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In this paper, a unified method is developed to analyze free vibrations of the three-layer functionally graded cylindrical shell with non-uniform thickness. The middle layer is composed of two-dimensional functionally gradient materials (2D-FGMs), whose thickness is set as a function of smooth continuity. Four sets of artificial springs are assigned at the ends of the shells to satisfy the arbitrary boundary conditions. The Sanders’ shell theory is used to obtain the strain and curvature-displacement relations. Furthermore, the Chebyshev polynomials are selected as the admissible function to improve computational efficiency, and the equation of motion is derived by the Rayleigh–Ritz method. The effects of spring stiffness, volume fraction indexes, configuration on of shell, and the change in thickness of the middle layer on the modal characteristics of the new structural shell are also analyzed.

Image dehazing aims to recover a clean image from a hazy image, which is a challengingly longstanding problem. In this paper, we propose an Ensemble Multi-scale Residual Attention Network (EMRA-Net) to directly generate a clean image, which include two parts: a three-scale residual attention CNN (TRA-CNN), and an ensemble attention CNN (EA-CNN). In TRA-CNN, we employ wavelet transform to obtain the downsampled images, instead of using common spatial downsampling methods, such as nearest downsampling and strided-convolution. With the help of wavelet transform, we can avoid the loss of image texture details. Moreover, in each scale-branch, Res2Net modules are connected in series to make full use of the hierarchical features from the original hazy images, and channel attention mechanism is introduced to focus channel-dimension information. Finally, an EA-CNN is proposed to fuse coarse images generated from TRA-CNN into a refined clean image. Extensive experiments on the benchmark synthetic hazy datasets and the real-world hazy dataset prove that proposed EMRA-Net is superior to previous state-of-the-art methods both in subjective visual perception and objective image quality assessment metrics.

Recent decades have witnessed an increasing number of studies investigating petroleum systems with the application of rhenium-osmium (Re-Os) isotopic geochemistry. Here, we review the use of the 187Re-187Os geochronometer with respect to the geochemical behaviour of rhenium and osmium in hydrocarbon-related geological processes. The Re-Os budget in hydrocarbon source rock predominantly originates from natural water columns during its deposition. Open seawater tends to have a homogeneous Os isotopic composition because its residence time in seawater is longer than the time taken for ocean mixing. On the contrary, restricted water bodies (e.g., lakes) may have heterogeneous Os isotopic compositions due to the greater amount of terrigenous input. Hydrogenous Re and Os atoms are sequestered from the water body into sedimentary organic matter and transferred into crude oil through thermal maturation of organic matter. Thermal maturation likely does not significantly alter the Re-Os isotopic systematics of the source rock as a Re-Os isochron age of 442±21 Ma (2σ) is yielded in this study for over matured source rocks within the Silurian Longmaxi Formation from the Sichuan Basin. Re-Os atoms are mainly hosted by the highly polar/aggregating/aromatic asphaltenes in hydrocarbons, possibly chelating with organic complexes or occurring as metalloporphyrins. Resin and aromatic hydrocarbons also contribute to the Re-Os budget, but are 2 to 3 orders of magnitude lower than that of asphaltenes, whereas saturates do not contain appreciable Re-Os contents. The distribution of Re-Os atoms in hydrocarbons is heterogeneous because the duplicate analysis of pure single bitumen samples yields similar 187Os/188Os ratios whereas variable 187Re/188Os ratios. The Re-Os system in crude oils can be reset during transport away from the source rocks, with Os-rich organic fractions more readily expelled than Re-rich fractions. Contact with metal-rich fluids (e.g., hydrothermal fluid) or compositional changes related to asphaltene contents (e.g., deasphalting, biodegradation, thermal cracking and thermochemical sulphate reduction) are also likely to alter the Re-Os systematics in hydrocarbons. These geochemical features enable the 187Re-187Os isotopic system to have robust applicability for petroleum system investigations, which may use the Re-Os radiometric tool for: (1) stratigraphic correlation of source rocks, (2) dating geological events altering the asphaltene content in hydrocarbon such as hydrocarbon generation, thermochemical sulphate reduction, etc., and, (3) fingerprinting hydrocarbons. Regardless of the robustness of the 187Re-187Os geochronometer for petroleum system investigations, there are several pending questions such as partitioning between solid organic species or between organic matter and sulphide, chelating sites in hydrocarbons and Os isotopic equilibration between hydrocarbon subfractions. To improve the understanding of the Re-Os behaviour in petroleum systems, we underscore multi-proxies-based geochemistry (e.g., inorganic-organic geochemistry) and experimental studies (e.g., hydrous pyrolysis).

The vibration dissipation mechanism of the rotating blade with a dovetail joint is studied in this paper. Dry friction damping plays an indispensable role in the direction of vibration reduction. The vibration level is reduced by consuming the total energy of the turbine blade with the dry friction device on the blade-root in the paper. The mechanism of the vibration reduction is revealed by the variation of the friction force and the energy dissipation ratio of dry friction. In this paper, the flexible blade with a dovetail interface feature is discretized by using the spatial beam element based on the finite element theory. Then the classical Coulomb-spring friction model is introduced to obtain the dry friction model on the contact interfaces of the tenon-mortise structure. What is more, the effects of the system parameters (such as the rotating speed, the friction coefficient, the installation angle of the tenon) and the excitation level on blade damping characteristics are discussed, respectively. The results show that the variation of the system parameters leads to a significant change of damping characteristics of the blade. The variation of the tangential stiffness and the position of the external excitation will affect the nonlinear characteristics and vibration damping characteristics.

Crowd counting has captured wide attention in computer vision, which aims to accurately count the number of people in still images or video scenes. However, it’s still a challenging task due to the scale variation and cluttered background in crowd scenes. In this paper, we propose a 2-stage Double Attention convolutional neural network for crowd counting, and call it 2-DA-CNN, which could deal with scale variation and cluttered background in crowd counting. The proposed 2-DA-CNN includes three parts. The first part is the front-end module which consists of a set of convolution operations, whose function is to extract abundant feature of crowd. The second part is the first double attention module, which contains trunk branch and mask branch. The former is mainly composed by multi-column CNN module, which is to deal with scale variation in crowd scenes. The latter can generate two masks, which aims to assign interesting regions reasonably in cluttered situation. The third part is the second double attention module, similar to the first double attention module, which can enhance the performance of multi-column CNN module further. In addition, we propose progressive training method to improve the drawback of using geometry-adaptive kernels to generate ground truth. The experimental results on three mainstream datasets (ShanghaiTech part B, ShanghaiTech part A and UCF_CC_50) suggest that the proposed 2-DA-CNN is competitive with the state-of-the-art methods.

