Application of the method of multiple scales to unravel energy exchange in nonlinear locally resonant metamaterials

In this paper, the effect of weak nonlinearities in 1D locally resonant metamaterials is investigated via the method of multiple scales. Commonly employed to the investigate the effect of weakly nonlinear interactions on the free wave propagation through a phononic structure or on the dynamic response of a Duffing oscillator, the method of multiple scales is here used to investigate the forced wave propagation through locally resonant metamaterials. The perturbation approach reveals that energy exchange may occur between propagative and evanescent waves induced by quadratic nonlinear local interaction

РАЗВИТИЕ ИНСТРУМЕНТАРИЯ ОБЩЕСТВЕННОГО УПРАВЛЕНИЯ: ПРОБЛЕМЫ, ПЕРСПЕКТИВЫ

The need to transform the present Russian economics public administration mechanism relates to changes in the public administration’s object and subject as well as with the aims and tasks of rendering public services. Main principles of the new approach to the use of public administrationinstruments are trust, approach to information, openness, responsibility, result, account for budget possibilities and consistency.Необходимость трансформации механизма общественного управления в современной экономике России связана с изменением объекта и субъекта общественного управления, с целями и задачами предоставления общественных услуг. Основными принципами нового подхода к использованию инструментов общественного управления являются доверие, доступ к информации, открытость, ответственность, результат, соотнесение с бюджетными возможностями и последовательность

Model reduction in computational homogenization for transient heat conduction

International audienceThis paper presents a computationally efficient homogenization method for transient heat conduction problems. The notion of relaxed separation of scales is introduced and the homogenization framework is derived. Under the assumptions of linearity and relaxed separation of scales, the microscopic solution is decomposed into a steady-state and a transient part. Static condensation is performed to obtain the global basis for the steady-state response and an eigenvalue problem is solved to obtain a global basis for the transient response. The macroscopic quantities are then extracted by averaging and expressed in terms of the coefficients of the reduced basis. Proof-of-principle simulations are conducted with materials exhibiting high contrast material properties. The proposed homogenization method is compared with the conventional steady-state homogenization and transient computational homogenization methods. Within its applicability limits, the proposed homogenization method is able to accurately capture the microscopic thermal inertial effects with significant computational efficiency

ЖИЛИЩНО-КОММУНАЛЬНЫЕ УСЛУГИ И ИХ ЗНАЧИМОСТЬ В ТРАНСФОРМАЦИИ СИСТЕМЫ МЕСТНОГО САМОУПРАВЛЕНИЯ

It is theoretically possible to introduce public administration in the field of rendering housing/communal services in Russia; however, a number of problems are to be solved for this purpose. In order to make this specific industry to develop in the above direction, state administration and local self-administration are to be combined and possibilities provided by each of these administration types used.Общественное управление в сфере предоставления жилищно-коммунальных услуг в России теоретически возможно, однако для этого необходимо решить целый ряд проблем. Для развития данной отрасли в этом направлении требуется сочетать государственное управление с местным самоуправлением, используя возможности каждого из этих видов управления

Enriched Computational Homogenization Schemes Applied to Pattern-Transforming Elastomeric Mechanical Metamaterials

Elastomeric mechanical metamaterials exhibit unconventional mechanical behaviour owing to their complex microstructures. A clear transition in the effective properties emerges under compressive loading, which is triggered by local instabilities and pattern transformations of the underlying cellular microstructure. Such transformations trigger a non-local mechanical response resulting in strong size effects. For predictive modelling of engineering applications, the effective homogenized material properties are generally of interest. For mechanical metamaterials, these can be obtained in an expensive manner by ensemble averaging of the direct numerical simulations for a series of translated microstructures, applicable especially in the regime of small separation of scales. To circumvent this expensive step, computational homogenization methods are of benefit, employing volume averaging instead. Classical first-order computational homogenization, which relies on the standard separation of scales principle, is unable to capture any size and boundary effects. Second-order computational homogenization has the ability to capture strain gradient effects at the macro-scale, thus accounting for the presence of non-localities. Another alternative is micromorphic computational homogenization scheme, which is tailored to pattern-transforming metamaterials by incorporating prior kinematic knowledge. In this contribution, a systematic study is performed, assessing the predictive ability of computational homogenization schemes in the realm of elastomeric metamaterials. Three representative examples with distinct mechanical loading are employed for this purpose: uniform compression and bending of an infinite specimen, and compression of a finite specimen. Qualitative and quantitative analyses are performed for each of the load cases where the ensemble average solution is set as a reference.Comment: 32 pages, 19 figures, 1 table, abstract shortened to fulfil 1920 character limi

Revisiting the martensite/ferrite interface damage initiation mechanism:The key role of substructure boundary sliding

