Numerical Simulation Test Research Articles

Blade mass imbalance identification and estimation for three-bladed wind turbine rotor based on modal analysis

Early detection of rotor imbalance is one promising approach to address wind turbine durability. This work proposes a novel blade mass imbalance identification and estimation method for the wind turbine rotor. The method is capable of identifying the presence of a wind turbine rotor mass imbalance. In addition, if a mass imbalance exists in the wind turbine rotor, this method can identify which blade is imbalanced, and then quantify the imbalance severity. The remediation to balance the wind turbine rotor is also provided. The advantages of this method include that only a handful of data is required as input variables (which are the frequencies and modes shapes of all first-order modes) and the method can be applied to a stationary (non-rotating) rotor prior to the first operation. The decision-making process of this method is fast and reliable. The performance of the method is illustrated with the help of both numerical simulation and experimental tests. Model to test correlation and direct blade physical measurements are also conducted to validate the ability of the method to both identify mass imbalance and quantify the degree of mass imbalance. This method was demonstrated to be a high-fidelity tool for identifying the imbalance of the wind turbine rotor and it is also applicable to the wind turbines operating in the field. In addition, this method also shows strong potential to be extended to other wind turbine configurations and even other rotating machinery such as propellors and symmetric, repeated structures.

On determination of the complex voltage ratio using the ellipse-fitting algorithm in the case of an ill-conditioned scattering matrix

The article analyzes three modified versions of the standard ellipse fitting algorithm (EFA), which enables the determination of the complex voltage ratio (CVR) for extremely small values of the phase shift angle when the input scattering matrix of sampled data is poorly conditioned. The novelty of the method is in the use of EFA twice for the sequence of samples shifted by the same angle value, but with opposite signs. The results of the numerical simulation tests are confirmed by the results of measurements carried out in the sampling system using the NI PXI 4461 data acquisition module.

The Coupling Relationship between Building Morphology and Outdoor Wind Environment in the High-Rise Dormitory Area in China

A good outdoor wind environment can guarantee the safety and comfort of student activities. It is also conducive to building energy-saving and low-carbon goals. In this study, the high-rise dormitory area of a university was selected as a research object in the cold region. The study used a combination of numerical simulation and orthogonal tests to analyze the weighting of the influencing factors of the wind environment and to recommend the optimal design scheme. The results indicated that the building layout, building length, width, and height all had different degrees of influence on the outdoor wind environment of the dormitory area. For the slab-type high-rise dormitory, the influence weight of the layout was the strongest, followed by the building height, the width, and, finally, the length. The optimal scheme is a staggered layout with a building length of 50 m, width of 18 m, and height of 85.2 m. The wind environment in this situation performed well in winter and summer. For the tower-type high-rise dormitory, the influence weight of the building height was the greatest, followed by the width, the length, and then the layout. The optimal scheme is a staggered layout with a building length of 26 m, width of 24 m, and height of 85.2 m. The wind environment in this situation performed well. Overall, the study scrutinized the coupling relationship between building morphology and wind environment from the meso-level perspective. At the micro level, we constructed the design method for the dormitory building morphology by considering the wind environment performance as the target. It can assist designers in making decisions during the planning and design phases of project construction to facilitate the positive design of buildings.

Numerical Simulation and Wind Tunnel Test of a Variable Geometry Auxiliary Inlet for a Wide-Body Aircraft Environmental Control System

A variable geometry auxiliary inlet for a wide-body aircraft environmental control system with moveable deflectors operating in a large mass flow rate range is studied through numerical simulation and wind tunnel tests, which yields a design method for the variable geometry auxiliary inlet with high performance. The characteristics of the flow field are studied by numerical simulation. The results show that the favorable pressure gradient and the roll-up vortices are the major impetus that inhales the incoming flow into the inlet. The law of regulation and the performance variation under different conditions are obtained by wind tunnel test. The flow coefficient increases first but then decreases with the increase in the inlet opening, and the pressure rise ratio and total pressure recovery coefficient increase first and then decrease with the increase in the mass flow rate. In general, under the condition of a high Mach number (Ma > 0.4), the inlet opening of this test configuration should not exceed 50%. The deflectors can maintain the normal work of the environmental control system by moving properly to control the mass flow rate of the auxiliary inlet.

