Coupling of RANS and BEM Solvers for Simulation of Propeller Behind the Hull in Full Appended Model

To design a propeller for ship power plant,the interaction between ship hull and propeller must be taken into account.The main concern is to apply the wake effect of ship stern on the propeller performance.In this paper,a coupled BEM(Boundary Element Method)/RANS(Renolds-Averaged Navier−Stokes)solver is used to simulate propeller behind the hull in the self-propulsion test.The motivation of this work is to develop a practical tool to design marine propulsion system without suffering long computational time.An unsteady boundary element method which is also known as panel method is chosen to estimate the propeller forces.Propeller wakes are treated using a time marching wake alignment method.Also,a RANS code coupled with VoF equation is developed to consider the ship motions and wake field effects in the problem.A coupling algorithm is developed to interchange ship wake field to the potential flow solver and propeller thrust to the RANS code.Based on the difference between hull resistance and the propeller thrust,a PI controller is developed to compute the propeller RPM in every time step.Verification of the solver is carried out using the towing tank test report of a 50 m oceanography research vessel.Wake factor and trust deduction coefficient are estimated numerically.Also,the wake rollup pattern of the propeller in open water is compared with the propeller in real wake field.

Subcutaneous pedicled propeller flap technique for microscopic reconstruction of eyelid defects

AIM:To describe the subcutaneous pedicled propeller flap technique for the microscopic reconstruction of eyelid defects and evaluate its outcomes.METHODS:The clinical data of 23 patients(23 eyes)who underwent microscopic reconstruction of eyelid defects with the subcutaneous pedicled propeller flap technique were retrospectively analyzed.All patients underwent eyelid tumor resection and one-stage microscopic reconstruction with the subcutaneous pedicled propeller flap for anterioror posterior-layer eyelid defects.The survival rate of the propeller flap,eyelid function and appearance,tumor recurrence rate,and patient satisfaction were evaluated after the surgery.RESULTS:The patients consisted of 12 men and 11 women,aged 31–82y(mean,58.9y).The longest followup time was 5y,and the shortest was 3mo.All the propeller flaps survived well.There was no significant difference in color and luster between the flap and adjacent tissues,and there was no dog ear phenomenon.No obvious scarring was observed.There were no obvious abnormalities of eyelid morphology or function,and no adverse complications such as exposure keratitis,entropion,ectropion,ptosis,and eyelid retraction.No tumor recurrence was found at the time of the last follow-up.All patients were satisfied with the surgical results.CONCLUSION:The subcutaneous pedicled propeller flap technique for the microscopic reconstruction of eyelid defects has satisfactor y outcomes in terms of eyelid function and esthetics,and merits clinical application.

Propeller技术在消除踝关节磁共振成像运动伪影及改善图像质量中的应用研究

目的:探讨螺旋桨采集(Propeller)技术在消除踝关节磁共振成像运动伪影以及改善图像质量中的应用效果。方法:选取2022年1月—2023年6月济南市第三人民医院行踝关节常规磁共振检查且图像存在运动伪影的60例患者为研究对象,出现伪影时采取Propeller扫描,对使用技术前后图像质量进行比较,评估Propeller技术的应用价值。结果:应用Propeller技术可显著减少运动伪影,且大幅度提高了图像质量,保证阅片的顺利完成。横断位PDWI扫描与矢状位T_2WI扫描应用Propeller技术前后的图像质量评定结果比较,差异有统计学意义(P <0.05)。结论:在踝关节磁共振检查中应用Propeller技术有助于消除运动伪影,改善图像质量,对临床阅片与诊断均有积极作用。

Method of Determining Windmill Characteristics of Propeller Engine

Taking the model for propeller transport aircraft as the research object,according to the transient windmill characteristics in the process of stop feathering and starting in the air,the simulation calculation of different flight heights,blade angles and rotation speeds was carried out,and the transient windmill resistance of the propeller was quantitatively given.The engine torque was calculated by using the simulation model are compared and verified using the flight test data,and the maximum error was 7􀆰4%.In the windmill state,the airflow works on the propeller,and the airflow velocity behind the propeller disk decreases,wrapping the entire nacelle surface.In the process of parking feathering,the blade angle decreases slightly at first,and then increases rapidly under the action of the large⁃pitch oil pressure,and the speed of rotation increases gradually.When the blade angle at 30°,the windmill resistance at-108 kgf.In the process of starting,the propeller speed increases and the propeller resistance increases first and decreases.When the propeller returns to 14°,the transient windmill resistance at-1720 kgf.