The vibration reduction characteristics of the flexible blade with a dovetail joint and underplatform damper are studied in this paper. Considering the influence of the platform mass on the inheren...

A cation-exchange resin is commonly used to separate Sr from geological and environmental samples. AG50 resin is the most traditional cation-exchange resin and has the advantages of good reusability and low cost. Although AG50 resin can meet the demands of most conventional geological samples, eliminating 87Rb isobaric interference from samples with high Rb/Sr ratios (>30) is difficult during one-step separation. Separating Sr twice using AG50 resin is the general approach to Rb removal. The two-step separation method is time consuming and leads to a low Sr yield. This study aimed to improve the sample throughput and overcome the problem of 87Rb isobaric interference from imperfect separation. A new separation method involving hydrofluoric acid (HF acid) coprecipitation combined with a cation-exchange resin (i.e. AG50 resin) for samples with high Rb/Sr ratios was developed. HF acid was used as a coprecipitator to remove most Rb (>90%) and recover Sr before performing AG50 column chemistry. The reliability of this method was examined using the rhyolite standard JR-2, a typical sample with a high Rb/Sr ratio (Rb/Sr = 37.36). Results in the JR-2 case showed that approximately 92% of Rb and most of the matrix elements (K, Ti, Fe, Al, Mn and Na) could be removed effectively. Moreover, Sr recovery exceeded 91% during HF acid coprecipitation. After the removal of Rb by HF acid coprecipitation, the Sr fraction with high purity was easily obtained through one-step separation using the AG50 resin column. However, we found that the removal rates of Rb and some matrix elements (such as Al and Na) were strongly affected by the composition of Al–Ca–Mg in samples. Our separation method is more suitable for samples with high Rb/Sr ratios and low Ca and Mg contents. A series of silicate rock reference materials were selected to evaluate the applicability of our method, and the Sr isotopic results were consistent with previously reported values. Overall, this rapid, simple and low-cost method shows great potential for the separation of Sr from geological samples with high Rb/Sr ratios, such as alkaline feldspar granite, alkaline granite and alkaline rhyolite.

Reducing the impact of hazy images on subsequent visual information processing is a challenging problem. In this paper, combining with atmospheric scattering model, we propose an end-to-end multi-scale feature multiple parallel fusion network called MMP-Net for single image haze removal. The MMP-Net includes three components: multi-scale CNN module, residual learning module and deep parallel fusion module. 1) In multi-scale CNN module, a multi-scale convolutional neural network (CNNs) is adopted to extract different scales features from whole to local, and these features are fused multiple times in parallel. 2) In residual learning module, residual blocks are introduced to deeply learn detailed features, which can recover more image details. 3) In deep parallel fusion module, those features from residual learning module are deeply merged with the fused features from CNNs, and finally used to recover a clean haze-free image via the atmospheric scattering model. The experimental results show that on the average of three datasets (SOTS, HSTS, and D-Hazy), proposed MMP-Net improves PSNR from 20.91db to 22.21db and SSIM from 0.8720 to 0.9023 over the best state-of-the-art DehazeNet method. What’s more, MMP-Net gains the best subjective visual quality on real-world hazy images.

This study derived a novel computation algorithm for a mechanical system with multiple friction contact interfaces that is well-suited to the investigation of nonlinear mode characteristic of a coupling system. The procedure uses the incremental harmonic balance method to obtain the nonlinear parameters of the contact interface. Thereafter, the computed nonlinear parameters are applied to rebuild the matrices of the coupling system, which can be easily solved to calculate the nonlinear mode characteristics by standard iterative solvers. Lastly, the derived method is applied to a cycle symmetry system, which represents a shaft-disk-blade system subjected to dry friction. Moreover, this study analyzed the effects of the tuned and mistuned contact features on the nonlinear mode characteristics. Numerical results prove that the proposed method is particularly suitable for the study of nonlinear characteristics in such nonlinear systems.

This paper analyzes the intermittent operation on the ground temperature recovery of borehole heat exchanger (BHE) fields. The outlet fluid temperature is regarded as the field measurement to study...

Considering the large-deformation hypothesis, the modeling and nonlinear vibration characteristics of symmetrically 3-layer composite thin circular cylindrical shells with arbitrary boundary conditions are analyzed by applying four sets of artificial springs. Firstly, by employing a set of orthogonal polynomials and trigonometric functions, the energy equations of the shells are derived with Donnell's nonlinear thin-shell theory. Then, the arbitrary boundary conditions are simulated by imposing the equivalent elastic constraint to obtain the potential energy of the edges of the shell, which can be universally applicable to all classical boundary conditions. The vibration equation is obtained by using the Lagrange equation method. In order to obtain correct numerical results, several comparisons of linear and nonlinear results are carried out to validate the approach method in the present study; meanwhile, the calculation convergence is checked. At last, the influence of boundary conditions, geometric parameters, symmetrical lamination schemes and damping coefficients on the nonlinear amplitude-frequency characteristics of symmetrically 3-layer composite thin circular cylindrical shells are investigated. The numerical results indicate that the present method is powerful to calculate the nonlinear vibration response characteristics of symmetrically 3-layer composite circular cylindrical thin shells subjected to various boundary conditions.

