A generalized flexibility matrix–based objective function utilized for structure damage identification is firstly constructed. After transforming the damage identification into a constrained nonlinear least squares optimization problem, the trust-region algorithm is applied to find the solution of the inverse problem in multiple damage cases. Thereinto, the sensitivity analysis of the objective function with respect to the design variables is derived using the Nelson's method. At last, two numerical examples with several damage cases are investigated, including a steel truss bridge model as well as a drilling rig derrick model. Based on the computational results, it is evident that the presented approach provides excellent validity and reliability for the large and complicated engineering structures.
{"title":"Structural damage identification using an optimization technique based on generalized flexibility matrix","authors":"Qianhui Gao, Zhu Li, Yongping Yu, S. Zheng","doi":"10.1093/jom/ufad047","DOIUrl":"https://doi.org/10.1093/jom/ufad047","url":null,"abstract":"A generalized flexibility matrix–based objective function utilized for structure damage identification is firstly constructed. After transforming the damage identification into a constrained nonlinear least squares optimization problem, the trust-region algorithm is applied to find the solution of the inverse problem in multiple damage cases. Thereinto, the sensitivity analysis of the objective function with respect to the design variables is derived using the Nelson's method. At last, two numerical examples with several damage cases are investigated, including a steel truss bridge model as well as a drilling rig derrick model. Based on the computational results, it is evident that the presented approach provides excellent validity and reliability for the large and complicated engineering structures.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"31 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139163289","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study aims to assess the power cycling lifetime of the solder die attach of the silicon (Si) power metal-oxide-semiconductor field-effect transistor (MOSFET) modules in an SOT-227 package in a three-phase bridge inverter. This goal is achieved through a loose one-way coupling framework that incorporates a thermal computational fluid dynamics (CFD) model for temperature estimation and a transient thermal-mechanical finite element model (FEM) that accounts for the time-dependent viscoplastic behavior of the solder die attach through the Anand viscoplastic constitutive model for thermal-mechanical responses assessment. To facilitate an accurate prediction of the solder die attach lifetime during power cycling, a physical lifetime prediction model is constructed through the strain-based Coffin-Manson Eq. together with the experimental lifetime data and the corresponding calculated equivalent viscoplastic strain increments. Furthermore, parametric study via the coupling framework is conducted to examine the effect of cooling, operating and structural parameters on the solder die attach lifetime, and also to identify the most crucial design parameters. At last, experimental design using a Taguchi method is conducted to seek the optimal level combination of design parameters for enhanced power cycling lifetime of the solder die attach.
{"title":"Solder die attach lifetime characterization of SOT-227 power MOSFET module in a three-phase inverter under power cycling","authors":"Hsien-Chie Cheng, Chih-Wei Hsu","doi":"10.1093/jom/ufad043","DOIUrl":"https://doi.org/10.1093/jom/ufad043","url":null,"abstract":"\u0000 This study aims to assess the power cycling lifetime of the solder die attach of the silicon (Si) power metal-oxide-semiconductor field-effect transistor (MOSFET) modules in an SOT-227 package in a three-phase bridge inverter. This goal is achieved through a loose one-way coupling framework that incorporates a thermal computational fluid dynamics (CFD) model for temperature estimation and a transient thermal-mechanical finite element model (FEM) that accounts for the time-dependent viscoplastic behavior of the solder die attach through the Anand viscoplastic constitutive model for thermal-mechanical responses assessment. To facilitate an accurate prediction of the solder die attach lifetime during power cycling, a physical lifetime prediction model is constructed through the strain-based Coffin-Manson Eq. together with the experimental lifetime data and the corresponding calculated equivalent viscoplastic strain increments. Furthermore, parametric study via the coupling framework is conducted to examine the effect of cooling, operating and structural parameters on the solder die attach lifetime, and also to identify the most crucial design parameters. At last, experimental design using a Taguchi method is conducted to seek the optimal level combination of design parameters for enhanced power cycling lifetime of the solder die attach.