An efficient method for estimating time-varying convective heat transfer coefficient based on boundary condition transfer technique

Accurate determination of time-varying convective heat transfer coefficient (CHTC) is the main content of many engineering applications. In view of some problems existing in the determination of time-varying CHTC, this paper develops an estimation scheme using the boundary condition transfer technique. In the new scheme, the estimation of CHTC is transformed into the estimation of known fluid temperature. Then, according to the estimation results of fluid temperature, the discrete values of characteristic variable are weighted comprehensively to obtain the estimated results of time-varying CHTC. Numerical simulation tests are mainly adopted so as to validate the above scheme. The developed scheme is also compared with the traditional method, which can better reveal the performance of the former. Effects of some important parameters such as the number of unknown variables, fluid temperature and measurement noise on the estimation results are illustrated specifically. Results demonstrate that the proposal can effectively determine the time-varying CHTC and improve the computational efficiency. Moreover, the proposed method also reduces the effects of fluid temperature on the forecast results, which is helpful for the accurate determination of time-varying CHTC.

Semi-Analytical Solution of Transverse Vibration of Cylinders with Non-Circular Cross-Section Partially Submerged in Water

The free transverse vibration of a surface-piercing, vertical cylinder partially submerged in water was studied. The cylinder had an arbitrary non-circular, but symmetric, cross-section in the vibration direction. The water was assumed to be an incompressible and inviscid fluid. The effect of the surface waves of water was neglected in the analysis. The exact solution of velocity potential of water was derived by the method of separation of variables. The unknown coefficients in the solution of the velocity potential were expressed in the form of integral equations, including the dynamic deformation of the beam. Then, the governing differential equation of bending vibration of the cylinder under the hydrodynamic pressure was obtained. The Galerkin method was used to obtain the eigenvalue equation by expanding the wet modes of the cylinder into a series of dry modes. The elliptical cylinders partially submerged in water were taken as the numerical example. The accuracy of the proposed method was evaluated by the convergence studies. As a consequent result, the non-dimensional added virtual mass incremental (NAVMI) factor solutions were compared to the present Galerkin solutions, which can be used as a benchmark test for more sophisticated numerical simulations of computational fluid dynamics.

Vibration characteristics and cross-feedback control of magnetically suspended blower based on complex-factor model

The research of vibration characteristics and active control methods of the magnetically suspended blower (MSB) are conducted for mitigation of the vibration amplitudes and the dynamic displacements of rotor shaft of the MSB at high speed. Firstly, the dynamic models with four degrees of freedom (DOFs) of the rotor shaft in the MSB are established. Secondly, the vibration characteristics of rotor shaft considering the rotor unbalance and misalignment are analyzed using the complex-factor model. Furthermore, the complex-factor and complex-exponential function cross-feedback models are respectively used to suppress the vibration amplitudes and the dynamic displacements of rotor shaft. Both numerical simulation and experimental tests of the cross-feedback model are conducted to verify the models. It is shown that a wide cutoff frequency of low-pass filter (LPF) could mitigate the precession, and a wide cutoff frequency of high-pass filter (HPF) could suppress the nutation. The proposed complex-exponential function cross-feedback model could be used to reduce the precession amplitude of the rotor shaft by 38.88%, and mitigate its nutation by 60.42%.

