This paper concentrates on simulating fracture in thin walled single-lap joints connected by resistance spot-welding (RSW) process which were subjected to tensile loading. For this purpose, three sets of lap-joints with different spot configurations were tested to achieve the joints’ tensile behavior. To simulate the joints tensile behavior, firstly a 2D axisymmetric finite element (FE) model was used to calculate residual stresses induced during the welding process. Then the results were transferred to 3D models as pre-stress. In this step, cohesive zone model (CZM) technique was used to simulate fracture in the models under tensile load. Cohesive zone parameters were extracted using coach-peel and shear lap specimens. The results were employed to simulate deformation and failure in single lap spot weld samples. It has been shown that considering the residual stresses in simulating deformation and fracture load enables quite accurate predictions.
Effects of working parameters on performance characteristics of hydrostatic turntable are researched by applying the fluid-structure-thermal coupled model. Fluid-structure interaction (FSI) technique and computational fluid dynamics (CFD) method are both employed by this new model, and thermal effects are also considered. Hydrostatic turntable systems with a series of oil supply pressures, various oil recess depth and several surface roughness parameters are studied. Performance parameters, such as turntable displacement, system flow rate, temperature rise of lubrication, stiffness and damping coefficients, are derived from different working parameters (rotational speed of turntable and exerted external load) of the hydrostatic turntable. Numerical results obtained from this FSI-thermal model are presented and discussed, and theoretical predictions are in good agreement with the experimental data. Therefore, this developed model is a very useful tool for studying hydrostatic turntables. The calculation results show that in order to obtain better performance, a rational selection of the design parameters is essential.
A numerical study is carried out on particle deposition in ducts with either convex or concave wall cavity. Results show that, if compared with smooth duct, particle deposition velocities (Vd+) increase greatly in ducts with wall cavities. More specifically, for τ+<1, Vd+ increase by about 2–4 orders of magnitude in the cases with the convex and concave wall cavities; for τ+>1, Vd+ grows relatively slower. Enhancement of particle deposition with wall cavities is caused by the following mechanisms, i.e., interception by the wall cavities, expanded deposition area, and the enhanced flow turbulence. In general, addition of wall cavities is contributive for particle deposition, so it provides an efficient approach to remove particles, especially with small size, e.g., PM2.5. Moreover, the convex wall cavity leads to a larger increment of Vd+ than the concave wall cavity. However, taking pressure loss into account, though Vd+ is relatively lower, duct with the concave wall cavity is more efficient than that with the convex wall cavity.
To achieve excellent tracking accuracy, a coarse-fine dual-stage control system is chosen for inertially stabilized platform. The coarse stage is a conventional inertially stabilized platform, and the fine stage is a secondary servo mechanism to control lens motion in the imaging optical path. Firstly, the dual-stage dynamics is mathematically modeled as a coupling multi-input multi-output (MIMO) control system. Then, by incorporating compensation of adaptive model to deal with parameter variations and nonlinearity, a systematic robust H∞ control scheme is designed, which can achieve good tracking performance, as well as improve system robustness against model uncertainties. Lyapunov stability analysis confirmed the stability of the overall control system. Finally, simulation and experiment results are provided to demonstrate the feasibility and effectiveness of the proposed control design method.
To the existing spectrum sharing schemes in wireless-powered cognitive wireless sensor networks, the protocols are limited to either separate the primary and the secondary transmission or allow the secondary user to transmit signals in a time slot when it forwards the primary signal. In order to address this limitation, a novel cooperative spectrum sharing scheme is proposed, where the secondary transmission is multiplexed with both the primary transmission and the relay transmission. Specifically, the process of transmission is on a three-phase time-switching relaying basis. In the first phase, a cognitive sensor node SU1 scavenges energy from the primary transmission. In the second phase, another sensor node SU2 and primary transmitter simultaneously transmit signals to the SU1. In the third phase, the node SU1 can assist the primary transmission to acquire the opportunity of spectrum sharing. Joint decoding and interference cancellation technique is adopted at the receivers to retrieve the desired signals. We further derive the closed-form expressions for the outage probabilities of both the primary and secondary systems. Moreover, we address optimization of energy harvesting duration and power allocation coefficient strategy under performance criteria. An effective algorithm is then presented to solve the optimization problem. Simulation results demonstrate that with the optimized solutions, the sensor nodes with the proposed cooperative spectrum sharing scheme can utilize the spectrum in a more efficient manner without deteriorating the performance of the primary transmission, as compared with the existing one-directional scheme in the literature.