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"85 25","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138957772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Developing an accurate and reliable computational tool for traffic flow prediction has always been an active research topic in transportation engineering and planning. The available predictive tools generally fall into parametric, nonparametric, and PDE-based approaches. In particular, the machine learning methods, such as the long short-term memory (LSTM) networks, belong to the nonparametric methods. This study proposes the data assimilation technique with LSTM for predicting highway traffic flows. The proposed method is developed under the framework of the extended Kalman filter (EKF) algorithm, which consists of two key components: the analysis and prediction steps. As the numerical simulator, a kernel component of the predictive tool, we use an explicit (EX) Godunov's scheme to discretize the Lighthill-Whitham- Richards model, where the MacNicholas formulation is used as the fundamental relation between the velocity and density. EKF combines LSTM prediction from two perspectives. In practical scenarios, future data at the upstream or downstream boundary points are unavailable. Therefore, the predicted values generated by LSTM are employed to set boundary conditions. Furthermore, two stages in EKF assimilate the LSTM predicted values, known as pseudo-observations, and the observed data in order with background values obtained through numerical simulation and observed data whenever available. This assimilation process aims to obtain a better initial condition for subsequent predictions, resulting in improved accuracy. Based on traffic data for the historical Hsuehshan Tunnel highway traffic data in Taiwan, the numerical results demonstrate that our method can effectively reduce the observation error and outperforms three baselines: EX, EKF, and LSTM.
{"title":"Data-driven numerical simulation with extended Kalman filtering and long short-term memory networks for highway traffic flow prediction","authors":"Chung- Yu Shih, Chia-Ming Chang, Bo-Fan Wu, Chia-Hui Chang, Feng-Nan Hwang","doi":"10.1093/jom/ufad046","DOIUrl":"https://doi.org/10.1093/jom/ufad046","url":null,"abstract":"\u0000 Developing an accurate and reliable computational tool for traffic flow prediction has always been an active research topic in transportation engineering and planning. The available predictive tools generally fall into parametric, nonparametric, and PDE-based approaches. In particular, the machine learning methods, such as the long short-term memory (LSTM) networks, belong to the nonparametric methods. This study proposes the data assimilation technique with LSTM for predicting highway traffic flows. The proposed method is developed under the framework of the extended Kalman filter (EKF) algorithm, which consists of two key components: the analysis and prediction steps. As the numerical simulator, a kernel component of the predictive tool, we use an explicit (EX) Godunov's scheme to discretize the Lighthill-Whitham- Richards model, where the MacNicholas formulation is used as the fundamental relation between the velocity and density. EKF combines LSTM prediction from two perspectives. In practical scenarios, future data at the upstream or downstream boundary points are unavailable. Therefore, the predicted values generated by LSTM are employed to set boundary conditions. Furthermore, two stages in EKF assimilate the LSTM predicted values, known as pseudo-observations, and the observed data in order with background values obtained through numerical simulation and observed data whenever available. This assimilation process aims to obtain a better initial condition for subsequent predictions, resulting in improved accuracy. Based on traffic data for the historical Hsuehshan Tunnel highway traffic data in Taiwan, the numerical results demonstrate that our method can effectively reduce the observation error and outperforms three baselines: EX, EKF, and LSTM.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"113 12","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138959230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tohya Kanahama, Carol Lee Chalermsin, Motohiro Sato
In previous research on the mechanical instability of trees based on mechanical theory, wild tree has been modeled as a cantilever which was perfectly attached to the ground. However, experimental research has identified two failure modes, including root turnover and self-buckling of the trunk. This suggests that the imperfect fixation caused by root-soil interaction must be considered when discussing tree stability. The purpose of this study is to clarify the self-buckling characteristics of wild trees considering soil instability. To account for the resistance moment caused by the interaction between the root and soil, trees as cantilevers fixed to the ground by a rotational spring were modeled. In this model, the self-buckling problem was formulated considering the rotational rigidity of the spring, and the formula derived for the critical height and buckling mode. As a result, the formula for critical height considering rotational rigidity was obtained, and it was found that the buckling modes can be classified into the rigid-body mode and beam mode based on the rotational rigidity. By comparing this result with the statistical law based on the measurement of real trees reported in previous research, it was determined that real trees were designed based on beam mode. This suggests that the wild tree skillfully balances the moment of resistance caused by the interaction between the root and soil to prevent “uprooting,” which is extremely fatal for trees. Moreover, it was also found that the safety factor of trees for self-buckling is ensured enough to prevent the beam mode.
