Geometric Scale Research Articles

The deflection platform phenomenon of functionally graded flexoelectric simply supported nanobeam

Direct flexoelectricity appears in dielectrics as a kind of coupling effect of electric field and elastic strain gradient. Its strong size dependence makes it effective in nanostructures. In this paper, based on the flexoelectric theory and mixed finite element method (FEM), the mechanical properties of the two-dimensional functionally graded (FG) flexoelectric nanobeam are studied, and the phenomenon of the deflection platform is found. By applying various types of loads to FG nanobeams, the influence of geometric parameters, length scale, and material distribution on the phenomenon of the deflection platform is discussed. According to the simulation results, it is found that the aspect ratio and the length scale of the beam will change the shape of the deflection platform, making it change regularly among various shapes. The geometric size will greatly increase the height of the platform, but it has little effect on the dimensionless deflection. Reasonable material distribution can enhance the internal coupling effect, increase the height of the platform and reduce the required load. Our results suggest that when studying nano-scale flexoelectric models, the deflection platforms or similar phenomena should be considered.

Geometric Distortion Correction of Images Received From Biometric Fingerprint Devices

The quality of fingerprint images is very important for recognition and identification in biometric systems. Geometric distortions and different image scales may worsen fingerprint recognition. It is necessary to adjust distortions and scale in biometric finger capture systems. Algorithms for correcting distortions and scale are investigated, analyzed, and developed in this paper. A polynomial model of second order is used as a mathematical model of spatial distortions. To correct the brightness of image points, bicubic interpolation is used.

Geometrical scale multiplier of the ring laser gyro with resonator containing a dielectric medium

An analysis of the literature shows that there are at least six qualitatively different analytical expressions for the geometric scale factor of a laser gyroscope with a flat- a mirror resonator containing a solid dielectric medium with a refractive index along the entire perimeter. According to one of these expressions, the parameter is inversely proportional to the value . In the article, is the expression for confirmed.

Numerical and Experimental Investigation on the Scaling Law of Strip Model Foundation on Cohesionless Soils

In this study, a revised scaling law for laboratory test models of strip foundations on cohesionless soils is proposed. The centrifuge model tests were conducted on a strip model foundation at four different gravity levels (1 g, 5 g, 7.5 g, and 10 g), and the test results were used to calibrate numerical simulations. A set of numerical models were created to simulate full-scale tests and laboratory-scale tests. From the numerical simulations, the behavior of a foundation in the centrifuge model test is similar to that of the full-scale test but is different from the behavior in the laboratory-scale test under the 1 g condition. A parametric study was performed by varying the key variables that are internal friction angle, foundation width, and gravitational acceleration. The stress scale ratio is approximate to the geometric scale ratio in the 1 g model test. However, the settlement conversion requires both the geometric scale ratio and the settlement scale ratio newly proposed. The settlement scale ratio increases with increasing the internal friction angle and geometric scale ratio; accordingly, an equation for calculating the settlement scale ratio is proposed.

Multi-Objective Optimization Design of Geometric Parameters of Atrium in nZEB Based on Energy Consumption, Carbon Emission and Cost

Through the detailed design of the passive design of the geometric parameters of the atrium, it is beneficial to achieve the design goal of a nearly zero-energy building. In the architectural design stage, the geometric design parameters of the atrium are verified and evaluated with different objectives such as energy consumption, carbon emissions, and costs, and then the most appropriate solution according to different design requirements is selected, which can reduce energy consumption and save costs. This paper proposes a method to optimize the energy consumption of a building’s atrium. Taking Jinan City as an example, this paper conducted 1260 energy consumption simulations for buildings with different geometric parameters of the atrium, based on the investigation of the geometric scale and energy consumption of the multi-story office buildings with near-zero energy consumption in cold areas with atriums. The degree of influence of each parameter on building energy consumption was determined. Finally, the parameter selection combination with the best effect is proposed. The results show that the selected four parameters are significantly related to energy consumption, and a new atrium design parameter was found through the combined analysis of the parameters: the body shape coefficient of the atrium. It was found that the importance of atrium design parameters on building energy consumption is as follows: the body shape coefficient of the atrium, the height-span ratio of the atrium (DSR), the atrium building volume ratio (VR), the skylight area ratio (SR), the atrium width-to-depth ratio (FDR). Seven groups of optimal design parameters were obtained by analyzing the design decisions with energy consumption as the target. Taking carbon emission and cost as the targets, three groups of optimal design parameters were obtained according to the Pareto frontier solution set, such as DSR = 2, VR = 0.13, SR = 0.1, and FDR = 2.5. It provides some references and ideas for the optimization of the energy consumption of the atrium of multi-story nearly zero-energy office buildings in the cold regions of China.