Numerical simulation and field tests on vertical load bearing behaviour of bored root piles

Bored root piles are a new type of pile in which the load-bearing capacity can be significantly improved by jacking prefabricated roots into the soil through reserved holes. In this study, numerical simulations and computations are incorporated with field tests to fully investigate the complex load-bearing behaviour of bored root piles under vertical loading. The established numerical model is validated using a measured load-displacement curve obtained from self-balanced field tests. Using the validated numerical model, the load-transfer mechanism is investigated in terms of the load-displacement curve, axial force, shaft friction, and load-share ratios of different components. Results show that the roots share a significant proportion of the load, whereas the load-share ratios of the different root layers indicate temporal and sequence effects. Parametric studies are performed to investigate the effects of different root configurations on the vertical load-bearing behaviour of bored root piles. The results show that root layer spacing is the most important factor affecting the load-bearing capacity. Three failure modes of bored root piles are formulated in terms of root layer spacing. The results of this study can facilitate the design and application of bored root piles.

Simulation of pyroshock environment and effect rules of shock response spectrum

AbstractThe high-frequency and high-amplitude pyroshock environment during the service of the spacecraft will cause damage to the equipment. Here, we develop a shock test device based on air cannon to simulate the above pyroshock environment. Then, a finite element model was established by explicit dynamic software ANSYS/LS-DYNA, and the simulation results were proved to be consistent with the test data. Based on the theory of Shock Response Spectrum (SRS), the effects of device parameters such as pressure, bullet material and resonant plate material on SRS were investigated via numerical simulation and shock test. This study shows that the amplitude of SRS increases with the increase of pressure in the range of 0.15–0.60 MPa, and the break frequency amplitude has a square root function relationship with the pressure. Additionally, the high-frequency amplitude of SRS was affected by the energy transfer efficiency of the bullet.

Fatigue cracking characteristics of components stiffened with vertical ribs under eccentric loading in steel bridge deck

The components in orthotropic steel decks are generally in an eccentrically loaded state for the nonuniformly distributed wheel loads. By conducting numerical simulation and fatigue tests of components stiffened by the vertical rib (CVR) with single butt weld, the propagation law of CVR cracks under eccentric loading were analyzed. By comparing with components stiffened by U-ribs (CUR), the difference of crack-growth characteristics between components with single and multi butt welds under eccentric loading was explored. The results show that CVR cracks will initiate at the eccentrically loaded side of the weld and propagate obliquely, but still perform the bilateral cracking mode as that under symmetric loading. The CUR and CVR cracks present the same three-stage characteristics of fast-slow-rapid growth and components will accelerate to failure in the third stage, which shall be avoided. The section-damage rate of CUR will be greatly relieved for the unilateral cracking under eccentric loading compared with that of bilateral cracking under symmetric loading, which delays the crack to enter the rapid-growth stage. Since there’s little effect of eccentric loading on the demarcations of crack-growth stages in CVR, it is reasonable to take the demarcation 80 mm between the second and third crack-growth stages as the warning length for maintenance. The semi-elliptical CVR cracks will quickly penetrate base metal after extending to 75 % of thickness with the average ratio of crack depth to length being 0.09, which can be treated as the operation timing of maintenance methods for non-penetrating cracks.

A Comparative Study of Structural Deformation Test Based on Edge Detection and Digital Image Correlation.

Digital image-correlation (DIC) algorithms rely heavily on the accuracy of the initial values provided by whole-pixel search algorithms for structural displacement monitoring. When the measured displacement is too large or exceeds the search domain, the calculation time and memory consumption of the DIC algorithm will increase greatly, and even fail to obtain the correct result. The paper introduced two edge-detection algorithms, Canny and Zernike moments in digital image-processing (DIP) technology, to perform geometric fitting and sub-pixel positioning on the specific pattern target pasted on the measurement position, and to obtain the structural displacement according to the change of the target position before and after deformation. This paper compared the difference between edge detection and DIC in accuracy and calculation speed through numerical simulation, laboratory, and field tests. The study demonstrated that the structural displacement test based on edge detection is slightly inferior to the DIC algorithm in terms of accuracy and stability. As the search domain of the DIC algorithm becomes larger, its calculation speed decreases sharply, and is obviously slower than the Canny and Zernike moment algorithms.

