Under proper loading conditions, micro-to-nanoscale heterogeneities (i.e., the bond system) that are commonly found within the materials of a system can coalesce until causing macroscopic alterations of the system properties. The bond system is responsible for atypical and invariant-scale non-linear elastic processes in granular media, from laboratory-tested materials (mm) to the Earth’s crust (km). The unusual observed behavior involves slow recovery, or relaxation, of the elastic properties after dynamic loading. Several models have been designed to explain non-linear elasticity, although their physics is still partially unknown. Here, we show that recovery processes are also observed at intermediary scales (m) in civil engineering structures, and that they might be related to structural health due to the healing of cracks. For Japanese buildings subjected to earthquakes, we observe rapid co-seismic reductions of their resonance frequency, followed by fascinating recoveries over different time-scales: over short times (i.e. seconds) for a single earthquake; over intermediate times (i.e. months) for a sequence of aftershocks; and over long times (i.e. years) for a series of earthquakes. By comparing two buildings with different damage levels after the 2011 Tohoku earthquake, we show how relaxation models can characterize the level of cracking caused by damaging events. Our results bridge the gap between the laboratory and seismological observation scales, verifying in this way the universality of recovery processes, and demonstrating their value for the detection and characterization of damage.
A study is considered to a steady, two-dimensional boundary layer flow of an incompressible MHD fluid for the Blasius and Sakiadis flows about a flat plate in the presence of thermo-diffusion (Dufour) and thermal-diffusion (Soret) effects for variable parameters. The governing partial differential equations are transformed into a system of nonlinear ordinary differential equations using similarity variables. The transformed systems are solved numerically by Runge-Kutta Gills method with shooting techniques. The variations of the flow velocity, temperature and concentration as well as the characteristics of heat and mass transfer are presented graphically with tabulated results. The numerical computations show that thermal boundary layer thickness is found to be increased with increasing values of Eckert number (Ec), Prandtl number (Pr) and local Grashof number (Gr_x) for both Blasius and Sakiadis flow. The Blasius flow elevates the thickness of the thermal boundary layer compared with the Sakiadis flow. The local magnetic field has shown that flow is retarded in the boundary layer but enhances temperature and concentration distributions.
High duty engineering component life is usually demonstrated through extensive testing and statistical analysis applied to empirical curve-fit equations. Because of this, the extent of the testing required is huge and costly: it must consider the load cycle range and test to high numbers of cycles. Furthermore, this testing must be repeated for every material, method of manufacture, and subsequent post-processing. Additive Manufacturing (AM) for high duty components has brought to the fore the question of the effect of porosity and surface roughness on fatigue life. Because there is relatively little service life experience, it is possible that the testing approach could also fail to represent conservatively the true life of a critical component. The authors propose the development of a fatigue model based on well-established engineering physics principles, by creating computational specimens with modelled surface roughness and porosity, and subjected to cyclic loading using Finite Element Analysis. They show that the combination of roughness features and sub-surface pores leads to an equivalent plastic strain distribution pattern that suggests an emergent physical process. Such a phenomenological understanding of the fatigue failure process should lead to improved life prediction techniques, more cost effective test procedures, and the development of better AM methods.
Reduction in the torsional vibration of heavy rotors like turbo-generator rotor is important for the safe and efficient functioning of the power plant. In this paper theoretical study is performed to control the torsional vibration in the turbo-generator rotor using piezoelectric material as sensor and actuator. Polyvinylidene fluoride (PVDF) layer is used as sensor and actuator. Proportional and velocity feedback is used as control law. The variation in the electromagnetic torque of synchronous generator during various electrical faults is evaluated using dq0 model. Finite element method is used to model the rotor elements. The coupled equations are solved in MATLAB using Newmark-beta integration method. The coupling elements of turbine and generator are most susceptible to the shear failure so torsional vibration of coupled rotor on coupling elements are compare for controlled and uncontrolled scenario. Simulation results show that for actively controlled rotor significant reduction in the amplitude of torsional vibrations is observed.
Aerospace components and its coatings are required to possess excellent surface properties namely: fatigue, wear and corrosion resistance over a wide temperature range. Stainless steels, titanium, nickel superalloy and more recently high entropy alloys have been used to improve the exterior properties of these components. In this study, AlCoCrFeNiCu and AlTiCrFeCoNi High Entropy Alloys were successfully fabricated using laser additive manufacturing to produce coatings on a mild steel base plate. The influence of the laser parameters (laser power and scan speed) on the microstructure, hardness and coat geometry (height, width and depth) were also investigated. The results revealed that coatings homogeneously adhered to substrate. The optimum processing parameters for both alloys with defect free structures at a preheat temperature of 400 °C, were at 1200-1600 W at 8-12 mm/s with the layers composed of both FCC and BCC phases. The laser parameters affected the geometry, quality and hardness. The results showed that optimizing the laser parameters achieved by preheating temperature invariably improved the performance of the alloys with potential coatings and aerospace structural applications.