Multi-temporal Cloud Pixels Reconstruction Method for Optical Remote Sensing Satellite Images

Bachground: The existence of cloud pixels reduces the practicability of optical satellite remote sensing data. Existing problems: Existing cloud reconstruction methods generally cannot solve the following problems:(1)Large-scale thick cloud cannot be well reconstructed. (2)There are high requirements for reconstructed data. (3)Most data used to reconstructed are single temporal images. Ways: In order to overcome these problems, a new multi temporal weighted aggregation method is proposed. Specifically, we adopt a multi-temporal iterative aggregation method for cloud pixels to reconstruct and a multi-temporal weighted aggregation method for cloud shadow pixels to reconstruct. Result: Finally, the experiment proves that our method can quickly and accurately complete the cloud reconstruction, and under the effective uniform color strategy, a cloud- free image with accurate geometric position and uniform gray scale can be obtained. Conclusion: Experiments prove that the pixel reconstruction method proposed in this paper has achieved good cloud and cloud shadow pixel reconstruction effects in different types of ground objects.

An investigation into the effect of water injection parameters on synergetic mining of geothermal energy in mines

Cooling energy demands are high and increase with the mining depths in conventional mine cooling systems, which account for the most of the total energy consumption. The synergetic mining of mine geothermal energy (SMGE) is a subversive and promising approach for heat hazard control of deep mines with the advantage of low energy consumption and low cost. In this study, the similarity criteria for the similar simulation of SMGE are deduced by the equation analysis method, and the similarity criteria number between the full-scale model and the reduced-scale model is determined. Based on the geometric scale ratio of 1:100, a simulation experiment system including ventilation system and geothermal exploitation system is established. In addition, the influence of water injection parameters on cooling effect of roadway and heat recovery performance of the SMGE system is investigated. The results indicate that the temperature of surrounding rock is cooled gradually during the water injection and heat recovery in rock formation, which reduces the temperature increase rate of airflow in the roadway. When the injection water temperature is reduced from 28 °C to 11.5 °C, the cooling rate of roadway can be observable increased, but it results in a faster temperature decrease in production water with time. Increasing the water injection time from 35 min to 65 min will give rise to the temperature reduction degree of surrounding rock and decrease to the temperature increase rate of airflow in roadway. And the time of water injection is directly proportional to the water production flow rate in production well, but inversely proportional to the temperature in production water. A high injection rate facilitates the cooling rate of the roadway and increases the range of heat recovery in formation, but a small flow rate can achieve a better ultimately cooling effect under the same total water injection volume. Decreasing the water injection rate from 1.6 L/min to 0.6 L/min will increase the time of stable production flow and the rate of reduce in water temperature in the production well. Furthermore, changes in the level of the injection well position will result in different injected water seepage characteristics, which affects the cooling effect of roadway and heat recovery performance of the SMGE system simultaneously.

Investigations of Hydrodynamic Force Generated on the Rotating Cylinder Implemented as a Bow Rudder on a Large-Scale Ship Model

This paper presents experimental studies of the force generated on the rotating cylinder implemented as a bow rudder on a large-scale ship model. The research focused on the maneuverability of the unit equipped with a rotating cylinder (RC) in the front part of the model and its future use as a steering device on small draft river barges. The study presented in this paper is a continuation of the research carried out using the small physical model of a river push train in 1:20 geometric scale equipped with two bow RCs and open water tests of separated rotating cylinders carried out in a flume tank. The experimental test setup with RC installed on the model in 1:24 geometric scale allowed to compare the parameters of standard maneuvers performed with the use of RC and without it. The proposed method based on the measurement of the ship model trajectory during maneuvers allowed to compare the hydrodynamic steering force generated by RC with the steering force generated by the conventional stern spade rudder. The results of the experiments compared with empirical models show a similar trend. RC dynamics was tested for rotational speeds up to 570 RPM (revolutions per minute) and ship model velocity up to 1 m/s. The rotating cylinder generated velocity field is presented and phenomena influencing the generated hydrodynamic force are discussed.