Study and Validation of a Novel Grouting Clamp Type Deepwater Oilfield Pipeline Repair Method Based on Computational Fluid Dynamics

In order to handle the corrosion of underwater production pipe sinks in deepwater oil fields, a non-solid phase silicone plugging agent, an external clamp, and an underwater injection tool are combined in this paper’s innovative pipeline repair technique proposal. The optimal main agent to curing the agent ratio for non-solid phase silicone plugging agents was found to be 100:25, which was achieved through an experimental examination of the curing process. The compressive and cementing strength changes in the curd plugging agent were disclosed by testing and evaluating the mechanical behavior of the plugging agent. In addition, the limits of the compressive and cementing strength were found to be 143 MPa and 11.6 MPa, respectively. Based on this, a computational-fluid-dynamics(CFD)-based analytical approach of the complicated flow field in a deep sea environment on the eroding impact of a plugging agent was developed. Through numerical simulation testing, the mathematical relationship between the plugging agent’s maximum pressure and the flow field’s velocity was established. The limits of saltwater and petroleum oil on the erosion of the plugging agent were found to be 4.19 MPa and 3.29 MPa, respectively, which are values that are far below their strength limits. In this way, the viability and efficacy of this novel pipeline repair technique were confirmed. The study presented in this paper sets the groundwork for an in-depth analysis and optimization of novel corrosion control solutions for deepwater oil field subsea process pipes.

An alternative switching filtered-x LMS algorithm for road impact noise control in vehicle

An adaptive switching FxLMS algorithm is proposed to deal with the problem that the performance of the active control system of interior noise drops sharply when come across road impact. According to the state of the system, the algorithm updates the weight coefficient of the control filter in two different ways. Firstly, the normalization algorithm is adopted to improve the convergence speed. After convergence, the relationship between iteration step size and residual error is established by using deformed Gaussian function. The adverse effects of road impact will be dealt with by a new iteration step. On the premise of increasing a small amount of calculation, it improves the convergence speed of the system and ensures the steady-state performance of the system. Numerical simulation and real vehicle test verify the effectiveness of the proposed algorithm in the face of road impact.

A new creep contact model for frozen soils and its application

To study the bond effect on the creep mechanical properties of frozen soils, a creep contact model for frozen soils is proposed based on the generalized Kelvin body. Tensile and shear strength micro-parameters were introduced to reflect the cementation properties of frozen soils. A subroutine (DLL), called by the particle flow program (PFC3D), was generated using the language C++. Triaxial creep tests were carried out on frozen soils under different axial stress conditions. A comparison of the numerical simulation and laboratory test results showed that the proposed contact model can well reflect the creep mechanical properties of frozen soils. Based on the calibrated model micro-parameters, a series of triaxial creep simulations were carried out to study the effects of the cementation state, confining pressure, and damage state on the creep mechanical properties. The simulation results showed that the cementation state, confining pressure, and damage state have important influences on the creep mechanical properties of frozen soils. The characteristics of the creep curves, number of cracks, and number of force chains with the creep time were thoroughly analyzed. These results can provide a basis for studies on macro-meso creep mechanical properties of frozen soils.

Study on drainage mode and anti-clogging performance of new waterproofing and drainage system in a tunnel

With an increase in tunnel construction and retention, traditional waterproofing and drainage systems have been unable to meet the needs of tunnels in heavy rainfall areas, and disasters such as tunnel lining cracking, leakage, and even collapse, occur frequently. In order to ensure the safe operation and maintenance of tunnels, this paper analyses the characteristics of the traditional waterproofing and drainage system, and puts forward a new drainage structure through numerical simulation and indoor testing. This structure removes the circular drainage blind pipe and adds a convex shell drainage plate between the waterproof board and the secondary lining. The research shows that the new drainage system greatly decreases the water pressure in the easily blocked area of the drainage structure. With the special surface discharge model, the external water pressure of the lining far away from the blocked area can quickly fall back to the normal level. In addition, the drainage capacity of different waterproof and drainage boards is different. With an increase in support pressure, the drainage capacity decreases; the geotextile decreases the most, followed by the capillary drainage board and then the convex shell drainage board. At the same time, after the muddy water drainage test of the three materials, it is found that the convex shell type drainage plate has the best anti-sludge performance. The research in this paper provides a beneficial attempt for the design of waterproofing and drainage structure of a water-rich karst tunnel, and provides a guarantee for the safe operation and maintenance of the tunnel.

