There is a general consensus that mixed forests offer ecological and productivity advantages over singlespecies forests in most situations, e.g., higher habitat heterogeneity, high water-holding capacity, and greater diversity of species composition [1][2][3][4]. Meanwhile, studies have explored ways to convert pure plantations into mixed forests [5]. Nevertheless, for secondary forests, including those resulting from deforestation and damage by natural hazards, few studies exist, and still fewer compare mixed stands with pure tree species stands.Historically the Greater Khingan Mountains were rich in forest resources. However, due to severe damage from wildfires, especially in 1987, and continuous deforestation due to logging over many years, the forest status has been degraded, resulting in higher rates of
In a pair of actual gears alternating meshing process, the transmission system errors and thermal elastic deformation of the gear teeth can cause gears in the meshing zone to form high contact pairs inconsistently mesh-in and mesh-out points to deviate from the theoretical line, which will lead to sudden changes in meshing velocity and an instantaneous meshing effect. Offline meshing impact generates large additional loads, and it increases the vibration and noise of gear transmission system. Further, the gear teeth mesh-in impact is significantly greater than that of gear teeth mesh out. Therefore, to analyze the impact with the minimum value of gear teeth mesh in, the initial mesh-in points need to be determined, and the meshing impact velocity and impact force of teeth meshing-out need to be calculated. The optimized meshing tooth-pair contact interface (CI) anti-impact numerical calculation mode is validated using the loaded teeth contact analysis method.
Abstract. Strip reforms with widths of 6 m, 10 m, 14 m and 18 m were carried out in a low-quality broadleaf mixed forest in Greater Khingan Mountains. The influence of time on soil properties, including physical and chemical properties, were analysed on the basis of data of the soil components obtained from nine consecutive years (from 2010 to 2018). In the meantime, a principal component analysis was used to determine the weight of each soil indicator, and the fuzzy comprehensive index method was applied to provide further insight into the variation of soil quality. We found that most soil physical properties were damaged by cutting within 3 years and can be restored after 6 years. Over the 9 years, soil physical properties displayed some differences across cutting strip widths, while chemical properties did not display any differences. In terms of chemical properties, they need more time to recover. In view of the current research years, the soil quality could not be restored in the 18-m harvesting zone within nine years. The cutting width of 10 m is more obvious than that of other transformation widths, so 10 m is the best width for cutting strips for the forest. This study has important implications for sustainable management of the mixed natural broadleaf forest in the study region and beyond. A larger width of the cutting strip in this type of forest in the region should be avoided. Moreover, for forest soil conditions, we need to continue long-term observations.
In the process of gear meshing, it is an inevitable trend to encounter failure cases such as contact friction thermal behavior and interface thermoelastic scuffing wear. As one of the core influencing factors, the gear meshing contact interface micro-texture (CIMT) significantly restricts the gear transmission system (GTS) dynamic characteristics. This subject intends to the contact characteristic model and interface friction dynamics coupling model of meshing gear pair with different CIMT. Considering the influence of gear meshing CIMT on distribution type of hydrodynamic lubricating oil film, contact viscous damping and frictional thermal load, the aforementioned models have involved time-varying meshing stiffness (TVMS) and static transmission error (STE). Based on the proposed models, an example verification of meshed gear pair (MGP) is analyzed to reveal the influence of CIMT on the dynamic characteristics of GTS under a variety of micro-texture configurations and input branch power and rated speed/shaft torque conditions. Numerical simulation results indicate that the influence of CIMT on gear dynamic response (including meshing interface frictional thermal load, malicious damping and impact vibration in the off-line direction of the action) is extremely restricted by the transient contact regularity of the meshing gear surface. Meshing gears dynamic characteristics (especially vibration and noise) can be obviously and effectively adjusted by setting a regular MGP with CIMT instead of random gear surfaces.
This study conducts an analytical investigation of the dynamic response characteristics of a two-stage series composite system (TsSCS) with a planetary transmission consisting of dual-power branches. An improved incremental harmonic balance (IHB) method, based on the arc length extension technique, is proposed. The results are compared with those of the numerical integration method to verify the feasibility and effectiveness of the improved method. Following that, the multi-scale perturbation (MsP) method is applied to the TsSCS proposed in this paper. The frequency response equations of the primary resonance, subharmonic resonance, and superharmonic resonance are solved to generate the frequency response characteristic curves of the planetary transmission system in this method. A comparison between the results obtained by the MsP method and the numerical integration method proves that the former is ideal and credible in most regions. Considering the parameters of TsSCS excitation frequency and damping, the nonlinear response characteristics of steady-state motion are mutually converted. The effects of the time-varying parameters and the nonlinear deenthing caused by the gear teeth clearance on the amplitude-frequency characteristics of TsSCS components are studied in this special topic.
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