the right radiator-sidepod setup, giving optimal performance. The flow of coolant inside the radiator, as well as external air flow through sidepod, is considered for realistic results in numerical analysis. Various radiator dimensions and sidepod designs are considered in the scope of this paper. The heat transfer simulation is performed in ANSYS Fluent, and their results compared. The final radiator-sidepod setup concluded as optimal setup in this study provided an average temperature drop of 2.9 °C through experiment and 2.72 °C through numerical analysis, providing uniform airflow through the radiator face with less dirty air.</div></div>

The solid-liquid two-phase flow equations of the draining-sand jet pump have been established according to the RNG k-e two-equation turbulence model. On this basis, the numerical analysis models of different diameter fitting of the nozzle and the throat were established. Then, the characteristics of efficiency and outlet pressure of the diffuser and solid phase ratio and velocity field distribution and pressure field distribution were analyzed by the computer software of computational fluid dynamics. The numerical analysis results were studied and contrasted with another one. To reduce or eliminate the contrary velocity vector of the solid-liquid two-phase flow and to increase degree and range of the vacuum are the key techniques for improving the comprehensive properties of the draining-sand jet pump by optimizing the diameter fitting of the nozzle and the throat. They have been proved by the results of numerical analysis and the production experiment.

The paper aims to conduct systematic experimental and numerical studies on the joining of thick austenitic stainless-steel plates using Electron Beam Welding (EBW). The experimental phase entails welding two plates, each 12 mm thick, in a butt joint configuration under fully clamped conditions using EBW. This process involves recording parameters and temperature profiles during welding, followed by post-weld measurements of the weld pool size. The thick plate weld joint was then subjected to numerical simulation, incorporating welding parameters and plate holding conditions during welding. A three-dimensional moving conical heat source with a Gaussian distribution of power was utilized in the numerical analysis. To minimize welding variables, a correlation between parameters of the heat source model and welding outcomes was established using the numerical analysis results. Calibration of heat source model parameters was achieved by comparing numerical analyses with experimental results of temperature profile and weld pool sizes of the plate weld joint, validating the estimation procedure. Furthermore, bead-on-plate analyses were conducted using various accelerating voltage, beam current, and constant speed to demonstrate the efficacy and suitability of the developed correlation and heat source model. These bead-on-plate results were also compared with experimental data. Subsequently, residual stresses and distortions in the plate weld joint were predicted using numerical analyses and compared with existing literature

In the present study, the amount of fragments generated and their travel distances due to vehicle collision with concrete median barrier (CMB) was analyzed and predicted. In this regard, machine learning was applied to the results of numerical analysis, which were developed by comparing with field test. The numerical model was developed using smoothed particle hydrodynamics (SPH). SPH is a mesh-free method that can be used to predict the amount of fragments and their travel distances from concrete structures under impact loading. In addition, deep neural network (DNN) and gradient boosting machine (GBM) were also employed as machine learning methods. In this study, the results of DNN, GBM, and numerical analysis were then compared with the conducted field test. Such comparisons revealed that numerical analysis generated lower error than both DNN and GBM. When prediction results of both the amount of fragments and their travel distances were considered, the result of DNN showed smaller errors than that of GBM. Therefore, in studies where machine learning is used to predict the amount of fragments and their travel distances, careful selection of an appropriate method from the various available machine learning methods such as DNN, GBM, and random forest is absolutely important.

Seismic performance evaluation for dam safety evaluation has been continually conducted. However the behavior analysis for the spillway pier which is known as the weak point of dam is seldom reported. Therefore, this study performed the static loading tests for a prototype structures as elementary tests for the final seismic performance evaluation of dam safety. The prototype of pier structure has 1/20 scale and it adopts to strength model. And cracking loads and ultimate loads of real structures are calculated through numerical analysis using commercial FEM program (ABAQUS). The results of this study show some difference between the results of prototype tests and the results of numerical analysis. Also, the ultimate and cracking loads can be estimated through the prototype loading test and numerical analysis.

Refrigerators are comprised of compressors, condensers, expansion valves, and evaporators. Among these parts, a compressor accounts for the majority of power consumed by a refrigerator. Therefore, it is important to improve the efficiency of a compressor to save the electrical energy consumed in a household. In this study, the variation in energy efficiency ratio (EER) with respect to muffler shape was examined for a linear compressor suction system. Furthermore, two cases, namely the baseline model and modified model, were considered. For numerical analysis, a one-dimensional lumped model and CFD coupled model were adopted. The numerical analysis results indicated that the modified model improved EER by approximately 0.49% in comparison with the baseline model. Hence, the modified model was more effective in energy saving. Additionally, the experimental results were qualitatively consistent with the numerical analysis results.