Reasonable Support Technology of Full-Stress Anchoring Technology of Advance Roadway: A Case Study

Based on the engineering background of providing advance support for the working face of mining roadways, this paper studies the reasonable support technology of advance roadway roofs by combining theoretical analysis, numerical simulation, and field tests. Based on the geological conditions of the 1304 working face of Yineng Coal Mine, the FLAC3D numerical simulation software was used to compare and analyze the effects of the original single hydraulic prop advance support and the bolt-mesh-cable support without the single hydraulic prop. The results show that although the deformation of the surrounding rock is reduced under the support of the single hydraulic prop, the convergence of the roof and floor of the roadway and the left and right sides are still as high as 288 mm and 308 mm, respectively, which does not meet the requirements for safe production. Based on this problem, this study proposes full-stress anchoring technology. FLAC3D numerical simulation software is used to simulate and analyze the supporting effect of the full-stress anchoring support technology in advanced mining roadways. The results of numerical simulation experiments show that the convergence of the roof and floor and the convergence of the left and right sides of the roadway surrounding rock are 33 mm and 52 mm, respectively, which have a good control effect on the roadway surrounding rock. The field test of bolt full-stress anchoring support technology was carried out in the return air roadway of the 1304 working face. The deformation of the surrounding rock of the roadway was monitored by setting up stations. The measured results show that the maximum roof and floor convergence of the roadway is 42 mm, and the maximum convergence of the two sides of the roadway is 69 mm, which meets the requirements for safe mining on site. In this study, by comparing with the advance support effect of the original single hydraulic prop, the rationality of the full-stress anchoring technology of the mining roadway in the advance section of the working panel is determined. The use of bolt full-stress anchoring instead of the traditional single hydraulic prop for advanced support has a better surrounding rock control effect and a lower support cost. This is a new technology for advanced support of surrounding rock in mining roadways, which enriches the control technology of roadway surrounding rock and also provides technical reference for other similar engineering cases.

Numerical and experimental investigations of mechanical properties of AW 6005-T6 Aluminium alloy butt weld joint using GMAW process

This study aimed to investigate the effect of the welding heat input on the heat affected zone (HAZ) of AW 6005-T6 aluminium alloy for a butt-welded joint using gas metal arc welding. The determination of the thermal cycles, metallography, and the resulting mechanical properties in the zone makes its possible. The study involved using a welding experiment, numerical simulation, physical simulation, and mechanical tests. The welding was carried out using the pulsed gas metal arc welding (GMAW) transfer and type J thermocouples were used to develop the thermal cycles in the HAZ. Simufact® Welding was utilized for the numerical simulation. Optical microscope was used to evaluate the microstructures and Vickers microhardness test was done along the weld cross-section. The HAZ was located on the weld cross-section with a mean hardness of 63.7 HV0.1, which is considerably lower when compared with the base metal (BM) which has a hardness of 100 HV0.1. This indicates thermal softening occurred due to the heat input to the material. There is a match in the hardness values of the Gleeble samples and the locations on the weld cross section suggested by the model showing validity of the simulation. It is important to note the fact that there is an influence of heat input into aluminum AW 6005-T6 weld joints and its mechanical properties in the design of welding process parameters for automotive parts. The welding parameters can be optimized to decrease the heat input into the weld, as this can directly affects the mechanical properties in the HAZ.