Electrical modeling of vehicular antennas is required for design of modern vehicle-to-everything communication networks. However, full-wave modeling and the existing equivalent source methods still ask for long computation time. To address this issue, a fast simulation method is proposed in this paper: a sparse equivalent source model is developed based on Huygens’ principle where a vehicular antenna is made equivalent to magnetic current placed on a finite conducting plate. The image theory and the uniform theory of diffraction are then applied, a modified Green’s function is derived, and the sparse equivalent source model is constructed to replace the original vehicular antenna. Because of its simple geometry and material, in comparisons with the existing methods, the proposed model uses significantly less expenditures for simulation of vehicular antennas while has better accuracy due to the consideration of the finite conducting plate. Simulations are performed to demonstrate the effectiveness and advantages of the proposed method, and a real-world experiment is designed and conducted to demonstrate the superiority of the proposed method with real measurement data. It is shown that the proposed method can save simulation time by four times, with less than 1-dB error compared to measurement.

The drum-disk-shaft system is a significant part of the aero-engine rotor structure and directly influences the rotor dynamics. The dynamic model of a drum-disk-shaft structure was established considering the elastic support, flexible connection, and the Coriolis and centrifugal effects on the drum due to the rotation. The effects of support stiffness, coupling stiffness and rotating speed on vibration behaviors of the system were investigated. Some results were obtained. It is found that the disk's vibration and the drum's translational motion are coupled whatever the circumferential number (n) is, and the local deformation of the drum is coupled with the disk's vibration only under n = 1. When n is equal to 1, the more veering phenomena can be found during the process of the variation of the coupling stiffness, and support stiffness and the mode shapes are plotted to show the phenomena. At last, the effect of rotating speed on the frequencies of the coupling system was investigated. It is shown that the forward and backward traveling waves are generated in all the modes of the system under n = 1 due to the rotating speed and coupling effects, but only in the modes of the drum as n is not equal to 1. Also, the coupling stiffness and support stiffness can significantly affect the critical speed of the system.

A dynamic model of the rotating shrouded blade is established, considering the shroud mass, the Coriolis force, and the centrifugal stiffening effect. And a macroslip model of dry friction with variable normal load is established to simulate the separation-contact-stick-slip state of the shroud. The Lagrangian equation is utilized to solve the differential motion equation, and the Galerkin method is used for discretization. The influence of shroud structure’s parameters such as rotational speed, contact angle, friction coefficient, clearance, and shroud position on the damping effect of the shroud is reviewed by means of amplitude-frequency response and energy through the Newmark-β numerical method. The results demonstrate that the damping effect of the shroud by contact is more obvious than by friction and the amplitude-frequency curve of the shrouded blade shows a strong hard nonlinear phenomenon.

An improved principle is proposed in this paper to achieve a more efficient amplitude suppression of an oscillating pendulum by a controllable moving mass. By establishing the governing equation of the pendulum with a moving mass, several suppression rules are presented to stipulate the motion parameters of the moving mass. The damping ratio is introduced to quantify the suppression effects generated by the mass intermittent motion. With the verification of the accuracy of the present model, some simulation has been taken to get the maximum damping ratio and solve the problem of the nonsynchronous motion. The simulation results show that the new principle is a more powerful control method for the oscillation problem of a pendulum. It is suggested that the new method should carry out the relevant active control experiment in the future research.

In this paper, the effects of ground surface boundary conditions, especially diurnal shading, on performance of horizontal ground source heat pump (GSHP) systems were studied. Firstly, a GSHP system model, which consists of the heat transfer of horizontal ground heat exchangers (GHEs) and the integration of the heat pump, and the ground surface boundary model are introduced. The diurnal shading model for canyon streets is also introduced. Then, effects of ground surface boundary conditions and shading on horizontal GSHP systems are studied. Results show that different assumptions on ground surface boundary conditions have significant impact on outcomes and should carefully be considered during analysing. The outlet fluid temperature and fluctuation in North-South (N-S) streets are higher than those of East-West (E-W) streets. The increase in street aspect ratios and latitudes could decrease sunshine exposure time of the streets. Daily variations of solar radiation and shading influence the outlet temperatures of horizontal GHEs up to buried depth of 2.5 m. Therefore, the effects of solar radiation and shading should be considered when studying shallow horizontal GHEs.

To investigate the nonlinear vibration behavior of bolted joined cylindrical-cylindrical shell, a macroslip model was considered into the radial connection at the interface between the shell segments. Based on Sanders’ shell theory and the connection condition, the vibration differential equation of the structure was established. The mono-harmonic method was used to linearize the connection model and incremental harmonic balance method was used to obtain the results of the dynamic response. First, to test the accuracy of the present method, the frequency analysis was done and the results were compared with those by ANSYS and a good agreement was shown. Then, the convergence of the method was discussed. And finally, the effects of the preload of bolts, excitation amplitude, frictional coefficient and connection stiffness on the forced response were studied. The soft nonlinearity of the response curves was easily obtained under some conditions. The results show the resonance frequency and amplitude are sensitive to the preload of bolts, excitation amplitude, frictional coefficient and connection stiffness. The results reveal the dynamic characteristics of bolted joined cylindrical-cylindrical shell and would be of signification for shell structure design and vibration control.

The purpose of this paper is to investigate the coupling vibration characteristics of a flexible shaft-disk-blades system with mistuned features. There are some new phenomena due to the coupling effects of shaft-bending, shaft-torsion, disk-transverse and blade-bending. In this investigation, this paper mainly focuses on the influence of mistuned features of the blade's length and the stagger angle. It is found that there are four types of coupling modes: the coupling mode of shaft bending, disk transverse and blade bending (SDB), the coupling mode of shaft torsion disk transverse-blade bending (TDB), the coupling mode of disk transverse and blade bending (DB), the repeated mode of blade bending-blade bending (BB). With the effect of mistuned features, the natural frequencies and the coupling mode type will change correspondingly. With the mistuning value of blade length employed in this study, the TDB mode in the tuned system will disappear and shift into TSDB mode instead, and one of the repeated SDB modes will be replaced by STDB modes. Due to this mistuned features, the blades and disk experience a certain degree of vibration localization phenomenon. Different from the length feature, the influence of mistuning values of blade's stagger angle mainly take effect on the coupling modes. At last, by inspection on the Campbell diagrams, the influence of rotational speed on the transformation of natural frequencies is illustrated on the tuned/mistuned flexible shaft-disk-blades coupling structure.

