插装阀阀芯优化与仿真分析     

王欲进  潘思意 《中国农机化学报》2021,42(12):137

插装阀在静止状态下，由于静摩擦的原因，导致阀芯与阀套出现卡滞现象；在运动状态下，由于压差和阀芯微偏移的原因造成阀芯与阀套发生磨损；为此提出一种新型的带有导流槽的插装阀阀芯。基于缝隙流动和液压卡紧分析，建立插装阀阀芯与阀套间隙的CFD优化仿真模型，通过N-S方程、伯努利方程和卡紧力方程联立得到阀芯与阀套间卡紧力的推导公式。基于CFD仿真模拟分析，比较新型阀芯与原阀芯不同模型间隙的切线应力、压力分布规律，结果表明：在入口压力为12 MPa时，原阀芯的切线应力在12 000 Pa上下波动，大于新型阀芯切线应力4 200 Pa；在入口压力为8 MPa时，原阀芯的切线应力在7 200 Pa上下波动，大于新型阀芯切线应力3 000 Pa；且原阀芯切线应力的波动范围远大于新型阀芯。新型阀芯在阀套间的受力更加平稳，磨损更小。研究结果为插装阀优化以及减少能量损失和改善润滑条件提供理论指导和依据。  相似文献   

手动比例复合阀在中高压液压绞纲机中的应用     

南秀蓉  陈玉芳 《农机化研究》2006,(10):200-202

中高压液压技术在海洋捕捞机械—绞纲机中的使用推动了我国渔业机械的发展,手动比例复合阀在中高压液压技术上的应用则大大加快了液压绞纲机在国内渔业生产中的普及。目前,我国浙江、江苏、福建、广东和山东等省沿海渔民使用的绞纲机普遍采用带手动比例复合阀的液压系统。为此,对手动比例复合阀换向、溢流、调速集成等功能进行了分析。  相似文献   

可控止回阀水力特性的测试研究     

马爱凤 《湖南农业大学学报(自然科学版)》1993,20(6)

本文运用水流相似原理，对可控止回阀的流阻系数曲线和动水力矩，进行了系统的水力模型试验研究，为该阀的节能效益和技术开发的可行性，提供了必要的科学依据，其流阻系数值为０．１９，优于液控蝶阀。  相似文献   

Comparison of N-terminal pro-atrial natriuretic peptide and three cardiac biomarkers for discriminatory ability of clinical stage in dogs with myxomatous mitral valve disease     

Mizuki OGAWA  Yasutomo HORI  Nobuyuki KANNO  Naoki IWASA  Takeshi TOYOFUKU  Noriko ISAYAMA  Akane YOSHIKAWA  Ryota AKABANE  Atsushi SAKATANI  Hirosumi MIYAKAWA  Huai-Hsun HSU  Yuichi MIYAGAWA  Naoyuki TAKEMURA 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2021,83(4):705

Plasma N-terminal pro-atrial natriuretic peptide (NT-proANP) concentration increases with progression of myxomatous mitral valve disease (MMVD) in dogs. This multicentre, prospective study compared plasma NT-proANP, N-terminal pro-brain natriuretic peptide (NT-proBNP), ANP, and cardiac troponin I (cTnI) concentrations in dogs with MMVD for their characteristics and discriminatory ability to detect cardiac dilatation and congestive heart failure (CHF). Thirty-six healthy dogs and 69 dogs with MMVD were included. Clinical variables were obtained via physical examination, thoracic radiography, and echocardiography. The discriminatory ability of each cardiac biomarker (CB) to determine the presence or absence of cardiac dilatation (event 1) and CHF (event 2) was evaluated using the receiver operating characteristic curves. Plasma NT-proANP, NT-proBNP, and ANP concentrations showed a significant association with the left atrium/aorta ratio (P<0.01). The area under the curve of plasma NT-proANP and NT-proBNP concentrations were 0.72 and 0.75, respectively in event1 and 0.72 and 0.76, respectively in event2. Plasma NT-proANP and NT-proBNP concentrations showed sensitivity 80.0 and 80.0%; specificity 67.6 and 64.7% in event1 (cutoff value; 8,497.81 pg/ml and 1,453.00 pmol/l, respectively) and sensitivity 85.7 and 81.0%; specificity 60.4 and 64.6% in event2 (cutoff value; 8,684.33 pg/ml and 1,772.00 pmol/l, respectively). In dogs with MMVD, plasma NT-proANP, NT-proBNP, and ANP concentrations increase with left atrial enlargement. Particularly, plasma NT-proANP and NT-proBNP concentrations appeared to be equally useful in the discriminatory ability to detect cardiac dilatation and CHF.  相似文献   

Quantification of reservoir bags as airway pressure-limiting devices in a nonrebreathing system     

Tamas D. Ambrisko  Arnon Gal  Jesus N. Sarol  Ashley Mitek  Christina Braun 《Veterinary anaesthesia and analgesia》2021,48(2):205-212