A Case Study of Cutting Performance by a Transverse Cutting Head Based on Three-Dimensional Particle Flow Model

Roadheaders have been increasingly used in a variety of tunnel cross-sections and roadway excavations. The appropriate setting of key construction parameters of the roadheader can maintain the excellent cutting performance of the roadheader during excavation. In this respect, this paper reviews in detail the previous studies on various experiments and numerical simulations affecting the cutting performance parameters of roadheader. A method for simulating the breaking process during the mechanical cutting of rock was then introduced using the Particle Flow Code in 3 Dimensions (PFC3D). In the numerical simulations, we used the parallel bond model to simulate the studied rock material and completed the calibration of the mesoscopic parameters by numerical simulation tests. In the simulations, we set different cutting modes, cutting depths and cutting thicknesses to study the rock breaking process of the transverse cutter head in a highly weathered granite environment from a microscopic perspective. The simulations indicated that the cutting mode, cutting depth and cutting thickness have significant effects on the cutting force and specific energy consumption. It is feasible to use the available space to the fullest and effectively reduce the wear of the picks by adopting the undercutting mode. The cutting efficiency can be improved and the specific energy consumption of cutting can be significantly decreased by increasing the cutting depth. The optimal cutting depth for highly weathered granite is 13 cm. As the cutting thickness increases, the cutting head's normal and rolling forces increase linearly, and the cutting efficiency improves. Under the condition of highly weathered granite, the maximum cutting thickness of the Erkat ER1500 transverse cutting head is 12.5 cm. Overall, the results indicate that the discrete element method is a powerful tool for simulating rock cutting process.

Stress Relief and Permeability Enhancement with Hydraulic Fracturing in Overlying Key Strata of Deep and Soft Coal Seams.

The technical problems of high in situ stress, high gas pressure, high gas content, and low coal seam permeability are widespread in deep soft coal seam excavation, which leads to frequent occurrences of dynamic phenomena, such as coal cannons and blowout holes. Based on the high-pressure hydraulic fracturing technology and process, this study puts forward a new technology of gas drainage in deep and soft coal seams by fracturing the overlying key strata to cut off the stress transmission path among coal and rock strata. According to the theories of key layer and masonry beams, the distribution locations of the main and subkey strata are determined, and based on uniaxial compression and Brazilian splitting experiments, the mechanical parameters of key stratum were tested. Combined with the results of numerical simulation and field test, initial pressure and fracturing radius of hydraulic fracturing technology for overlying key strata were determined, the stress relief effect and permeability variation law of coal seam after hydraulic fracturing in the main and subkey strata were analyzed, and then technical schemes for simultaneous fracturing of the key layer were designed. Field application results showed that the stress concentration phenomenon in soft coal seam excavation had been alleviated, and the stress relief effect of coal seam and the permeability were increased obviously. The volume and concentration of gas drainage were increased by 10 and 11%, respectively, the gas amount by 1.22 times; the frequency of dynamic phenomena such as coal cannons decreased by 95%, the gas concentration in return air flow by 20% during mining processes. This paper provided an innovative technical idea and process for gas control in deep and soft coal seam excavation, which could effectively solve the common and difficult problems about frequent occurrences of excessive gas concentration and dynamic phenomena.

Postfault optimal islanding of smart grids using a reinforcement learning approach

AbstractThis paper presents a method for optimal reconfiguration of smart grids following the occurrence of short circuit faults. Due to restoration delays, the aim of the proposed approach is to save the maximum possible number of loads by forming stable islands and serving loads with Distributed Energy Resources (DERs). The islanding plan aims to prevent island instability and to help DERs continue supplying the maximum number of loads by the optimal network reconfiguration. Fault isolation is carried out by the protection system and the proposed procedure is commenced right after the fault isolation by controlling the condition of the network remote‐controlled switches. The proposed islanding plan is a novel method by this paper in the management of the postfault conditions of smart grids. Furthermore, a Q‐learning reinforcement approach is presented as the optimization tool because of its great capability and fast response for the determination of optimal reconfiguration. Numerous simulation tests for various fault locations on a 6‐bus and a 33‐bus test networks show the effectiveness of the proposed method in the improvement of postfault network reliability and sustainability.