scholarly journals Numerical Derivation of Buckling Knockdown Factors for Isogrid-Stiffened Cylinders with Various Shell Thickness Ratios

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Han-Il Kim ◽  
Chang-Hoon Sim ◽  
Jae-Sang Park ◽  
Keejoo Lee ◽  
Joon-Tae Yoo ◽  
...  
Keyword(s):  
Shell Thickness ◽  
Control Method ◽  
Computation Time ◽  
Initial Imperfection ◽  
Equivalent Model ◽  
Detailed Model ◽  
Buckling Loads ◽  
Global Buckling ◽  
Displacement Control Method ◽  
Factor Function

This study is aimed at providing a numerical derivation of the shell knockdown factors of isogrid-stiffened cylinders under axial compressive loads. The present work uses two different analysis models such as the detailed model with modeling of numerous stiffeners and the equivalent model without modeling of stiffeners for isogrid-stiffened cylinders. The single perturbation load approach is used to represent the geometrically initial imperfection of the cylinder. Postbuckling analyses using the displacement control method are conducted to calculate the global buckling loads of a cylinder. The shell knockdown factor is numerically derived using the obtained global buckling loads without and with the initial imperfection of the isogrid-stiffened cylinder. The equivalent model is more efficient than the detailed model in terms of modeling time and computation time. The present knockdown factor function in terms of the shell thickness ratio (radius to thickness) for the isogrid-stiffened cylinder is significantly higher than NASA’s knockdown factor function; therefore, it is believed that the present knockdown factor function can facilitate in developing lightweight launch vehicle structures using isogrid-stiffened cylinders.

Post-Buckling Behavior of Z-Shaped Columns under Variables of Lengths and Initial Imperfections

2013 ◽  
Vol 437 ◽  
pp. 62-65
Author(s):  
Ji Nao Zhang
Keyword(s):  
Failure Modes ◽  
Control Method ◽  
Three Dimensional ◽  
Initial Imperfection ◽  
Maximum Load ◽  
Element Analysis ◽  
Initial Imperfections ◽  
Solution Methods ◽  
Post Buckling ◽  
Displacement Control Method

This paper conducts three-dimensional, nonlinear finite element analysis to investigate the results of using different solution methods and the influence of initial imperfections and material plasticity on failure modes and maximum load of various Z-shaped column lengths; it also compares the column buckling responses between various lengths, each with different initial imperfections. Further analyses include investigating the element suitability and computational costs. Results showed that both displacement control method and Riks method are fully capable of receiving promising results from this analysis. In terms of the effects of initial imperfection and material plasticity on the maximum load that column could carry, the imperfection is the major contributing factor when the column is long whereas the plasticity is the major contributing factor when the column is short.

scholarly journals The Effect of General Imperfections on the Buckling of Cylindrical Shells

1969 ◽  
Vol 36 (1) ◽  
pp. 28-38 ◽  
Author(s):  
Johann A´rbocz ◽  
Charles D. Babcock
Keyword(s):  
Axial Load ◽  
Circular Cylindrical Shell ◽  
Three Dimensional ◽  
Initial Imperfection ◽  
Buckling Load ◽  
Data Recording ◽  
Buckling Loads ◽  
Recording Process ◽  
Global Buckling ◽  
Experimental Values

An experimental and theoretical investigation of the effect of general imperfections on the buckling load of a circular cylindrical shell under axial compression was carried out. A noncontact probe has been used to make complete imperfection surveys on electro-formed copper shells before and during the loading process up to the buckling load. The data recording process has been fully automated and the data reduction was done on an IBM 7094. Three-dimensional plots were obtained of the measured initial imperfection surfaces and of the growth of these imperfections under increasing axial load. The modal components of the measured imperfection surfaces were also obtained. The theoretical solution located the limit points of the postbuckled states. A simplified imperfection model was used consisting of one axisymmetric and two asymmetric components. For global buckling the correlation between the theoretical buckling loads and the experimental values was found to be good.

Active Noise Hybrid Feedforward/Feedback Control Using Neural Network Compensation*

2001 ◽  
Vol 124 (1) ◽  
pp. 100-104 ◽  
Author(s):  
Zhang Qizhi ◽  
Jia Yongle
Keyword(s):  
Neural Network ◽  
Noise Control ◽  
Control Method ◽  
Active Noise Control ◽  
Equivalent Model ◽  
Gradient Descent Method ◽  
Nonlinear Simulation ◽  
Control Approach ◽  
Active Noise ◽  
Nonlinear Noise

The nonlinear active noise control (ANC) is studied. The nonlinear ANC system is approximated by an equivalent model composed of a simple linear sub-model plus a nonlinear sub-model. Feedforward neural networks are selected to approximate the nonlinear sub-model. An adaptive active nonlinear noise control approach using a neural network enhancement is derived, and a simplified neural network control approach is proposed. The feedforward compensation and output error feedback technology are utilized in the controller designing. The on-line learning algorithm based on the error gradient descent method is proposed, and local stability of closed loop system is proved based on the discrete Lyapunov function. A nonlinear simulation example shows that the adaptive active noise control method based on neural network compensation is very effective to the nonlinear noise control, and the convergence of the NNEH control is superior to that of the NN control.

