modal synthesis
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2021 ◽  
Vol 5 (OOPSLA) ◽  
pp. 1-29
Author(s):  
Kia Rahmani ◽  
Mohammad Raza ◽  
Sumit Gulwani ◽  
Vu Le ◽  
Daniel Morris ◽  
...  

Multi-modal program synthesis refers to the task of synthesizing programs (code) from their specification given in different forms, such as a combination of natural language and examples. Examples provide a precise but incomplete specification, and natural language provides an ambiguous but more "complete" task description. Machine-learned pre-trained models (PTMs) are adept at handling ambiguous natural language, but struggle with generating syntactically and semantically precise code. Program synthesis techniques can generate correct code, often even from incomplete but precise specifications, such as examples, but they are unable to work with the ambiguity of natural languages. We present an approach that combines PTMs with component-based synthesis (CBS): PTMs are used to generate candidates programs from the natural language description of the task, which are then used to guide the CBS procedure to find the program that matches the precise examples-based specification. We use our combination approach to instantiate multi-modal synthesis systems for two programming domains: the domain of regular expressions and the domain of CSS selectors. Our evaluation demonstrates the effectiveness of our domain-agnostic approach in comparison to a state-of-the-art specialized system, and the generality of our approach in providing multi-modal program synthesis from natural language and examples in different programming domains.


2021 ◽  
Vol 11 (18) ◽  
pp. 8600
Author(s):  
Yinxin Yu ◽  
Xiaolong Jin ◽  
Yanming Fu ◽  
Tianyu Zhao

This paper conducts a coupled vibration analysis of a two-stage bladed disk rotor system. According to the finite element method, the bladed disk rotor system is established. The substructure modal synthesis super-element method (SMSM) with a fixed interface and free interface is presented to obtain the vibration behaviors of the rotor system. Then, the free vibration results are compared with the ones calculated by the cyclic symmetry analysis method to validate the analysis in this paper. The results show that the modes of the two-stage bladed disk not only include the modes of the first- and second-stage bladed disk, but also the coupled modes of the two-stage bladed disk.


Author(s):  
Yekai Sun ◽  
Jie Yuan ◽  
Alessandra Vizzaccaro ◽  
Loïc Salles

AbstractThe nonlinear modes of a non-conservative nonlinear system are sometimes referred to as damped nonlinear normal modes (dNNMs). Because of the non-conservative characteristics, the dNNMs are no longer periodic. To compute non-periodic dNNMs using classic methods for periodic problems, two concepts have been developed in the last two decades: complex nonlinear mode (CNM) and extended periodic motion concept (EPMC). A critical assessment of these two concepts applied to different types of non-conservative nonlinearities and industrial full-scale structures has not been thoroughly investigated yet. Furthermore, there exist two emerging techniques which aim at predicting the resonant solutions of a nonlinear forced response using the dNNMs: extended energy balance method (E-EBM) and nonlinear modal synthesis (NMS). A detailed assessment between these two techniques has been rarely attempted in the literature. Therefore, in this work, a comprehensive comparison between CNM and EPMC is provided through two illustrative systems and one engineering application. The EPMC with an alternative damping assumption is also derived and compared with the original EPMC and CNM. The advantages and limitations of the CNM and EPMC are critically discussed. In addition, the resonant solutions are predicted based on the dNNMs using both E-EBM and NMS. The accuracies of the predicted resonances are also discussed in detail.