{"title":"Mechanical Instability of Heavy Column with Rotational Spring","authors":"Tohya Kanahama, Carol Lee Chalermsin, Motohiro Sato","doi":"10.1093/jom/ufad035","DOIUrl":"https://doi.org/10.1093/jom/ufad035","url":null,"abstract":"\u0000 In previous research on the mechanical instability of trees based on mechanical theory, wild tree has been modeled as a cantilever which was perfectly attached to the ground. However, experimental research has identified two failure modes, including root turnover and self-buckling of the trunk. This suggests that the imperfect fixation caused by root-soil interaction must be considered when discussing tree stability. The purpose of this study is to clarify the self-buckling characteristics of wild trees considering soil instability. To account for the resistance moment caused by the interaction between the root and soil, trees as cantilevers fixed to the ground by a rotational spring were modeled. In this model, the self-buckling problem was formulated considering the rotational rigidity of the spring, and the formula derived for the critical height and buckling mode. As a result, the formula for critical height considering rotational rigidity was obtained, and it was found that the buckling modes can be classified into the rigid-body mode and beam mode based on the rotational rigidity. By comparing this result with the statistical law based on the measurement of real trees reported in previous research, it was determined that real trees were designed based on beam mode. This suggests that the wild tree skillfully balances the moment of resistance caused by the interaction between the root and soil to prevent “uprooting,” which is extremely fatal for trees. Moreover, it was also found that the safety factor of trees for self-buckling is ensured enough to prevent the beam mode.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"27 3","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139002411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As semiconductor manufacturing enters the era of sub-10 nm and 3D stacking, “cleanliness” in the process becomes a crucial factor for process yield. The measurement of nanoparticle concentration, size, and shape in various solutions that may cause contamination during the manufacturing process is currently an important research topic. Although there are various nanoparticle measurement techniques available, further technological development and breakthroughs are still needed for measuring low concentrations and complex mixtures of nanoparticles. Therefore, in this study, we attempted to address the measurement challenges posed by mixed particles by applying Asymmetric Flow Field-Flow Fractionation (AF4) in combination with Dynamic Light Scattering (DLS) and Ultraviolet (UV). The strategy involved separating the samples before measurement. For a nanomixture containing five different sizes of gold nanoparticles (AuNPs) with diameters of 20 nm, 40 nm, 60 nm, 80 nm, and 100 nm, three different methods were employed to control the driving force for particle separation during the elution stage: constant cross flow rate, linearly decreasing cross flow rate, and exponentially decreasing cross flow rate. The results demonstrated that different flow rate control methods indeed yielded variations in nanoparticle separation, with the constant flow rate method showing the best separation efficiency. Additionally, it was observed that the thickness of the experimental chamber played a significant role in affecting the retention time of the nanoparticles during separation.
