Minimum Allowable Length Research Articles

Multiscale study on determining representative volume elements size for mechanical behaviours of complex polymer nanocomposites with nanoparticulate agglomerations

Representative volume elements (RVE) have been widely employed to describe and predict the various effective properties of heterogeneous composite systems. In this present study with an interphase property degradation model, a multiscale analysis is performed to investigate the mechanical behaviours of polymer nanocomposites containing nanoparticulate agglomerations. Using the Fourier transform approach on the structural property variation at given cell lengths, the smallest RVE size (the minimum allowable length for an approximate description of the material system) is determined based on the coefficient of variation. It is reasonable to select an RVE size that is equal to a quarter of the most dominant wavelength as the minimum RVE size. A novel user-defined factor-based approach similar to the concept of margin of error is proposed to determine the optimal sampling number at a specific RVE size. The precision approach can provide accurate estimation of the mechanical properties of the nanocomposites with reduced computational cost.

Special Limit Condition Of Reinforced Concrete Structures And Its Normalization

One of the ways to improve the resilience of buildings in the event of failure of the bearing structure or emergency, seismic effects is a more complete account of the behavior of elements and their mates at short-term action of loads and dynamics of change of the scheme of the bearing system of the building. To do this, it is advisable to allow more cracks to open, the development of deflections and partial destruction of some sections, which contradicts the current criteria for the first and second limit states that ensure the operational suitability of structures and buildings. Therefore, it is necessary to introduce specific standards of a special limit state for structures. A special limit state is the stage of operation of the structure after reaching the load-bearing capacity for the first and the deformation limits for the second limit states. Exceeding this state, in which the structures do not fully meet the functional requirements, leads to their collapse. The implementation of this limit state is most appropriate in load-bearing systems with a high degree of static indeterminability and constructive interaction of all bearing elements. The introduction and consideration of a special limit stress-strain state of reinforced concrete structures make it possible to detect significant strength and deformation reserves, even after significant fragmentation of the compressed concrete zone and, as a result, reducing the working section of the structure. As the main criteria of a particular limit state for reinforced concrete structures, it is recommended to adopt: the ultimate deformations of compressed concrete and tensile reinforcement with higher values than permissible under normal conditions; as well as the deflections of elements, provided that the minimum allowable length of the zone of bearing and anchorage of reinforcement.

Визначення мінімально припустимої довжини рукава пожежного кран-комплекту

Визначення мінімально припустимої довжини рукава пожежного кран-комплекту

Clear Structural Topology Optimization Designs Including Minimum Allowable Length Scale Limit on Fabrication Holes

Clear Structural Topology Optimization Designs Including Minimum Allowable Length Scale Limit on Fabrication Holes

К ВОПРОСУ О ЦЕЛЕСООБРАЗНОСТИ ИЗМЕНЕНИЯ ПРОМЫСЛОВЫХ МЕР НА ПРОМЫШЛЕННЫЙ ВЫЛОВ ВОБЛЫ И СОМА В ВОЛГО-КАСПИЙСКОМ БАССЕЙНЕ (АСТРАХАНСКАЯ ОБЛАСТЬ)

Fisheries measures is an instrument allowing to regulate fish catch pressing to the aquatic bio-resources stocks. Roach and sheatfish are the species which are exploited in industrial and amateur fisheries of the Volga-Caspian basin (the Astrakhan region). According to the Fishery Regulations, today the minimum allowable length for roach is 17 centimeters, and for sheatfish it is 60 centimeters. According to the results of retrospective analysis of stocks dynamics, commercial catch of roach and cheatfish, experience in changing fisheries measures for roach and sheatfish in the Volga-Caspian basin, changing fisheries measures for these species has been found inexpedient. The current fisheries measures for commercial catch of roach allows to exploit only the reproductive part of the population, minimizing losses of restocking. Also, the work shows that a change of fisheries measures for sheatfish will lead to the decrease of the commercial catch of sheatfish and objects of its ration. In general, it must be stressed that changing fisheries measures will lead to redistribution of roach and sheatfish catches between the main participants (commercial fishers, amateur fishers and poachers), but not in favor of the official fish catching

Maximizing bandgap width and in-plane stiffness of porous phononic plates for tailoring flexural guided waves: Topology optimization and experimental validation