Characterizing vibrational behavior of a large airship based on scaled model test and analysis

PurposeThis study aims to assess the vibrational behavior of a large transport airship based on finite element (FE) simulation and modal testing of its scaled model.Design/methodology/approachA full-size parametric FE model of the airframe was established according to the structural layout of the composite beam-cable airframe of the airship, and vibrational analysis of the airframe was conducted. The influence of cable pre-tension load on the inherent properties of the airframe was investigated. Based on the simplification of the full-size FE model, scaled numerical and test models of the airframe, with a geometric scale factor of 1:50, were established and built.FindingsThe simulation and test results of the scaled models indicated that the mode shapes of the full-size and scaled models were similar. The natural frequencies of both the full-size and scaled models complied with the theoretical similarity relation of the frequency response.Originality/valueThis study demonstrated that the vibrational test results of the scaled model with very large scaling can be used to characterize the modal properties of the beam-cable airframe of a large transport airship.

Brain-Inspired Navigation Model Based on the Distribution of Polarized Sky-Light

This paper proposes a brain-inspired navigation model based on absolute heading for the autonomous navigation of unmanned platforms. The proposed model combined the sand ant’s strategy of acquiring absolute heading from the sky environment and the brain-inspired navigation system, which is closer to the navigation mechanism of migratory animals. Firstly, a brain-inspired grid cell network model and an absolute heading-based head-direction cell network model were constructed based on the continuous attractor network (CAN). Then, an absolute heading-based environmental vision template was constructed using the line scan intensity distribution curve, and the path integration error was corrected using the environmental vision template. Finally, a topological cognitive node was constructed according to the grid cell, the head direction cell, the environmental visual template, the absolute heading information, and the position information. Numerous topological nodes formed the absolute heading-based topological map. The model is a topological navigation method not limited to strict geometric space scale, and its position and absolute heading are decoupled. The experimental results showed that the proposed model is superior to the other methods in terms of the accuracy of visual template recognition, as well as the accuracy and topology consistency of the constructed environment topology map.

Reduced modelling and global instability of finite-Reynolds-number flow in compliant rectangular channels

Experiments have shown that flow in compliant microchannels can become unstable at a much lower Reynolds number than the corresponding flow in a rigid conduit. Therefore, it has been suggested that the wall's elastic compliance can be exploited towards new modalities of microscale mixing. While previous studies mainly focused on the local instability induced by the fluid–structure interactions (FSIs) in the system, we derive a one-dimensional (1-D) model to study the FSI's effect on the global instability. The proposed 1-D FSI model is tailored to long, shallow rectangular microchannels with a deformable top wall, similar to the experiments. Going beyond the usual lubrication flows analysed in these geometries, we include finite fluid inertia and couple the reduced flow equations to a novel reduced 1-D wall deformation equation. Although a quantitative comparison with previous experiments is difficult, the behaviours of the proposed model show, qualitatively, agreement with the experimental observations, and capture several key effects. Specifically, we find the critical conditions under which the inflated base state of the 1-D FSI model is linearly unstable to infinitesimal perturbations. The critical Reynolds numbers predicted are in agreement with experimental observations. The unstable modes are highly oscillatory, with frequencies close to the natural frequency of the wall, suggesting that the observed instabilities are resonance phenomena. Furthermore, during the start-up from an undeformed initial state, self-sustained oscillations can be triggered by FSI. Our modelling framework can be applied to other microfluidic systems with similar geometric scale separation under different operating conditions.

Seismic Response of a Liquefiable Site-Underground Structure System

To study the dynamic response of a saturated sand-underground structure system subjected to earthquakes, a series of shaking table tests with a geometric scale ratio of 1/30 were conducted. Based on the experimental acceleration records of testing soil deposits, the relationship between dynamic shear stress and horizontal soil displacement was analyzed by the 1D shear beam inverse calculation method. Meanwhile, the development law of the equivalent dynamic horizontal subgrade reaction coefficient and the dynamic strain of the sidewall in the underground structure has also been discussed. The testing results indicate that the dynamic shear stress of the soil deposit under the bottom plate of the underground structure is larger than that of the soils surrounding the sidewall and above the roof plate; in addition, the soil displacement tends to decrease with the buried depth. The dynamic shear stress–displacement hysteretic loop of the soil deposits tends to be plump as the input amplitude increases. The spectral characteristics of ground motions obviously influence both the dynamic shear stress–displacement hysteretic curve and the excess pore water pressure ratio of saturated sand soil, especially under medium and strong excitations. The equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of soil depth, and the difference between the coefficient above and underneath the underground structure model can reach 7.589 MN/m3. On the contrary, the equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of the input amplitude of ground motions, and the maximum reduction ratios of the coefficient are 74.4%, 66.7%, and 47.3%, corresponding to the El-Centro, Kobe, and Wolong ground motions, respectively. The soil liquefaction has a certain effect on the equivalent dynamic horizontal subgrade reaction coefficient. In general, the dynamic strain at the top of the sidewall in the underground structure is higher than that at the bottom of the sidewall, which illustrates that the deformation of underground structures is in good agreement with the seismic deformation mode of soil deposits.

