Dynamic behavior of an agricultural power take-off driveline for rattle noise reduction: Part 1. Effect of spline tolerance on the power take-off rattle noise

An agricultural tractor has a power take-off (PTO) driveline that is directly connected to the engine to improve its power transmission efficiency. The PTO driveline comprises various mechanical components coupled by a spline joint. The spline coupling tolerance causes collisions between various mechanical parts of the PTO driveline and affects gear collision, thereby causing rattle noise. Therefore, the aim of this study is to conduct a dynamic behavior analysis to predict the gear rattle noise level of a PTO driveline. The dynamic behavior of the PTO driveline was analyzed through 1D simulations, and the results confirmed that the dynamic behavior changes according to rotation speed. Experimental verification of the dynamic behavior analysis results confirmed that the dynamic behavior changes as the main engine excitation-component amplification changes and then decreases at a relatively high rotation speed. Additionally, the dynamic behavior changes of the PTO driveline resulted in a jumping phenomenon that occurs rapidly at a specific rotation speed. The amplification of the engine’s main components was reduced from 3 to 4 times to 1.2 times owing to the jumping phenomenon; the noise level of the gear rattle was also reduced by approximately 10.9 dB(A).     

Analysis of the PTO load of a 75 kW agricultural tractor during rotary tillage and baler operation in Korean upland fields

In this paper, the PTO severeness of an agricultural tractor during rotary tillage and baler operation was analyzed. The S–N curves of the PTO driving gears were obtained through fatigue life test. To obtain the S–N curves of the PTO driving gears, the breakage time and rotational speed of the gears were measured through observation of the bending stress with changing torque. The torque acting on the PTO was measured and analyzed during rotary tillage and baler operation. Rotary tillage and baler operation were conducted at two ground speeds and two PTO rotational speeds at upland field sites with similar soil conditions, respectively. The load data were inverted to a load spectrum using rain-flow counting and SWT equations. Modified Miner’s rule was used to calculate the partial damage sum. The severeness was defined as the relative ratio of the damage sum. The results showed that the damage of the PTO increased when the ground speed or the PTO rotational speed increased. The effect of the PTO rotational speed on the severeness of the PTO was more significant than that of the ground speed. The severeness of the PTO of rotary tillage was greater than that of baler operation.     

An experimental study on the impact of the rear track width on the stability of agricultural tractors using a test bench

The aim of this paper is to study the effect that the rear track width and additional weight placed on the wheels has on the stability of a tractor when driving on side slopes. With the help of a specially constructed test bench the reactions on the wheels under static load were measured for rear track width of 1500, 1650 and 1800 mm. The roll angle of the test bench was gradually increased. The analysis of the experimental results showed that the static limit of overturn was considerably improved, when the width of the rear track was 1650 mm and an additional weight had been used for the uphill wheel.     

A study on the effect of electronic engine speed regulator on agricultural tractor ride vibration behavior

In this study, the effect of electronic speed adjustment on tractor ride vibration levels is examined. With normal pedal operation the engine rotational speed drops with an increasing load. The electronic regulator provides a constant speed mode of operation independent of the load. Vibration levels were measured under different operating conditions and surfaces. As a first series of tests, the tractor was driven on a conglomerate bituminous track at speeds of 20, 25 and 28 km/h. Vibration was measured upon the surface of the operator seat simultaneously in the x, y and z directions. The reference axis system was that defined by the ISO 2631-1 [1]. The weighted r.m.s. acceleration was found to be between 8% and 8.6% higher for the case where operation with electronic speed adjustment had been selected. Secondly, cultivating was chosen as the field task and the vibration was measured while the tractor was traversing a rough farm track at speeds of 6, 7.5 and 9 km/h. In this case, the vibration levels with automatic speed adjustment were between 4.3% and 8.6% lower than when driving with normal foot pedal operation. From the above results, we may infer that electronic speed regulation should not be used in transportation on asphalt country roads. On the contrary, it seems that electronic regulation has an advantage when used in typical field tasks such as cultivating.     

An improved sample-and-hold reconstruction procedure for estimation of power spectra from LDA data

Techniques for deriving the auto or power spectrum (PSD) of turbulence from laser Doppler anemometry (LDA) measurements are reviewed briefly. The low pass filter and step noise errors associated with the sample-and-hold process are considered and a discrete version of the low pass filter for the resampled signal is derived. This is then used to develop a procedure by which the PSD estimates obtained from sample and hold measurements can be corrected. The application of the procedures is examined using simulated data and the results show that the frequency range of the analysis can be extended beyond the Nyquist frequency based on the mean sample rate. The results are shown to be comparable to those obtained using the method of Nobach et al. (1998) but the new procedures are more straightforward to implement. The technique is then used to determine the PSD of real LDA data and the results are compared with those from a hot wire anemometer.     

