柴油机曲柄连杆机构多体动力学仿真分析

基于多体系统动力学理论,实现对某柴油机曲柄连杆机构的动力学仿真分析,得到了活塞侧推力、曲柄销受力及主轴颈载荷等动力学参数。通过活塞侧推力和曲柄销受力的传统算法与现代算法的对比,证实基于现代算法的柴油机曲柄连杆机构的动力学仿真分析的方便性与先进性,并为此类型柴油机曲柄连杆机构的优化设计提供了依据。     

基于ADAMS的柴油机曲轴多体动力学仿真

以某多缸发动机曲轴为例,采用动力学分析软件ADAMS对曲轴-连杆-活塞机构进行多刚体动力学仿真;结合有限元软件MSC.Patran/Nastran,运用模态分析技术,得到曲轴固有频率及振型,对曲轴刚柔混合体模型进行柔体动力学仿真,得到曲轴动态应力分布变化,更真实地反映了曲轴的工作情况。     

船舶Ⅴ型柴油机曲轴多体动力学分析

针对Ⅴ型柴油机曲轴系统,将有限元法和多体动力学法结合一起,进行虚拟仿真计算分析.首先通过三维软件和有限元软件建立曲轴、轴承座及活塞等多体动力学模型,模拟发动机实际工况,通过多体动力学仿真分析得出曲轴加速度、速度和位移等数据.通过计算得出,采用有限元和多体仿真结合的手段,能够有效模拟柴油机曲轴动力学特性.     

基于DYTRAN的发动机曲轴系冲击动力学仿真

基于TBD234V6发动机曲轴的有限元模型,建立了包括柔性曲轴、活塞组、连杆组及飞轮在内的发动机刚柔体混合动力学仿真模型,介绍了冲击环境冲击谱的描述方法以及结构动力响应向设计冲击谱换算的方法和原则,并基于冲击因子法和BV043/73标准,在非线性瞬态动力学软件MSC.DYTRAN中,对该型曲柄连杆机构进行了冲击响应分析.综合采用了曲柄连杆机构整体有限元分析、接触算法、非线性瞬态动力学分析方法等手段,在1 500 r/min工况下,对发动机进行刚柔体混合动力学仿真,得到了发动机的连杆颈负荷、主轴颈负荷及最大动态应力等仿真结果.计算结果表明所采用的方法是合理和有效的.     

船舶V型柴油机曲轴多体动力学分析

针对V型柴油机曲轴系统,将有限元法和多体动力学法结合一起,进行虚拟仿真计算分析。首先通过三维软件和有限元软件建立曲轴、轴承座及活塞等多体动力学模型,模拟发动机实际工况,通过多体动力学仿真分析得出曲轴加速度、速度和位移等数据。通过计算得出,采用有限元和多体仿真结合的手段,能够有效模拟柴油机曲轴动力学特性。     

曲柄连杆机构多体系统动力学与油膜动力润滑耦合仿真研究

笔者针对某柴油发动机的曲柄连杆机构系统,使用adams中的engine模块,引入柔性的液压轴承,建立了曲柄连杆机构柔性多体系统动力学与油膜动力润滑的耦合模型,进行了忽略油膜动力润滑和考虑系统动力学与油膜动力润滑耦合两种情况下的仿真分析,并对仿真结果进行了比较。而且进一步得到了曲轴轴心轨迹曲线,最小油膜厚度等参数,为后续内燃机整机噪声分析和预测,提供更为准确的边界条件。     

曲轴系统动力学特性的数字化仿真与试验研究

利用ADAMS建立了一种柴油机曲轴系统的刚性体和柔性体的动力学模型,通过仿真测试,得到柴油机的主轴承载荷,活塞侧向力等仿真数据,并针对两种系统分别对其特性进行了比较分析,将计算结果与试验结果进行比较,证明了仿真分析的可靠性,为此类型柴油机的曲轴轴系动力学耦合分析和优化设计提供了依据。     

基于多体动力学的479Q发动机连杆载荷与强度分析

以479Q汽油机为研究对象,建立了曲轴、连杆和活塞的三维几何模型和多体动力学模型。载荷边界条件采用真实示功图和负载数据,得到了做功行程中作用于连杆两端的载荷谱。采用惯性释放技术计及惯性力对连杆应力的影响,计算得到了做功行程中任意时刻连杆的动态应力场。对静力计算方法和惯性释放方法进行了对比,后者得到的动态应力场更加接近真实情况。根据曲轴转速为2 000 r/min时的气缸压力测试曲线(最高燃烧压力4.6 MPa)和对应的发动机扭矩(165 N.m),计算得到连杆最大轴向载荷为26 kN,最大工作应力为259MPa。根据局部应力应变法,该工况下的寿命为2.941×1016转,连杆近似为无限寿命。     

全浮式活塞销运动特性研究

基于弹流润滑理论、平均流量模型及微凸峰接触理论,综合采用有限元法、有限差分法和基于模态压缩法的多体动力学仿真方法对发动机中全浮式活塞销(浮式销)的运动特性进行了研究,并考察了磨合过程中连杆小头衬套表面粗糙度的降低对活塞销运动特性的影响。研究结果表明:活塞销转速在压缩上止点前迅速增大,在排气冲程后半段和吸气冲程前半段转速基本相同,且循环平均转速方向与曲轴旋转方向相反;由小头衬套产生的驱动活塞销转动的摩擦力矩变化曲线存在三个峰值,而由活塞销孔产生的阻碍活塞销转动的摩擦阻力矩变化曲线存在两个峰值;随着磨合过程中小头衬套粗糙度的降低,活塞销的循环平均转速减小。     

不同曲轴平衡率下柴油机主轴承润滑特性分析及变壁厚优化设计

基于弹性流体动压润滑及多体动力学理论,以某船用大功率柴油机主轴承为研究对象,考虑曲轴主轴承的弹性变形、表面粗糙度、供油特性等因素,建立主轴承的弹性液体动力学仿真分析模型;通过试验对该模型建立方法进行了验证.基于该模型,分析了曲轴平衡率对主轴承最小油膜厚度、最大油膜压力、轴心轨迹及滑油填充率等润滑特性参数的影响规律,并就...     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Contents in Volume 23,2014

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Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.