Simulated microgravity (s-µg) devices provide unique conditions for elucidating the effects of gravitational unloading on biological processes. However, s-µg devices are being increasingly applied for mechanobiology studies without proper characterization of the mechanical environment generated by these systems, which confounds results and limits their interpretation. Furthermore, the cell culture methodology central to s-µg approaches introduces new conditions that can fundamentally affect results, but these are currently not addressed. It is essential to understand the complete culture environment and how constituent conditions can individually and synergistically affect cellular responses in order to interpret results correctly, otherwise outcomes may be misattributed to the effects of microgravity alone. For the benefit of the growing space biology community, this article critically reviews a typical s-µg cell culture environment in terms of three key conditions: fluid-mediated mechanical stimuli, oxygen tension and biochemical (cell signalling). Their implications for biological analysis are categorically discussed. A new set of controls is proposed to properly evaluate the respective effects of s-µg culture conditions, along with a reporting matrix and potential strategies for addressing the current limitations of simulated microgravity devices as a platform for mechanobiology.
Two filters using Defected Ground Structures have been proposed. First, a multiple frequency band stop filter utilizing a semi-H defect in the ground plane is presented. This structure is then prototyped on a Rogers 4350B substrate of overall size 45 mm $\times$ 15 mm, and external SMD capacitors have been employed to control the resonance of the circuit, for the stopband frequencies of 433 MHz, 700 MHz and 915 MHz. An equivalent circuit is also proposed for this multi-band design. The second filter is a combination of a band-stop and band-pass filter in one structure. The filter, operating with a controllable passband and stopband frequency is fabricated, on Rogers 4350B lossy substrate, to validate the EM and circuit simulation results. Two SMD capacitors have been loaded in the filter to control the pass band and stop band frequencies of the filter with a structure size of 20 mm x 20 mm. Furthermore, a novel equivalent circuit model encompassing the band-pass and band-stop frequency response of the DGS based filter is proposed.
In the biopharmaceutical industry, Raman spectroscopy is now a proven PAT tool that enables in-line simultaneous monitoring of several CPPs and CQAs in real-time. However, as Raman monitoring requires multivariate modeling, variabilities unknown by models can impact the monitoring prediction accuracy. With the widespread use of Raman PAT tools, it is necessary to fix instrumental variability impacts, encountered for instance during a device replacement. In this work, we investigated the impact of instrumental variability between probes inside a multi-channel analyzer and between two analyzers, and explored solutions to correct them on model prediction errors in cell cultures. We found that the Kennard Stone Piecewise Direct Standardization (KS PDS) method enables to lower model prediction errors and that only one batch with the unknown device in the calibration dataset was sufficient to correct the prediction gap induced by instrumental variability. As a matter of fact, during device replacement a first cell culture monitoring can be performed with the KS PDS method. Then, the new data obtained can be inserted in the calibration dataset to integrate instrumental variability in the chemometric model. This methodology provides good multivariate calibration model prediction errors throughout the instrumental changes.
This is a fundamental study addressing the articulation of knowledge from the context of the fourth industrial revolution (Industry 4.0). Industry 4.0 employs embedded systems (e.g., cyber-physical systems) to perform cognitive tasks. These systems cannot work without applying digitized knowledge. As a result, the digitization of knowledge-intensive activities (knowledge acquisition, representation, dissemination, utilization, and management) is critical for Industry 4.0. Before digitizing the knowledge and knowledge-intensive activities, a fundamental question arises: What is knowledge in Industry 4.0? This study answers this question. In doing so, this study first reviews the definitions of knowledge reported in the extant literature of epistemology, engineering design, manufacturing, organization science, information science, and education science. This study then defines that a piece of knowledge consists of three elements, namely, claim, provenance, and inference. Such a definition helps overcome the circularity and ambiguity in the definitions of knowledge reported so far. This definition results in four types of knowledge, namely, definitional, deductive, inductive, and creative knowledge. These types of knowledge are exemplified using some real-life scenarios relevant to engineering design and manufacturing. The exemplified pieces of knowledge are also represented by using knowledge graphs (concept maps) so that the contents can easily be digitized for human and machine learning. The outcomes of this study are the fundamentals based on which more sophisticated methods and tools can be developed to perform the cognitive tasks relevant to Industry 4.0.
In this paper, a highly robust antenna for omnidirectional circular polarized communication in the harsh environment at 2.45 GHz ISM frequency band is proposed based on a transparent structure. Circular polarization has been realized utilizing a combination of two magnetic and electric dipoles. The antenna is covered with a quarter wavelength layer of plexiglass to achieve desired robustness and visible light transparency. Meanwhile, it can integrate with solar cells because of the high transparency of glass to simultaneously propagate signals and harvest energy. The gain and bandwidth of the antenna are 1.7 dBi and 300 MHz, respectively. The antenna's axial ratio is achieved less than 3 dB within the bandwidth showing circular polarization behavior. The proposed compact antenna is numerically and experimentally analyzed and compared together, having a suitable agreement. In another aspect, the structure can give promising openings to enhance the propagating properties, which could generate critical advantages for real-world multifunctional applications.