For rigid-flexible coupling multi-body with variable topology, such as the system of internally carried air-launched or heavy cargo airdrop, in order to construct a dynamic model with unified form, avoid redundancy in the modeling process and make the solution independent, a method based on the equivalent rigidization model was proposed. It divides a system into independent subsystems by cutting off the joints, of which types are changed with the operation process of the system. And models of different subsystems can be constructed via selecting suitable modeling methods. Subsystem models with flexible bodies are on the basis of the equivalent rigidization model which replaces the flexible bodies with the virtual rigid bodies. And the solution for sanction, which is based on the constraints force algorithm (CFA) and vector mechanics, can be independent on the state equations. The internally carried air-launched system was taken as an example for verifying validity and feasibility of the method and theory. The dynamic model of aircraft-rocket-parachute system in the entire phase was constructed. Comparing the modeling method with the others, the modeling process was programmed; and form of the model is unified and simple. The model, method and theory can be used to analyze other similar systems such as heavy cargo airdrop system and capsule parachute recovery system.
Reasons and realities such as being non-linear of dynamical equations, being lightweight and unstable nature of quadrotor, along with internal and external disturbances and parametric uncertainties, have caused that the controller design for these quadrotors is considered the challenging issue of the day. In this work, an adaptive sliding mode controller based on neural network is proposed to control the altitude of a quadrotor. The error and error derivative of the altitude of a quadrotor are the inputs of neural network and altitude sliding surface variable is its output. Neural network estimates the sliding surface variable adaptively according to the conditions of quadrotor and sets the altitude of a quadrotor equal to the desired value. The proposed controller stability has been proven by Lyapunov theory and it is shown that all system states reach to sliding surface and are remaining in it. The superiority of the proposed control method has been proven by comparison and simulation results.
Multiple UAVs are usually deployed to provide robustness through redundancy and to accomplish surveillance, search, attack and rescue missions. Formation reconfiguration was inevitable during the flight when the mission was adjusted or the environment varied. Taking the typical formation reconfiguration from a triangular penetrating formation to a circular tracking formation for example, a path planning method based on Dubins trajectory and particle swarm optimization (PSO) algorithm is presented in this paper. The mathematic model of multiple UAVs formation reconfiguration was built firstly. According to the kinematic model of aerial vehicles, a process of dimensionality reduction was carried out to simplify the model based on Dubins trajectory. The PSO algorithm was adopted to resolve the optimization problem of formation reconfiguration path planning. Finally, the simulation and vehicles flight experiment are executed. Results show that the path planning method based on the Dubins trajectory and the PSO algorithm can generate feasible paths for vehicles on time, to guarantee the rapidity and effectiveness of formation reconfigurations. Furthermore, from the simulation results, the method is universal and could be extended easily to the path planning problem for different kinds of formation reconfigurations.
Cavitation is a destructive phenomenon in control valves. In order to delay cavitation, a multi-series of perforated cylindrical plates, called trims, are used. Previously, the effects of orifice diameter and different types of trims have been investigated. In this study, by numerical analysis, a globe control valve was investigated by employing four different cases (without trim, with one trim, with two and three trims) and the impact of the number of these trims on the intensity, formation region and the initiation point of cavitation was analyzed. It was found that the addition of one stage or two stages of trims reduces the intensity and delays the onset of cavitation, relative to the valve without trim. However, no significant differences in terms of intensity and initiation point of cavitation were observed in the cases where two or three trims were used. Therefore, due to the high cost of producing the trims, and the severe drop in flow coefficient, it is not economically and technically justified to increase the number of trims to more than three.
For unacceptable computational efficiency and accuracy on the probabilistic analysis of multi-component system with multi-failure modes, this paper proposed multi-extremum response surface method (MERSM). MERSM model was established based on quadratic polynomial function by taking extremum response surface model as the sub-model of multi-response surface method. The dynamic probabilistic analysis of an aeroengine turbine blisk with two components, and their reliability of deformation and stress failures was obtained, based on thermal-structural coupling technique, by considering the nonlinearity of material parameters and the transients of gas flow, gas temperature and rotational speed. The results show that the comprehensive reliability of structure is 0.9904 when the allowable deformations and stresses of blade and disk are 4.78×10–3 m and 1.41×109 Pa, and 1.64×10–3 m and 1.04×109 Pa, respectively. Besides, gas temperature and rotating speed severely influence the comprehensive reliability of system. Through the comparison of methods, it is shown that the MERSM holds higher computational precision and speed in the probabilistic analysis of turbine blisk, and MERSM computational precision satisfies the requirement of engineering design. The efforts of this study address the difficulties on transients and multiple models coupling for the dynamic probabilistic analysis of multi-component system with multi-failure modes.
