Finite Element Program Research Articles

Rehabilitation and Strengthening of Damaged Reinforced Concrete Beams Using Carbon Fiber-Reinforced Polymer Laminates and High-Strength Concrete Integrating Recycled Tire Steel Fiber

Currently, millions of tires are consumed annually, which necessitates the efficient disposal of these quantities of spent tires and the development of means to convert them into useful materials. This research deals with the effect of adding the steel fibers extracted from used car tires (RSFs) to incorporate them as concrete components to obtain high-strength concrete (HSC). The HSC was used in this paper to strengthen the pre-damaged beams by jacking. In the first phase, twelve beams were subjected to an overload equal to 80% of their total expected bearing capacity to obtain damaged RC beams, while one beam was loaded to failure (reference beam, RB0). In the second phase, the damaged beams were strengthened with HSC jacketing integrating RSFs with three contents (0, 0.25, and 0.5%) or by HSC jacking and bonded CFRP laminates to the bottom surface of the jacket. Moreover, the Abaqus finite element (FE) program was implemented to simulate the upgraded damaged beams. The result ensured enhanced HSC compressive and tensile strengths by 11.6–14.4% and 11.6–20.9% as the RSF % increased from 0 to 0.25 and 0.5%, respectively. Using the HSC jacket with 0, 0.25, and 0.5% RSF to strengthen the RC-damaged beams increased the load capacity by 8.8, 14.5, and 20.1%, respectively compared to RB0. Furthermore, strengthening the damaged RC beams with both HSC jacket and CFRP laminates enhanced their load capacity by 41.9, 45.5, and 50.3% as the HSC integrated 0, 0.25, and 0.5% RSF, respectively, compared to RB0. Finally, the FE model could reveal several aspects related to the behavior of the damaged beams strengthened with jackets and CFRP laminates and the interaction between the different beam components.

COMPUTER SIMULATION AND FIELD EVALUATION OF TRANSVERSE JOINTS IN RIGID PAVEMENTS

A methodology for evaluating the condition of portland cement concrete pavement joints by nondestructive deflection testing is presented. A finite element program, JSLAB, was used to conduct a parametric study of the pavement properties that affect deflections and stresses. The modulus of subgrade reaction, K, and the modulus of dowel/concrete interaction, G, were identified as variables that signifi­ cantly affect joint behavior. A chart was developed which can be used to predict the effective K and G for a joint. The absolute deflection of the slab corner, and the effi­ciency of the joint are needed for the evalua­tion. Field measurements made at eight in­ service pavements are presented to illustrate the use of the methodology. An analysis also shows that the modulus of dowel/concrete interaction can have a significant effect on transverse cracking.

COMPARISON OF ROLLER COMPACTED CONCRETE PAVEMENT RESPONSES TO STATIC AND DYNAMIC LOADS

The objective of the study was to compare Roller Compacted Concrete (RCC) pavements responses to static and dynamic loads. Two sets of non-destructive load testing were performed on RCC pavements. The first set used static loading and dynamic loading was utilized for the second. Static loading was provided by front wheels of a Letro-Porter (front loader) and a Heavy Weight Deflectometer (HWD) was used for dynamic loading. A back-calculation procedure for estimating concrete pavement parameters is also presented. The Roller Compacted Concrete pavements were located at Moran Terminal, Boston, Massachusetts. The pavement consisted of a RCC layer of 38 cm (15 in.), a 23-cm (9-in.) gravel subbase and a compacted subgrade. The RCC layer was constructed in three lifts from bottom to top of 14, 14, and 10 cm (5.5, 5.5 and 4 in.). Four slabs were selected for testing. Strains and deflections were measured for static loading tests. A Benkelman beam was used for measuring the static load induced deflections. Deflection basins were determined during HWD tests. Load transfer efficiency at cracks and construction joints was also measured for both tests. The back-calculation procedure has been demonstrated to be satisfactory in estimating in situ pavement material properties. Using estimated RCC elastic moduli and estimated moduli of subgrade reaction, the stresses in the slabs caused by the static loads were computed by the finite element computer program JSLAB and compared to field measured stresses. It was found that the computed stresses were always greater than the measured values. A factor of safety of about 4% can be expected when HWD deflection data are used in place of static vehicle test data in rigid pavement analysis and design.

