16,110 research outputs found


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    The article presents the results of the analysis of mechanical behavior of mechanical layered structures with metamaterial interlayers under dynamic loading. These structures can be used in lightweight structures for damping dynamic loads in transport and aerospace engineering. Structural elements with layers of the mechanical metamaterials have a low specific mass density and high specific strength characteristics. These multilayer structures have a high specific ability to absorb and dissipate the energy of external dynamic loads too. The results of numerical simulation of the response of multilayer structures to dynamic impacts obtained in this work indicate high specific energy absorption and dissipative properties, which make it possible to weaken the pulse amplitude after passing through the layered system and attenuate of cyclic impacts amplitudes. The results obtained indicate the possibility of creating effective mechanical damping structures of the type under discussion

    Enabling Faster Locomotion of Planetary Rovers with a Mechanically-Hybrid Suspension

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    The exploration of the lunar poles and the collection of samples from the martian surface are characterized by shorter time windows demanding increased autonomy and speeds. Autonomous mobile robots must intrinsically cope with a wider range of disturbances. Faster off-road navigation has been explored for terrestrial applications but the combined effects of increased speeds and reduced gravity fields are yet to be fully studied. In this paper, we design and demonstrate a novel fully passive suspension design for wheeled planetary robots, which couples a high-range passive rocker with elastic in-wheel coil-over shock absorbers. The design was initially conceived and verified in a reduced-gravity (1.625 m/s2^2) simulated environment, where three different passive suspension configurations were evaluated against a set of challenges--climbing steep slopes and surmounting unexpected obstacles like rocks and outcrops--and later prototyped and validated in a series of field tests. The proposed mechanically-hybrid suspension proves to mitigate more effectively the negative effects (high-frequency/high-amplitude vibrations and impact loads) of faster locomotion (>1 m/s) over unstructured terrains under varied gravity fields. This lowers the demand on navigation and control systems, impacting the efficiency of exploration missions in the years to come.Comment: 8 pages, 13 figure

    Damped harmonic oscillator revisited: the fastest route to equilibrium

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    Theoretically, solutions of the damped harmonic oscillator asymptotically approach equilibrium, i.e., the zero energy state, without ever reaching it exactly, and the critically damped solution approaches equilibrium faster than the underdamped or the overdamped solution. Experimentally, the systems described with this model reach equilibrium when the system's energy has dropped below some threshold corresponding to the energy resolution of the measuring apparatus. We show that one can (almost) always find an optimal underdamped solution that will reach this energy threshold sooner than all other underdamped solutions, as well as the critically damped solution, no matter how small this threshold is. We also comment on one exception to this for a particular type of initial conditions, when a specific overdamped solution reaches the equilibrium state sooner than all other solutions. We confirm some of our findings experimentally.Comment: 9 pages of main text + supplementary material. The biggest changes compared to the previous version are in section IIIC, that section has been somewhat shortened and written more clearly. Also, some typos and similar errors in supplementary materials have been corrected. The paper is accepted for publication in American Journal of Physic

    Identification of Control-Related Signal Path for Semi-Active Vehicle Suspension with Magnetorheological Dampers

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    This paper presents a method for the identification of control-related signal paths dedicated to a semi-active suspension with MR (magnetorheological) dampers, which are installed in place of standard shock absorbers. The main challenge comes from the fact that the semi-active suspension needs to be simultaneously subjected to road-induced excitation and electric currents supplied to the suspension MR dampers, while a response signal needs to be decomposed into road-related and control-related components. During experiments, the front wheels of an all-terrain vehicle were subjected to sinusoidal vibration excitation at a frequency equal to 12 Hz using a dedicated diagnostic station and specialised mechanical exciters. The harmonic type of road-related excitation allowed for its straightforward filtering from identification signals. Additionally, front suspension MR dampers were controlled using a wideband random signal with a 25 Hz bandwidth, different realisations, and several configurations, which differed in the average values and deviations of control currents. The simultaneous control of the right and left suspension MR dampers made it necessary to decompose the vehicle vibration response, i.e., the front vehicle body acceleration signal, into components related to the forces generated by different MR dampers. Measurement signals used for identification were taken from numerous sensors available in the vehicle, e.g., accelerometers, suspension force and deflection sensors, and sensors of electric currents, which control the instantaneous damping parameters of MR dampers. The final identification was carried out for control-related models evaluated in the frequency domain and revealed several resonances of the vehicle response and their dependence on the configurations of control currents. In addition, the parameters of the vehicle model with MR dampers and the diagnostic station were estimated based on the identification results. The analysis of the simulation results of the implemented vehicle model carried out in the frequency domain showed the influence of the vehicle load on the absolute values and phase shifts of control-related signal paths. The potential future application of the identified models lies in the synthesis and implementation of adaptive suspension control algorithms such as FxLMS (filtered-x least mean square). Adaptive vehicle suspensions are especially preferred for their ability to quickly adapt to varying road conditions and vehicle parameters

