Transonic wing flutter predictions by a loosely-coupled method

Coupled Fluid-Thermal Investigation on Drag and Heat Reduction of a Hypersonic Spiked Blunt Body with an Aerodisk

Aerospace ◽

10.3390/aerospace9010019 ◽

2021 ◽

Vol 9 (1) ◽

pp. 19

Author(s):

Bing Fan ◽

Jie Huang

Keyword(s):

Heat Flux ◽

Drag Reduction ◽

Stagnation Temperature ◽

Total Drag ◽

Coupled Method ◽

Loosely Coupled ◽

Fluid Field ◽

Structural Temperature ◽

Relative Errors ◽

Spiked Models

In the traditional investigations on the drag and heat reduction of hypersonic spiked models, only the aerodynamic calculation is performed, and the structural temperature cannot be obtained. This paper adopted the loosely coupled method to study its efficiency of drag and heat reduction, in which the feedback effect of wall temperature rise on aeroheating is considered. The aeroheating and structural temperature were obtained by the CFD and ABAQUS software respectively. The coupling analysis of the hypersonic circular tube was carried out to verify the accuracy of the fluid field, the structural temperature, and the coupled method. Compared with experimental results, the calculated results showed that the relative errors of stagnation heat flux and stagnation temperature were 1.34% and 4.95% respectively, and thus the effectiveness of the coupled method was verified. Installing a spike reduced the total drag of the forebody. The spiked model with an aerodisk reduced the aeroheating of the forebody, while the model without an aerodisk intensified the aeroheating. The spiked model with a planar aerodisk had the best performance on drag and heat reduction among all the models. In addition, increasing the length of the spike reduced the drag and temperature of the forebody. With the increase of the length, the change rates of drag, pressure, heat flux, and temperature decreased gradually. Increasing the diameter of the aerodisk also reduced the temperature of the forebody, while the efficiency of forebody drag reduction first increased and then decreased. In conclusion, the heat and drag reduction must be considered comprehensively for the optimal design of the spike.

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Long Baseline Tightly Coupled DGNSS Positioning with Ionosphere-Free Inter-System Bias Calibration

Remote Sensing ◽

10.3390/rs13010067 ◽

2020 ◽

Vol 13 (1) ◽

pp. 67

Author(s):

Jianhua Cheng ◽

Chao Jiang ◽

Liang Li ◽

Chun Jia ◽

Bing Qi ◽

...

Keyword(s):

Satellite System ◽

Base Station ◽

Coupled Method ◽

Loosely Coupled ◽

Long Term Stability ◽

Long Baseline ◽

Positioning Method ◽

Tightly Coupled ◽

System Bias ◽

Global Navigation Satellite

Based on the statistical stability of the inter-system bias (ISB), we propose a tightly coupled Differential Global Navigation Satellite System (DGNSS) positioning method by using ionosphere-free combination for the long baseline applications. The proposed method is compatible with the traditional Radio Beacon (RBN) base station implementation. The tightly coupled DGNSS positioning method is utilized at the long baseline rover by eliminating the effect of ionosphere delay with ionosphere-free (IF) based differential ISB calibration. The improved positioning model strength can be obtained with the proposed method when compared with the traditional loosely coupled method, particularly under the satellite-deprived environment. GNSS datasets of different baselines were collected to test the proposed method. The results of the ISB stability show that the ISB has long-term stability and needs to be calibrated when the receiver is rebooted. The positioning results show that when compared with the IF-based loosely coupled method, the IF-based tightly coupled DGNSS method based on ISB calibration can obtain better positioning performance of accuracy and continuity within 240 km baselines.

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A hybrid solution for studying vibrations of coupled train–track–bridge system

Advances in Structural Engineering ◽

10.1177/1369433217691775 ◽

2017 ◽

Vol 20 (11) ◽

pp. 1699-1711 ◽

Cited By ~ 21

Author(s):

Zhihui Zhu ◽

Wei Gong ◽

Lidong Wang ◽

Issam E Harik ◽

Yu Bai

Keyword(s):

Equation Of Motion ◽

Time Dependent ◽

Integration Scheme ◽

Train Track ◽

Strongly Coupled ◽

Coupled Method ◽

Loosely Coupled ◽

Hybrid Solution ◽

Track Bridge ◽

Bridge System

This article develops a hybrid model to analyse the dynamic interactions between a train, tracks and a bridge. The model couples the train and track subsystems to form an integrated time-dependent subsystem through a vertically interacting wheel–rail model. In turn, this time-dependent subsystem is coupled with the bridge subsystem by enforcing the compatibility of forces at the contact points between the track and the bridge. A new hybrid solution algorithm is proposed which combines the strongly coupled method and the loosely coupled method to numerically solve the equation of motion of the coupled train–track–bridge system in the time domain. The integrated time-dependent equation of motion of the train–track subsystem is solved by applying the strongly coupled method. The equilibrium equations of the train–track subsystem and bridge subsystem are then solved via the loosely coupled method using the Newmark integration scheme. Significantly faster convergence can be achieved by avoiding the iterative equilibrium calculations between the wheel and the rail, and the total computational efficiency increases significantly because of the considerably smaller size of the time-dependent equations of motion and larger integration time step. The accuracy and computational cost of the proposed method are validated and compared to the existing models using a case study on the vibration of a cable-stayed bridge.

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