Flexible sensors with wide sensing ranges require responsiveness under tiny and large strains. However, the development of strain sensors with wide detection ranges is still a great challenge due to the conflict between the tiny strain requirements of sparse conductive networks and the large strain requirement of dense conductive networks. Herein, we present a facile method for fabricating a gradient conductive network composed of sparse and dense conductive networks. The surface penetration technology in which carbon black (CB) penetrated from the natural rubber latex (NRL) glove surface to the interior was used to fabricate a gradient conductive network. The prolonged immersion time from 1 to 30 min caused the penetration depth of CB to increase from 2 to 80 μm. Moreover, CB formed hierarchical rough micro- and nanoscale structures, creating a superhydrophobic surface. The gradient conductive network of sensors produced an ultrawide detection range of strain (0.05-300%) and excellent reliability and reproducibility. The sensors can detect a wide range of human motions, from tiny (wrist pulse) to large (joint movements) motion monitoring. The flexible sensors attached to a flexible basement can be used to detect pressure in a wide detection range (1.7-2900 kPa). Pressure responsiveness was used to detect the weight, sound pressure, and dripping of tiny droplets. The sensor showed an excellent response to organic solvents, and the response intensity increased with the increasing swelling degree of the solvent for NRL.

Poly-ether-ether ketone (PEEK) is a great potential thermoplastic in industry and medical treatment and health. In this work, PEEK/graphene oxide (GO) and PEEK/MoS2 composites were prepared by a novel hot isostatic pressing method. The addition of GO alters the tribological behaviors mechanism, fatigue wear mechanism is predominant to PEEK/GO composites. However, the combination of abrasive and adhesive wear mechanisms is observed for PEEK/MoS2 composites and PEEK. The reason for this is that the hardness and tensile strength of composites are increased with the appropriate addition of GO. The response time to stable friction state of PEEK/GO and PEEK/MoS2 composites is reduced in comparison with PEEK, which is conducive to shorten running-in time, reduce the energy consumption, and improve the tribological performances of composites. The addition of GO and MoS2 can effectively decrease the friction coefficient and wear rate, and the optimal content of GO and MoS2 was 0.7 wt.% and 15 wt.%, respectively. The results indicate that PEEK/GO and PEEK/MoS2 are impressive composites that possess super tribological properties.

In this work, a continuum model is proposed to simulate and interpret the coupling vibration characteristics of a rotating disk-beam system with the dovetail interfaces. The dovetail interface feature is represented by a macroslip dry friction model. The present study also derives a new mode function to simulate the vibration of a rotating beam with loosely assembled dovetail attachment. The new proposed mode function is validated by comparing the natural characteristics and vibration response with those obtained from a finite element (FE) model. At last, based on the nonlinear response results obtained by the Newmark-β method, the effects of different parameters on the nonlinear dynamics of the coupling system are discussed. The following interesting phenomena have been revealed: the flexible disk can impose different influences on the response characteristics of the rotating beam. The effects of dry friction on the beam’s energy dissipation are significant, especially at a low rotational speed. Further analysis yields that the excitation level and friction coefficient also exhibit a significant impact on the damping effect of dry friction. Consequently, it should be noted that the optimal values of the contact surface’s parameters allow achieving a better damping effect in the engineering practice.

Natural characteristics of thin-wall pipe of the compressor under uniformly distributed pressure were presented in this paper based on a cylindrical shell model. In the traditional method, the beam model was usually used to analyze the pipe system. In actual fact, the pipe segment of the compressor was always broken in the form of a long crack or a partial hole and the phenomenon was hardly explained by beam model. According to the structure characteristic of compressor pipe segment, whose radius is large and thickness is little, shell model shows the advantage in this kind of pipe problem. Based on Sanders’ shell theory, the vibration differential equation of pipe was established by applying the energy method. The influences of length to radius ratio (L/R), thickness to radius ratio (h/R), circumferential wave number (n) and pressure (q) on the natural frequencies of pipe were analyzed. The study shows: Pressure and structural parameters have a great effect on the natural characteristics of the pipe. Natural frequency increases as the pressure increases, especially for the higher mode. The sensitivity of natural frequency on pressure becomes stronger with h/R ratio increases; when L/R ratio is greater than a certain critical value, the influence of the pressure on natural frequency will no longer be obvious. The value of n corresponding to the minimum natural frequency also depends on the value of pressure. In the end, analysis of the forced vibration of a specific pipeline model was given and the modal shapes were illustrated to understand the break of the pipe. The research here will provide the theory support for the dynamic design of related pressure pipe and further experiment study should be employed.

Modeling and free vibration analysis of bolted joined cylindrical-cylindrical shell were presented in this paper. First, a new analytical model was established for bolted joints. Second, based on Sanders’ shell theory, the dynamic equation of substructure of the assembly structure was formed. Then, by using the connection condition, into which the coupling stiffness between the segments was considered, the vibration differential equation of the assembly structure was established. Finally, the vibration characteristics of bolted joined cylindrical-cylindrical shell were obtained. To test the accuracy of the present method, the frequencies and mode shapes under some special connecting condition were examined with the results obtained by ANSYS and a good agreement was shown. Further, the number of bolts, connecting stiffness and length ratio of the two segments have a significant influence on natural frequency parameters and mode shapes of symmetrical and unsymmetrical structures. The results reveal the vibration characteristics of bolted joined cylindrical-cylindrical shell and are presented to provide useful information for future research. Moreover, some new results would be of signification for assembly structure design and vibration control.

The continuum model of flexible shaft-disk-blades coupling system is established to investigate the coupling vibration among shaft-bending, shaft-torsion, disk-transverse and blade-bending. The influence of shaft bending rigidity, disk transverse rigidity and rotational speed on natural frequencies and mode shapes are particularly researched. The present paper discovers that when shaft bending is negligible, there are three types of coupling modes, shaft torsion-disk transverse-blade bending (TDB), disk transverse-blade bending (DB) and blade bending-blade bending (BB). As shaft goes further flexible, the shaft bending-disk bending-blade bending (SDB) mode occurs. What’s more important is that shaft bending only couples with disk’s 1-nodal diameter mode. Then the influence of disk transverse on coupling vibration is studied. With the decrease of disk’s transverse rigidity, the repeated BB modes bifurcate into BB and DB modes, TB (shaft torsion-blade bending) and SB (shaft bending-blade bending) modes shift to TDB and SDB modes, respectively. Besides, disk’s n-nodal (n ≥ 2) diameter modes always couples with blade bending when β ≠ 0°. At last, the effect of rotational speed on the frequencies is investigated, concluding that shaft flexibility and disk flexibility can significantly affect the critical speeds of the system.