Physical model test and parametric optimization of a hydroelectric generating system with a coaxial shaft surge tank

The novel structure of the surge tank is often designed in hydropower stations, for example, the Coaxial Shaft Surge Tank (CSST). Reasonable mathematical modeling and physical model verification are effective methods in dealing with novel structure tanks. This study aims to analyze the influence of geometric and hydraulic parameters on the hydraulic characteristics of the Hydroelectric Generating Systems (HGS) with CSST in the transient process. First, the mathematical model of CSST and the physical model of HGS with a geometric scale of 42.33 are established. The correctness of the mathematical model is verified by the physical model test. Second, an evaluation method is proposed to optimize the specific transient parameters of HGS. The results show that the sensitivity coefficient of the diversion tunnel diameter to the highest surge in CSST is 6.09, and the impedance hole coefficient φ of CSST to the maximum water hammer pressure of the spiral casing reaches 13.47. The results also indicate that changing the diameter of the penstock can adjust the maximum water hammer pressure while keeping the surge wave in CSST unchanged. This research provides design guidance and a theoretical basis to design HGS and improve its operational safety.

Multi-electrode piezoelectric plates as non-reciprocal metamaterials

Non-reciprocal transmission of elastic waves through a solid is an exciting phenomenon that could open up new applications for elastic metamaterials. Non-reciprocal transmission of elastic waves can be achieved with spatio-temporally modulated boundary conditions. Some previous studies of non-reciprocal metamaterials have used uniformly modulated piezoelectric patches on metal host beams. Those beams have the advantage of electrically tunable boundary conditions due to the electro-mechanical coupling in piezoelectric patches, but are multi-material composites that are not easy to scale down. Instead, we show multi-electrode (patterned) piezoelectric plates, which are practical for a large range of geometric scales and frequencies, can exhibit non-reciprocal transmission with spatio-temporally modulated shunted circuits connected to the electrodes. In this work a study of sub-wavelength, ultrasonic band gaps that arise from shunted circuits on piezoelectric plates will be presented. The achievement of spatio-temporal modulation by using time-modulated capacitor-inductor circuits that vary in phase with their neighbors will be discussed. The results of frequency domain simulations of non-reciprocal transmission will be presented, and future directions for this research will be discussed. [Work funded by the Office of Naval Research.]

Application of Rotationally Symmetrical Triangulation Stereo Vision Sensor in National Dance Movement Detection and Recognition

Information acquisition is an important branch of information science. It is the product of the development and cross-integration of traditional sensing technology and other multidisciplines. It is characterized by the high precision, high speed, integration, and intelligence of information acquisition. An important part of information acquisition, it studies how to acquire the geometric structure and scale information of objects in three-dimensional space. With the continuous development of the level, the acquisition of 3D information has become more and more important in scientific research and industrial production. This paper takes 3D information acquisition technology as the main line. From the perspectives of fusion, effectiveness, physical limit, and measurement efficiency, high-resolution 3D information acquisition techniques are studied. In this paper, the upper and lower limb movements of each behavioral segment are segmented according to the difference. An omnidirectional stereo vision sensor composed of a single camera and two secondary conical mirrors is designed, which solves the problems of large size, narrow field of view, and asynchronous image acquisition of traditional binocular vision sensors, effectively ensuring image perspective. The invariance of projection avoids image distortion caused by curved mirror imaging and reduces the difficulty of subsequent work. The three-dimensional Delaunay triangulation algorithm is used to replace the traditional Poisson reconstruction algorithm to generate the triangular mesh model. The triangular mesh model obtained by the multiview stereo reconstruction algorithm is relatively rough. This article uses Zbrush’s ZRemesher and geometric-divide functions to smooth and simplify the model. The results show that the accuracy of the algorithm proposed in this paper is as high as 89.25% in the motion recognition of body elements. The dynamic mapping method is used to map the texture of the triangular mesh model, so that the realism of the model reaches 91.23%.

