Equivalent Numerical Model Research Articles

Optimized identification process of equivalent wind load calculations for offshore wind turbines under standstill conditions

In engineering, the wind excitations acting on the offshore wind turbine (OWT) structure cannot be obtained directly by the measured method. The traditional load simulation way may lead to poor accuracy because of the deviation between actual operational conditions and simulation environment parameters or load coefficients, which are always selected based on load spectrums, small scale model tests and engineering experience. To solve this project problem, an equivalent wind load optimization model and parameter identification process of OWT was established under the standstill conditions. Afterwards, two key load parameters in load model respectively called constant drag coefficient and unsteady lift coefficient can be obtained through recursive call on numerical model and feedback analysis using particle swarm optimization (PSO) algorithm based on measured vibration data. The applicability and accuracy of proposed calculation process was verified through an equivalent numerical model of OWT considering different particle position and wind speed. Further, the optimization identification on equivalent wind load and the drag and lift coefficients of one OWT was achieved based on measured data. It is illustrated that the identified drag coefficients show a drop trend from 0.629 to 0.154, consistent with the parameter range of 0.20–0.60 obtained from model experiments, before the wind speed reaches 6.0 m/s and then rise obviously with the increase of wind speed. On the contrary, the range of optimized lift coefficients form 0.133–0.480, which is as familiar as the experimental parameter range of 0.10–0.30, reflects a certain increase trend. Finally, the comparison between identified wind excitations and calculated loads based on the measured strain data explain that the proposed load optimization identification process have a good credibility on actual OWT.

Improved magnetic-based apparatus enables non-destructive and high sensitive steel-bar corrosion detection

Steel-bar corrosion can not only induce corrosion cracking, but also cause the bearing capacity decline of concrete structures. This contribution reported an improved magnetic-based steel bar corrosion detection apparatus with simple structure and high accuracy. Accelerated corrosion tests on steel rebar were carried out to calibrate the accuracy of the magnetic-based corrosion detection apparatus. A parameter of sensitivity coefficient, k, was proposed to evaluate the corrosion detection sensitivity of the apparatus. An equivalent numerical model was established based on multi-physical simulation to quantify the corrosion degrees and explore the impacts of the frame internal structural parameters. Results show that k is stable and changes linearly with the diameter of steel rods tested. Increasing frame width and foot length can increase k, and adding extra calibration magnetic circuits leads to reduction in k. Overall, the modified magnetic-based apparatus provides a simple, reliable, accurate and non-destructive method for steel corrosion detection.

A MICRO APPROACH TO VALIDATE THE GURSON YIELD CRITERIA AT MACRO LEVEL

In the present work, an effort has been made to validate Gurson yield criteria at the macro level with an equivalent numerical model at the micro level. The continuum body at macroscale has been assumed as periodically arranged stackable unit cells each containing a single void at microscale. A hexagonal cylinder containing a spherical void is considered as the shape of the unit cell; for simplicity, the hexagonal cylinder is modeled as a circular cylinder which allows simpler axisymmetric loading. Furthermore, due to symmetry, only a quarter of the geometry is required to model. A good comparison between both models is obtained for the different void radii.

An equivalent numerical model for calculating shot peening bending deformation based on the laser forming method

Shot peen forming is an essential method for forming large-size thin-walled structural parts in the aerospace field. However, the complex elastic–plastic deformation involved in the forming process presents a challenge in calculating directly the deformation response under the specified peening parameters. The energy of the shot beam in the shot peen forming process is equivalently converted to that of the laser beam in the laser forming process, enabling the equivalent simulation of macroscopic deformation of the shot-peened workpiece using the laser-induced temperature field. It is proven that the essential factors affecting the laser forming process are the laser power, scanning speed, the width and thickness of the plate. When other parameters remain constant, the equivalent laser energy can be determined by the impact energy of the shot beam and the equivalence factor. The average error of the proposed model is 5.068%, with a maximum error of less than 10%, demonstrating a well agreement between the simulation and test results. Furthermore, the equivalent numerical model is used to examine the influence of process parameters on shot peen forming, indicating that the radius of curvature produced by shot peen forming increases with nozzle speed and plate thickness, but decreases with air pressure.