This work investigates the effects of different operation modes on the restoration performance and operation characteristics of a ground source heat pump (GSHP) system backfilled with phase change materials (PCM). A numerical GSHP system model considering site conditions and dynamic loads was developed and validated. The effects of daily working schedules, load features and operation schedules of short time period operation modes, and phase-transition temperature of PCM grout were explored. The results show that PCM grout is more suitable for buildings with less-persistent thermal demand considering the importance of restorability. Operating the GSHP with cooling & heating alternate load is the most effective way to improve the overall performance of the system, but a suitable operation schedule should be used. Decreasing the cycle ratio is the best method to promote the system performance under the same hourly load intensity, while for the operation schedules with higher hourly load intensity, a shorter cycle period is recommended. The phase-transition temperature of PCM grout influences the system stability and sustainability greatly as it controls when the melting occurs. The grout with the phase-transition temperature of 20.4 °C is demonstrated to be the most suitable one under our conditions as it provides relatively stable and effective performance over the entire summer and has a higher utilization ratio of the latent heat.

Based on Sanders shell theory, modeling and dynamic analysis of bolted joined cylindrical shell were studied in this paper. When subjected to external excitations, contact state such as stick, slip and separation may occur at those locations of bolts. Considering these three contact states, an analytical model of cylindrical shell with a piecewise-linear boundary was established for the bolted joined cylindrical shell. First, the model was verified by the simplified line system, and the effects of stiffness in connecting interface and the number of bolts on natural frequency and mode shape were investigated. Then, through the response under instantaneous excitation, damping characteristic of the system was proved which is caused by the friction model. Last, the effects of external load frequency, response location, excitation amplitude and connecting parameters including stiffness and preload were numerically investigated and fully explained by 3-D frequency spectrum. The results indicated that periodic motion, times periodic motion and even chaotic motion were observed based on different parameters.

In underground confined spaces with a crowded population, the thermal environment will be hot-humid and occurred with high CO2 concentration. Investigating the combined effect of increased temperature, relative humidity and CO2 concentration on human responses is important for confined spaces. In this paper, 32 subjects were exposed to different combinations of air temperature (Ta), relative humidity (RH) and CO2 concentrations in an underground climate chamber, with thermal response, physiological response and acute health symptoms being investigated. Results show that: at a Ta of 28 °C, RH of 65% and CO2 level of 12,000 ppm, thermal sensation votes (TSV) and thermal acceptability (TA) did not significantly changed, while a significant change was recorded with a RH of 85%. When CO2 concentration increased to 8000 ppm, the subjects' perceived air quality acceptability significantly decreased at Ta of 33 °C, however it did not significantly change at Ta of 28 °C and RH of 65%. Maximum mean skin temperature and wetness difference did not exceed 0.3 °C and 0.15 units between the different exposure conditions, respectively. Significant changes of headaches were observed when CO2 concentrations increased to 12,000 ppm at a RH of 85%, but the difference was not statistically significant at a RH of 65%. This indicated that the combined effects of high Ta, RH and CO2 concentration lead to different human responses.

To study the effects of using phase change materials (PCMs) as grout on the efficiency of a ground source heat pump (GSHP) system, a numerical GSHP system model was established in this study, considering both the site conditions and dynamically changing loads regulated by the heat pump. First, system efficiencies of using an ordinary grout and two other PCM grouts were investigated and compared. Second, the applicability of PCM grouts to different soil environments was investigated by analyzing the effects of subsurface characteristics on the heat exchanger efficiency. Finally, the appropriate operation mode for PCM-backfilled GSHP system was determined by comparing the effects of daily running modes with various intermittent ratios on the system performance. The results show that it is necessary to consider the effect of heat pump, especially for poor heat transfer conditions. PCM grouts with a low thermal conductivity will significantly reduce the system efficiency, whereas PCM grouts with a thermal conductivity comparable to that of an ordinary grout will improve the efficiency and operational stability of a GSHP system. A higher soil thermal conductivity and Darcy velocity improve the heat exchanger efficiency, and PCM grouts with a high thermal conductivity are more suitable for areas where the groundwater is not rich. Sufficient recovery time is necessary and important for a PCM-backfilled GSHP system to ensure operational stability and sustainability and the effectiveness of thermal radius reduction.

In the real application, digital images may undergo the process of acquisition, compression, and transmission, which causes the excess blurring, quantization, and noise. However, the metrics of image quality assessment for multiply distorted images are very limited. In this paper, we propose a new multi-scale learning quality-aware features blind image quality assessment algorithm for multiply distorted images by using both local phase and local amplitude. In the new model, a distorted image is decomposed into three scales by Gabor transform, and its phase congruency image (PCI), phase congruency covariance maximum image (PCCmax), and phase congruency covariance minimum image (PCCmin) are produced. Then, we calculate contrast sensitivity function and gray level-gradient co-occurrence matrix features from distorted image and its PCI, PCCmax, and PCCmin, and mean value of intensity of PCI, PCCmax, PCCmin, and overlapping blocked local amplitude of distorted image. At last, SVR is used to build the approximating function between these features and subjective mean opinion scores. Both local phase and local amplitude features are extracted at multi-scale images, which supply more flexibility than the previous single-scale methods in incorporating the variations of viewing scene. Comparative experiments between our proposed metric and the state-of-the-art full-reference and no-reference metrics are conducted on two newly released multiply distorted image databases (LIVEMD and MDID2013) that demonstrate the effectiveness of our proposed method.

