Vibration characteristic analysis and optimization of rotor hub for helicopters based on genetic algorithm

The aero-elastic response of the blades is affected by the structure style of the rotor hub. The fatigue life of the structure and the vibration level of the entire helicopter are directly affected by the aero-elastic response of the blades. Therefore, its vibration characteristics and aero-elastic response shall be considered emphatically during structure design. The flapping and lead-lag characteristics of the rotor hub were tested experimentally in the paper. It was shown in results that a big vibration displacement was generated from the rotor hub under two working conditions. However, a larger vibration displacement was generated from the flapping than that of the lead-lag. Therefore, it is necessary to conduct optimization design to the rotor hub. Analysis was carried out to aero-elastic dynamics of bearing-less rotor. Afterwards, a multi-objective optimization model for reducing vibration and aero-elastic dynamic of bearing-less rotor was built. Pareto front of multi-objective optimization design for bearing-less rotor was acquired by Genetic Algorithm (GA). To reduce the optimization burdens, the aero-elastic dynamic model was replaced by Radial Basis Function (RBF) model during the optimization. To decrease the computational costs, the sample points with the minimum point set center deviation of the current surrogate model were added gradually. Meanwhile, the design schemes of Pareto front were ranked by TOPSIS to select the design scheme with the maximum satisfaction. Comparison was carried out between the rotor design scheme with the maximum satisfaction and the unoptimized model in terms of modal frequency, modal shape and vibration load of the hub. The results showed that the dynamic performance of the optimized rotor was improved significantly. The method in this paper also provided an important reference for multi-objective optimization of aero-elastic dynamic and engineering design of other rotors

1-(2,4-Dinitro­phen­yl)-3,3-dinitro­azetidine

In the title compound, C9H7N5O8, the dihedral angle between the mean plane of the azetidine ring and that of the benzene ring is 26.1 (1)°; the planes of the two nitro groups of the azetidine ring are aligned at 88.7 (1)°

Single machine scheduling with exponential time-dependent learning effect and past-sequence-dependent setup times

AbstractIn this paper we consider the single machine scheduling problem with exponential time-dependent learning effect and past-sequence-dependent (p-s-d) setup times. By the exponential time-dependent learning effect, we mean that the processing time of a job is defined by an exponent function of the total normal processing time of the already processed jobs. The setup times are proportional to the length of the already processed jobs. We consider the following objective functions: the makespan, the total completion time, the sum of the quadratic job completion times, the total weighted completion time and the maximum lateness. We show that the makespan minimization problem, the total completion time minimization problem and the sum of the quadratic job completion times minimization problem can be solved by the smallest (normal) processing time first (SPT) rule, respectively. We also show that the total weighted completion time minimization problem and the maximum lateness minimization problem can be solved in polynomial time under certain conditions

Unsupervised 3D Perception with 2D Vision-Language Distillation for Autonomous Driving

Closed-set 3D perception models trained on only a pre-defined set of object categories can be inadequate for safety critical applications such as autonomous driving where new object types can be encountered after deployment. In this paper, we present a multi-modal auto labeling pipeline capable of generating amodal 3D bounding boxes and tracklets for training models on open-set categories without 3D human labels. Our pipeline exploits motion cues inherent in point cloud sequences in combination with the freely available 2D image-text pairs to identify and track all traffic participants. Compared to the recent studies in this domain, which can only provide class-agnostic auto labels limited to moving objects, our method can handle both static and moving objects in the unsupervised manner and is able to output open-vocabulary semantic labels thanks to the proposed vision-language knowledge distillation. Experiments on the Waymo Open Dataset show that our approach outperforms the prior work by significant margins on various unsupervised 3D perception tasks.Comment: ICCV 202

Generating axial magnetic fields via two plasmon decay driven by a twisted laser

We propose a new way of axial magnetic fields generation in a non-relativistic laser intensity regime by using a twisted light carrying orbital angular momentum (OAM) to stimulate two-plasmon decay (TPD) in a plasma. The growth of TPD driven by an OAM light in a Laguerre-Gauss (LG) mode is investigated through three dimensional fluid simulations and theory. A theory based on the assumption that the electron plasma waves (EPWs) are locally driven by a number of local plane-wave lasers predicts the maximum growth rate proportional to the peak amplitude of the pump laser field and is verified by the simulations. The OAM conservation during its transportation from the laser to the TPD daughter EWPs is shown by both the theory and the simulations. The theory predicts generation of ~40T axial magnetic fields through the OAM absorption via TPD, which has perspective applications in the field of high energy density physics.Comment: 6 pages, 3 figures

catena-Poly[[[bis­(4-methyl­benzoato-κ2 O,O′)zinc(II)]-μ-4,4′-bipyridine-κ2 N:N′] tetra­hydrate]

The asymmetric unit of the title compound, {[Zn(C7H7O2)2(C10H8N2)]·4H2O}n, contains a highly distorted octa­hedral ZnII metal center strongly coordinated by two N atoms of two 4,4′-bipyridine (4,4′-bipy) ligands and chelated by two 4-methyl­benzoate anions. The crystallographic inversion center and glide plane present at the center of the C—C single bond of 4,4′-bipy, along with the cis coordination motif of the 4,4′-bipy, lead to one-dimensional zigzag chains. There are a large number of water mol­ecules in the crystal structure, which also form one-dimensional chains through O—H⋯O hydrogen bonds

Factors Affecting the Price of Commercial Housing in Haikou Housing

This paper uses the grey correlation degree and factor analysis method to carry out empirical research on the main influencing factors of residential price extraction in Haikou City according to the data of Haikou City from 2013 to 2018 as a sample. The research results show that the factors affecting housing prices can be divided into two aspects. From the economic level, the impact of population, regional GDP and per capita disposable income are positive effects. They promote economic growth to increase housing prices. From the perspective of expenditure levels, expected housing prices, investment costs, and consumer price index will affect housing prices by influencing consumers and investors spending decisions. On the whole, the key factors affecting house prices are mainly policies, population movements, economic growth, and total investment costs