2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Bin Bai ◽  
Qi Yang ◽  
Guang Wei Zhu ◽  
Qi Liang Wu ◽  
Xin ye Li

An improved component modal synthesis-based nonproportional mistuning method (ICMS-NPMM) is proposed to investigate mistuned turbine blisks (MTBs) since the high-fidelity finite element models (HFEMs) involve large number of computations, which leads to low calculation efficiency. To reduce degrees of freedom and suppress the flutter of MTB, it is divided into mistuned blade structure and tuned disk structure, and the intentional mistuning is considered. Furthermore, the mistuned parameters, nonproportional mistuning, and complex loads are also considered. Firstly, the basic theory of ICMS-NPMM is investigated; secondly, the model of MTB is established via ICMS-NPMM; finally, the intentionally mistuned design of modal shape amplitudes (MSAs) is investigated via ICMS-NPMM. The results indicate that the calculation efficiency is enhanced via ICMS-NPMM relative to that of via HFEM. In addition, the sensitivity and the flutter are decreased; meanwhile, the amplitude fluctuations of MSAs are distinctly decreased and become comparatively smooth. This investigation provides an important guidance for the vibration characteristic study of complex mechanical structures in engineering practice.


Author(s):  
Y. Ni ◽  
W. Zhang ◽  
Y. Lv

To investigate the structural dynamic characteristics of a folding wing effectively, a fast structural dynamic modeling approach is proposed. Firstly, the interface compatible relationship of the traditional fixed interface component modal synthesis method is modified, and the internal force of the interface is completely expressed in the structural dynamic equation, so that the influence of the connection stiffness on the wing structure dynamics can be considered. Then, on the basis of the fixed interface component modal synthesis method, the main mode of fixed-loaded interface is introduced to establish the mixed-loaded interface component modal synthesis method, which makes it feasible to accurately reflect the influence of elasticity and inertia of fuselage and outer wing on inner wing. The structural dynamics modeling method based on two different kinds of component modal synthesis method analyzed and deduced in detail. The application of component modal synthesis method in the fast structural dynamics modeling of folding wing is achieved. The whole program is compiled in MATLAB. At the same time, the dynamic characteristics of the folding wing with different folding angles, different connections and different connection positions is investigated. The results of the method proposed in this paper are compared with the results of the repeated finite model established in MSC.NASTRAN to verify the effectiveness from the aspects of natural frequency and vibration mode.


Author(s):  

A new approach to obtain an iterative Newton formula for finding an equation solution, by using modal control theory for linear discrete systems when solving problems of observation or identification is presented. The decomposition method as a modal control method, which allows obtaining analytical solutions, is used. Keywords Newton’s iterative formula; numerical solution of the equation; decomposition method of modal synthesis; linear discrete system


Author(s):  
Samuel Quaegebeur ◽  
Benjamin Chouvion ◽  
Fabrice Thouverez ◽  
Loïc Berthe

Abstract Cyclic structures such as turbomachinery present material and geometrical variations between sectors. These discrepancies are called mistuning and break the cyclic symmetry of the structure. Computing the forced response of mistuned cyclic structures is thus a numerical challenge. The Component Nonlinear Complex Mode Synthesis (CNCMS) is one of the few nonlinear reduced-order model formulations that allow to compute the nonlinear response of tuned and mistuned structures. It has been validated successfully for friction problems. However, in the presence of geometric nonlinearities, internal resonances may arise and they cannot be captured correctly with the CNCMS method. The purpose of this work is therefore to present a new methodology for developing a nonlinear reduced-order model that can successfully capture internal resonances for tuned and mistuned structures. This method, called Component Mode Synthesis with Nonlinear Re-evaluation (CMSNR), is based on a variation of the CNCMS approach. The final modal synthesis uses a multi-harmonic procedure and a re-evaluation of the nonlinear forces on each sector independently. The performance and limitations of the proposed approach are assessed using a simplified example of a blisk subject to polynomial nonlinearities. Different internal resonances are exhibited and studied depending on the type of excitation force and on the level of mistuning.