两跨输电线非线性主共振响应分析

研究两跨输电线非线性共振响应问题,应用Hamilton变分原理推导了两跨输电线的振动微分方程以及对应的边界条件。利用Galerkin离散方法和多尺度法,得到了单模态主共振响应。研究结果表明:幅频响应曲线表现出软、硬弹簧性质,随着外激励幅值的增大,输电线系统响应由软弹簧性质向硬弹簧性质转换;系统阻尼减小或外激励幅值增大时,系统幅值个数也随之发生变化,表现出多值和跳跃现象。     

Analysis of hysteresis and phase shifting phenomena in unsteady three-dimensional wakes

The aerodynamic characteristics of automobiles are greatly influenced by the unsteady change in the direction of relative airflow. The aim of this paper is to analyse how such a change influences vehicle wake flow patterns. An analysis was conducted on a simplified model capable of reproducing the typical structures encountered under the aerodynamic conditions of an automobile. The results were processed by mapping the steady and unsteady total pressure losses around the model. The findings should enable automobile development engineers inter alia to identify and analyse the physical phenomena that occur when a vehicle is subjected to a sudden gust of side wind.List of symbols B rod - l length of rod B (m) - angle of rod B (degrees) - D disk - P connection point between disk D and rod B - M _o drive motor of disk D - O centre of rotation of disk D - e radius of disk D (m) - angle of disk (degrees) - t moment of time t (s) - _o angle (degrees) at instant of time t=0 - d diameter of model (m) - C centre of rotation of model - x _c abscissa of centre of rotation C of model (m) - M connection point between model and rod B - pi value=3.14159 - incidence of model (degrees) - _M maximum value of incidence (degrees) - _m minimum value of incidence (degrees) - angular amplitude (degrees) - _c critical angle of incidence (degrees) for steady evolutions - critical angle of incidence (degrees) for the unsteady evolutions - ̄ mean angle of incidence (degrees) - angle (degrees) of the model such that =+ - pulse (rad s^–1) - T period (s) - f frequency (Hz) - R radius of model in meter (m) - velocity vector of incident airflow - V _o intensity of velocity vector (m s^–1) - P _io total pressure associated with upstream airflow velocity (Pa) - P _i local total pressure (Pa or J m^–3) - density (kg m^–3) - C _x drag coefficient - total pressure coefficient - (m, n) dimensions of grid: lines m, columns n - x X coordinate of sampling plane (m) - y _j Y coordinate of point of index j for j[1,n] - z _k Z coordinate of point of index k for k[1,m] - P _i (x,y _j ,z _k ,(t)) continuous data of unsteady total pressure (Pa) - discrete data of unsteady total pressure (Pa) - N number of tomographic images, from 1 upwards over an oscillation period T - maximum value of total pressure coefficients for steady evolutions - maximum value of total pressure coefficients for unsteady evolutions and increasing incidences - maximum value of total pressure coefficients for unsteady evolutions and decreasing incidences - differential between and - differential between and - phase shifting (degrees)     

Chaotic oscillation of a nonlinear power system

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Experimental investigation of the performance of a thermoelectric generator based on Peltier cells

An experimental investigation is carried out to characterize the performance of thermoelectric modules used for electric power generation over a range of different resistance loads. The performance of a Peltier cell used as a thermoelectric generator is evaluated in terms of power output and conversion efficiency. The results show that a thermoelectric module is a promising device for waste heat recovery.     

Reflection and transmission of plane waves from fluid-piezothermoelastic solid interface

The reflection and transmission of plane waves from a fluid-piezothermoelastic solid interface are studied. The expressions for amplitude ratios and energy ratios corresponding to reflected waves and transmitted waves are derived analytically. The piezo-thermoelastic solid half-space is assumed to have 6mm type symmetry and assumed to be loaded with water. The effects of angle of the incidence, the frequency, the specific heat, the relaxation time, and the thermal conductivity on the reflected and transmitted energy ratios are studied numerically for a particular model of cadmium selenide (CdSe) and water. Some special cases are also studied.     