The paper presents results of numerical parametric analysis of an energy harvester based on the construction of cantilever beam. The device has two-layered section made of polymer substrate and piezoelectric ceramic PZT as an active layer. A determination of an impact of harvester operating parameters (resistance and excitation amplitude), PZT layer thickness and PZT type on electrical output of the beam and maximum stress values in both layers was the aim of conducted numerical analysis. Performed numerical analyses allow to choose selected parameters values of given cantilever beam harvester which make it possible to receive the most preferable results in the field of material stress and generated electrical energy.

Energy consumption for air conditioning purposes accounts for 60-80% of electricity used in Qatar. As District Cooling Plants (DCPs) has a potential to reduce energy consumption and CO2 emissions, Qatar and GCC are continuously shifting paradigm towards adoption of DC plants to satisfy the rapidly growing demand in all sectors. However, DC plants usually rely on wet cooling towers for disposing the excess heat to the ambient. Hence the efficiency of DCPs is significantly influenced by the cooling tower effectiveness in heat disposal, which is dominated by latent heat or evaporation of water in a counter atmospheric current air stream. Operation district cooling plants (DCPs) under extremely high humidity in summer represents one of the major thermodynamic limitations in terms of maintain the outlet water temperature of cooling towers (i.e. chiller's condenser cooling water) as low as possible to guarantee higher efficiency of DCPs. The cooling tower efficiency degrades considerably at higher relative humidity of air, which approaches saturation limits in summer, where the cooling demand is high. The ambient wet-bulb (WB) temperature is a limiting factor for the capacity of cooling towers (CT), which determines the inlet cooling water temperature to the chiller's condenser (outlet water temperature from the CT). Due to prevailing weather conditions in Qatar and GCC, this temperature is designed based on 31 °C WB temperature in summer, which result in a 34 °C inlet condenser cooling water temperature. This represents a thermodynamic limitation to reduce the energy consumption of chillers, which lies under the focus of this study. Desiccant cooling is an environmentally attractive alternative to conventional mechanical air-conditioning, especially for air dehumidification purposes. It does not require ozone depleting refrigerants and it can be run off low temperature solar heat or waste heat. The electrical coefficient of performance of desiccant cooling can be above 20, making it over 6 times more efficient than conventional air cooled vapor compression system. This project seeks to develop new processes to reduce air humidity and WB temperature by around 6 °C prior to entering the CT to break the above mentioned thermodynamic limitation. Air dehumidification takes place using liquid to air membrane (3-fluid LAMEEs) for further dehumidification of air. A hybrid solar PV-Thermal system is used for regeneration of both desiccant systems. Lumped and numerical analysis has been conducted using COMSOL Multiphysics software to predict the outlet air temperature and humidity for 3-fluid LAMEEs when used for air cooling and dehumidifying. Results of the numerical and lumped analysis showed that the 3-fluid LAMEE alone can effectively decrease the humidity content of ambient air by up to 40%, while the outlet air temperature can be reduced by 6 °C. Accordingly, the inlet cooling water temperature to the chiller's condenser (outlet water temperature from the CT) can be reduced to 27-28 C, which provides a potential saving of around 25% in energy consumption of the Chiller in district cooling plants.

This paper presents a numerical finite element model (FEM) investigation on the overall buckling behaviour of hot-rolled (HR), submerged arc welded (SAW) and high-frequency welded (HFW) steel circular columns under axial compression. Three dimensional FEM of circular hollow sections were developed using shell elements considering material nonlinearities, geometric imperfections and residual stress. The established FEM was used to simulate experimental studies conducted by past researchers. Good agreement has been found between numerical analysis and past researchers results, which has validated the reasonability of the FEM to carry out further investigation. Based on the validated FEM, numerical analysis incorporating 180 numerical generated HR, SAW and HFW steel circular columns with various section sizes and slenderness were carried out. The numerical analysis results were compared with the existing column design curves in Chinese, European and American codes. The numerical results showed that the design resistances for hot-rolled and welded steel circular columns calculated based on design curve a in both GB 50017-2003 and Eurocode 3 and the design formula in ANSI/AISC 360-2016 should be accepted. In addition, to further improve the design efficiency, new column design curves for hot-rolled and welded steel circular columns were recommended based on the expressions in GB 50017-2003 and Eurocode 3.