丘陵山地无人车振动特性试验研究

为探索丘陵山地无人车振动特性,以丘陵山地无人车为研究对象,进行了振动特性试验。在无人车车体选择11个测试点,设计6组试验方案,综合分析测点位置、发动机油门大小和路面不平度对无人车振动特性的影响。试验结果表明,测点3（车架左前部）是无人车整车最合适安装传感器位置,在无人车正常行走、油门1/2位置、挂1档工况下,加速度最大值为47.4 m/s2,加速度最小值为-50.36 m/s2,加速度平均幅值为5.092 m/s2,加速度有效值仅为6.864 m/s2,说明该测点振动表现稳定;其他合适的测点为测点4和测点9。发动机油门大小对于加速度最大值、加速度最小值、加速度平均幅值、加速度方根幅值、加速度有效值均有显著影响,同一测点下,油门1/2和油门3/4相比较初始油门,加速度平均幅值增大297.1%和322.8%。路面不平度对于无人车振动有显著影响：在水泥路面上,无人车底盘加速度值最小,而在沙壤土、黏土和干沙土三种路况下,底盘加速度值分别增加81.23%,77.91%和1.31%。同时提出降低发动机高频振动、增加阻尼、传感器工作时降低行驶速度等减振措施。     

青香蕉多次敲击力学特性及易损性评估

香蕉通常在绿硬期（即青香蕉）进行采运,在此过程中果指与作业部件和相邻果指之间易发生反复碰撞。为探明果指的机械性质,减少香蕉采运过程中的碰撞损伤,该研究针对不同生长位置的果指进行了敲击试验。通过方差分析检验了敲击次数、敲击能量和生长位置对果指力学特性（加速度峰值和恢复系数）及易损性（损伤尺寸和敏感度）的影响。结果表明,敲击能量越高,加速度越大,恢复系数越小,损伤尺寸和敏感度越大,果指越易损伤;在果指塑性变形对应的敲击能量阈值内,加速度、恢复系数与损伤尺寸随次数以非线性方式增加,但增量主要集中在初始5次,而损伤敏感度则以非线性方式递减,随着敲击次数的增加,果指的易损性呈非线性降低。越靠近果轴底端且在内排生长的果指,越易损伤。该研究成果可为香蕉采运等过程中的防护措施与风险因素的管理提供依据。     

Bovine placental lactogen invokes rapid growth in chinook salmon

The effect of recombinant bovine placenta) lactogen (rbPL) treatment upon growth of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum) (14.0 ± 0.31 g wet wt), was examined over a period of 6 weeks. Experimental animals were either injected (5 μg rbPL g^?1 week^?1), implanted with a cholesterol pellet containing 0.4 mg rbPL (approximately 4 μg g^?1 week^?1), or orally and rectally intubated with 7.5 μg rbPL g^?1 week^?1. Control animals were injected with bovine serum albumen (BSA), 5 μg g^?1 week^?1, implanted with a placebo or orally intubated (7.5 μg BSA g^?1 week^?1). Significant (P < 0.05) growth acceleration was recorded for rbPL-injected and pellet-implanted groups from week 2 onwards when compared against all other groups. Oral or rectal intubation of rbPL (7.5 μg rbPL g^?1 week^?1), however, was without effect. Condition factor decreased in all groups, but was significantly lower in rbPL-injected and pellet-implanted fish at trial end when compared against controls. No differences were recorded between groups for per cent body moisture or relative gut length. Hepatosomatic index was significantly (P < 0.05) higher in rbPL-injected and rbPL-implanted chinook salmon versus other fish.     