Impact of cooling rate on mechanical properties and failure mechanism of sandstone under thermal–mechanical coupling effect

High geo-temperature is one of the inevitable geological disasters in deep engineering such as resource extraction, space development, and energy utilization. One of the key issues is to understand the mechanical properties and failure mechanism of high-temperature rock disturbed by low-temperature airflow after excavation. Therefore, the experimental and numerical investigation were carried out to study the impact of cooling rate on mechanical properties and failure mechanism of high temperature sandstone. First, uniaxial compression experiments of high temperature sandstone at different real-time cooling rates were carried out to study the mechanical properties and failure modes. The experimental results indicate that the cooling rate has a significant effect on the mechanical properties and failure modes of sandstone. The peak strain, peak stress, and elastic modulus decrease with an increase in cooling rate, and the fragmentation degree after failure increases gradually. Moreover, the equivalent numerical model of heterogeneous sandstone was established using particle flow code (PFC) to reveal the failure mechanism. The results indicate that the sandstone is dominated by intragrain failure in the cooling stage, the number of microcracks is exponentially related to the cooling rate, and the higher the cooling rate, the more cracks are concentrated in the exterior region. Under axial loading, the tensile stress is mostly distributed along the radial direction, and the damage in the cooling stage is mostly due to the fracture of the radial bond. In addition, axial loading, temperature gradient and thermal stress mismatch between adjacent minerals are the main reasons for the damage of sandstone in the cooling stage. Moreover, the excessive temperature gradient in the exterior region of the sandstone is the main reason for the damage concentration in this region.

Research on performance degradation analysis method of offshore concrete piers in cold regions

Due to the influence of periodic tidal changes, the offshore reinforced concrete (RC) bridge piers in cold regions have been subjected to seawater freeze-thaw cycles (FTCs), which seriously affects the service performance of bridges. Based on this, the RC precast segment of the bridge pier under seawater FTCs was carried out, and the FTCs damage distribution was obtained by ultrasonic tomography technology. Considering the critical saturation theory, temperature distribution characteristics, pore crystallization theory and pore pressure model, the prediction method on the FTCs damage was established from micro-scale. Subsequently, the equivalent numerical simulation model of RC pier with FTCs was established from multi-scale. The test and calculation results show that the micro-calculation model can well simulate the pore accumulation and pore transformation, which can well describe the pore evolution behavior of concrete under FTCs. Moreover, the hysteretic curve obtained by the equivalent model is in good agreement with the test result. With the increasing FTCs, the peak load of the RC pier decreases gradually, which the FTCs damage seriously affects the mechanical properties of the RC pier, and there is an obvious FTCs damage limit in the RC piers.

Seismic Performance Evaluation According to HSS and CFST Columns of 3D Frame Buildings with Rubber Friction Bearing (RFB).

This study has been conducted to observe nonlinear time history analysis of a 3D-office building frame where performance has been examined in the presence of base isolation and a bracing system. This steel structure has an underground story surrounded by stiff well-graded sand and is assumed to be located in an intense seismic area. The static and dynamic experimental performance of a Rubber Friction Bearing (RFB) has been considered, and an equivalent numerical model has been used in finite element software, which provides a satisfactory relationship between experimental and numerical prediction. The results show that the story drift and post-earthquake damage of the frame reduced significantly due to the presence of RFB devices. These isolators are most effective in moderate earthquakes. The presence of a minimum number of Steel Buckling Restrained Braces (BRBs) systems improve structural performance under moderate and strong ground motions by reducing story drift and residual damage. Hollow Steel Section (HSS) and Concrete-Filled Steel Tube (CFST) sections have been used in the simulation process, and it was found that the HSS system is susceptible to damage even if both seismic protection systems have been considered. The findings provide important conclusions to select suitable seismic protection for this type of structure, which is limited by simulation study due to the absence of experimental observation.

