The role of precessing vortex core in two combustion regimes: Numerical simulation studies

Zhenlin Wang,Xiangsheng Li,Zhenping Feng,Zhao Yang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1

Large Eddy simulation (LES) with finite rate chemistry was used to investigate the combustion dynamics in a lab-scale PRECCINSTA combustion chamber. Transient three dimensional numerical simulations were carried out at two different thermal powers (10 kW and 35 kW) with a fixed equivalence ratio of 0.7. The predicted results were compared with the experimental data and good agreements were found between them. In the cold flow field under both conditions, a precessing vortex core (PVC) in the inner shear layer (ISL) existing between the swirling jet and the inner recirculation zone (IRZ). However, two different flow and combustion dynamics were observed when combustion occurred. At thermal power of 10 kW, there was a V-shaped flame and the combustion of the flame was stable. The PVC disappeared and the vortices arrangement was symmetrical in the ISL. However, at 35 kW, there was a M-shaped flame with a PVC in the ISL and combustion instability triggered. In depth analysis of the characteristics of flow, temperature and heat release field, we found that the flame surface was wrinkled periodically by the PVC which enhanced the mixing between the cold fresh gas and hot burned products. Then, the mixture was ignited locally and heat release was rapid in the middle of the combustion chamber. These effects were directly related to the periodic vortices motion which was induced by PVC. It was confirmed that the influence of PVC on flame surface and heat release is an important factor for triggering the combustion instability at thermal power of 35 kW. The zone division based on different roles of flow/flame and thermoacoustic coupling was also discussed to illustrate the combustion instabilities caused by PVC.

Design of mechanical coxa joints based on three-degree-of-freedom spherical parallel manipulators

Yanbiao Li,Zhenlin Jin,Zhongfei Wang,Ming-sheng Jin,Yi Liu 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.1

We addressed the issue of the design of mechanical coxa joints based on three-degree-of-freedom spherical parallel manipulators using the parameter statistics optimum method based on index atlases. The coxa joints have the advantages of high payload, high accuracy, and good technological efficiency. The first step of the design and prototyping used in this paper develops the direct and inverse displacement equations from the layout feature of the mechanical coxa joints. Then, the shapes of a constant-orientation workspace of the mechanical coxa joints are described, and the effects of the design parameters on the workspace volume are studied quantitatively. The next step deals with the graphical representation of the atlases that illustrates the relationship between performance evaluation index and design parameters based on the kinematics and torque analysis of the mechanical coxa joints. Finally, the geometric parameters of the coxa joints are obtained by the parameter statistics optimum method based on the index atlases. Considering assembly conditions, the design scheme of the mechanical coxa joints is developed, which provides a theoretical basis for the application of the mechanical coxa joints.

Multi-objective optimization design of a centrifugal impeller by positioning splitters using GMDH, NSGA-Ⅲ and entropy weight-TOPSIS

Xing Xie,Zhenlin Li,Baoshan Zhu,Hong Wang,Wenwu Zhang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.5

A centrifugal impeller with splitters was designed by three-dimensional (3D) inverse design method, and its efficiency, velocity non-uniformity at impeller exit and maximum equivalent stress of blades were optimized by providing the suitable blade stacking angle, work ratio and circumferential location of the splitter. First, 80 samples were generated by optimal Latin hypercube technique and the corresponding impellers were designed by 3D inverse design. Using computational fluid dynamics (CFD) and fluid structure interaction (FSI), the optimization objectives were obtained. Then, the group method of data handling (GMDH) artificial neural networks was established to link the design parameters and objectives by the specific formulas. The reference-point-based non-dominated sorting genetic algorithm (NSGA-Ⅲ) was applied to search the Pareto front. Finally, the preferred impeller was selected by adopting entropy weight and the method of technique for order preference by similarity to an ideal solution (TOPSIS). The results showed that the splitter of the preferred impeller had a circumferential location of 0.58, blade stacking angle of 28° and work ratio of 0.48. The nonuniformity at impeller exit and maximum equivalent stress of blades of preferred impeller obtained by NSGA-Ⅲ were decreased, while the efficiency was improved.

Uniform Microstructure and Excellent Corrosion Resistance of HVOF-Sprayed CoCrNi Medium-Entropy Alloy Coating in Fluoride Ion Environment

Dongbao Huang,Zhenlin Xu,Xiquan Jia,Haitao Yu,Yizhu He,Zhenqi Dong,Shenshen Li,Hui Zhang 대한금속·재료학회 2024 METALS AND MATERIALS International Vol.30 No.1

To solve the corrosion problem of the copper plates caused by fluoride ions, the Ni55 and CoCrNi medium-entropy alloycoatings were prepared via high-velocity oxygen fuel technology. The corrosion resistance of the Ni55 and CoCrNi coatingsin NaF solution was compared through electrochemical experiments and immersion corrosion experiments. The Ni55coating contained complex precipitated phases, resulting in preferential corrosion at the phase boundaries between the γ-Nisolid solution and the precipitated phases. The composition of the CoCrNi coating was more homogeneously distributed,and mainly uniform corrosion occurred. The corrosion products of the two coatings in the NaF solution were both complexescomposed of metal oxides and fluorides. Compared with the Ni55 coating, the passive film formed on the CoCrNi coatinghad a more uniform and protective property; therefore, the CoCrNi coating had better corrosion resistance. This researchcan pave a pathway for developing coating on copper and its alloys with excellent corrosion resistance.