Aiming at the problem that traditional lung nodules detection method can only get low sensitivities with a lot of false positives, we propose a new framework of ensemble of convolutional neural networks (E-CNNs) and use it to significantly reduce the number of false positive on lung nodules detection in chest radiographs (CXRs). First, unsharp mask technique is used to enhance the nodules in the CXRs. Then, we cut patches in the $229\times229$ image containing or not containing nodule from the enhanced CXRs, which correspond to the positive and negative samples. Third, three optimized CNNs of different input sizes and different depths, namely, CNN1, CNN2 and CNN3, are constructed to detect lung nodule separately, and their input sizes are $12\times12$ , $32\times32$ , and $60\times60$ , and the number of layers are 5, 7, and 9, separately. Finally, a logical AND operator is used to fuse the results of CNN1, CNN2, and CNN3, and E-CNNs are constructed for detecting lung nodules. Our experimental results on the Japanese Society of Radiological Technology database show our proposed E-CNNs attain a sensitivity of 94% and 84% with an average of 5.0 false-positives (FPs) per image and 2.0 FPs per image, respectively, in a five-fold cross-validation test, which far outperforms the state of the art.

Research and development of wireless power transfer (WPT) systems has attracted much attention in recent years for their potential widespread applications. One of the much desirable features of a WPT system is load-independence. In this letter, we propose the insertion of a simple T-type network into a multi-receiver WPT magnetically coupled resonant WPT system to achieve the load-independence. We then present theoretical analysis, simulation, and experimental verifications; as a result, they lay the foundation for further investigations, improvements, and implementations of realistic WPT systems.

Isotope dilution thermal ionization mass spectrometry (ID-TIMS) is considered the “gold standard” for obtaining precise 87Rb/86Sr and 87Sr/86Sr isotope ratios and accurate elemental concentrations of Rb–Sr. However, the classical ID-TIMS technique is laborious and time-consuming because the purified Rb and Sr fractions must be individually loaded onto different independent filaments due to severe 87Rb isobaric interference on 87Sr. To overcome this issue, we developed a new method whereby Rb and Sr were sequentially measured by TIMS on the same filament, without venting, to obtain both ratios of 87Rb/86Sr and 87Sr/86Sr and concentrations of Rb and Sr. Results obtained from six silicate powders of certified reference materials are in good agreement with recommended values within ±0.002% for the 87Sr/86Sr ratio, ±2% for the 87Rb/86Sr ratio and the Rb and Sr elemental contents. The only exception is JG-1a, with slightly higher 87Rb/86Sr and slightly lower 87Sr/86Sr. This new method improved the analytical efficiency and sample throughput without compromising the analytical accuracy and precision. The filament consumption is reduced by 50% compared with conventional methods and therefore significantly reduces operation costs.

In this paper, a new method for rapid oscillation suppression using phase delay motion of the movable pivot is designed. The pivot’s continuous motion control with a lagging phase difference is realized by taking the pendulum’s time delay angle as an input. Based on the intermittent motion control method, the pivot’s continuous motion is used as an auxiliary motion path to trigger the pivot’s intermittent action lagging behind the pendulum motion. The effects of time delay difference and pivot movement distance on the suppression efficiency are analyzed by setting up an experimental device. The principle of the pivot motion with time delay difference to suppress the oscillation is described. Moreover, the energy absorption factor is proposed to evaluate the quality of control methods. The effects of intermittent motion time and suppression efficiency are discussed. The proposed method can provide a practical, theoretical reference on rapid oscillation suppression of pendulum structure.

This study aimed to investigate the effect of changing ambient conditions on the accuracy and stability of ground thermal conductivity, λs, using the thermal response test (TRT). First, a detailed numerical model considering the heat fluxes on the field surface of TRT was developed. Then, the numerical model was compared with that with the adiabatic surface boundary in two representative test seasons. After that, the impacts of three parameters associated with the surface heat fluxes, including the surface absorptivity, evaporation coefficient, and surface infrared emissivity on the λs were analyzed. Lastly, statistical analyses with various ambient conditions were employed to evaluate the degree of estimated λs deviating from its actual value in different specifications of TRT and actual ground thermal conductivities. Results show that the surface absorptivity can be generally seen as the most significant contributory factor to the uncertainty of λs. The λs is overestimated and the uncertainty of TRT is aggravated by considering the changing ambient conditions, especially when the depth of drilling test well is short and the actual λs is high. For such conditions, the heat insulation on the test site surface is highly recommended considering the acceptable accuracy of λs with the adiabatic boundary.

A modeling method of bolt connections considering micro-slip characteristics is presented based on the improved Iwan model in this paper. Furthermore, the Chebyshev polynomials are used as the admissible displacement functions to study the bolted flange cylindrical shell’s vibration characteristics by the Sanders’ shell theory. It is worth noting that the mechanical model of bolted joints takes into account the nonlinear characteristics of micro-sliding motion between the connection interfaces and different tensile and compression stiffness. Moreover, to reproduce the micro-slip motion between the interfaces, we propose an improved Iwan model considering the spatial distribution characteristics of the contact pressure and the variable normal contact load. The effects of the flange geometry, preload of bolts, and excitation amplitude on the natural frequency and vibration response of the shell are investigated.

Ground thermal conductivity, λs, is one of the important design factors for the ground source heat pump system. This study aimed to investigate the effect of environmental thermal disturbance on the λs estimation during the thermal response test (TRT), which is interpreted by the infinite line source model. For this purpose, a detailed numerical model considering the heat exchange between the circulating fluid inside the above-ground pipe of TRT rig and the outdoor environment in two representative seasons was developed. The numerical model was compared with the model with the adiabatic boundary assigned to the outer surface of above-ground pipe to evaluate the fluctuations of λs on account of the atmospheric disturbance. The parametric and sensitivity analyses were carried out to quantify the impacts of TRT seasons and above-ground pipe parameters including the surface absorptivity, thickness, and thermal conductivity of insulation material, and the length of the above-ground pipe on the λs and corresponding design borehole length. An approach of prolonging the TRT duration was proposed to impair the disturbance when the pipe is not insulated. Results show that λs fluctuates strongly and is largely misestimated considering the atmospheric disturbance, especially when TRT duration is limited. The λs varies widely as the length of above-ground pipe, insulation surface absorptivity, and insulation thermal conductivity increase, insulation thickness decreases, and TRT starts in summer. The pipe length is the most significant factor to the uncertainty of λs. The test time is recommended to last at least 3 days in summer and 3.6 days in winter when the pipe is not wrapped by a layer of insulation material. This study quantitatively assesses the impacts of environmental thermal disturbance during the TRT and gives guidance to carry out TRT properly.