{"title":"Nanoparticles separation by different conditions at asymmetric flow field- flow fractionation","authors":"C. L. Chiang, C. W. Yeh","doi":"10.1093/jom/ufad036","DOIUrl":"https://doi.org/10.1093/jom/ufad036","url":null,"abstract":"\u0000 As semiconductor manufacturing enters the era of sub-10 nm and 3D stacking, “cleanliness” in the process becomes a crucial factor for process yield. The measurement of nanoparticle concentration, size, and shape in various solutions that may cause contamination during the manufacturing process is currently an important research topic. Although there are various nanoparticle measurement techniques available, further technological development and breakthroughs are still needed for measuring low concentrations and complex mixtures of nanoparticles. Therefore, in this study, we attempted to address the measurement challenges posed by mixed particles by applying Asymmetric Flow Field-Flow Fractionation (AF4) in combination with Dynamic Light Scattering (DLS) and Ultraviolet (UV). The strategy involved separating the samples before measurement. For a nanomixture containing five different sizes of gold nanoparticles (AuNPs) with diameters of 20 nm, 40 nm, 60 nm, 80 nm, and 100 nm, three different methods were employed to control the driving force for particle separation during the elution stage: constant cross flow rate, linearly decreasing cross flow rate, and exponentially decreasing cross flow rate. The results demonstrated that different flow rate control methods indeed yielded variations in nanoparticle separation, with the constant flow rate method showing the best separation efficiency. Additionally, it was observed that the thickness of the experimental chamber played a significant role in affecting the retention time of the nanoparticles during separation.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"5 s1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138971942","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The gantry machining center is popular for various fabrication, such as milling and tapping. However, thermal errors introduced by the rotation of spindle, workpiece processing, and cooling significantly degrade fabrication precision. The objective of this study is to establish an appropriate and efficient thermal error prediction model for the spindle of gantry machining center. The model will then aid real-time compensation for the error. Firstly, this study presents a systematic strategy for selecting key temperature points on the gantry machining center, reducing the number of required sensors. Subsequently, a thermal error model is developed based on the selected key temperature points. The model will be capable of predicting thermal errors in the x- and z-direction. Finally, this work both validates the thermal error model and exhibits real-time compensation capabilities using a real machine.
龙门加工中心常用于各种加工，如铣削和攻丝。然而，主轴旋转、工件加工和冷却带来的热误差会大大降低加工精度。本研究的目的是为龙门加工中心的主轴建立一个适当而有效的热误差预测模型。该模型将有助于对误差进行实时补偿。首先，本研究提出了在龙门加工中心上选择关键温度点的系统策略，从而减少了所需传感器的数量。随后，根据选定的关键温度点开发了热误差模型。该模型能够预测 X 和 Z 方向的热误差。最后，这项工作不仅验证了热误差模型，还利用实际机床展示了实时补偿功能。
{"title":"An efficient thermal error prediction model using neural networks and key temperature points for gantry machining centers","authors":"Hao-Sung Chiu, Chin-Han Chang, Yu-Chen Huang, Yung-Chieh Lai, Cheng-Jyun Yang, Yu-Bin Chen","doi":"10.1093/jom/ufad042","DOIUrl":"https://doi.org/10.1093/jom/ufad042","url":null,"abstract":"\u0000 The gantry machining center is popular for various fabrication, such as milling and tapping. However, thermal errors introduced by the rotation of spindle, workpiece processing, and cooling significantly degrade fabrication precision. The objective of this study is to establish an appropriate and efficient thermal error prediction model for the spindle of gantry machining center. The model will then aid real-time compensation for the error. Firstly, this study presents a systematic strategy for selecting key temperature points on the gantry machining center, reducing the number of required sensors. Subsequently, a thermal error model is developed based on the selected key temperature points. The model will be capable of predicting thermal errors in the x- and z-direction. Finally, this work both validates the thermal error model and exhibits real-time compensation capabilities using a real machine.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"59 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139003189","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The rose-window instability (RWI) is an electrohydrodynamic instability occurring in a dielectric liquid subjected to an electric field. This instability leads to variations in the shape of the liquid and its spreading. Despite the significance of the RWI, there have been limited studies, especially concerning dielectric droplets. Thus, the aim of this study is to investigate the characteristic of rose-window instability in silicone oil droplets exposed to corona discharge. The study examines the effects of electrode gap, applied voltage, and viscosity on the formation of RWI. Increasing the electrode gap results in an enlarged rose-window lattice, accompanied by a decrease in the number of lattices. This can be attributed to a more diffusive ionic flow and a more pronounced inhomogeneity of charge distribution across the droplet surface. On the other hand, higher voltages, which enhances the ionic flow, accelerate the formation of RWI and lead to a larger inner diameter. Viscosity has little influence on the geometry of the lattice. However, droplets with low viscosity exhibit a more rapid development of instability. The observation suggests that the small Ohnesorge number, influenced by factors such as viscosity and surface tension, may play a role in the development of the rose-window instability. The influence of surface tension, although not the main focus of the study, cannot be completely disregarded as it is interconnected with the Ohnesorge number and may contribute to the observed results.