ObjectiveTo evaluate the influence of reservoir bag types, volumes and previous use on the peak pressures (Pmax) and the times to develop 30 cmH₂O pressure (P30) within a nonrebreathing system with a closed adjustable pressure-limiting (APL) valve.Study designIn vitro study using three-way factorial design with repeated measure on one factor.SubjectsA total of 75 new anesthesia reservoir bags (five types, three volumes, five bags from each type × volume). The bag types were reusable latex (RL), disposable latex (DL) and three disposable neoprene (DN-1, DN-2 and DN-3).MethodsEach bag was tested three times (treatments): new, after prestretching and 1 week later. The bags were attached to a Bain system and anesthesia machine with closed APL valve and patient port with O₂ flow 2 L minute^–1 until Pmax was reached. The Pmax and time to reach P30 values were determined from recorded pressure traces. General linear mixed model analysis was used to examine the effects of bag type, volume and treatment. One-sided 95% upper prediction limits of Pmax were calculated to test the null hypothesis that predicted Pmax of new bags would be ≥ 50 cmH₂O for each factor combination.ResultsRL bags were the least and DN-3 bags were the most compliant. Prestretching increased compliance in all bag types. Smaller bags of RL, DL and DN-1 were less compliant than larger ones. The predicted Pmax values were < 50 cmH₂O only for DN-3 bags after prestretching. The time to reach P30 was critically low when using 0.5 L bags (median 17 seconds).Conclusions and clinical relevanceTo minimize the risk of barotrauma, highly compliant reservoir bags (e.g. DN-3) are recommended and reusable bags should be avoided. Bags should be prestretched before first use, 0.5 L bags should be avoided and fresh gas flow minimized.  相似文献   

Flash flood simulation and valve behavior of Mytilus galloprovincialis measured with Hall sensors     

Piero ADDIS  Alberto ANGIONI  Viviana PASQUINI  Angelica GIGLIOLI  Valeria ANDREOTTI  Stefano CARBONI  Marco SECCI 《Integrative zoology》2021,16(2):138-148

Mussels close their shell as a protective strategy and the quantification of this behavioral marker may represent an alarm signal when they are exposed to environmental stressors. In the present study, we investigated the ability of the Mediterranean mussel Mytilus galloprovincialis to recover and then the resilience or inertia of valve activity after a pulsing exposition to diverse levels of salinity (5, 10, 20, and 35 PSU as reference value). The trial simulated an event of drastic and sudden reduction of seawater salinity thus mimicking an event of flash flood from intense rain. Valve gaping and movements were measured in continuous cycle for 10 days using a customized magneto-electric device which uses Hall sensors. Results showed that under normal conditions of salinity (35 PSU), the general pattern of valve movements was a continuously open state with sporadic spikes indicating a closing motion. At salinity of 5, PSU mussels reacted by closing their valves, leading to a 77% mortality on the 4th day. At salinity of 10, PSU animals were observed with closed valves for the entire duration of the exposure and no mortality occurred, they showed a significant reduction in the valve activity once the reference value of salinity was re-established. In contrast, salinity of 20 PSU did not trigger a significant behavioral response. Interestingly, there no define rhythms of valve movements were recorded during salinity challenges.  相似文献   

直通式调节阀内部流场分析     

李海峰  马若群 《中国农村水利水电》2015,(1)

基于CFD对直通式调节阀内部流场进行了二维数值模拟,并得到了内部流动参数的可视化图形。对比25%和5%两种开度下,阀门处的压力,速度以及能量损失都存在很大的差异。25%开度下的压力、流速有明显的下降趋势,而5%开度下压力和速度则迅速变化。+两种开度下产生的涡流位置不同,5%开度下能量损失比25%开度下的要大。  相似文献   

Breeding Restrictions Decrease the Prevalence of Myxomatous Mitral Valve Disease in Cavalier King Charles Spaniels over an 8‐ to 10‐Year Period          下载免费PDF全文

A.C. Birkegård  M.J. Reimann  T. Martinussen  J. Häggström  H.D. Pedersen  L.H. Olsen 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2016,30(1):63-68

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Prevalence and prognostic role of L wave and selected clinical and echocardiographic variables in dogs with atrial fibrillation     

Giovanni Romito  Stefana Darida  Carlotta Valente  Helen Poser  Barbara Contiero  Mario Cipone  Carlo Guglielmini 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2023,37(1):47-57

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矩形节流阀片可调油气弹簧旁通阀流量设计研究   总被引：2，自引：0，他引：2  

周长城  顾亮 《拖拉机与农用运输车》2006,33(2):13-16

给出了油气弹簧结构原理图,通过油气弹簧活塞与活塞杆的受力分析,对油气弹簧的承压面进行了研究,可知油气弹簧的阻尼力与油气弹簧活塞和油气弹簧缸筒内径之间的环形面积有关,对矩形节流阀片建立了力学模型,对矩形节流阀片的弯曲变形进行了分析,并在此基础上对油气弹簧的开阀速度、开阀压力以及油气弹簧流量进行了探讨,根据旁通阀打开所设计油气弹簧阻尼比,对旁通阀打开后可调油气弹簧的最大开阀速度和开阀压力进行了分析,对旁通阀的流量进行了研究和分析,最后对可控油气弹簧进行了阻力特性试验。可知,旁通阀最大流量设计方法正确的,利用控制电流可以实现对可调油气弹簧阻尼特性的控制。  相似文献