Phononic crystal plates (PhPs) with porous heterogeneities manufactured through perforation of a uniform plate comprise effective wave reflecting interfaces and are free from complexities and interfacial imperfections associated with fabricating bi-material designs. However, numerical optimization of such porous PhPs for maximized bandgap efficiency naturally leads to topologies with isolated solid domains, or disconnected island-like features. Requiring PhPs to exhibit an adequate stiffness is, therefore, an important design consideration. This paper presents a multi-objective topology optimization study with experimental validation to explore the relationship between bandgap efficiency and effective in-plane stiffness, introducing topologies exhibiting superior properties compared to those reported in earlier works. Topology optimization is performed in two stages: first, at a relatively coarse resolution followed by a topology optimization on a refined mesh. The minimum allowable length scale of features is maintained across the mesh refinement, and thus the refined stage primarily leads to optimization of the feature boundaries, which is shown to significantly enhance response. Bandgap of fundamental flexural guided wave modes is studied herein, and it is shown how bandgap efficiency is degraded by increasing the in-plane stiffness. Distinct stiff and compliant topology modes are realized in the intermediate section of the optimized Pareto fronts which offer variation of structural stiffness while having almost the same bandgap efficiency, with potential application as base cells in design of gradient phononic lattices. A subset of promising stiff and compliant optimized topologies are manufactured by water-jetting of an aluminum plate and experimentally tested to validate the calculated bandgap efficiencies and effective elastic properties.

Traffic Control Strategy for a Surface Street on an Expressway-Arterial Corridor

Off-ramp area congestion and off-ramp queue spill over are wide-spread reasons for expressway traffic jams in China. A control strategy was developed to reduce the number of collisions between expressway and surface street vehicles and to reduce spill over by controlling the surface street vehicles to improve the traffic conditions near expressway off-ramps. This control algorithm monitors the traffic conditions at the off-ramp using occupancy rates and a performance index for the surface street vehicles, and then optimizes the control signal split and cycle length for the surface street vehicles assuming that the off-ramp queue is shorter than the minimum allowable length. Simulations indicate improvements in the traffic flow with the average vehicle travel time nearly 10% less and the off-ramp queue reduced significantly.

Topology optimization with multiple phase projection

Topology optimization is a powerful tool capable of generating new solutions to engineering design problems. While these designs may offer optimal performance in a computational setting, it is not uncommon for them to be impractical or unrealizable from engineering or fabrication points-of-view. This challenge motivates the present work. A methodology is proposed for restricting the minimum length scale of each material phase used in the design. The technique allows a designer to, for example, prescribe a minimum allowable length scale of structural members (solid phase) as well as the minimum allowable length scale on holes (void phase). The proposed approach utilizes the Heaviside Projection Method (HPM) to continuum topology optimization. Each material phase is associated with a design variable field that is projected onto element space using regularized Heaviside functions. The fields are independently projected and the resulting distributions are assembled to yield topology. The technique is demonstrated on classic topology optimization problems including minimum compliance, heat conduction, and compliant mechanisms. Solutions are shown to be near-discrete topologies satisfying minimum length scale criterion placed on each phase. Control over length scale is achieved implicitly and therefore the technique does not require additional constraints.

Constructal design of a thermoelectric device

Finite time thermodynamics, a subfield of irreversible thermodynamics, is employed to model a cascaded thermoelectric generator, which incorporates all the essential features of a real heat engine. Control volume formulation of a cascaded thermoelectric element was carried out over a small but finite temperature gap to comply with the principles of irreversible thermodynamics. Three important dimensionless parameters are identified to designate poor Thomson effect; low thermal conductivity and low electrical resistivity of a good semiconductor or semimetal. For ideal values of these parameters it has been demonstrated that exactly half of the Joulean heat arrives at both hot and cold junction when temperature maximum passes through the longitudinal center of the thermoelectric element. In general when Thomson heat cannot be neglected, the maximum and the minimum permissible length of any individual module of a cascaded thermoelectric device is predicted involving thermoelectric properties of the materials and passing current. It is observed that maximum permissible length is devoid of dependence on applied temperature gradient whereas the minimum allowable length is not. When half the Joulean heat affects hot end and half the cold side, thermal conductance inventory is allocated equally between the high and low temperature side for best possible device performance. Finally, it has been argued that the choice of constancy of total conductance is not only a natural constraint but also a purely realistic design criterion for heat engines or refrigerators. Such design prescriptions those lead to the prediction of shape and structure in any flowing system is reported in open literature as constructal principle.

Predicted curvatures and stresses in a fiber-optic interconnect subjected to bending

Simple formulas are obtained for the evaluation of the curvatures and stresses in a fiber-optic interconnect subjected to mechanical bending due to linear and angular misalignments of its end cross-sections. In addition, it is shown how to consider the compression caused by the thermal contraction mismatch of the glass material with the material of the enclosure. The obtained formulas can be helpful when predicting the added transmission losses and the maximum stress in optical interconnects experiencing bending. Particularly, they enable one to establish the allowable misalignments in, and/or the minimum allowable length of, the interconnect, which are permissible from the standpoint of its optical performance and mechanical reliability.

Bending performance of clamped optical fibers: stresses due to the end off-set

Misalignment of the openings in the frame and the terminal fixture could cause significant bending stresses in an optical fiber located within this frame. We developed simple and easy-to-use formulas which enable one to evaluate these stresses and determine the minimum allowable length of the clamped portion of the fiber for the given misalignment. Our stress analysis model considers the favorable effect of the fiber coating compliance. The results can be of help in the physical design of optical interconnects with misalignments.