Progressive Collapse of Steel Structures Under Blast Loads Considering Soil‐Structure Interaction

This study focuses on the effect of soil‐structure interaction on the occurrence of progressive collapse due to an external blast. Therefore, a 3‐story fixed base steel moment‐resisting frame structure was first modeled and subjected to an external blast load. Then, the same structure was modeled considering soil‐structure interaction. In another stage of this study, the effect of plan irregularity on progressive failure resulting from the explosion was investigated, assuming the presence or absence of soil‐structure interaction. The direct simulation method and alternative load path method are all employed to simulate the progressive collapse process of steel frames using the commercial finite element program LS‐DYNA. The results of the numerical simulations demonstrated that the presence of soil‐structure interaction, significantly influences the response of the structure to the blast and this interaction increases the likelihood of progressive failure occurring even at symmetric and asymmetric structures. It was also shown that silty sand soil yields more critical conditions than other types of soil in the event of failure after the occurrence of an explosion in the structure.

Impact of material property variations and sensor positioning on the coating thickness determination of steel sheets using eddy current testing

Purpose This paper aims to investigate the reliable thickness, and more generally, the geometric and material parameter determination of thin electrically conductive and diamagnetic coatings on conductive and ferromagnetic substrates, e.g. steel, using eddy current testing (ECT). Design/methodology/approach The analytical model of an ECT coil arrangement known from the literature is analyzed to evaluate the numerical simulation performed by a Finite Element (FE) program. The latter is used to investigate the influence of the sheet edge on the measurement result. Finally, a measurement setup is presented and the unknown geometric and material parameters are estimated from measurement data of different sample sheets at different air gaps. Findings Generally, valid mesh rules are found for a very accurate FE analysis of eddy current problems with large air gaps. The influence of large air gaps on the parameter estimation is emphasized. Moreover, the formulated hypotheses can be widely confirmed by measurements. Research limitations/implications In this paper, electrical steel sheets coated with a conductive oven-cured ink are used. This sample configuration creates a discrete transition between the substrate and the coating as present in the analytical modeling approaches. Furthermore, the ferromagnetic substrate’s nonlinear B-H curve is not considered in the analytical model so far. Originality/value The analytical model is known from the literature. However, real practical measurements have not been carried out with the discussed setup. Furthermore, well-known literature on eddy current measurements usually only considers constant and very small air gaps.

The effect of impactor shape on low velocity impact behavior of cylindrical sandwich structures with trapeozidal core

The aim of this study is to investigate the impact performance of a cylindrical sandwich structure with Trapeozidal core under different geometries of impactors using the finite element method. The effects of impactor shape, facesheets thickness and impact point on peak contact force, absorbed energy efficiency, maximum displacement and damage deformation are investigated. Progressive damage analysis based on the Hashin damage criterion was performed using MAT 54 material model in LS DYNA finite element program for low velocity simulations. The impact behavior was investigated by creating a Cohesive Zone Model (CZM) based on bilinear traction-separation law while providing the connection between the core structure and its surfaces. At the end of the study, it was determined that the contact force values at P2 were higher than P1. Peak force variation values for cylinder, cone and sphere tipped impactors at P1 and P2 points were 43.5%, 132.3% and 62.2%, respectively. Core support has a significant effect on the contact force. The peak force value and energy absorption efficiency value obtained with the Cone impactor are higher than the others. For all three impactors, it was determined that the largest and dominant damage type was matrix damage.