A novel independent heat extraction-release double helix energy pile: Numerical and experimental investigations of heat extraction effect

The application of ground source heat pump buried pipe can meet the requirements of concealment, protection and high reliability in civil air defense works, but the thermal imbalance in operation restricts the performance of system. To alleviate the problem of underground thermal imbalance, a novel independent heat extraction-release double helix energy pile was proposed, and a two-dimensional equivalent numerical model was developed and verified. Based on the numerical model, a comparison was made between independent operation of heat release and joint operation of heat release and heat extraction, and “effectiveness Ω” and “saturation degree Se” were defined as the evaluation index to research the heat extraction effects of different conditions during joint operation, the results showed that the average temperature rise in the backfill area of joint operation is 54.5% lower than that of independent operation, the heat-extracting pipe can effectively take away the heat accumulated in the energy pile area. The lower the inlet temperature of the heat-extracting pipe is, the better the heat extraction effect is. When the flow rate is about 50L/h, both the saturation degree and effectiveness are high, which has a better heat transfer effect. The larger the pipe diameter is, the greater the total heat extraction capacity of the heat-extracting pipe is, and the more favorable to the heat extraction, but the improvement effect is gradually declining, the diameter of the heat-extracting pipe is more applicable around 20 mm. For pipe length, when the effectiveness of the heat-extracting pipe is low, the length of the heat-extracting pipe can be properly reduced, which can reduce the initial cost, but when the effectiveness is close to 1, further reducing the pipe length will weaken the heat extraction of the heat-extracting pipe.

An expansion based on System Equivalent Model Mixing: From a limited number of points to a full-field dynamic response

A high-resolution dynamic response is important for characterizing a system’s dynamic properties. Measurements involving a limited number of points on the structure can be expanded to unmeasured points through approximation or model-based expansion techniques that rely on the introduction of a numerical model. Recently, an expansion method called System Equivalent Model Mixing (SEMM) was proposed where a numerical DoF set is used to extend an experimental model with limited measurement points. The concept of SEMM is similar to the well-known SEREP and VIKING expansion methods, but it is defined in the frequency domain. Using the dynamic substructuring approach, the equivalent experimental and numerical models are coupled so that the hybrid model inherits the dynamic properties of both models. Although the method has been well adopted, there is still no comprehensive phenomenological analysis to determine the influence of the method’s parameters on the consistency of the hybrid model and thus on the accuracy of the expansion process. This paper addresses the issue by evaluating the accuracy of the SEMM expansion process, focusing on the influence of the regularity of the so-called equivalent numerical model. The introduction of quasi-equivalent numerical models into SEMM is analysed here, which can differ not only with respect to the mass and stiffness properties but also in terms of the geometry and boundary conditions. The parametric study was carried out on a real component of a household appliance, and the most influential parameters in terms of accuracy of the SEMM expansion process were identified. The analysis showed that accurate expansion results, with a small number of experimental points, is achieved if only those points are well scattered across the analysed system.

Seismic response of electrical cabinets considering primary-secondary structure interaction with contact nonlinearity of anchors

ABSTRACT Seismic assessment of safety-related equipment in a Nuclear Power Plant (NPP) is more demanding compared to general structures owing to their role in the safe operation and shutdown of the plant. In-cabinet response spectra (ICRS) is thereby generated to qualify the performance of the sensitive devices installed in a cabinet. This study presents the effect of post-installed anchor interaction on the seismic response of an electrical cabinet to drive the ICRS considering primary-secondary interaction (PSSI). Nonlinear hysteretic shear behavior of the anchor connection and its interaction with the floor was considered. An equivalent numerical model was developed to imitate the nonlinear behavior of the anchor bolt. The numerical behavior of anchor was validated using the recent available experimental results. A parametric study for the coupled and uncoupled condition was also considered. The seismic response manifests the nonlinear interaction of anchor bolt that is significant to be considered. The response amplification in a coupled system with anchors nonlinearity is more significant than the floor response spectra (FRS) method and the fixed boundary condition. Moreover, for tuned and nearly tuned primary-secondary systems under the linear and nonlinear connection is also addressed.