车辆手动变速箱油的摩擦学性能研究

根据手动变速箱油(MTF)的物理化学特性和手动变速箱的工作特点,研制了手动变速箱油,通过SRV-IV往复摩擦试验机比较了市售的国外品牌手动变速箱油的摩擦性能,并利用三维非接触表面轮廓仪观察了磨斑表面的磨痕变化.结果表明:研制的手动变速箱油在保持物理化学特性的基础上,在不同温度条件下,摩擦学性能优于进口手动变速箱油;同时发现MTF比GL-4更适合用于手动变速箱的润滑.     

Two-dimensional unsteady laminar flow of a power law fluid across a square cylinder

The two-dimensional and unsteady free stream flow of power law fluids past a long square cylinder has been investigated numerically in the range of conditions 60≤Re≤160 and 0.5≤n≤2.0. Over this range of Reynolds numbers, the flow is periodic in time. A semi-explicit finite volume method has been used on a non-uniform collocated grid arrangement to solve the governing equations. The global quantities such as drag coefficients, Strouhal number and the detailed kinematic variables like stream function, vorticity and so on, have been obtained for the above range of conditions. While, over this range of Reynolds number, the flow is known to be periodic in time for Newtonian fluids, a pseudo-periodic flow regime displaying more than one dominant frequency in the lift is observed for shear-thinning fluids. This seems to occur at Reynolds numbers of 120 and 140 for n=0.5 and 0.6, respectively. Broadly speaking, the smaller the value of the power law index, lower is the Reynolds number of the onset of the pseudo-periodic regime. This work is concerned only with the fully periodic regime and, therefore, the range of Reynolds numbers studied varies with the value of the power law index. Not withstanding this aspect, in particular here, the effects of Reynolds number and of the power law index have been elucidated in the unsteady laminar flow regime. The leading edge separation in shear-thinning fluids produces an increase in drag values with the increasing Reynolds number, while shear-thickening fluid behaviour delays this separation and shows the lowering of the drag coefficient with the Reynolds number. Also, the preliminary results suggest the transition from the steady to unsteady flow conditions to occur at lower Reynolds numbers in shear-thinning fluids than that in Newtonian fluids.     

Reflection and transmission of obliquely incident Rayleigh surface waves by a viscoelastic interphase

The reflection and transmission of obliquely incident Rayleight surface waves by an interphase between two quarter spaces of identical or different materials, have been investigated. The mechanical behavior of the interphase is represented by a thin viscoelastic layer. By using the full space Green's functions due to a spatially harmonic line load, the mathematical statement of the 3-dimension problem is reduced to a 2-dimension system of singular integral equations. The far-field behavior of the scattered waves leads to the definition of reflection and transmission coefficients,R andT. The system of the singular integral equations are solved forR andT with the boundary element method. The results are presented for selected values of the elastic constants of the joined quarter spaces, the parameters of the interphase and the incident angles of Rayleigh surface waves.     

Exact solution of sound reflection on infinite laminated plate and transmission through it

An exact solution is proposed in this paper based on the elasticity theory for sound reflection from an infinite laminated plate and transmission through it, and some phenomena of sound propagation in an isotropic media are also discussed. Some examples given here could be used to test approximate models of laminated plates.     

Unsteady aerodynamic forces and power requirements of a bumblebee in forward flight

Aerodynamic forces and power requirements in forward flight in a bumblebee (Bombus terrestris) were studied using the method of computational fluid dynamics. Actual wing kinematic data of free flight were used in the study (the speed ranges from 0 m/s to 4.5 m/s; advance ratio ranges from 0–0.66). The bumblebee employs the delayed stall mechanism and the fast pitching-up rotation mechanism to produce vertical force and thrust. The leading-edge vortex does not shed in the translatory phase of the half-strokes and is much more concentrated than that of the fruit fly in a previous study. At hovering and low-speed flight, the vertical force is produced by both the half-strokes and is contributed by wing lift; at medium and high speeds, the vertical force is mainly produced during the downstroke and is contributed by both wing lift and wing drag. At all speeds the thrust is mainly produced in the upstroke and is contributed by wing drag. The power requirement at low to medium speeds is not very different from that of hovering and is relatively large at the highest speed (advance ratio 0.66), i.e. the power curve is J-shaped. Except at the highest flight speed, storing energy elastically can save power up to 20%–30%. At the highest speed, because of the large increase of aerodynamic torque and the slight decrease of inertial torque (due to the smaller stroke amplitude and stroke frequency used), the power requirement is dominated by aerodynamic power and the effect of elastic storage of energy on power requirement is limited.The project supported by the National Natural Science Foundation of China (10232010) and the National Aeronautic Science fund of China (03A51049)The English text was polished by Xing Zhang.     