Author(s):  
Е.М. Васильев ◽  
Е.А. Сердечная ◽  
А.В. Таволжанский

Решается задача синтеза систем модального управления с высоким порядком астатизма. Показано, что традиционный подход к решению этой задачи, заключающийся в последовательном и независимом обеспечении требований к характеру переходного процесса и к показателям его точности, сталкивается с необходимостью принятия проектных решений при неполных условиях. Игнорирование указанного обстоятельства на практике приводит к получению компромиссных результатов с нежелательными отклонениями от технических требований. При проектировании высокоточных систем такие отклонения становятся недопустимыми. Для преодоления указанной трудности предложен переход к интервальным методам постановки и решения задач модального синтеза. Теоретическая возможность такого перехода основана на избыточном многообразии возможного размещения собственных чисел характеристической матрицы системы в её спектре. Рассмотрен пример реализации указанной возможности для системы с модальным регулятором, в структуру которой введена дополнительная обратная связь по выходу. Для этой структуры сформирована система ограничений, накладываемых на спектр указанной матрицы, которые определяют одновременное выполнение требований к монотонности переходного процесса, времени регулирования и к точности отработки гармонических воздействий. Отмечено, что неединственность получаемого решения создаёт предпосылки для многоальтернативного подхода к проектированию системы. Возможности интервального анализа продемонстрированы также на примере системы, в структуру которой введён дифференцирующий наблюдатель задающего воздействия. Показано, что в результате такого анализа могут быть получены граничные условия задачи синтеза, гарантирующие получение требуемых показателей качества системы. Для всех примеров, рассмотренных в работе, представлены результаты имитационного моделирования, подтверждающие работоспособность предложенного метода The article solves problem of synthesis of modal control systems with high astatism order. It shows that the traditional approach to solving this problem, which consists in consistent and independent provision of requirements for the nature of the transient process and for the indicators of its accuracy, faces the need to carry out synthesis under incomplete conditions. Ignoring this circumstance leads to the search for compromise solutions and unwanted deviations from technical requirements. When designing high-precision systems, such deviations become unacceptable. To overcome this difficulty, a transition to interval methods for formulating and solving modal synthesis problems is proposed. The theoretical possibility of such a transition is based on the excessive variety of possible placement of the eigenvalues of the characteristic matrix of the system in its spectrum. An example of the implementation of this possibility is considered for a system with a modal controller, in the structure of which additional output feedback is introduced. For this structure, a system of restrictions imposed on the spectrum of the specified matrix is formed, which determine the simultaneous fulfillment of the requirements for the monotonicity of the transient process, the regulation time and the accuracy of working out harmonic influences. It is noted that the non-uniqueness of the obtained solution creates the preconditions for a multi-alternative approach to system design. The possibilities of interval analysis are also demonstrated by the example of the synthesis of a system, into the structure of which a differentiating observer of the setting action is introduced. It is shown that as a result of such an analysis, the boundary conditions of the synthesis problem can be obtained, which guarantee the obtaining of the required quality indicators of the system. For all the examples considered in the work, the results of simulation are presented, which confirm the efficiency of the proposed synthesis method


Author(s):  
Samuel Quaegebeur ◽  
Benjamin Chouvion ◽  
Fabrice Thouverez ◽  
Loïc Berthe

Abstract Cyclic structures such as turbomachinery present material and geometrical variations between sectors. These discrepancies are called mistuning and break the cyclic symmetry of the structure. Computing the forced response of mistuned cyclic structures is thus a numerical challenge. The Component Nonlinear Complex Mode Synthesis (CNCMS) is one of the few nonlinear reduced-order model formulations that allow to compute the nonlinear response of tuned and mistuned structures. It has been validated successfully for friction problems. However, in the presence of geometric nonlinearities, internal resonances may arise and they cannot be captured correctly with the CNCMS method. The purpose of this work is therefore to present a new methodology for developing a nonlinear reduced-order model that can successfully capture internal resonances for tuned and mistuned structures. This method, called Component Mode Synthesis with Nonlinear Re-evaluation (CMSNR), is based on a variation of the CNCMS approach. The final modal synthesis uses a multi-harmonic procedure and a re-evaluation of the nonlinear forces on each sector independently. The performance and limitations of the proposed approach are assessed using a simplified example of a blisk subject to polynomial nonlinearities. Different internal resonances are exhibited and studied depending on the type of excitation force and on the level of mistuning.


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