Mechanical Response and Failure Analysis of Stainless-Steel Beams Exposed to Elevated Temperatures

This research investigates the structural behaviour of stainless-steel beams (SSBs) when subjected to extreme temperatures, specifically in the context of fire-induced deformations. High temperatures, typical of fire occurrences, exert large thermal loads on SSBs, leading in material property changes that make the metal more brittle, stiffer, and brittle. The objective of this study is to investigate extensively the behaviour of SSBs under the combined impact of heat transfer and applied loads, with a focus on substantial deflections. To completely assess the performance of SSBs, we undertake parametric investigations and systematic research efforts. The initial phase comprises a thorough review of relevant data about the behaviour of SSBs at increased temperatures. Afterwards, a parametric study of the web section is conducted to determine the performance of the SSBs under exposure to fire and applied stresses. In order to ease the numerical research, the finite element (FE) program ABAQUS CAE is used to simulate stainless steel I-section beams of varying diameters subjected to realistic fire conditions according to the ISO 834 standard fire curve. The average discrepancy between numerical forecasts and experimental data for six separate models about the final temperature readings is 2.74 percent. Prior to actual collapse, the axial displacement of the SSBs decreases by around 7.5%, showing significant temperature influences on their strength. In addition, the axial deformation of the SSBs exhibits greater displacements in the web portion than in the flange section following fire exposure and loading. This discovery highlights the need to take into account the unique thermal expansion and stiffness characteristics of the web and flange components during fire occurrences. Utilising the finite element approach in ABAQUS reveals the resistance of SSBs to increased temperatures. The findings highlight the potential advantages of using stronger SSBs to maximise the structural response under fire conditions. This study gives useful insights into the thermal behaviour of SSBs and has important implications for building fire-resistant structures, boosting the fire safety of constructions, and enhancing their resistance against fire risks.

Determination of Strength Parameters of Composite Reinforcement Consisting of Steel Member, Adhesive, and Carbon Fiber Textile.

The main aim of the study was the determination of the strength parameters of composite bonded joints consisting of galvanised steel elements, an adhesive layer, and Carbon-Fiber-Reinforced Plastic (CFRP) fabric. For this purpose, shear laboratory tests were carried out on 60 lapped specimens composed of 2 mm thick hot-dip galvanised steel plates of S350 GD. The specimens were overlapped on one side with SikaWrap 230 C carbon fibre textile (CFT) using SikaDur 330 adhesive. The tests were carried out in three series that differed in overlap length (15 mm, 25 mm, and 35 mm). A discussion on the failure mechanism in the context of the bonding capacity of the composite joint was carried out. We observed three forms of joint damage, namely, at the steel-adhesive interface, fibre rupture, and mixed damage behaviour. Moreover, an advanced numerical model using the commercial finite element (FE) program ABAQUS/Standard and the coupled cohesive zone model was developed. The material behaviour of the textile was defined as elastic-lamina and the mixed-mode Hashin damage model was implemented with bi-linear behaviour. Special attention was focused on the formulation of reliable methodologies to determine the load-bearing capacity, failure mechanisms, stress distribution, and the strength characteristics of a composite adhesive joint. In order to develop a reliable model, validation and verification were carried out and self-correlation parameters, which brought the model closer to the laboratory test, were proposed by the authors. Based on the conducted analysis, the strength characteristics including the load-bearing capacity, failure mechanisms, and stress distribution were established. The three forms of joint damage were observed as steel-adhesive interface failure, fibre rupture, and mixed-damage behaviour. Complex interactions between the materials were observed. The most dangerous adhesive failure was detected at the steel and adhesive interface. It was also found that an increase in adhesive thickness caused a decrease in joint strength. In the numerical analysis, two mechanical models were employed, namely, a sophisticated model of adhesive and fabric components. It was found that the fabric model was very sensitive to the density of the finite element mesh. It was also noticed that the numerical model referring to the adhesive layer was nonsensitive to the mesh size; thus, it was regarded as appropriate. Nevertheless, in order to increase the reliability of the numerical model, the authors proposed their own correlation coefficients α and β, which allowed for the correct mapping of adhesive damage.