{"title":"A Study on Rose-Window Instability in a Dielectric Droplet Exposed to Corona Discharge","authors":"Yi-Jen Chiou, Chiang Fu, Ying-Hao Liao","doi":"10.1093/jom/ufad041","DOIUrl":"https://doi.org/10.1093/jom/ufad041","url":null,"abstract":"\u0000 The rose-window instability (RWI) is an electrohydrodynamic instability occurring in a dielectric liquid subjected to an electric field. This instability leads to variations in the shape of the liquid and its spreading. Despite the significance of the RWI, there have been limited studies, especially concerning dielectric droplets. Thus, the aim of this study is to investigate the characteristic of rose-window instability in silicone oil droplets exposed to corona discharge. The study examines the effects of electrode gap, applied voltage, and viscosity on the formation of RWI. Increasing the electrode gap results in an enlarged rose-window lattice, accompanied by a decrease in the number of lattices. This can be attributed to a more diffusive ionic flow and a more pronounced inhomogeneity of charge distribution across the droplet surface. On the other hand, higher voltages, which enhances the ionic flow, accelerate the formation of RWI and lead to a larger inner diameter. Viscosity has little influence on the geometry of the lattice. However, droplets with low viscosity exhibit a more rapid development of instability. The observation suggests that the small Ohnesorge number, influenced by factors such as viscosity and surface tension, may play a role in the development of the rose-window instability. The influence of surface tension, although not the main focus of the study, cannot be completely disregarded as it is interconnected with the Ohnesorge number and may contribute to the observed results.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"121 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138981654","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Whole brain models are a valuable tool to gain a better understanding of cerebral blood flow and metabolism. Recent work has developed multi-compartment models of blood flow and oxygen transport that can be used in a Finite Element framework to simulate whole brain behaviour with low computational expense, helping to move such tools towards clinical application. However, the transport of fluid between the vascular space and the interstitial space has not yet been considered in detail in this context, despite this playing an important role in several cerebrovascular diseases. In this study, an extended framework is proposed to include this transport, coupled with a linear elastic model of tissue displacement to simulate the movement of fluid and the resulting displacement of brain tissue. This framework is compared in detail with previous models. The resulting Eqs. are found to exhibit multiple time scales, and a separation of scales is performed to analyse the behaviour at different time scales. Finally, a simplified model is proposed that can be easily implemented within existing computational frameworks, providing a valuable extension of the pathological conditions that can be simulated.
{"title":"Interstitial fluid transport in a multi-compartment model of cerebral blood flow","authors":"Stephen Payne","doi":"10.1093/jom/ufad040","DOIUrl":"https://doi.org/10.1093/jom/ufad040","url":null,"abstract":"\u0000 Whole brain models are a valuable tool to gain a better understanding of cerebral blood flow and metabolism. Recent work has developed multi-compartment models of blood flow and oxygen transport that can be used in a Finite Element framework to simulate whole brain behaviour with low computational expense, helping to move such tools towards clinical application. However, the transport of fluid between the vascular space and the interstitial space has not yet been considered in detail in this context, despite this playing an important role in several cerebrovascular diseases. In this study, an extended framework is proposed to include this transport, coupled with a linear elastic model of tissue displacement to simulate the movement of fluid and the resulting displacement of brain tissue. This framework is compared in detail with previous models. The resulting Eqs. are found to exhibit multiple time scales, and a separation of scales is performed to analyse the behaviour at different time scales. Finally, a simplified model is proposed that can be easily implemented within existing computational frameworks, providing a valuable extension of the pathological conditions that can be simulated.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"52 17","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138588298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. X. Huang, P. H. Chung, K. M. Chung, C. Y. Huang
Vortex generators (VGs) are typically positioned upstream of a boundary layer separation region. Their effectiveness depends on incoming flow conditions (Mach number, Reynolds number and boundary layer characteristics), geometrical configuration (vane or ramp, height, width, and angle of incidence) and spacing. Device-induced vortices and following decay allow VGs to be used as a passive control device. This study uses pressure-sensitive paint (PSP) to determine the global surface pressure pattern for a flat plate flow in the presence of VGs (counter-rotating vanes, co-rotating vanes and ramps). The freestream Mach number is 0.64 and 0.83. The ratio between the height of the VGs and the incoming boundary layer thickness is 0.2, 0.5 and 1.0. The standard deviation in the spanwise pressure in the streamwise direction is used to determine the downstream influence of turbulent flow past VGs. Increasing the height of VGs causes device-induced vortices to propagate farther downstream.