Hydraulic Performance of Geotextile Sand Containers for Coastal Defenses

Laboratory experiments were performed in the wave flume of the Laboratorio di Idraulica e Costruzioni Marittime of the Università Politecnica delle Marche (Ancona, Italy) to study the hydrodynamic performance of coastal protection structures made of a new type of geotextile sand containers (GSCs). Such structures are used as softer and flexible alternatives to traditional hard coastal defenses made of concrete or rubble mound material. The GSC structures can also be used as temporary coastal protections during the winter period. The physical model reproduced two main configurations: in the former one, the GSCs were used as coastal revetments with three different slopes. In the latter one, the GSCs were applied to make detached submerged breakwaters with different submergences and berm widths. The geometric scale of the models was 1:10, and the weight of each GSC in the prototype was 5 t. The geotextile material of the containers and the wave characteristics were reproduced by using the Reynolds and the Froude similarity criteria, respectively. Reflection coefficients and hydraulic stability behaviors for the revetments, as well as transmission coefficients and piling-up amount for breakwaters, were obtained.

Static pushover test of spring-underground structure system for seismic performance analysis of underground structure

The static test is appropriate for studying the seismic performance of underground structures due to the large size of the model structure and the controllable stress level. By setting elastic elements around the model structure, the static pushover test of the spring-underground structure system could simulate the initial stress state of the underground structure and soil-structure interactions during the pushover process. Taking the Daikai subway station damaged in the 1995 Hanshin earthquake in Japan as the model structure, a series of static pushover tests of underground structures with a geometric scale of 1/5 were performed. The impact of vertical ground motion on the seismic performance of underground structures was studied by conducting two static pushover tests of spring-underground structure system under different vertical loads; the impact of surrounding soil on the seismic performance and failure process of underground structures was studied by conducting static pushover tests with and without springs under the same vertical load. The relationship between the horizontal pushover force and the structural interstory drift, the concrete strain change process of structural weak vertical member, the structural failure phenomenon, and the seismic performance of the test object can be obtained from the tests, which can provide valuable information for experimental research on the seismic performance of underground structures. The test results demonstrate that the vertical ground motion decreases the ductility of underground structure, and the surrounding soil improves the lateral collapse resistance of underground structure.

Design and operational considerations of packed-bed membrane reactor for distributed hydrogen production by methane steam reforming

Methane steam reforming will still account for most of hydrogen production in the coming decades. Membrane reactor can play a key role in both energy saving and process/equipment compactness, particularly for its decentralized applications. Here we design a particles-based packed-bed membrane reactor and explore the operational window and design challenges by conducting systematic study experimentally and computationally, particularly emphasizing geometrical scale of membrane reactor and catalyst activity. The results show that membrane reactor presents maximum hydrogen flux by consuming unit methane under the optimized operation conditions of GHSV (i.e., 1134 hr−1) and steam-to-carbon ratio (i.e., 2), and computational study shows that optimal operation window is around 30 atm and 773.15 K. Moreover, the design criteria of “Catalyst activity – Membrane performance – Radial depth” is revealed quantitatively and catalyst activity is identified as the key limiting factor for further process intensification. Briefly, these results shed some lights on operation, optimal design, and further improvement of membrane reactor in methane steam reforming.

Geometric linguistic scale and its application in multi-attribute decision-making for green agricultural product supplier selection

Establishing long-term cooperative relationships with reliable suppliers of green agricultural products is essential to the sustainable development of fresh supermarkets. Qualitative attributes in such a multi-attribute decision-making problem have spawned the analyses on linguistic evaluations that are close to people's cognition and expression habits. There is still a challenge to capture the mathematical implications of linguistic evaluations and link them with decision-maker's psychology. To address this issue, this paper introduces a geometric linguistic scale which is characterized by the proportional relations between progressive grades and their corresponding fuzzy implications. Aggregation methods based on the geometric linguistic scale are developed to handle decision matrices with direct linguistic evaluations, full pairwise comparisons and partial pairwise comparisons, respectively. A consistency repairing process is presented to improve the reliability of pairwise comparisons. We further investigate a real-world problem concerning green agricultural supplier selection to illustrate the proposed method. The rational range of the scale parameter and consistency index are analysed through a sensitivity analysis.

Experimental complex flow patterns in the pump intake with a low water level

The present paper is an extension of the authors’ previous work [1], and the goal is to analyze and reveal the complex flow patterns in the pump intake with a low water level (lower than the critical water level) through PIV Technology (Particle Image Velocimetry). The results show that: the lower the water level (a) the geometric scale of the free-surface vortices increases, which potentially leads to pulling more air into the pipe system and the pump units of the pump station; (b) the sidewall-attached vortices have a larger geometric scale; (c) more backwall- and floor-attached vortices are captured, and their geometric scale is large. In brief, the experimental data of the paper indicate that the free-surface, backwall-, and floor-attached vortices are the main characters of the pump intake with a low water level. In engineering, the vortex suppression/eliminating devices in the vicinity of these locations should be emphasized.