Growth enhancement following dietary delivery of recombinant porcine somatotropin to diploid and triploid coho salmon (Oncorhynchus kisutch)

Diploid (2n) and triploid (3n) coho salmon were fed upon control (diet 1), recombinant porcine somatotropin (rpST)-supplemented (diet 2; 20 μg rpST/g body wt/day) or rpST/antacid/detergent-containing feed (diet 3; 20, 100 &; 20 μg/g body wt/day respectively) for 16 wk. Fish were weighed and measured bimonthly and their relative performances assessed. By wk 4, 2n and 3n groups fed upon diet 2 were significantly heavier and longer than control 2n fish. At the termination of the trial, diet 3 fed animals were greater in weight than all other treatment groups. Diet 3 salmon also returned better feed conversion efficiencies than either diet 1 or 2 groups. RpST therapy induced a 28.7% and 60.2% increase in group wt for 3n diet 2/3 coho versus (?vs?) controls. Likewise, 2n rpST-treated fish increased wt ?vs?2n control coho by 17% and 50% respectively over the same period. No differences were recorded between groups for body moisture, but diet 2, 3n and both diet 3 groups exhibited decreased condition factors when compared to control fish (p ≤ 0.05).     

Post-earthquake Residual Deformation Prediction of SDOF System

Accurately predicting the residual displacement of reinforced concrete (RC) structures after an earthquake is of great significance in post-earthquake structural performance evaluation and control. To study the residual deformation of the structure, seismic time-history responses of single degree-of-freedom (SDOF) systems with different parameters were analyzed. Based on the analytical results, simplified models for estimating the likely residual deformations of structures characterized by Takeda and Kinematic hysteretic models were proposed respectively, and the residual deformation was found to be sensitive to hysteretic characteristics, stiffness ratio of structures, peak ground acceleration (PGA), as well as maximum elasto-plastic deformation. A case study for RC single-column bridge pier was provided to illustrate the process of residual deformation calculation and post-earthquake performance evaluation by using the proposed methods. Calculation results indicate that the residual deformation of the single-column pier characterized by the Takeda model often is much larger than that of columns characterized by the Kinematic model.     

The Use of a Technical Device for Testing the Sport-Functional Properties of Riding Surfaces

The riding surface is an important and modifiable factor in the development injuries in sport horses. An objective and simple examination of the sport-functional properties of riding surfaces, such as shock absorption, is thus desirable. The aim of the present study was to evaluate the use of a handy device to test the sport-functional properties of riding surfaces. Therefore, a technical device, called Artificial Athlete, was used on five riding surfaces: two sand–synthetic indoor arenas, one sand–sawdust indoor arena, and two outdoor arenas, one with a sand footing layer and one with a grass surface. The shock absorption, the energy restitution, and the vertical deformation measurements were acquired by the Artificial Athlete. Additionally, the hoof acceleration of six warmblood horses trotting by hand on the five investigated riding surfaces was recorded. The parameters of the Artificial Athlete and the acceleration data during hoof landing were compared. The outcome of the statistical analysis illustrated that the shock absorbing parameter was not in agreement with the results of the acceleration data, whereas the results of the vertical deformation parameter were mostly in accordance with the results of the hoof-acceleration measurement. In conclusion, the use of the Artificial Athlete for testing the sport-functional properties of riding surfaces was assessed as unsuitable because of the large deviations between the results of the shock absorption measured by the Artificial Athlete and the hoof-acceleration data. However, it could be shown that the vertical deformation parameter could be helpful in the assessment of the sport-functional quality of riding surfaces.     

The effect of size on the mechanical properties of the myotomal-skeletal system of rainbow trout (Salmo gairdneri)

The length and mean cross-sectional area of the myotome of rainbow trout,Salmo gairdneri, scale isometrically with total length (L, cm) and L² respectively for fish from 5 to 35 cm in length. The net maximum force, (F, kN·m^–2) developed by a single twitch of thein situ myotome on one side of the body, and measured normal to the hypural complex increased as; F=1.05×10^–3·L^2.6, and maximum lateral velocity (W, m·s^–1) at the hypural plate as; W=0.29 L^–0.47. Maximum power (P, W) increased as; P=7.64×10^–5·L^3.06. Acceleration rates predicted from these data do not agree well with observations. In addition, except for small fish, predicted maximum speeds differed from those calculated from minimum twitch times of excised muscle blocks and stride length, the popular method for estimating maximum speed. It is suggested that temporal summation of twitches must occur in larger fish. This could provide forces matched to inertial loads which are important in fitness-critical maneuvers.     