{"title":"Downstream influence of turbulent flow past vortex generators","authors":"Y. X. Huang, P. H. Chung, K. M. Chung, C. Y. Huang","doi":"10.1093/jom/ufad039","DOIUrl":"https://doi.org/10.1093/jom/ufad039","url":null,"abstract":"\u0000 Vortex generators (VGs) are typically positioned upstream of a boundary layer separation region. Their effectiveness depends on incoming flow conditions (Mach number, Reynolds number and boundary layer characteristics), geometrical configuration (vane or ramp, height, width, and angle of incidence) and spacing. Device-induced vortices and following decay allow VGs to be used as a passive control device. This study uses pressure-sensitive paint (PSP) to determine the global surface pressure pattern for a flat plate flow in the presence of VGs (counter-rotating vanes, co-rotating vanes and ramps). The freestream Mach number is 0.64 and 0.83. The ratio between the height of the VGs and the incoming boundary layer thickness is 0.2, 0.5 and 1.0. The standard deviation in the spanwise pressure in the streamwise direction is used to determine the downstream influence of turbulent flow past VGs. Increasing the height of VGs causes device-induced vortices to propagate farther downstream.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"124 10","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study established a Computational Fluid Dynamics (CFD) model based on a dynamic mesh strategy to conduct a comprehensive numerical investigation of the performance of the E1619 propeller in open water tests. To capture the turbulence flows around the propeller, a large eddy simulation (LES) turbulence model was implemented. In order to validate the simulation results, a series of open water tests were conducted in the towing tank at National Cheng Kung University, resulting in a successful achievement of total uncertainties of less than approximately 6%. The approach of simultaneous grid and time refinement was utilized to perform the discretization analysis. Eventually, the simulation results were employed to analyze the hydrodynamic performance and flow structure around the propeller, resulting in a conclusion based on the attained level of accuracy. The results indicate that the cases for a propeller with a strut exhibit favorable predictions compared to those of a single propeller, with error values for the thrust coefficients and propeller efficiencies falling below 6%. On the other hand, the torque coefficient was more accurately estimated for the cases of a single propeller than for those of a propeller with a strut, with error values below 2%.
{"title":"The CFD Simulation of E1619 Propeller Open Water Tests Validated by the EFD in the NCKU Towing Tank","authors":"Yu-Hsin Lin, Ahmad Darori Hasan","doi":"10.1093/jom/ufad034","DOIUrl":"https://doi.org/10.1093/jom/ufad034","url":null,"abstract":"This study established a Computational Fluid Dynamics (CFD) model based on a dynamic mesh strategy to conduct a comprehensive numerical investigation of the performance of the E1619 propeller in open water tests. To capture the turbulence flows around the propeller, a large eddy simulation (LES) turbulence model was implemented. In order to validate the simulation results, a series of open water tests were conducted in the towing tank at National Cheng Kung University, resulting in a successful achievement of total uncertainties of less than approximately 6%. The approach of simultaneous grid and time refinement was utilized to perform the discretization analysis. Eventually, the simulation results were employed to analyze the hydrodynamic performance and flow structure around the propeller, resulting in a conclusion based on the attained level of accuracy. The results indicate that the cases for a propeller with a strut exhibit favorable predictions compared to those of a single propeller, with error values for the thrust coefficients and propeller efficiencies falling below 6%. On the other hand, the torque coefficient was more accurately estimated for the cases of a single propeller than for those of a propeller with a strut, with error values below 2%.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":"54 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139266200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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