A novel 2-D equivalent numerical model of helix energy pile based on heat transfer characteristics of internal heat convection

Numerical modeling has been widely used to simulate the heat transfer of ground heat exchanger (GHE), However, there is a lack of analysis and comparison of different models and methods, for helix energy pile, there is a lack of an efficient and accurate numerical model to study the complex heat transfer problems. In this paper, taking a novel truncated cone helix energy pile (CoHEP) as the object, a two-dimensional(2-D) equivalent heat conduction model considering the heat transfer characteristics of the heat convection in the buried pipe was established, at the same time, a three-dimensional(3-D) full scale model and a 2-D ring coils model were established. By comparing the simulation results of three numerical models with the experimental results under the same conditions, the effects and suggestions of meshing on different models, the model characteristics and main error sources of different models were analyzed. The long-term and short-term simulation results and temperature distribution characteristics of different models were further analyzed. The study shows that the 3-D model has the highest accuracy in the simulation process, but the simulation efficiency is low, and it is easy to be affected by meshing. The 2-D ring coils model has high simulation efficiency, but the long-term simulation error is large, and the thermal influence radius of the pipe is smaller than the actual situation. For the 2-D equivalent model, the simulation error is small, and the thermal influence radius is close to those of the 3-D full scale model, and the effect of long-term simulation is obviously better than that of the 2-D ring coils model. The results indicate that the 2-D equivalent model effectively improves the simulation accuracy of the 2-D heat conduction numerical model, it can obtain the temperature distribution inside and outside the buried pipe which is closer to the actual situation with less calculation and higher simulation accuracy.

Intraductal Tissue Sampling Device Designed for the Biliary Tract.

Clinical sampling of tissue that is read by a pathologist is currently the gold standard for making a disease diagnosis, but the few minimally invasive techniques available for small duct biopsies have low sensitivity, increasing the likelihood of false negative diagnoses. We propose a novel biopsy device designed to accurately sample tissue in a biliary stricture under fluoroscopy or endoscopic guidance. The device consists of thin blades organized around the circumference of a cylinder that are deployed into a cutting annulus capable of comprehensively sampling tissue from a stricture. A parametric study of the device performance was done using finite element analysis; this includes the blade deployment under combined axial compression and torsion followed by an axial ‘cutting’ step. The clinical feasibility of the device is determined by considering maximum deployment forces, the radial expansion achieved and the cutting stiffness. We find practical parameters for the device operation to be an overall length of 10 mm and a diameter of 3.5 mm for a n}{}50~mu text{m}n blade thickness, which allow the device to be safely deployed with a force of 10N and achieve an expansion over 3x its original diameter. A model device was fabricated with these parameters and a n}{}75~mu text{m}n thickness out of a NiTi superalloy and tested to validate the performance. The device showed strong agreement with an equivalent numerical model, reaching a peak force within 2% of that predicted numerically and fully recovering after compression to 20% of its length. Clinical and Translational Impact Statement–This pre-clinical research conceptually demonstrates a novel expandable device to biopsy tissue in narrow strictures during an ERCP procedure. It can greatly improve diagnostic tissue yield compared to existing methods.