Propeller Torque Load and Propeller Shaft Torque Response Correlation During Ice-propeller Interaction

Ships use propulsion machinery systems to create directional thrust. Sailing in ice-covered waters involves the breaking of ice pieces and their submergence as the ship hull advances. Sometimes, submerged ice pieces interact with the propeller and cause irregular fluctuations of the torque load. As a result, the propeller and engine dynamics become imbalanced, and energy propagates through the propulsion machinery system until equilibrium is reached. In such imbalanced situations, the measured propeller shaft torque response is not equal to the propeller torque. Therefore, in this work, the overall system response is simulated under the ice-related torque load using the Bond graph model. The energy difference between the propeller and propeller shaft is estimated and related to their corresponding mechanical energy. Additionally, the mechanical energy is distributed among modes. Based on the distribution, kinetic and potential energy are important for the correlation between propeller torque and propeller shaft response.

Hydrodynamic Efficiency Improvement of the High Skew Propeller for the Underwater Vehicle Under Surface and Submerged Conditions

An algorithm based on the Boundary Element Method(BEM)is presented for designing the High Skew Propeller(HSP)used in an Underwater Vehicle(UV).Since UVs operate under two different kinds of working conditions(i.e.surface and submerged conditions),the design of such a propeller is an unwieldy task.This is mainly due to the fact that the resistance forces as well as the vessel efficiency under these conditions are significantly different.Therefore,some factors are necessary for the design of the opti-mum propeller to utilize the power under the mentioned conditions.The design objectives of the optimum propeller are to obtain the highest possible thrust and efficiency with the minimum torque.For the current UV,the main dimensions of the propeller are pre-dicted based on the given required thrust and the defined operating conditions.These dimensions(number of blades,pitch,diameter,expanded area ratio,thickness and camber)are determined through iterative procedure.Because the propeller operates at the stern of the UV where the inflow velocity to the propeller is non-uniform,a 5-blade HSP is preferred for running the UV.Finally,the propel-ler is designed based on the numerical calculations to acquire the improved hydrodynamic efficiency.

Ice-Class Propeller Strength and Integrity Evaluation Using Unified Polar ClassURI3 Rules

A systematic method was developed for ice-class propeller modeling,performance estimation,strength and integrity evaluation and optimization.To estimate the impact of sea ice on the propeller structure,URI3 rules,established by the International Association of Classification Societies in 2007,were applied for ice loading calculations.An R-class propeller(a type of ice-class propeller)was utilized for subsequent investigations.The propeller modeling was simplified based on a conventional method,which expedited the model building process.The propeller performance was simulated using the computational fluid dynamics(CFD)method.The simulation results were validated by comparison with experimental data.Furthermore,the hydrodynamic pressure was transferred into a finite element analysis(FEA)module for strength assessment of ice-class propellers.According to URI3 rules,the ice loading was estimated based on different polar classes and working cases.Then,the FEA method was utilized to evaluate the propeller strength.The validation showed that the simulation results accorded with recent research results.Finally,an improved optimization method was developed to save the propeller constituent materials.The optimized propeller example had a minimum safety factor of 1.55,satisfying the safety factor requirement of≥1.5,and reduced the design volume to 88.2%of the original.

磁共振成像PROPELLER数据网格化中的采样密度补偿新算法

PROPELLER磁共振数据的重建是一个典型的K空间非笛卡尔采样数据的重建问题.由于现有网格化重建算法中的密度补偿需要计算每个采样点的密度补偿系数,须对非笛卡尔分布的数据进行卷积运算,给定N采样点,该卷积运算需要N×N/2次距离运算,由于PROPELLER采集的数据量N很大,计算耗时非常长.本文提出PRO-PELLER数据网格化重建中的密度补偿新算法,通过基于网格化分量全为1的向量来计算在均匀网格点上的采样密度分布值进而加以补偿,使得算法复杂度大大下降.实验表明,本文算法比现有算法的运行时间缩短400多倍,而重建质量与原有算法基本相同.