scholarly journals Analysis on the value of stiffness of the dual joint straightness notch joint of beams due to cyclic lateral load

2021 ◽  
Vol 921 (1) ◽  
pp. 012019
Author(s):  
M R Nur ◽  
H Parung ◽  
A A Amiruddin
Keyword(s):  
Control Method ◽  
Monolithic Column ◽  
Precast Concrete ◽  
European Convention ◽  
Building Structures ◽  
Earthquake Loads ◽  
Cyclic Lateral Load ◽  
Beam Type ◽  
Column Joint ◽  
Displacement Control Method

Abstract Precast concrete is an answer to the demands of building structures that save time, but cannot be used widely because of the reliability of the connection, especially during an earthquake, the desired earthquake-resistant building structure must have sufficient strength and rigidity. Stiffness is one of the factors that determine the response of a structure to earthquake loads. When connected with earthquake loads, a structure must have sufficient rigidity so that its movement during an earthquake can be limited. This study aims to determine and analyze the stiffness in the double columns straight joint beam notches due to lateral cyclic load. By dividing 3 (three) types of test specimens, namely Monolithic column Beam, Type 1 Column Joint (SBK), and Type 2 Column Beam Joint (SBK). The connection used is a double straight notch and using the grouting method. Testing and analysis using the Displacement Control Method with the European Convention for Constructional Steelwork (ECCS) 1986 standards. The results showed the monolith column Column (BK) specimens have a greater stiffness value compared to SBK 1 specimens and SBK 2 specimens.

Pseudo-Dynamic Testing Method Based on External Displacement Control

2012 ◽  
Vol 204-208 ◽  
pp. 2428-2432
Author(s):  
Da Peng Wang ◽  
Shi Zhu Tian
Keyword(s):  
Control Method ◽  
Dynamic Testing ◽  
Fast Response ◽  
Displacement Sensor ◽  
Internal Displacement ◽  
Displacement Control ◽  
Loop Control ◽  
Testing Technology ◽  
Hydraulic Servo ◽  
Displacement Control Method

In order to accelerate the velocity and improve the accuracy of the pseudo-dynamic testing，the external displacement control method is put forward based on the hardware control. The internal displacement sensor of the actuator is invalid on control and substituted by the LVDT displacement sensor connected with the specimen. The process of the feedback displacement and command error compensation is quickly implemented by the internal closed-loop control of the actuator. Compared with the iteratively approximate load control, this method not only makes the testing velocity fast, but also enables the error between command and feedback to be “zero”. The fast pseudo-dynamic testing about a cantilever beam is carried out by applying appropriate PID parameters of the actuator. The testing result shows that although this method has rather high requirements in the control system and electro-hydraulic servo load device, and the risk to some extent, the fast response of the actuator can be firmed by applying appropriate PID control parameters. This method provides a fast testing technology for velocity-dependent structures or specimens.

scholarly journals Digital Luminaire Design Using LED Digital Twins—Accuracy and Reduced Computation Time: A Delphi4LED Methodology

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4979 ◽  
Author(s):  
Marc van der Schans ◽  
Joan Yu ◽  
Genevieve Martin
Keyword(s):  
Computation Time ◽  
Domain Model ◽  
Digital Design ◽  
Junction Temperature ◽  
System Level ◽  
Detailed Model ◽  
Calculation Time ◽  
Digital Twins ◽  
Level Model ◽  
Led Luminaire

Light-emitting diode (LED) digital twins enable the implementation of fast digital design flows for LED-based products as the lighting industry moves towards Industry 4.0. The LED digital twin developed in the European project Delphi4LED mimics the thermal-electrical-optical behavior of a physical LED. It consists of two parts: a package-level LED compact thermal model (CTM), coupled to a chip-level multi-domain model. In this paper, the accuracy and computation time reductions achieved by using LED CTMs, compared to LED detailed thermal models, in 3D system-level models with a large number of LEDs are investigated. This is done up to luminaire-level, where all heat transfer mechanisms are accounted for, and up to 60 LEDs. First, we characterize a physical phosphor-converted white high-power LED and apply LED-level modelling to produce an LED detailed model and an LED CTM following the Delphi4LED methodology. It is shown that the steady-state junction temperature errors of the LED CTM, compared to the detailed model, are smaller than 2% on LED-level. To assess the accuracy and the reduction of computation time that can be realized in a 3D system-level model with a large number of LEDs, two use cases are considered: (1) an LED module-level model, and (2) an LED luminaire-level model. In the LED module-level model, the LED CTMs predict junction temperatures within about 6% of the LED detailed models, and reduce the calculation time by up to nearly a factor 13. In the LED luminaire-level model, the LED CTMs predict junctions temperatures within about 1% of LED detailed models and reduce the calculation time by about a factor of 4. This shows that the achievable computation time reduction depends on the complexity of the 3D model environment. Nevertheless, the results demonstrate that using LED CTMs has the potential to significantly decrease computation times in 3D system-level models with large numbers of LEDs, while maintaining junction temperature accuracy.