Martensite/ferrite (M/F) interface damage plays a critical role in controlling failure of dual-phase (DP) steels and is commonly understood to originate from the large phase contrast between martensite and ferrite. This however conflicts with a few, recent observations, showing that considerable M/F interface damage initiation is often accompanied by apparent martensite island plasticity and weak M/F strain partitioning. In fact, martensite has a complex hierarchical structure which induces a strongly heterogeneous and orientation-dependent plastic response. Depending on the local stress state, (lath) martensite is presumed to be hard to deform based on common understanding. However, when favourably oriented, substructure boundary sliding can be triggered at a resolved shear stress which is comparable to that of ferrite. Moreover, careful measurements of the M/F interface structure indicate the occurrence of sharp martensite wedges protruding into the ferrite and clear steps in correspondence with lath boundaries, constituting a jagged M/F interfacial morphology that may have a large effect on the M/F interface behaviour. By taking into account the substructure and morphology features, which are usually overlooked in the literature, this contribution re-examines the M/F interface damage initiation mechanism. A systematic study is performed, which accounts for different loading conditions, phase contrasts, residual stresses/strains resulting from the preceding martensitic phase transformation, as well as the possible M/F interfacial morphologies. Crystal plasticity simulations are conducted to include inter-lath retained austenite (RA) films enabling the substructure boundary sliding. The results show that the substructure boundary sliding, which is the most favourable plastic deformation mode of lath martensite, can trigger M/F interface damage and hence control the failure behaviour of DP steels. The present finding may change the way in which M/F interface damage initiation is understood as a critical failure mechanism in DP steels

A multi-scale framework to predict damage initiation at martensite/ferrite interface

Martensite/ferrite (M/F) interface damage largely controls failure of dual-phase (DP) steels. In order to predict the failure and assess the ductility of DP steels, accurate models for the M/F interfacial zones are needed. Several M/F interface models have been proposed in the literature, which however do not incorporate the underlying microphysics. It has been recently suggested that (lath) martensite substructure boundary sliding dominates the M/F interface damage initiation and therefore should be taken into account. Considering the computationally infeasibility of direct numerical simulations of statistically representative DP steel microstructures, while explicitly resolving the interface microstructures and the sliding activity, a novel multi-scale approach is developed in this work. Two scales are considered: the DP steel mesostructure consisting of multiple lath martensite islands embedded in a ferrite matrix, and the microscopic M/F interfacial zone unit cell resolving the martensite substructure. Based on the emerging microscopic damage initiation pattern, an effective indicator for the M/F interface damage initiation is determined from the interface microstructural unit cell response, along with the effective sliding in this unit cell. Relating these two effective quantities for different interface microstructural configurations leads to an effective mesoscale model relating the interface damage indicator to the sliding activity of the martensite island in terms of the mesoscopic kinematics. This microphysics-based M/F interface damage indicator model, which could not be envisioned a-priori, is fully identified from a set of interfacial unit cell simulations, thus enabling the efficient prediction of interface damage initiation at the mesoscale. The capability of the developed effective model to predict the mesoscopic M/F interface damage initiation is demonstrated on an example of a realistic DP steel mesostructure

ЖИЛИЩНО-КОММУНАЛЬНОЕ ХОЗЯЙСТВО КАК ОБЪЕКТ ОБЩЕСТВЕННОГО УПРАВЛЕНИЯ

Theoretical examination proves that public management in the field of providing housing and communal services is possible. Problems available in the field of providing municipal public services may be solved through combination of the state management and the local selfmanagement.It is reasonable that further development of the sphere of providing housing and communal services be effected through creation and implementation of single managing open joint-stock holding communal companies. Most important management instruments in this sphere are monitoring and benchmarking.Теоретический анализ показывает возможность общественного управления в сфере предоставления жилищно-коммунальных услуг. В сфере общественных муниципальных услуг имеются проблемы, которые можно решить сочетанием государственного управления и местного самоуправления. Дальнейшее развитие сферы услуг ЖКХ целесообразно вести путем создания и задействования единых управляющих организаций в форме открытого акционерного общества (коммунального холдинга). Важнейшими инструментами управления в этой сфере являются мониторинг и бенчмаркинг

Multilayered Inclusions in Locally Resonant Metamaterials: Two-Dimensional Versus Three-Dimensional Modeling

Locally resonant metamaterials (LRMs) controlling low-frequency waves due to resonant scattering are usually characterized by narrow band gaps (BGs) and a poor wave filtering performance. To remedy this shortcoming, multiresonant metamaterial structures with closely located BGs have been proposed and widely studied. However, the analysis is generally limited to two-dimensional (2D) structures neglecting the finite height of any real resonator. The aim of this paper is the comparison of the wave dispersion for two-and threedimensional (3D) metamaterial models and evaluation of the applicability ranges of 2D results. Numerical study reveals that dual-resonant structures with cylindrical inclusions possess only a single (compared to two in the 2D case) BG for certain height-to-width ratios. In contrast, the wave dispersion in metamaterials with multiple spherical resonators can be accurately evaluated using a 2D approximation, enabling a significant simplification of resource-consuming 3D models

ЗАДАЧА МИНИМАЛЬНОГО ПОПОЛНЕНИЯ ДВУДОЛЬНОГО ГРАФА

In this article we show that the clustering minimum biclique completion problem is NP-complete in the class of P4-free bipartite graphs. We have also proposed a dynamic programming algorithm for that problem restricted to 2K2-free bipartite graphs.Рассматривается графовая задача, в которой задан двудольный граф с выделенной долей и требуется добавить в граф наименьшее число дополнительных ребер так, что множество вершин выделенной доли получившегося графа можно разбить на заданное число непустых множеств, каждое из которых содержит только вершины с одинаковыми окружениями. В работе установлено, что задача является NP-трудной в классе P4-свободных двудольных графов и предлагается алгоритм, который решает задачу в классе 2K2-свободных двудольных графов