Responses of the ground and adjacent pile to excavation of U-shaped tunnel

Although there are many studies on the impact of tunnel on the surrounding environment, most of them focused on the circular tunnels but very few on U-shaped tunnels. In order to obtain a better understanding of the impact of U-shaped tunnel excavation on the ground and adjacent pile foundations, a simplified analytical method is developed in this work. The U-shaped tunnel is projected into a unit circle using conformal mapping method. The displacement and stress of the soil around the tunnel are solved analyzed. The settlement of a single pile is obtained by the complex variable function and the load transfer method. The influence of grouting is considered in the calculation. The analytical solution is verified by the simulation results given by an equivalent numerical model and validated with the field-measured data in an engineering case in Beijing.

High-Frequency Vibration Analysis and Optimization of Irregular Wear of Pantograph Carbon Strips

The irregular wear of carbon current collector pantograph strips increases the railway maintenance costs and introduces safety hazards in the railway operation. This paper presents a method for analyzing the irregular wear of carbon strips with numerical dynamic analyses and modal tests. The carbon strips were studied in laboratory tests, and an equivalent numerical model for the investigation of their irregular wear and performance improvement was established. The results from the computational simulations were evaluated based on the laboratory results, and the correlation between the high-frequency vibration and irregular wear of the carbon strips was studied. The irregular wear contour of the carbon strips coincides with the high-frequency mode shape according to the experimental and numerical results. Moreover, the dynamic design for carbon strips was optimized with the validated computational model. The results suggest that the optimized schemes effectively mitigate the irregular wear of carbon strips.

Path loss modeling and verification of implantable human-body communication based on a point source field.

Deep brain stimulation is a method of nerve regulation that uses human body conductance characteristics; signals are diffused and transmitted through human tissues to regulate diseases. We analyzed the distribution and the transmission mechanism of implantable electrical signals from a point source field in the human body using the point source field implanting channel model. The model was established using a mathematical modeling method, with reasonable boundary conditions and assumptions. Further, we established an equivalent numerical solution model to verify its accuracy and compared the model to published experimental results to evaluate its consistency. The analysis results of the two models revealed that both had errors of < 1%. A comparison of the experimental results to published experimental data revealed that the error between the two was < 4 dB, and the model displayed excellent consistency. Our proposed model is accurate and exhibits good consistency with published experimental results. We therefore conclude that the proposed model is reliable.

Dynamical systems approach for the evaluation of seismic structural collapse and its integration into PBEE framework

The development of collapse fragility curves is an essential requirement for the assessment of the collapse risk of structures. These fragility curves depend on the structural collapse capacity that is evaluated in terms of either the intensity measure (IM) or the damage measure (DM); such as the engineering demand parameter (EDP). In turn, collapse capacity estimates are sensitive to the method employed for their assessment. Conventionally, the IM and DM rules are employed in conjunction with incremental dynamic analyses (IDA) to quantify the collapse capacity of a structure. However, this approach has been criticised for being subjective in nature, since it depends on the structural response approaching predetermined threshold values. Therefore, it does not relate to the actual dynamic instability. Although the selection of these thresholds stems from the results of experimental investigations and equivalent numerical models and serve as an indirect check for dynamic instability, the present study seeks to provide a mathematical basis for defining collapse criteria. A dynamical system approach is used to formulate a mathematical criterion for defining P-Delta instability induced seismic collapse in single-degree-of-freedom (SDOF) structures. The non-linear SDOF structure is considered as a non-autonomous, non-smooth system, and is studied as an ensemble of different sub-systems. Collapse is defined as the point when the dominant system eigenmode of the structure changes from stable to unstable, and remains unstable as the structure collapses. This approach can be applied to first mode governed multi-degree-of-freedom (MDOF) structures when studied as an equivalent SDOF structure. It is found that the dynamical systems approach results in higher deformations at collapse when compared to the conventional IM/DM rule based approach, suggesting the conservatism involved in the latter. However, it results in lower deformations at collapse when compared to the energy criterion, which relies on the occurrence of large deformations to predict collapse. Furthermore, the derived fragility curves show that the proposed approach yields lower probabilities of collapse when compared to the conventional method. Therefore, the proposed method can be used an alternative method for the performance design of structures.