In this work, the effects of load optimization and geometric arrangement on borehole heat exchanger (BHE) fields have been studied. A ground source heat pump (GSHP) system model is introduced, and validated against both the experimental and modelling results from literature. Based on the GSHP system model, optimization strategies are applied on the BHE fields. The results show that, compared with the single BHE, thermal interaction in BHE fields is obvious when the pipe spacing is limited and the building load is unbalanced. Improving the side BHEs’ load helps in enhancing the performance of BHE fields, whereas slightly inferior results are achieved by improving the middle BHEs’ load. When the groundwater flow is considered, optimized-load BHE fields can keep the maximum outlet fluid temperature 7.99% lower than that for the BHE fields with equal loads. For the geometric arrangement, increasing the number of side BHEs and downstream BHEs contributes to the spreading of released heat, which improves the efficiency of the system.

In bedrock geology districts, the stratum in the ground heat exchanger (GHE) borehole varies along the vertical direction. In this paper, the layered subsurface is investigated and the ground temperature variations are studied based on the test systems. Under 60 days’ heat injection and 65 days’ self-regeneration test in the borehole-#2, the outlet temperature of the analytical homogeneous finite line source (FLS) model is 2.2 °C and 1.2 °C higher than the tested outlet temperature on at 30th and the 90th day, respectively. The temperature rises at radial distance of 3 m, 6 m and 9 m to the heat injection borehole at depth of 12 m, 25 m and 80 m are recorded and discussed. After 60 days’ heating, the temperature rises at radial distance of 3 m at depth of 12 m, 25 m and 80 m are 0.82 °C, 5.86 °C and 3.85 °C respectively. A numerical model considering five strata is developed according to the field investigations, and the axial temperature profiles of different layers at different distance under different heating time are presented and explored. It indicates that the layered subsurface and groundwater flow play the non-negligible role on evaluation performance of BHEs.

The influence of blade vibration on the nonlinear characteristics of rotor–bearing system is non-ignorable in estimating system performance. The extensive studies simplify the rotor system as lumped mass points. The influence of shaft’s bending and shear and the flexibility are usually ignored. The present paper is aim to analyze the nonlinear dynamic behavior of a continuum model. The continuum model of flexible blade–rotor–bearing coupling system is established, simplifying the shaft as Timoshenko beam. The Lagrange method is utilized to derive the differential equation of motion of system. Then, the nonlinear equations of coupling system are numerically solved using the Newmark- $$\upbeta $$ method. The results obtained through the proposed model are compared with the rotor–bearing system without the blades. The effect of several parameters such as rotational speed, the damping coefficient and the length of blade on the nonlinear dynamics of rotor system have been investigated. Inclusive of the analysis methods of bifurcation diagram, three-dimensional spectral plots, time-base analysis, Poincare maps and spectral plots are used to analyze the behavior of the coupling system under different operating conditions, which exhibits rich dynamic behavior of the system.

This study concerns the operation characteristics of horizontal spiral-coil ground source heat pump (GSHP) system. A numerical model is established, which takes into account the geothermal gradient, as well as the varying ambient air temperature. More importantly, a heat pump model is also included to consider dynamically-changing loads due to specific COP characteristics. The accuracy of the model is validated with experimental results in Metz’s work and the model presented by Mei. Circulating fluid temperatures are compared with and without considering the effect of heat pump COP. Influence factors affecting the operation characteristics of horizontal spiral-coil GSHP system are investigated and their influence degrees are also compared. Impacts of daily variations of thermal load and operation models on the performance of horizontal spiral-coil GSHP system are also investigated. Results show that without considering the effect of heat pump, the difference between average inlet fluid temperatures in cooling and heating models can be 4.1% and 11.5%. Among factors influencing the performance of horizontal spiral-coil GSHP system, soil thermal conductivity and pipe spacing are main factors. When analyzing the annual or average operation characteristics of horizontal GSHP system, daily variations of load can be neglected. Under the condition of equal total loads, the average performance of intermittent operation is poorer than continuous operation and day-high/night-low operation. And continuous operation has the best performance.

Stereoscopic image quality assessment (SIQA) is an essential and tricky part of image processing. Recently, many scholars have conducted image quality assessment in either spatial or frequency domain respectively. In this paper, we propose a no-reference stereoscopic image quality evaluation method by considering both complex contourlet and spatial features. Firstly, the original views are converted to the Lab color space. Then the luminance channel of Lab color space and the synthetic cyclopean image are calculated from the original stereo pairs. Next, the perceptual features of these types of images are extracted in the complex contour domain and the spatial domain respectively. Finally, all pre-extracted features are sent to the regression model for training and predicting image quality scores. Our experimental results show that the proposed algorithm achieves high consistency with human subjective perception, and compete with state-of-the-art algorithms.

A six-degree-of-freedom parallel manipulator system based on 6-PURU structure is developed for vehicles' motion simulation. The main research in this paper is focused on dynamic modeling of the proposed parallel system. The kinematic model of the proposed system is established via kinematic influence coefficient method, in which the velocity and acceleration mappings between the passive components and actuated components are more accurate compared to the equivalent 6-PUS or 6-PSS systems. Based on the kinematics analysis, the dynamic model of the parallel kinematic machine is then formulated via the principle of virtual work. Finally a numerical calculation is performed based on the proposed dynamic model which matches the simulation results of commercial software. The approach outlined in this paper is generic and can be extended to a variety of applications.

Two-dimensional partial least squares (2DPLS) is an effective two-view data analysis technique. However, conventional 2DPLS only takes into account the column information of two-dimensional images. In this paper, we simultaneously consider the column-wise and row-wise information of two-dimensional face images. We first propose a row-based two-dimensional PLS (r2DPLS) approach and then further present a novel double-directional PLS (D\(^{2}\)PLS) method. The proposed D\(^{2}\)PLS method can be optimized by two eigenvalue subproblems. Experimental results on the AR, Yale, and AT&T face databases show that our D\(^{2}\)PLS method can overall achieve better recognition accuracy than existing related methods.