低张MRCP结合Propeller LAVA动态增强扫描在壶腹周围病变中的应用价值研究

目的:探讨低张胰胆管水成像(magnetic resonance cholangiopancreatography,MRCP)结合Pro-pellerLAVA多期动态增强扫描在壶腹周围病变综合诊断中的临床应用价值。方法:对34例壶腹周围病变患者在常规MR扫描基础上行低张MRCP及十二指肠低张后PropellerLAVA多期动态增强扫描,对原始图像进行3DMIP及MPR重建后处理,观察病变的间接及直接征象并与临床随访及病理结果对照。结果:34例中31例梗阻性质诊断明确,1例胰头癌漏诊,2例炎症误诊为肿瘤,定性诊断准确率为91.2%。30例行PropellerLAVA增强扫描,直接征象显示率达93.3%,肿瘤浸润范围诊断符合率为80.8%。26例肿瘤性病变中壶腹部癌5例,胆总管远端癌11例、胰头癌9例、壶腹周围十二指肠腺癌1例,定位准确率分别为88.5%(23/26)、84.6%(22/26)、88.5%(23/26),十二指肠腺癌误诊为乳头癌。另外直观显示了4例病变局限、直径在2.0cm以内的早期壶腹周围癌。结论:低张MRCP结合PropellerLAVA动态增强扫描能够全面、直观显示壶腹部病变的间接及直接征象,在明确肿瘤性病变的范围及周围组织、血管浸润方面具有重要意义,对壶腹部较小或隐匿病变亦具有较高的应用价值。

磁共振成像PROPELLER采样数据重建中的运动估计新算法

PROPELLER(推进器)采样技术能够利用K空间中心重叠采样区域的数据来估计采集过程中受检查者的运动进而加以补偿,对运动伪影的消除效果非常显著。然而,由于其重建时的运动估计是基于最大化频域空间上相关系数的配准算法,该算法为了实现旋转估计与平移估计的分离,在进行旋转估计时,仅仅采用K空间数据的模,在数据量有限的情况下造成估计精度较低,在重建图像上表现为模糊及星条状伪影。本研究基于最大化图像空间上的互信息提出一种PROPELLER采样数据的运动估计新算法,首先由每个K空间带进行傅立叶逆变换后取模重建出系列临时图像,对这些图像进行模糊增强后以互信息作为相似性测度迭代搜索最优的运动参数。实验证明,该方法能显著提高PROPELLER采样数据重建中运动估计与补偿的精度,从而更好地消除伪影,特别是用于有运动时T1加权头部成像时。

PROPELLER技术在改善固定义齿脑梗塞患者图像伪影中的意义

目的探讨磁共振螺旋桨技术(periodically rotated overlapping parallel lines enhanced reconstruction,PROPELLER)在改善固定义齿脑梗塞患者MR图像伪影中的作用。方法对2013年1月至2015年1月来我科行MRI检查装有固定义齿的患者81例,分别采用PROPELLER DWI技术和常规FSE DWI序列进行头颅MRI扫描,对采集到的MRI图像进行观察。结果PROPELLER DWI检出脑梗塞病灶78例,未检出病灶3例分别是额叶1例,颞叶2例;FSE DWI检出脑梗塞病人20例,未检出病灶61例,额叶、颞叶、小脑及脑干出现伪影分别为19例、39例、1例、2例。结论 PROPELLER技术能有效消除磁敏感伪影,改善固定义齿脑梗塞患者的MR图像质量,增加脑梗塞病灶的检出率,对改善MR图像质量有非常好的作用。

