对数平均推动力法计算并流吸收塔的传质单元数

根据传质单元数的定义,对低浓度体系并流吸收塔传质单元数的对数平均推动力法计算公式进行了推导。并对公式的结构特点和使用窍门进行了分析。结果表明只要操作关系和相平衡关系都是线性的,不论是吸收还是解吸,并流操作传质单元数的对数平均推动力算法在结构上与逆流操作是一样的。该结构简单、易记,便于掌握。

关于填料吸收塔传质单元数的计算

本文对吸收塔传质单元数的两种计算方法——解析法和对数平均推动力法进行了分析和比较,揭示了对数平均推动力法结构简单易记、使用方便的独特优点,并通过具体例子介绍了使用对数平均推动力法计算传质单元数的注意事项及使用窍门。

INVESTIGATION OF FLIGHT DYNAMICS OF THRUST VECTORING AIRCRAFT USING EXTENDED CONTINUATION METHODS

This paper presents the flight dynamical behavior of the thrust vectoring aircraft with extended bifurcation and continuation methods. In contrast to the standard bifurcation and continuation methods, the extended methods are capable of calculating the continuation curves of the equilibrium points for the particular type of trimming flight. Therefore, these methods can not only give the performance measures of aircraft, but also determine the stability of trimming points. In this paper, the methods are used to verify the effectiveness of the thrust vectoring control law, to define the flight envelope boundary, to analyze the stability and controllability of trimming flight, and to predict the departures of the instable flight. The result shows that the extended methods provide more flight dynamic information and are useful in preliminary design of the thrust vectoring aircraft.

A recursive formulation based on corotational frame for flexible planar beams with large displacement

A forward recursive formulation based on corotational frame is proposed for flexible planar beams with large displacement.The traditional recursive formulation has been successfully used for flexible mutibody dynamics to improve the computational efficiency based on floating frame,in which the assumption of small strain and deflection is adopted.The proposed recursive formulation could be used for large displacement problems based on the corotational frame.It means that the recursive scheme is used not only for adjacent bodies but also for adjacent beam elements.The nodal relative rotation coordinates of the planar beam are used to obtain equations with minimal generalized coordinates in present formulation.The proposed formulation is different from absolute nodal coordinate formulation and the geometrically exact beam formulation in which the absolute coordinates are used.The recursive scheme and minimal set of dynamic equations lead to a high computational efficiency in numerical integration.Numerical examples are carried out to demonstrate the accuracy and validity of this formulation.For all of the examples,the results of the present formulation are in good agreement with results obtained using commercial software and the published results.Moreover,it is shown that the present formulation is more efficient than the formulation in ANSYS based on GEBF.

Adaptive variable structure control based on backstepping for spacecraft with reaction wheels during attitude maneuver

An adaptive variable structure control method based on backstepping is proposed for the attitude maneuver problem of rigid spacecraft with reaction wheel dynamics in the presence of uncertain inertia matrix and external disturbances. The proposed control approach is a combination of the backstepping and the adaptive variable structure control. The cascaded structure of the attitude maneuver control system with reaction wheel dynamics gives the advantage for applying the backstepping method to construct Lyapunov functions. The robust stability to external disturbances and parametric uncertainty is guaranteed by the adaptive variable structure control. To validate the proposed control algorithm, numerical simulations using the proposed approach are performed for the attitude maneuver mission of rigid spacecraft with a configuration consisting of four reaction wheels for actuator and three magnetorquers for momentum unloading. Simulation results verify the effectiveness of the proposed control algorithm.

Influence on the hydrodynamic performance of a variable vector propeller of different rules of pitch angle change

To design a more effective blade pitch adjustment mechanism,research was done on changes to the hydrodynamic characteristics of VVPs(Variable Vector Propeller) caused by different rules for changing pitch angle. A mathematical method for predicting the hydrodynamic characteristics of a VVP under unsteady conditions is presented based on the panel method. Mathematical models for evaluation based on potential flow theory and the Green theorem are also presented. The hydrodynamic characteristics are numerically predicted. To avoid gaps between panels,hyperboloidal quadrilateral panels were used. The pressure Kutta condition on the trailing edge of the VVP blade was satisfied by the Newton-Raphson iterative procedure. The influence coefficients of the panels were calculated by Morino's analytical formulations to improve numerical calculation speed,and the method developed by Yanagizawa was used to eliminate the point singularity on derivation calculus while determining the velocities on propeller surfaces. The calculation results show that it's best for the hydrodynamic characteristics of the VVP that pitch angle changes follow the sine rule.

An Unstructured Finite Volume Method for Impact Dynamics of a Thin Plate

The examination of an unstructured finite volume method for structural dynamics is assessed for simulations of systematic impact dynamics. A robust display dual-time stepping method is utilized to obtain time accurate solutions. The study of impact dynamics is a complex problem that should consider strength models and state equations to describe the mechanical behavior of materials. The current method has several features, l） Discrete equations of unstructured finite volume method naturally follow the conservation law. 2） Display dual-time stepping method is suitable for the analysis of impact dynamic problems of time accurate solutions. 3） The method did not produce grid distortion when large deformation appeared. The method is validated by the problem of impact dynamics of an elastic plate with initial conditions and material properties. The results validate the finite element numerical data

Structure buckling and non-probabilistic reliability analysis of supercavitating vehicles

To perform structure buckling and reliability analysis on supercavitating vehicles with high velocity in the submarine,supercavitating vehicles were simplified as variable cross section beam firstly.Then structural buckling analysis of supercavitating vehicles with or without engine thrust was conducted,and the structural buckling safety margin equation of supercavitating vehicles was established.The indefinite information was described by interval set and the structure reliability analysis was performed by using non-probabilistic reliability method.Considering interval variables as random variables which satisfy uniform distribution,the Monte-Carlo method was used to calculate the non-probabilistic failure degree.Numerical examples of supercavitating vehicles were presented.Under different ratios of base diameter to cavitator diameter,the change tendency of non-probabilistic failure degree of structural buckling of supercavitating vehicles with or without engine thrust was studied along with the variety of speed.

Simulation of two-phase plume field of liquid thruster

When the liquid propellant thruster works,its plume field would contain many propellant liquid droplets,especially at pulse state.Liquid droplets may move along with the gas flow and deposit on the components of spacecraft as contamination.The simulation of the plume field involving the gas molecules and liquid droplets is an important part in contamination studies of thruster plume.Based on the PWS software developed by Beihang University(BUAA),axial-symmetric two-phase direct simulation Monte Carlo(DSMC) method is used with the liquid droplet taken as a kind of solid particle.The computation of gas-to-particle effect and gas reflection on the particle surface are decoupled.The inter-particle collision is also considered.The gas parameters at nozzle exit of 120N engine after 20 ms pulse work are taken as the entrance condition of the numerical simulation.Four test cases are conducted for comparison of different collision modules.Simulation results show that the effects of liquid propellant droplets mainly concentrate near the axis line of engine.The particle-to-gas collision would cause evident differences in the gas field and subtle differences in the particle phase.The liquid droplets in the plume field are generally accelerated and convected by the gas molecules.The DSMC method is proved to be a feasible solver to numerically simulate the two-phase flow involving solid phase and rarefied gas flow.