Nonlinear H-infinity control for 4-DOF underactuated overhead cranes

2017 ◽  
Vol 40 (7) ◽  
pp. 2364-2377 ◽  
Author(s):  
Gerasimos Rigatos ◽  
Pierluigi Siano ◽  
Masoud Abbaszadeh
Keyword(s):  
Control Algorithm ◽  
Control Method ◽  
Control Program ◽  
Algebraic Riccati Equation ◽  
Equivalent Model ◽  
Underactuated System ◽  
H Infinity ◽  
Overhead Cranes ◽  
H Infinity Control ◽  
Approximate Linearization

The article proposes a nonlinear H-infinity control method for four degrees of freedom underactuated overhead cranes. The crane’s system is underactuated because it receives only two external inputs, namely a force that allows the motion of the bridge along the x-axis and a force that allows the motion of the trolley along the y-axis. A solution to the control problem of this underactuated system is obtained by applying nonlinear H-infinity control. The dynamic model of the overhead crane undergoes approximate linearization round local operating points which are redefined at each iteration of the control algorithm. These temporary equilibria consist of the last value of the crane’s state vector and of the last value of the control signal that was exerted on it. For the approximate linearization of the system’s dynamics, a Taylor series expansion is performed through the computation of the associated Jacobian matrices. The modelling errors are compensated by the robustness of the control algorithm. Next, for the linearized equivalent model of the crane an H-infinity feedback controller is designed. This requires the solution of an algebraic Riccati equation at each iteration of the computer control program. It is shown that the control scheme achieves H-infinity tracking performance, which implies maximum robustness to modelling errors and external perturbations. The stability of the control loop is proven through Lyapunov analysis.

Investigation of Robust Combination Control for Elastic Vehicle Based on Reduced-Order Model

2013 ◽  
Vol 378 ◽  
pp. 3-12
Author(s):  
Zi Jian Zhang ◽  
Bin Liu
Keyword(s):  
Circuit Design ◽  
Error Bounds ◽  
Control Method ◽  
Design Method ◽  
Reduced Order Model ◽  
Equivalent Model ◽  
Order Model ◽  
Reduced Order ◽  
Design Error ◽  
Low Order

Putting forward with an integrated flight and aeroelasticity control method of elastic air vehicle and aiming at the reduction errors introduced during combination dynamic model reduction, the paper adopts mixed sensitivity H∞control to design low-order combination control law that satisfies its robustness based on reduced-order model. Against to the wide reduced-order error bounds that may influence control performance, the two-circuit design method is used, and combined with inner-circuit suboptimal feedback design, error bounds of equivalent model are greatly narrowed. Without any orders extra added to the controllers, the outer-circuit robust controller designed on that basis will effectively improve the performance of the system, significantly superior to the single circuit design method. It is shown in simulation results that such low-order combination law will not only provide satisfactory robustness and performance, but will also effectively suppress the occurrence of servo flutter, while the greatly-reduced orders will be helpful for the realization of projects.

A Coherency-Based Equivalent Model of a Large Scale Wind Farm

2011 ◽  
Vol 347-353 ◽  
pp. 2342-2346
Author(s):  
Rong Fu ◽  
Bao Yun Wang ◽  
Wan Peng Sun
Keyword(s):  
Wind Power ◽  
Wind Turbines ◽  
Large Scale ◽  
Wind Farm ◽  
Dynamic Models ◽  
Wind Farms ◽  
Model Complexity ◽  
Equivalent Model ◽  
Detailed Model ◽  
Doubly Fed

With increasing installation capacity and wind farms penetration, wind power plays more important role in power systems, and the modeling of wind farms has become an interesting research topic. In this paper, a coherency-based equivalent model has been discussed for the doubly fed induction generator (DFIG). Firstly, the dynamic models of wind turbines, DFIG and the mechanisms are briefly introduced. Some existing dynamic equivalent methods such as equivalent wind model, variable speed wind turbine model, parameter identification method and modal equivalent method to be used in wind farm aggregation are discussed. Then, considering wind power fluctuations, a new equivalent model of a wind farm equipped with doubly-fed induction generators is proposed to represent the interactions of the wind farm and grid. The method proposed is based on aggregating the coherent group wind turbines into an equivalent one. Finally, the effectiveness of the equivalent model is demonstrated by comparison with the wind farm response obtained from the detailed model. The dynamic simulations show that the present model can greatly reduce the computation time and model complexity.

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