The influence of variable stiffness of teeth on dynamic loads in single-gear transmission

Summary In this paper, the influence of the variable stiffness of mating gear teeth on dynamic loads occurring between teeth in a single-gear transmission is investigated using a discrete-continuous model consisting of two torsionally deformable ponderable shafts and four rigid bodies. The stiffness is described by a harmonic function of time. Considerations by means of the wave method enable to determine dynamic loads in steady as well as in transient states. Numerical calculations are concentrated on the determination of the amplitudes of dynamic loads on gear teeth with respect to revolution per minute. Received 4 March 1997; accepted for publication 12 September 1997     

Analytical modeling of fluid loaded orthogonally rib-stiffened sandwich structures: Sound transmission

An analytic model is developed to investigate the wave propagation and sound transmission characteristics of an infinite sandwich structure reinforced by two sets of orthogonal rib-stiffeners when subjected to convective fluid-loaded pressure. The rib-stiffeners are assumed to be identical and uniformly spaced, which can exert not only tensional forces and bending moments but also torsional moments on the facesheets. Inertial terms of the tensional forces, bending moments and torsional moments are introduced to account for inertial effects arising from the mass of the rib-stiffeners. With the surrounding acoustic fluids restricted by the acoustic wave equation, fluid-structure coupling is considered by imposing velocity continuity condition at fluid-panel interfaces. By applying the Bloch theorem for periodic structures, the structural and acoustic responses are expressed in a superposition form of space harmonics for a given wavenumber. The application of the virtual work principle for one periodic element yields two infinite sets of simultaneous algebraic coupled equations, which are numerically solved by truncating them in a finite range insofar as the solution converges. The validity and feasibility of the analytic model is qualified by comparing model predictions with existing results, in which the necessity and advantage of the exact modeling of rib-stiffener motions are also demonstrated. Specifically, the influences of inertial effects arising from rib-stiffener mass, the periodicity spacing of rib-stiffeners, and the airborne as well as structure-borne paths on the transmission of sound across the sandwich structure are quantified and conclusions of significant practical implications are drawn.     

Analytical model of sound transmission through laminated composite cylindrical shells considering transverse shear deformation

Composite structures are often used in the aerospace industry due to the advantages offered by a high strength to weight ratio. Sound transmission through an infinite laminated composite cylindrical shell is studied in the context of the transmission of airborne sound into the aircraft interior. The shell is immersed in an external fluid medium and contains internal fluid. Airflow in the external fluid medium moves with a constant velocity. An exact solution is obtained by simultaneously solving the first-order shear deformation theory （FSDT） of a laminated composite shell and the acoustic wave equations. Transmission losses （TL） obtained from numerical solutions are compared with those of other authors. The effects of structural properties and flight conditions on TL are studied for a range of values, especially, the Mach number, stack sequences, and the angle of warp. Additionally, comparisons of the transmission losses are made between the classical thin shell theory （CST） and FSDT for laminated composite and isotropic cylindrical shells.     

Analysis of transmission load of agricultural tractors

The objectives of this study were to analyze the load acting on the input shaft of the transmission of an agricultural tractor when it conducts plowing, rotovating and transporting operations under the Korean farming conditions. A survey was conducted to investigate the operational characteristics of such tractor works. To measure the load, a torque transducer was developed and installed on the input shaft of the transmission. A radio telemetry system was used to transmit the strain signals from the torque transducer to a data acquisition system. The time histories of the measured torque signals were digitized and analyzed using the rain-flow cycle counting method to determine their cyclic distributions. The load spectra thus obtained from the different operations were compared and their severeness to the transmission was discussed.     

某输电线路铁塔覆冰条件下的失效模式分析

建立了覆冰荷载作用下寻找输电铁塔主要失效模式的方法,该方法以覆冰厚度为控制量,可以方便地获得铁塔的主要失效模式及其相应的极限覆冰厚度。分析了南方某既有输电线路铁塔在两种工况下的主要失效模式,指出该类铁塔的薄弱处位于挂导线处、上曲臂以及塔身上部。同时指出如果存在20％不平衡纵向张力,挂导线处及上曲臂的极限覆冰厚度接近于该...