The present article deals with thermally stratified stagnation-point flow saturated in porous medium on surface of variable thickness along with more convincing and reliable surface condition termed as melting heat transfer. Homogeneous–heterogeneous reaction and radiative effects have been further taken into account to reconnoiterproperties of heat transfer. Melting heat transfer and phenomenon of homogeneous–heterogeneous reaction have engrossed widespread utilization in purification of metals, welding process, electroslag melting, biochemical systems, catalysis and several industrial developments. Suitable transformations are utilized to attain a scheme of ordinary differential equations possessing exceedingly nonlinear nature. Homotopic process is employed to develop convergent solutions of the resulting problem. Discussion regarding velocity, thermal field and concentration distribution for several involved parameters is pivotal part. Graphical behaviors of skin friction coefficient and Nusselt number are also portrayed. Concentration of the reactants is found to depreciate as a result of strength of both heterogeneous and homogeneous reaction parameters. With existence of melting phenomenon, declining attitude of fluid temperature is observed for higher radiation parameter.
Based on the traditional hydraulic bulging process, an improved hydraulic bulging process with axial feeding in the bulging process was proposed. The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted. The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows, obtained from simulation and experiment, show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15% and 10%, respectively. And the wall thickness distribution of the metal bellows formed with improved process was more uniform. The strain values from the root to crown of the waveform increased gradually. However, the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.
The impact of the load on the shearer is mainly transmitted through cutting part. In this paper, in order to get the vertical steering vibration characteristics of the cutting part of the drum shearer, the working condition of coal mining machine is simplified. A simplified vertical steering model and the simplified vibration model of the whole cutting part of shearer are established. The vertical steering vibration process of the cutting unit is simplified into a single freedom and one forced vibration system under harmonic excitation. The dynamic response of the cutting part under sine excitation is obtained by using Matlab/Simulink for modeling and simulation. The influence of the support rigidity and damping of the high oil cylinder on the vertical steering vibration characteristics of the cutting part is analyzed. The results show that the damping of the cylinder can reduce the vibration of the system and the stability of the swing process of cutting the part is improved.
Investigations regarding the relation of noise performance for centrifugal pump operating in pump and turbine modes continue to be inadequate. This paper presents a series of comparisons of flow-induced noise for both operation modes. The interior flow-borne noise and structure modal were verified through experiments. The flow-borne noise was calculated by the acoustic boundary element method (ABEM), and the flow-induced structure noise was obtained by the coupled acoustic boundary element method (ABEM)/structure finite element method (SFEM). The results show that in pump mode, the pressure fluctuation in the volute is comparable to that in the outlet pipe, but in turbine mode, the pressure fluctuation in the impeller is comparable to that in the draft tube. The main frequency of interior flow-borne noise lies at blade passing frequency (BPF) and it shifts to the 9th BPF for interior flow-induced structure noise. The peak values at horizontal plane appear at the 5th BPF, and at axial plane, they get the highest sound pressure level (SPL) at the 8th BPF. Comparing with interior noise, the SPL of exterior flow-induced structure noise is incredibly small. At the 5th BPF, the pump body, cover and suspension show higher SPL in both modes. The outer walls of turbine generate relatively larger SPL than those of the pump.
Two new binary near-azeotropic mixtures named M1 and M2 were developed as the refrigerants of the high-temperature heat pump (HTHP). The experimental research was used to analyze and compare the performance of M1 and M2-based in the HTHP in different running conditions. The results demonstrated the feasibility and reliability of M1 and M2 as new high-temperature refrigerants. Additionally, the exploration and analyses of the support vector machine (SVM) and back propagation (BP) neural network models were made to find a practical way to predict the performance of HTHP system. The results showed that SVM-Linear, SVM-RBF and BP models shared the similar ability to predict the heat capacity and power input with high accuracy. SVM-RBF demonstrated better stability for coefficient of performance prediction. Finally, the proposed SVM model was used to assess the potential of the M1 and M2. The results indicated that the HTHP system using M1 could produce heat at the temperature of 130 °C with good performance.
