A New Analytical Formulation for the Dynamics of Multipocket Thin-Walled Structures Considering the Fixture Constraints

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Mouhab Meshreki ◽  
Helmi Attia ◽  
József Kövecses
Keyword(s):  
Dynamic Response ◽  
Ritz Method ◽  
Computation Time ◽  
Unit Element ◽  
Fixture Design ◽  
Prediction Errors ◽  
Computationally Efficient ◽  
Aerospace Structures ◽  
Thin Walled Structures ◽  
Thin Walled

Milling of thin-walled aerospace structures is a critical and challenging process. Available models for the prediction of the effect of the fixture on the dynamic response of flexible workpieces are computationally demanding and fail to represent practical cases for milling of thin-walled structures. Based on the analysis of typical structural components encountered in the aerospace industry, a generalized unit-element, with the shape of an asymmetric pocket, was identified to represent the dynamic response of these components. Accordingly, a computationally efficient dynamic model was developed to predict the dynamic response of typical thin-walled aerospace structures using the Rayleigh–Ritz method. In the formulation of this model, the dynamics of a 3D pocket is represented by an equivalent 2D multispan plate taking into account the effect of deformable fixture supports. The developed model was validated numerically and experimentally for different workpiece geometries and various types of loading. This model resulted in one to two orders of magnitude reduction in computation time when compared with the finite element models, with prediction errors less than 10%. The developed model meets the conflicting requirements of prediction accuracy and computational efficiency needed for interactive fixture design.

Development of a New Model for the Varying Dynamics of Flexible Pocket-Structures During Machining

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Mouhab Meshreki ◽  
Helmi Attia ◽  
József Kövecses
Keyword(s):  
Dynamic Models ◽  
Ritz Method ◽  
Computation Time ◽  
Dynamic Effect ◽  
Dynamic Responses ◽  
Prediction Errors ◽  
Continuous Change ◽  
Thin Walled Structures ◽  
Aspect Ratios ◽  
Thin Walled

Many of the aerospace components are characterized by having pocket-shaped thin-walled structures. During milling, the varying dynamics of the workpiece due to the change of thickness affects the final part quality. Available dynamic models rely on computationally prohibitive techniques that limit their use in the aerospace industry. In this paper, a new dynamic model was developed to predict the vibrations of thin-walled pocket structures during milling while taking into account the continuous change of thickness. The model is based on representing the change of thickness of a pocket-structure with a two-directional multispan plate. For the model formulation, the Rayleigh–Ritz method is used together with multispan beam models for the trial functions in both the x- and y-directions. An extensive finite element (FE) validation of the developed model was performed for different aspect ratios of rectangular and nonrectangular pockets and various change of thickness schemes. It was shown that the proposed model can accurately capture the dynamic effect of the change of thickness with prediction errors of less than 5% and at least 20 times reduction in the computation time. Experimental validation of the models was performed through the machining of thin-walled components. The predictions of the developed models were found to be in excellent agreement with the measured dynamic responses.

Dynamics Modeling and Analysis of Thin-Walled Aerospace Structures for Fixture Design in Multiaxis Milling

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Mouhab Meshreki ◽  
József Kövecses ◽  
Helmi Attia ◽  
Nejah Tounsi
Keyword(s):  
Dynamic Response ◽  
Dynamic Models ◽  
Analytical Description ◽  
Cutting Parameters ◽  
Computational Time ◽  
Model Parameters ◽  
Fixture Design ◽  
Dynamics Modeling ◽  
Aerospace Structures ◽  
Thin Walled

Milling of thin-walled aerospace structures is a critical process due to the high flexibility of the workpiece. Current practices in the fixture design and the choice of cutting parameters rely solely on conservative guidelines and the designer’s experience. This is a result of the lack of computationally efficient dynamic models to represent the dynamic response of the workpiece during machining, and the interaction between the workpiece, fixture and the cutting forces. This paper presents a novel dynamic formulation of typical thin-walled pockets encountered in aerospace structures. It is based on an analytical description of a five-sided pocket using a plate model. An off-line calibration of the model parameters, using global and local optimization, is performed in order to match the dynamic response of the pocket structure. The developed simplified model is based on Rayleigh’s energy method. Various pocket shapes are examined under different loading conditions and compared to finite element (FE) predictions and experimental results. In both cases, the results obtained by the developed model are in excellent agreement. This proposed approach resulted in one to two orders of magnitude reduction in computational time when compared to FE models, with a prediction error less than 10%.