Crashworthiness of Nomex® honeycomb-filled anti-climbing energy absorbing devices

To investigate the energy-absorption characteristics of thin-walled metals and Nomex® honeycomb composite structures, Nomex® honeycombs with five different specifications were applied to anti-climbing energy absorbing devices. Based on compression tests on Nomex® honeycombs, the equivalent numerical model for honeycombs was verified. A finite element model (FEM) for anti-climbing energy absorbing devices was established in Hypermesh. On this basis, the effects of parameters of different honeycombs on absorbed energy of energy-absorbing structure were analysed through LS-DYNA. The results showed that the energy absorption capacity of the anti-climbing energy absorbing devices mainly depended on honeycomb and thin-walled tubes. A Type-2 model exhibited the highest energy absorption capacity, at about 362 kJ, ACT1-3.2-144 honeycomb and thin-walled tubes absorbed energies of 198 and 149 kJ, respectively, which accounted for more than 95% of the total energy absorbed by the whole structure. The results also revealed that the corresponding average buffer force (484 kN) and the maximum peak buffer force (1226 kN) of the Type-2 model were also much greater than those of the other four structures. The buffer force of the Type-2 model remained within 300 to 1000 kN.

The mechanical modelling of nonhomogeneous reinforced structural systems by a coupled BEM formulation

This study presents an accurate numerical formulation for the mechanical modelling of nonhomogeneous reinforced structures. Structural systems complex and efficient utilise such composition, which are largely observed in mechanical, naval and automotive industries, for instance. The Boundary Element Method (BEM) represents mechanically the plane nonhomogeneous domains in the formulation, in which viscous and time independent mechanical behaviours are accounted. The reinforcements are modelled by 1D truss elements, which are either represented by the Finite Element Method (FEM) or the BEM. The reinforcements allow for elastoplasticity behaviour. The 1D BEM approach leads to accurate and stable results in comparison with classical FEM modelling. The proposed formulation is applied in the mechanical analysis of four complex nonhomogeneous reinforced structural systems. The results achieved by the proposed formulation are compared against the responses of equivalent numerical models available in the literature. The accuracy, stability and robustness of the proposed formulation, particularly when domains and reinforcements are represented by the BEM, are illustrated.

DEVELOPMENT OF THE COMPUTER PROGRAM OF CALCULATION OF CONCRETE BORED PILES IN SOIL GROUND OF ASTANA CITY

The current calculating theories of massive constructions are based on the simplified models without consideration of factors settlement as nonhomogeneous environments interaction, the interacting environments nonlinearity or considering them separately and conditionally. Therefore, equivalent numerical model designing of bored piles interaction with the soil mass and designing of a nonlinear technique of numerical calculation of similar systems on its basis is a modern and relevant task, which is an effective tool for a number of relevant geotechnical tasks solutions. The calculation of reinforced concrete bored pile with the real diagrams of a pile material deformation and surrounding rock massif has been presented in the article. The computer program allows receiving the strain-stress state of a pile and the surrounded massif as one heterogeneous body. New calculation approaches of the reinforced concrete bored pile can be used in the standards modernization when transferring from the regulatory framework of Kazakhstan to Euro code according to the reform concept.

Optimal Control Theory Applied to Unintended Source Control and Field Shaping for Time-Harmonic Electromagnetic Waves

This paper addresses the experimental control of time-harmonic electromagnetic waves. The underlying optimal control problem aims to find a set of values to apply to control sources, located in the controlled region or on its boundary, allowing any electromagnetic field caused by an undesired noise source to be suppressed or replaced by any other field map. After a presentation of the control method, illustrated with a few numerical applications, two experimental setups are considered. The first setup aims to control the voltage within a mixed microstrip/coaxial transmission line. In the second setup, the electric field inside a cross-shaped waveguide network is controlled. For both setups, the working frequency is chosen in the ultra-high frequency range, and a comparison is made to the results given by the equivalent numerical models.