转动副间隙对曲柄摇杆式分插机构性能的影响分析与试验

为了研究转动副间隙对曲柄摇杆式分插机构的影响,该文基于动力学理论及Lankarani-Nikravesh接触力模型,建立了含转动副间隙的曲柄摇杆式分插机构的动力学模型,并通过四阶龙格库塔法求解动力学模型。通过MATLAB仿真分析了转动副间隙对秧针尖的轨迹、速度、加速度和取秧位置的影响以及不同间隙大小和不同转动副含间隙对秧针尖加速度的影响。仿真分析结果表明,转动副间隙对秧针尖轨迹、速度和取秧位置的影响较小,对加速度的影响较大;随着转动副间隙的增大,分插机构取秧位置的偏离会增大,秧针尖的加速度的幅值和波动幅度会增大;在分析的3个转动副中,曲柄与连杆之间的转动副含间隙对秧针尖加速度的影响最大。通过试验与仿真对比得到基于Lankarani-Nikravesh接触力模型比基于连续接触模型更适用于含转动副间隙机构的分析。试验结果验证了基于Lankarani-Nikravesh接触力模型的仿真分析的正确性。研究结果为分插机构的结构优化设计和精度分配提供了参考。     

振动参数对果树采收影响的试验研究

从乔木类果品采收实际要求出发,旨在解决乔木类果树的连续机械振动采收问题。为此,进行了连续激振式采收过程中影响果树振动效果的试验。通过电动振动试验系统对果树主干不同位置进行夹持,施加不同类型激振力进行振动试验,利用动态信号测试分析系统进行数据采集和输出,获得不同振动频率、振幅下果树不同位置的加速度数据及曲线,并进行分析和对比。结果表明:当夹持主干的位置距离果树固定端为60cm、振动测试系统输出振动频率为25Hz、激振位移为5mm时,果树获得加速度较大;树枝和果实之间的相对加速度也较大。该试验为振动采收装置的研究提供必要的理论依据。     

Vibration analysis during grass harvesting according to ISO vibration standards

This research evaluated the working efficiency and comfort of operation by measuring vibration acceleration of tractors during grass harvesting. A real-time kinematic global positioning system and an inertial measurement unit installed in a tractor normally used by farmers during grass harvesting were used to acquire tractor vibration acceleration data. Analysis of the position and vibration acceleration data of tractors by a Fourier transformation yielded a power spectrum of vibration acceleration at each frequency (1-10 Hz) and position. The root mean square of vibration acceleration at each frequency (1-10 Hz) was calculated with the center frequency of the 1/3 octave bands (1.0, 1.25, 1.6, 2.0, 2.5, 3.15, 4, 5, 6.3, 8, and 10 Hz) based on ISO standards. To evaluate the working efficiency in the grassland, geographical information system maps were generated using the power spectrum of vibration acceleration and the limit on working time for each frequency that negatively affected the tractor driver. The vibration acceleration in the longitudinal (a_x) and lateral (a_y) directions at the center frequency of the 1/3 octave band below 2.0 Hz exceeded the fatigue-decreased proficiency and reduced the comfort boundaries stipulated in ISO 2631 (1974). In the area where working characteristics are severe, the vibration acceleration in the vertical direction (a_z) is high. The vibration acceleration in the a_z direction at the center frequency of the 1/3 octave band (5-10 Hz) clearly indicates discomfort during grass harvesting and a decrease in the work efficiency beyond 1 h. The total vibration acceleration (a_ν) at the center frequency of 5.0 Hz of the 1/3 octave band served to evaluate comfort in the whole field during grass harvesting—the a_ν value is higher than that at other frequencies. The area with severe working characteristics showed a higher a_ν value at the center frequency of 8.0 Hz than that at other frequencies.