Modeling the Varying Dynamics of Thin-Walled Aerospace Structures for Fixture Design Using Genetic Algorithms

2011 ◽  
Vol 223 ◽  
pp. 652-661
Author(s):  
Mouhab Meshreki ◽  
Helmi Attia ◽  
József Kövecses
Keyword(s):  
Numerical Models ◽  
Research Work ◽  
Computational Effort ◽  
Computational Time ◽  
Fixture Design ◽  
Structural Elements ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
High Flexibility ◽  
High Level

Fixture design for milling of aerospace thin-walled structures is a challenging process due to the high flexibility of the structure and the nonlinear interaction between the forces and the system dynamics. At the same time, the industry is aiming at achieving tight tolerances while maintaining a high level of productivity. Numerical models based on FEM have been developed to simulate the dynamics of thin-walled structures and the effect of the fixture layout. These models require an extensive computational effort, which makes their use for optimization very unpractical. In this research work, a new concept is introduced by using a multi-span plate with torsional and translational springs to simulate the varying dynamics of thin-walled structure during machining. A formulation, based on holonomic constraints, was developed and implemented to take into account the effect of rigid fixture supports. The developed model, which reduces the computational time by one to two orders of magnitude as compared to FE models, is used to predict the dynamic response of complex aerospace structural elements including pockets and ribs while taking into account different fixture layouts. The model predictions are validated numerically. The developed model meets the conflicting requirements of prediction accuracy and computational efficiency.

Dynamic Response of Pre/Post Buckled Thin-Walled Structure under Thermo-Acoustic Loading

2011 ◽  
Vol 80-81 ◽  
pp. 536-541 ◽  
Author(s):  
Yun Dong Sha ◽  
Ji Yong Li ◽  
Zhi Jun Gao
Keyword(s):  
Dynamic Response ◽  
Dynamic Responses ◽  
Transverse Displacement ◽  
Response Characteristics ◽  
Thin Walled Structures ◽  
Fem Method ◽  
Operating Environments ◽  
Thin Walled ◽  
Frequency Changes ◽  
High Level

Advanced aircraft and spacecraft structures are exposed to increasingly severe operating environments, including a combination of mechanical, aerodynamic, acoustic and thermal loads. Such loading conditions can cause thin-walled structures to respond in a nonlinear fashion and exhibit complex response characteristics. This paper investigates the dynamic response of pre/post buckled thin-walled structure under high level random acoustic loading. Firstly, different orders of critical buckling temperatures and modal frequencies under alternative temperatures are obtained using Finite Element Method (FEM), and the modal frequency changes in a disorder fashion are discussed in detail. Then with coupled BEM/FEM method, the dynamic responses including transverse displacement, strain and stress of a stiffened rectangular plate under thermo-acoustic loading are simulated. By comparing the response characteristics of the plate in pre/post buckled conditions, some valuable conclusions are derived, which can be used to explain the response behaviours of thin-walled structures.

Frame-Monolithic Technology of Construction of Low-Rise Buildings Made of Foam Gypsum and Steel Thin-Walled Structures

2018 ◽  
Vol 762 (8) ◽  
pp. 36-39 ◽  
Author(s):  
B.G. BULATOV ◽  
◽  
R.I. SHIGAPOV ◽  
M.A. IVLEV ◽  
I.V. NEDOSEKO ◽  
...  
Keyword(s):  
Thin Walled Structures ◽  
Thin Walled

Efficient Computing in Image Processing and DSPs with ASIP Based Multiplier

2019 ◽  
Vol 13 (2) ◽  
pp. 174-180
Author(s):  
Poonam Sharma ◽  
Ashwani Kumar Dubey ◽  
Ayush Goyal
Keyword(s):  
Image Processing ◽  
High Speed ◽  
Computation Time ◽  
Digital Signal ◽  
Instruction Set ◽  
Computationally Efficient ◽  
Specific Instruction ◽  
Processor Core ◽  
Speed Performance ◽  
Application Specific

Background: With the growing demand of image processing and the use of Digital Signal Processors (DSP), the efficiency of the Multipliers and Accumulators has become a bottleneck to get through. We revised a few patents on an Application Specific Instruction Set Processor (ASIP), where the design considerations are proposed for application-specific computing in an efficient way to enhance the throughput. Objective: The study aims to develop and analyze a computationally efficient method to optimize the speed performance of MAC. Methods: The work presented here proposes the design of an Application Specific Instruction Set Processor, exploiting a Multiplier Accumulator integrated as the dedicated hardware. This MAC is optimized for high-speed performance and is the application-specific part of the processor; here it can be the DSP block of an image processor while a 16-bit Reduced Instruction Set Computer (RISC) processor core gives the flexibility to the design for any computing. The design was emulated on a Xilinx Field Programmable Gate Array (FPGA) and tested for various real-time computing. Results: The synthesis of the hardware logic on FPGA tools gave the operating frequencies of the legacy methods and the proposed method, the simulation of the logic verified the functionality. Conclusion: With the proposed method, a significant improvement of 16% increase in throughput has been observed for 256 steps iterations of multiplier and accumulators on an 8-bit sample data. Such an improvement can help in reducing the computation time in many digital signal processing applications where multiplication and addition are done iteratively.

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