Open source board based acoustofluidic transwells for reversible disruption of the blood–brain barrier for therapeutic delivery

Ke Wang,Chao Sun,Povilas Dumčius,Hongxin Zhang,Hanlin Liao,Zhenlin Wu,Liangfei Tian,Wang Peng,Yongqing Fu,Jun Wei,Meng Cai,Yi Zhong,Xiaoyu Li,Xin Yang,Min Cui 한국생체재료학회 2023 생체재료학회지 Vol.27 No.00

Background Blood–brain barrier (BBB) is a crucial but dynamic structure that functions as a gatekeeper for the central nervous system (CNS). Managing sufficient substances across the BBB is a major challenge, especially in the development of therapeutics for CNS disorders. Methods To achieve an efficient, fast and safe strategy for BBB opening, an acoustofluidic transwell (AFT) was developed for reversible disruption of the BBB. The proposed AFT was consisted of a transwell insert where the BBB model was established, and a surface acoustic wave (SAW) transducer realized using open-source electronics based on printed circuit board techniques. Results In the AFT device, the SAW produced acousto-mechanical stimulations to the BBB model resulting in decreased transendothelial electrical resistance in a dose dependent manner, indicating the disruption of the BBB. Moreover, SAW stimulation enhanced transendothelial permeability to sodium fluorescein and FITC-dextran with various molecular weight in the AFT device. Further study indicated BBB opening was mainly attributed to the apparent stretching of intercellular spaces. An in vivo study using a zebrafish model demonstrated SAW exposure promoted penetration of sodium fluorescein to the CNS. Conclusions In summary, AFT effectively disrupts the BBB under the SAW stimulation, which is promising as a new drug delivery methodology for neurodegenerative diseases.

Laparoscopic radical cystectomy with pelvic lymph node dissection and ileal orthotopic neobladder by a total extraperitoneal approach: Our initial technique and short-term outcomes

Guanqun Zhu,Zongliang Zhang,Kai Zhao,Xinbao Yin,Yulian Zhang,Zhenlin Wang,Chen Li,Yuanming Sui,Xueyu Li,Han Yang,Nianzeng Xing,Ke Wang 대한비뇨의학회 2022 Investigative and Clinical Urology Vol.63 No.5

Purpose: With the increasing application of laparoscopic or robot-assisted radical cystectomy, a reliable and promising method is needed for reducing postoperative complications. We describe the short-term outcomes of totally extraperitoneal laparoscopic radical cystectomy (TELRC) with extraperitoneal pelvic lymph node dissection (EPLND) and extraperitoneal ileal orthotopic neobladder (EION) techniques. Materials and Methods: From January 2020 to December 2021, we performed TELRC and EPLND with EION in 72 patients in our center. The accompanying video highlights our novel techniques. The patients’ demographic data, intraoperative data, and perioperative complications were collected, and short-term oncological and functional results are reported. Results: All procedures were technically successful without conversion to open surgery. The patients’ mean body mass index was 26.22±5.71. Median age was 57.51±12.34 years. Average hospital stay was 13.78±4.62 days. Median intraoperative blood loss was 112.92±88.56 mL. No blood transfusion was needed during the operations and only one blood transfusion was performed during the perioperative period. Mean operating time was 259.44±49.84 minutes. Average cost was US$9,875.71±1,873.08. Postoperative short-term complications included short-term ileus (n=3), infection (n=13), leakage of urine (n=11), and lymph fistula (n=7). One late complication of unilateral vesicoureteral anastomotic stenosis occurred. The mean follow-up was 13.42±8.77 months, and no patient developed local or systemic recurrence. The short-term follow-up and small cohort of patients limited our evaluation of outcomes. Conclusions: TELRC with PLND and EION was technically feasible and clinically promising, with a reduced potential harm of postoperative complications. Long-term follow-up and a larger cohort of patients are needed for further study.

Atrial fibrillation in critically ill patients who received prolonged mechanical ventilation: a nationwide inpatient report

( Zhen Lin ),( Hedong Han ),( Wei Guo ),( Xin Wei ),( Zhijian Guo ),( Shujie Zhai ),( Shuai Li ),( Yiming Ruan ),( Fangyuan Hu ),( Dongdong Li ),( Jia He ) 대한내과학회 2021 The Korean Journal of Internal Medicine Vol.36 No.6

Background/Aims: To evaluate temporal trends of atrial fibrillation (AF) prevalence in critically ill patients who received prolonged mechanical ventilation (MV) in the United States. Methods: We used the 2008 to 2014 National Inpatient Sample to compute the weighted prevalence of AF among hospitalized adult patients on prolonged MV. We used multivariable-adjusted models to evaluate the association of AF with clinical factors, in-hospital mortality, hospitalization cost, and length of stay (LOS). Results: We identified 2,578,165 patients who received prolonged MV (21.27% of AF patients). The prevalence of AF increased from 14.63% in 2008 to 24.43% in 2014 (p for trend < 0.0001). Amongst different phenotypes of critically ill patients, the prevalence of AF increased in patients with severe sepsis, asthma exacerbation, congestive heart failure exacerbation, acute stroke, and cardiac arrest. Older age, male sex, white race, medicare access, higher income, urban teaching hospital setting, and Western region were associated with a higher prevalence of AF. AF in critical illness was a risk factor for in-hospital death (odds ratio, 1.13; 95% confidence interval, 1.11 to 1.15), but in-hospital mortality in critically ill patients with AF decreased from 11.6% to 8.3%. AF was linked to prolonged LOS (2%, p < 0.0001) and high hospitalization cost (4%, p < 0.0001). LOS (-1%, p < 0.0001) and hospitalization cost (-4%, p < 0.0001) decreased yearly. Conclusions: The prevalence of comorbid AF is increasing, particularly in older patients. AF may lead to poorer prognosis, and high-quality intensive care is imperative for this population.