The lower Ordovician mid-assemblage Formations in the central Ordos Basin of China host prolific gas resources, and most hydrocarbon reserves are stored in naturally-fractured reservoirs. Thus, fracture pathway systems may have a significant impact on reservoir performance. This article focuses on the core- and laboratory-based characterization of fractures. Through the developmental degrees, extended scale, output state and filling characteristics of various types of fractures, the results show that there are three distinct fracture types: 1) nearly vertical fractures, 2) oblique fractures, and 3) horizontal fractures. Based on a systematic study of the characterization of reservoir space, the main geologic setting of natural gas accumulation and the regional tectonic background, type 1 is mainly driven by the tectonic formation mechanism, and type 3 and parts of low-angle fractures in type 2 are induced by the diagenetic formation mechanism. While recovered paleopressure for methane-rich aqueous inclusions trapped in fracture-filling cement indicates that the fracture opening and growth are consistent with gas maturation and charge and such high-angle fractures in type 2 are caused by the compound formation mechanism. The fractures to hydrocarbon accumulation may play a more significant role in improving the quality of reservoir porosity. Furthermore, connected fractures, dissolved pores and cavities together constitute the three-dimensional pore-cave-fracture network pathway systems, with faults serving as the dominant charge pathways of highly pressurized gas in the study area. Our results demonstrate that protracted growth of a pervasive fracture system is not only the consequence of various formation mechanisms but also intrinsic to quasi-continuous accumulation reservoirs.
Based on the drilling, cores, logs, seismic, laboratory analysis and so on, reservoir characteristics and hydrocarbon accumulation of Carboniferous volcanic weathered crust in Zhongguai high area are studied. Volcanic rocks were formed in an island arc environment. The lithology is mainly andesite and tuff; Reservoir spaces are mainly secondary pore, fracture and their combination forms, fractures have a better effect on reservoir seepage; There are four layer structures of volcanic weathered crust, weathered clay layer, strongly weathered zone, weakly weathered zone and unweathered zone and strongly weathered zone is the best, which is the main reservoir development zone; The development of reservoir is mainly affected by weathering-leaching, lithology and lithofacies, and fault (fracture); Effective reservoirs could reach to 480 m thickness (high quality reservoirs are within 240 m). Carboniferous volcanic reservoirs are distributed along three zones, which are near the fault zone, high structural part, favorable lithofacies development zone, and one plane, which is near the unconformity.
Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule, a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constructed. The ultimate pull-out force and its corresponding failure mechanism through the upper bound limit analysis according to a variation principle are deduced. When the 2-layer overlying soil is degraded into single-layer soil, the model of ultimate pullout force could also be degraded into the model of single-layer soil. And the comparison between results of single-layer soil variation method and those calculated by rigid limit analysis method proves the correctness of our method. Based on that, the influence of changes of geotechnical parameters on ultimate pullout forces and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are analyzed. The results show that the ultimate pull-out force and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are affected by the nonlinear geotechnical parameters greatly. Thus, it is very important to obtain the accurate geotechnical parameters of 2-layer soil for the evaluation of the ultimate pullout capacity of the anchor plate.
Laboratory swelling deformation tests were carried out on compacted GMZ bentonite and bentonite-sand mixtures with 30% and 50 % sand contents at 20, 40, 60, 80 and 90 °C with infiltration of distilled water. Influence of temperature, initial dry density, and quartz sand content on the swelling deformation characteristic of compacted bentonite specimens was analyzed. Results indicate that the swelling deformation process is accelerated, and the maximum swelling strain increases with the increase in temperature, while the maximum swelling strain tends to be stable with increasing temperature. In the meantime, the temperature effects depend on both of the sand content and the initial dry density of the specimens, the increases of the maximum swelling strain induced by increasing temperature, are enlarged by increasing sand content or initial dry density. Adding of quartz sand to bentonite not only influences the integrality of bentonite specimen, but also increase the microfissuring in area on quartz sand, which are advantageous to the heat transfer, leading to the increase of swelling deformation capacity of the specimen. The increased dry density relatively increases the bentonite content, so the swelling property is enhanced. However, no change on mineral composition of bentonite was observed when temperature was changed from 20 to 90 °C.
The influence of enlarged section parameters on pressure transients of high-speed train passing through a tunnel was investigated by numerical simulation. The calculation results obtained by the structured and unstructured grid and the experimental results of smooth wall tunnel were verified. Numerical simulation studies were conducted on three tunnel enlarged section parameters, the enlarged section distribution along circumferential direction, the enlarged section area and the enlarged section distribution along tunnel length direction. The calculation results show that the influence of the different enlarged section distributions along tunnel circumferential direction on pressure transients in the tunnel is basically consistent. There is an optimal enlarged section area for the minimum value of the pressure variation amplitude and the average pressure variation in the tunnel. The law of the pressure variation amplitude and the average pressure variation of the enlarged section distribution along tunnel length direction are obtained.