    Mathematical Problems in Rock Mechanics and Rock Engineering

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    With increasing requirements for energy, resources and space, rock engineering projects are being constructed more often and are operated in large-scale environments with complex geology. Meanwhile, rock failures and rock instabilities occur more frequently, and severely threaten the safety and stability of rock engineering projects. It is well-recognized that rock has multi-scale structures and involves multi-scale fracture processes. Meanwhile, rocks are commonly subjected simultaneously to complex static stress and strong dynamic disturbance, providing a hotbed for the occurrence of rock failures. In addition, there are many multi-physics coupling processes in a rock mass. It is still difficult to understand these rock mechanics and characterize rock behavior during complex stress conditions, multi-physics processes, and multi-scale changes. Therefore, our understanding of rock mechanics and the prevention and control of failure and instability in rock engineering needs to be furthered. The primary aim of this Special Issue “Mathematical Problems in Rock Mechanics and Rock Engineering” is to bring together original research discussing innovative efforts regarding in situ observations, laboratory experiments and theoretical, numerical, and big-data-based methods to overcome the mathematical problems related to rock mechanics and rock engineering. It includes 12 manuscripts that illustrate the valuable efforts for addressing mathematical problems in rock mechanics and rock engineering

    Brittle Mineral Foam In A Sacrificial Cladding Solution For Blast Loading Mitigation

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    A ameaça de engenhos explosivos no campo de batalha continua a ser uma das formas mais eficazes de criar um grande número de baixas. Independentemente do alvo, estruturas ou veículos, é do interesse de países, como Portugal, que têm tropas destacadas em conflitos armados, para mitigar os seus efeitos. No caso dos veículos, estes possuem um sistema de proteção, como a blindagem, para mitigar os efeitos dos projéteis e fragmentos inimigos. No entanto, em caso de ataque com minas ou explosivos, a sua estrutura e os seus ocupantes continuam vulneráveis. Consequentemente, surge o objetivo deste estudo: criação e avaliação de um revestimento de sacrifício. Este sistema funcionará como uma solução para mitigar a quantidade de energia que a estrutura de principal tem de suportar e assim minimizar os seus danos. A solução de revestimento sacrificial adotada neste estudo baseia-se num núcleo de espuma mineral frágil. Este material tem a grande vantagem de ser leve, incombustível e económico. Além disso, tem também uma boa capacidade de absorção de energia. O desenvolvimento deste sistema e a avaliação do seu comportamento submetido a uma explosão ou a uma compressão dinâmica foi realizado através de campanhas experimentais e utilizando também a modelação numérica no software LS-Dyna. Foi verificada a capacidade de absorver energia e mitigar a ação de uma explosão através de um revestimento sacrificial com espuma mineral frágil. Foi verificado que o sucesso desta solução depende não só do seu núcleo mas também do elemento anterior, a placa frontal. Além disso, a própria geometria e configuração da espuma irá influenciar a sua eficiência de absorção

    От «Черного квадрата» до «Черного зеркала»: современное искусство в поисках света

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    A hundred years of history of contemporary art, notionally from the picturesque «Black Square» artwork by Malevich (1915) to the British TV series «Black Mirror» by Brooker (2011) and Ruben Östlund’s film «The Square» (2017) is in the focus of this study. The aim is to analyze the axiological foundations of modern art. Relevance of the chosen discourse is due, firstly, it’s enduring importance, and, secondly, major advances in the Architectonics of Culture – from the latest technologies as a factor of cultural development to mental perversions generated by those technologies. Formal, existential and institutional values are highlighted, basing on analysis of the proposed artworks as main axiological tags in current art practices. The formal ones serve to carry the value of novelty, conformity to modern technological platforms, the second – existential – a hardly compliable mix of tolerance and individuality (in terms of compliance with privacy), the third – values of authentication and multiplicativity. As the result of the study, the conclusion has been made that, despite the ironic pathos of postmodernism, art still remains a search space for new value configurations that represent the actual cultural architectonicsВ фокусе исследовательского внимания – сто лет истории современного искусства, условно – от живописной работы «Черный квадрат» Малевича (1915) до британского сериала «Черное зеркало» Брукера (2011) и фильма «Квадрат» Эстлунда (2017). Целью является анализ аксиологических оснований современного искусства. Актуальность избранного дискурса обусловлена, во‑первых, его непреходящей значимостью, во‑вторых, серьезными подвижками в архитектонике культуры – от новейших технологий как фактора культурного развития до порождаемых ими ментальных перверсий. На основании анализа предложенных произведений в качестве основных аксиомаркеров в области актуальных художественных практик выделены формальные, экзистенциальные и институциональные ценности. К первым предлагается отнести ценности новизны, соответствия современным технологическим платформам, ко вторым – сложно соблюдаемый микст толерантности и индивидуальности (в части соблюдения privacy), к третьим – ценности подлинности и мультипликативности. Делается вывод о том, что, несмотря на иронический пафос постмодерна, искусство все равно остается пространством поисков новых ценностных конфигураций, репрезентирующих актуальную культурную архитектоник