This paper presented a non-linear modeling approach for bolted joint connection interfaces and identified the micro-slip model’s parameters through quasi-static experiments based on an improved micro-slip model. Firstly, considering the contact pressure’s spatial distribution characteristics on the connection interface, a new density function of critical sliding force was proposed. The contact pressure is distributed annularly on the interface. Then, the critical sliding force’s density function was applied to the Iwan model, and an improved micro-slip model was proposed. The residual shear stiffness on the connection interface during macro-slip and separation was also taken into account simultaneously. The piecewise linear model and the improved micro-slip model were adopted to reproduce the different tensile and compressive stiffness of the bolted joint and the friction on the interface, and the non-linear mechanical model of the bolted joint was obtained. Finally, this paper proposed a method for parameter identification of the micro-slip model on the connection interface. The hysteresis loops were obtained through quasi-static shear experiments, and corresponding parameters were identified.

A nonlinear dynamic model of a rotating beam with dry friction support boundary conditions is developed, and the effectiveness of this model is verified by comparing it with the relevant literature. In the proposed model, a macro-slip friction model of the contact interfaces at the root of the beam with a dovetail tenon is established to characterize the friction on the beam. Furthermore, a time-domain solution and a linearization method of nonlinear friction force are proposed. The dynamic differential equations of the rotating beam are obtained conveniently by means of Chebyshev polynomials theory. Based on the developed model, the effect of the harmonic number on calculations is discussed by incremental harmonic balance method (IHBM). Moreover, the influences of friction coefficient, excitation amplitude, and rotational speed on the amplitude-frequency response of the system are analyzed. The results indicate that the higher-order harmonic components have significant influence on the nonlinear dynamic response of the tenon-mortise connected beam, which must be considered in the frequency-domain computation. When the contact interface slips, the contact stiffness decreases and the contact damping increases. With the rise of friction coefficient, rotational speed or the decreases of excitation amplitude, the range of slip zone narrows. The variation of amplitude-frequency curves is well explained from the perspective of contact stiffness and contact damping.

A unified method is presented to analyze free vibrations of dual-functional graded nanocomposite laminated cylindrical shells reinforced by carbon nanotubes (CNTs) under arbitrary boundary conditions. Especially, the matrix material of the carbon nanotubes is metal-ceramic functional gradient material (FGM), and the CNT is also assumed to be a gradient distribution in the matrix, constituting the dual-functional graded materials. Based on the first-order shear deformation theory (FSDT) and artificial spring technology, the Chebyshev polynomials was selected as the admissible function, and the Rayleigh-Ritz method was used to derive the vibration differential equation of the laminated shell. Further, the effects of volume fraction of CNTs, change of matrix material, the thickness of the middle layer, and geometric parameters on the natural frequency were discussed.

A novel dynamic model of a rotating variable-thickness pre-twisted blade with elastic constraints is established by using the shallow shell theory. The effects of Coriolis and centrifugal force due to the rotational motion are considered in the formulation. Based on the Lagrange equation, the natural frequencies and modes of a rotating pre-twisted blade are obtained by using orthogonal polynomials as admissible functions. The convergence analysis is studied, and the accuracy of the proposed model is verified by comparing it with the literature results and ANSYS data. A comprehensive parameter investigation of the effects of thickness-taper ratio, pre-twist angle, rotational speed, and connection stiffness on blades' modal characteristics is conducted. The results show that the phenomena of frequency locus veering, crossing, and coincidence. Furthermore, mode shape exchanging occurs with parameter changes.

This paper presents an investigation of the eigenvalues of veering and merging phenomena of a bladed disk system with contact features (an assembly bladed disk system). Of particular interest are the vibrational characteristics at rotational speed intervals at which the eigenvalue loci exhibit veering and merging phenomena. Furthermore, the current work attempts to investigate the interactions between the disk-dominated and blade-dominated families of modes in an assembly bladed disk system. In this regard, a representative model of an assembly bladed disk system is proposed, implementing an improved Euler-Bernoulli beam to model the rotating blade. The coupled equations of the bladed disk system are discretized using the modal functions which satisfy the eigenvalue problem. The change in modal properties of a blisk system with rotational speed is initially depicted to provide a reference for the analysis of a nonlinear system. Thereafter, the modal spectrum of the assembly bladed disk system is computed and analyzed by a frequency-domain method. Numerical analysis reveals that coupling interaction induces a series of eigenvalue veering and merging phenomena and that the modal frequencies at low rotational speeds are significantly affected by the nonlinearity of contact features. In particular, corresponding analysis of the mechanisms of these phenomena is presented. Furthermore, the present work also investigates the sensitivity of a low rotational speed interval and merging phenomena to several parameters.

No-reference/blind image quality assessment (NR-IQA/BIQA) algorithms play an important role in image evaluation, as they can assess the quality of an image automatically, only using the distorted image whose quality is being assessed. Among the existing NR-IQA/BIQA methods, natural scene statistic (NSS) models which can be expressed in different bandpass domains show good consistency with human subjective judgments of quality. In this paper, we create new ‘quality-aware’ features: the energy differences of the sub-band coefficients across scales via contourlet transform, and propose a new NR-IQA/BIQA model that operates on natural scene statistics in the contourlet domain. Prior to applying the contourlet transform, we apply two preprocessing steps that help to create more information-dense, low-entropy representations. Specifically, we transform the picture into the CIELAB color space and gradient magnitude map. Then, a number of ‘quality-aware’ features are discovered in the contourlet transform domain: the energy of the sub-band coefficients within scales, and the energy differences between scales, as well as measurements of the statistical relationships of pixels across scales. A detailed analysis is conducted to show how different distortions affect the statistical characteristics of these features, and then features are fed to a support vector regression (SVR) model which learns to predict image quality. Experimental results show that the proposed method has high linearity against human subjective perception, and outperforms the state-of-the-art NR-IQA models.