T1 FLAIR PROPELLER序列在3.0T磁共振颅脑增强成像上对抑制各种伪影的应用

目的:探讨3.0T磁共振上利用T1 FLAIR PROPELLER序列在颅脑增强成像时对消除各种血管搏动伪影及头部运动伪影和金属伪影等的应用价值。方法:对108例患者行常规头部平扫和增强检查,应用PROPELLER技术进行钆造影剂注射后的T1 FLAIR三平面扫描,与常规T1 FLAIR三平面序列进行对比,并进行图像伪影评价。结果:108例患者常规增强T1 FLAIR序列均有不同程度的血管搏动伪影,25例患者有明显的运动伪影,22例患者有金属伪影(固定义齿或手术缝合钉、钛板等),这些伪影严重影响图像质量,有部分导致诊断的假阳性判断。应用PROPELLER技术后的T1 FLAIR序列,对比发现,108例均明显消除了血管搏动伪影,106例没有明显运动伪影,22病例金属伪影均有所减轻,获得了有诊断价值的图像。两种序列图像质量有显著差异(P<0.01)。结论:应用PROPELLER技术的T1 FLAIR序列,能最大限度地消除头部增强扫描中的血管搏动伪影以及降低运动伪影、金属伪影,可提供更有临床诊断价值的理想图像。

磁共振Propeller技术消除伪影的临床应用

目的:探讨Propeller技术在临床的应用价值。方法:日常工作中随机对19例磁共振头颅检查中出现躁动或有固定金属异物患者,应用Propeller技术进行成像,与常规T2FRFSE序列、DWI序列进行对比扫描。其中因躁动产生运动伪影进行PropellerT2加权成像11例,因金属异物产生伪影进行PropellerDWI成像8例,同时进行PropellerT2WI、DWI成像5例。结果:19例应用Propeller技术进行T2WI、DWI成像消除因运动、金属引起的伪影均获得满意图像。结论:应用PropellerT2WI、DWI成像技术明显消除患者因运动或金属异物造成的伪影,可生成高分辨无伪影具有临床诊断意义的理想图像。

PROPELLER技术在头颅MR检查中的应用进展

磁共振检查技术,以其特有的无辐射、高分辨率成为目前最常用的检查手段之一。磁共振检查在获得良好的组织对比度的同时,也是存在伪影最多的检查方法,它的主要伪影包括设备伪影、运动伪影及磁敏感伪影。尤其是在高场强磁共振检查中,运动伪影和磁敏感伪影更为突出。如何避免因运动伪影、固定义齿产生的严重磁敏感伪影,以及呼吸运动等非刚性运动伪影是广大学者广泛关注与研究的问题。

Propeller技术消除头部磁共振伪影的应用

目的:探讨Propeller技术对减少头部运动伪影及磁敏感伪影的应用价值。方法:对53例磁共振头颅检查时躁动或难以自控的患者行常规FRFSE T2WI和Propeller T2WI轴位扫描;对31例常规扩散加权图像(DWI)磁敏感伪影明显者进行Propeller DWI扫描。观察并对照分析FRFSE T2WI和Propeller T2WI以及DWI与Propeller DWI的图像质量状况。结果:53例在T2WI存在明显运动伪影的患者,在行Propeller T2WI扫描后明显减少或消除了运动伪影,图像质量级别显著升高[(2.88±0.32,(1.11±0.30),P=0.00)]。31例在DWI有显著磁敏感伪影的患者,采用Pro-peller DWI后,明显消除磁敏感伪影,图像质量明显提高[(2.84±0.35,(1.06±0.17),P=0.00)]。结论:应用Propeller技术能够明显减少或消除T2WI及DWI上运动伪影及磁敏感伪影,显著改善图像质量。

基于Voronoi图的磁共振PROPELLER数据网格化算法

PROPELLER数据采集成像算法是磁共振成像中的一项新技术,由于其数据的网格化直接影响该成像算法的效果,因此提出一种基于Voronoi图的网格化算法.该算法对采样数据集进行网格分组查找,快速消除位置相同点;加入边缘闭包后进行Voronoi网格化,计算Voronoi网格面积并将其作为网格化的密度补偿权函数,提出基于网格分组的快速网格化算法并成像.实验表明,该算法运行速度快,成像清晰,图像对比度和细节较好,信噪比得到有效提高.