    Comprehensive computational investigations on various aerospace materials under complicated loading conditions through conventional and advanced analyses: a verified examination

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    Most failures develop as a result of a lack of resistivity information at the internal structure level during typical loading situations such as shock load and impact load. Impact loads have a significant impact on a component’s structural performance. A careful, organized examination of impact load settings and their side effects can reveal how well something can withstand peak loads. First, this study investigated the impact analyses on nine varied lightweight composite materials through a conventional experimental setup and computational tools. So, the best three lightweight materials are shortlisted for further investigation under complicated explicit analysis. Second, the study investigated the behavior of composite materials subjected to rapid loading circumstances in several real-time applications. The applications chosen include bullet crash analysis, unmanned aerial vehicle (UAV) propellers, and car bumpers. The three different principal composites, carbon fiber-reinforced polymer (CFRP), glass fiber-reinforced polymer (GFRP), and Kevlar fiber-reinforced polymer (KFRP), are selected and applied in crash analysis using ANSYS Workbench’s explicit technique-based finite element analysis (FEA). The comparison assessments are conducted using stumpy structural characteristics such as impact stress and equivalent strain. Two distinct grid convergence tests were performed to check whether the computational processes and discretization were correct. The standard methodologies were used on all three selected real-time applications, resulting in error percentages that were within acceptable bounds, ensuring the generation of dependable structural outputs. The ideal composite material is a Kevlar fiber-based composite with minimal defect affectability for all types of crash applications. Furthermore, multidisciplinary optimizations are performed, and the KFRP is verified to give good crash load resistance with reduced dense contribution

    Magnetic-plasmonic nanoparticles for multimodal bioimaging and hyperthermia.

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    257 p.El término "teranóstica" hace referencia a la integración inteligente de diagnósticos y terapias. Esta capacidad de obtener imágenes y tratar tumores simultáneamente con nanopartículas puede resultar ventajosa frente a las técnicas convencionales de diagnóstico y terapia. Así, una ventaja adicional tanto para la obtención de imágenes como para el tratamiento es poder estudiar las enfermedades in vitro utilizando diversos métodos de obtención de imágenes y combinándolos con tratamientos novedosos.La síntesis y optimización de nanopartículas híbridas que combinan propiedades magnéticas y plasmónicas se ha estudiado durante esta tesis. Además, estas nanoestructuras pueden funcionalizarse con moléculas adicionales para aplicaciones en imagen e hipertermia. La utilización de estas nanopartículas híbridas se ha estudiado para su uso específico como agentes de contraste para resonancia magnética, dispersión Raman mejorada en la superficie y microscopía de fluorescencia en modelos celulares 2D y 3D y en modelos ex vivo. Además, se ha evaluado la aplicación de los híbridos para calentamiento fototérmico en modelos celular 2D y 3D y etiquetado específico de células en modelos celulares 2D


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    Operational availability of naval aircraft through material readiness is critical to ensuring combat power. Supportability of aircraft is a crucial aspect of readiness, influenced by several factors including access to 9B Cognizance Code (COG) aviation consumable repair parts at various supply echelons. Rapidly evolving additive manufacturing (AM) technologies are transforming supply chain dynamics and the traditional aircraft supportability construct. As of June 2022, there are 595 AM assets within the Navy’s inventory—all for research and development purposes. This report simulates 9B COG aviation consumable fulfillment strategies within the U.S. Indo-Pacific sustainment network for a three-year span, inclusive of traditional supply support avenues and a developed set of user-variable capability inputs. Simulated probabilistic demand configurations are modeled from historical trends that exploit a heuristic methodology to assign a “printability” score to each 9B COG requirement, accounting for uncertainty, machine failure rates, and other continuous characteristics of the simulated orders. The results measure simulated lead time across diverse planning horizons in both current and varied operationalized AM sustainment network configurations. This research indicates a measurable lead time reduction of approximately 10% across all 9B order lead times when AM is employed as an order fulfillment source for only 0.5% of orders.NPS Naval Research ProgramThis project was funded in part by the NPS Naval Research Program.Lieutenant Commander, United States NavyApproved for public release. Distribution is unlimited