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In order to improve the strength and stiffness characteristics of truck carriage, a structural optimization scheme based on modal analysis was proposed, which could enhance the comprehensive mechanical performance while reducing weight. Based on finite element simulation, the natural frequencies and modal shapes of the carriage were obtained. Under braking conditions, piezoelectric accelerometer was used to capture vibration data of the suspension system, which also verified the accuracy of natural frequency calculation. Through sensitivity analysis, four dimensions of the side reinforcement were selected as design variables. The approximate model of the optimization objective was constructed using an approximation method, and multi-objective genetic algorithm was used to solve the design variables. The results show that the optimized structure can decrease the mass by 2.3 %, decrease the maximum stress by 10.9 %, and increase the first-order natural frequency by 23.4 %. [ABSTRACT FROM AUTHOR]

In order to improve the dynamic response characteristics of the steering mechanism, a research scheme for increasing the natural frequency based on lightweight design was proposed. Based on the finite element method and the collaborative optimization method, the modal characteristics and harmonic response characteristics of the model were studied and analyzed to verify the strength and stiffness performance of the optimized structure. The modal shapes between the free mode and the constrained mode were compared and analyzed. With the second-order natural frequency as the optimization objective, the response surface function of the equivalent stiffness was constructed. Through optimization calculation, the design variables that satisfy the constraint conditions can be obtained. The results show that the optimized structure can increase the second-order natural frequency by 14.4 % on the premise of reducing the mass by 5.2 %, effectively avoiding the excitation frequency of the engine. [ABSTRACT FROM AUTHOR]

The dynamic response characteristics of shock absorber have a crucial influence on the stability and safety performance of vehicles. Based on the finite element method, the modal simulation of the mechanical structure of shock absorber was conducted, and the natural frequencies and modal shapes were obtained. According to the dynamic stiffness test scheme, the first four natural frequencies were set as the excitation frequencies, and the response characteristics of displacement, damping force and dynamic stiffness were tested and analyzed. In the experimental loading scheme, shear force was applied to the damper, and the shear amplitude gradually increased from 0.5 mm. Three cycle tests were conducted to obtain the average evaluation value. The results show that although the natural frequencies of the mechanical structure of the shock absorber do not avoid the excitation frequency of the road surface, it still shows good dynamic response effects at low-order excitation frequencies. The elastic stiffness and damping stiffness of the shock absorber decrease with the increase of the shear amplitude, while the damping stiffness increases with the increase of the excitation frequency. [ABSTRACT FROM AUTHOR]

Track irregularity is the main source of excitation that affects the dynamic characteristics of a railway vehicle. It has a significant influence on the stability and safety of a vehicle. In this study, a detailed vehicle-ballasted track dynamic model was established. The vehicle and ballasted track were modeled by multibody software SIMPACK and finite element software Abaqus respectively. The two models were then coupled by FEMBS which is an interface program between finite element (FE) analysis codes and SIMPACK. Based on the dynamic model, the vehicle dynamic behaviors of German and Chinese high-speed railways under ballasted track irregularity were analyzed. The results show that the vehicle dynamic behavior has random characteristics and responds differently to different types of single or combined irregularities. Comparatively, the vehicle dynamic responses acquired from a certain Chinese railway line measured on-site are slightly higher than those from GRSLI. It is also observed that the amplitude of vehicle dynamic responses increased linearly with the train's speed, and the dynamic response under the combined irregularity is slightly higher than the dynamic response under a single irregularity. INSET: Rich hire private noise police. [ABSTRACT FROM AUTHOR]

Hemp ( Cannabis sativa ) is an annual multipurpose crop that is distributed worldwide. An efficient regeneration protocol is needed for hemp genetic transformation, micropropagation, and germplasm conservation. We describe here a rapid protocol for in vitro shoot regeneration that uses cotyledons as explants. We concluded that TDZ in MS medium is more efficient in inducing in vitro shoots from cotyledons than BA and ZT. The best result, 51.7% induction frequency and 3.0 shoots per shoot explant, was recorded in MS medium containing 0.4 mg l −1 TDZ and 0.2 mg l −1 NAA (T4N2). The in vitro shoots grew to the height of 1.5–2 cm in 3–4 weeks after culture initiation. At that time, approximately 80% of the shoots were rooted well in half-strength Ms medium combined with 0.5–2 mg l −1 IBA for 4–5 weeks before acclimation. It was observed that younger cotyledons (2–3 days after planting (DAP) were more useful as explants than older ones (5–6 DAP) because they had a significantly higher regeneration frequency. We cultured 3 DAP cotyledons of eight cultivars in T4N2 medium to test the efficiency. The regeneration frequency varied from 35.7% to 54.8%, which indicated that this regeneration protocol was effective, although partly genotype dependent. We regard this protocol as an alternative method for micropropagation and germplasm conservation, and the in vitro plantlets may be suitable to set up a transformation system. [ABSTRACT FROM AUTHOR]