磁共振Propeller技术消除患者因运动及磁敏感效应造成伪影的作用(英文)

背景:运动伪影及磁敏感伪影严重影响MR成像质量,Propeller技术采用填充模式,以辐射状的叶片用螺旋的方式采集数据,在很大程度上解决了运动伪影及磁敏感伪影的问题。目的:探讨Propeller技术在头部伪影消除的应用价值。设计、时间及地点:对比观察实验,于2006-07/2007-04在解放军成都军区昆明总医院完成。参试者:21例磁共振头颅日常检查中出现躁动或不能自控患者,5例固定义齿致磁敏感伪影明显者。方法:对21例磁共振头颅日常检查躁动或不能自控患者,常规T2FRFSE序列运动伪影明显,用Propeller技术进行T2WI扫描并进行对比;5例常规扩散加权图像序列磁敏感伪影明显者进行Propeller 扩散加权图像扫描并进行对比。主要观察指标:Propeller技术应用后运动伪影与磁敏感伪影的改变情况。结果:21例应用Propeller技术进行T2WI扫描明显减少或消除了运动伪影,5例Propeller扩散加权图像明显消除磁敏感效应引起的伪影,均生成较满意图像。结论:应用Propeller T2WI及扩散加权图像成像技术可以明显减少或消除患者因运动及磁敏感效应造成的伪影,显著提高图像质量,获得具有临床诊断价值的理想图像。

Scale effects on non-cavitation hydrodynamics and noise of highly-skewed propeller in wake flow

Regarding the scale effects on propeller＇s noncavitation hydrodynamics and hydroacoustics, three similar 7bladed highly-skewed propellers in the wake flow are addressed with diameters of 250, 500 and 1 000 mm, respectively. The discrete line-spectrum noise and its standardized spectrum level scaling law, together with the total sound pressure level are analyzed. The non-cavitation noise predictions are completed by both the frequency domain method and the time domain method. As a fluctuated noise source, the time-dependent fluctuated pressure and normal velocity distribution on propeller blades are obtained by the unsteady Reynolds-averaged Navier-Stokes （ URANS ） simulation. Results show that the pressure coefficient distribution of three propellers on the 0.7R section is nearly superposed under the same advance ratio. The periodic thrust fluctuation of three propellers can exactly reflect the tonal components of the axial passing frequency （APF） and the blade passing frequency （BPF）, and the fluctuation enhancement from the small to the middle propeller at the BPF is greater than that from the middle to the big one. By the two noise prediction methods, the increment of the total sound pressure level from the small to the big propeller differs by 2.49 dB. Following the standardized scaling law, the spectrum curves of the middle and big propellers are nearly the same while significantly differing from the small one. The increment of both the line-spectrum level and the total sound pressure increases with the increase in diameter. It is suggested that the model scale of the propeller should be as large as possible in engineering to reduce the prediction error of the empirical scalin~ law and weaken the scale effects.

PROPELLER磁共振成像数据重建中的仿射运动校正新算法

PROPELLER(Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction)磁共振成像方法对刚性运动伪影的消除效果非常显著,已经在头部磁共振成像中获得了成功应用.但是刚性运动一般仅存在于头部成像中,人体其它部位成像往往伴随着不同程度的软组织拉伸变形.对于这种软组织变形必须基于非刚性运动模型才能准确地进行描述并加以校正.本文将PROPELLER采样中的每个k-空间条经过傅立叶逆变换重建得到临时图像,通过基于仿射运动模型的图像配准算法获得非刚性运动信息,然后根据仿射变换的频域性质,对PROPELLER采样中的每个k-空间条进行校正,最后经网格化重建得到最终图像.仿真实验与真实数据实验表明,相对于现有的PROPELLER重建算法,本文所提算法对于刚性运动与仿射运动造成的伪影均具有很好的校正效果.

金属结扎丝对颅脑MR影像的影响与Propeller技术的临床应用

目的探讨金属结扎丝对头部MRI的影响及Propeller技术在消除头部金属伪影中的应用价值。方法对10例上颌前牙因外伤松动、脱位的患者,用金属结扎丝结扎固定后分别用FSE序列T1加权像,普通EPI扩散加权成像序列(EPIDWI)、Propeller扩散加权成像序列(PropellerDWI)成像并进行对比。结果10例患者在FSE序列T1加权像矢状面MRI中均有重度的磁敏感伪影;普通EPIDWI序列颅脑解剖组织处有明显的磁敏感伪影;PropellerDWI技术能明显减少磁敏感伪影生成满意的影像。结论金属结扎丝对颌面部及颅脑MR成像有较大的影响;PropellerDWI成像技术能明显消除磁敏感伪影获得具有临床诊断价值的理想影像。