PRELIMINARY ASSESSMENT OF THE POSSIBILITY OF DOUBLE-STRAND ROLLING AND SEPARATION OF REBAR WITH A DIAMETER OF 22 MM ON A 400/200 OF PJSC KAMET-STAL»

This paper presents proposals for the implementation of a new rolling-separation technology at Mill 400/200 of PJSC “KAMET-STAL” based on the results of mathematical modeling in the finite element program QForm. As part of this work, it is proposed to introduce a new variant of the rolling-splitting technology for rebar with a diameter of 22 mm. According to the proposal, rolled products in stands from 3H to 18H are manufactured in calibers and with settings that correspond to the calibration table for rolling rebars with a nominal diameter of 20 mm. According to this scheme, a double profile is formed in the 17H stand for cutting, and in the 18H stand, the billet is cut longitudinally into two halves with a diameter of 31 mm each. Further along the rolling process, an oval caliber of factory marking 8336 is installed in stand 19H to produce rebars with a nominal diameter of 22 mm (according to the current calibration table for rebars with a nominal diameter of 22 mm, the caliber of stand 15H). Rolls with a round caliber 8345 are installed in the 20H stand (according to the current calibration table for rebars with a nominal diameter of 22 mm – the caliber ofstand 16H). The final production of rebar with a nominal diameter of 22 mm is carried out in two passes in a high-speed 200/4 slitting line. To check the technical feasibility of rolling-separation of rebar profile with a nominal diameter of 22 mm according to the new scheme, the calculation of the deformed state of continuous rolling in the environment for modeling volumetric deformation problems of QForm UK version 10.2.1 was carried out. The model has a number of technical simplifications: all the equipment of the technological line is not taken into account and the distance between the stands is reduced. Simplifications do not reduce the accuracy of the calculation results. Calculations of the deformed state during hot rolling of steel rebar profile with a nominal diameter of 22 mm after separation were performed. The simulation results confirm the possibility of implementing the developed new production technology of rebar profile with a nominal diameter of 22 mm. Calculations showed that the new technology will make it possible to increase the state's productivity during the production of rebar profile with a nominal diameter of 22 mm by 28...29% compared to single thread rolling.

A hyperelastic constitutive model for soft elastomers considering the entanglement-dependent finite extensibility

In this paper, a novel hyperelastic constitutive model for soft elastomers is developed based on the concept of the tortuous tube. This model incorporates the finite extensibility of the polymer chain, the entanglement contribution to elasticity and the non-affine micro-to-macro scale transition in a unified way. To reflect the entanglement effect and its influence on the deformation of soft elastomers, the tortuous tube concept is introduced. The finite extensibility and conformational statistics of an entangled polymer chain in such a tortuous tube are clarified. By embedding the tortuous tube into the microsphere and employing the principle of minimum averaged free energy, a new non-affine scale transition rule is proposed to establish the relationship between the local deformation of a polymer chain at the microscopic scale and the overall deformation at the macroscopic scale. Based on the probability density function related to the conformational statistics, the Helmholtz free energy is established and further decoupled into a volumetric part and an isochoric part. The spatial Kirchhoff stress tensor and spatial elasticity tensor are derived from the newly established Helmholtz free energy. The proposed model is further implemented into the finite element program ABAQUS by writing a user-defined material subroutine. The prediction capability of the proposed model is verified by simulating the homogeneous and inhomogeneous deformations of soft elastomers under various loading modes, including uniaxial tension, uniaxial compression, pure shear, equi-biaxial tension, general biaxial tensile loadings, inflation and indentation. Moreover, the influence of entanglement concentration on the stretchability and stiffness of soft elastomers is predicted and discussed using the proposed model.

Development of a finite element program for acoustics

Acoustic is the study of mechanical waves in solids, liquid and gases. Altougth the differential equations describing these problems are well known, with analytical solutions for simple geometries and/or loads, there are no closed solution for general problems. Thus, it is common to sougth on numerical procedures to address such problems.This work addresses the simulation of mechanical waves in loseless air using the linear finite element method. Solution in both time and frequency domains are discussed and compared to theoretical results.

Numerical simulation of behavior of masonry mechanics made with ecological bricks

Soil-cement brick masonry structures have gained prominence in developing countries due to their practicality, low cost and excellent ecologically sustainable alternative. However, the literature presents few numerical studies on masonry structures in soil-cement bricks, since most of the studies carried out focus on concrete and ceramic bricks. Therefore, in this work, the finite element model of a small wall made of soil-cement brick with structural masonry mortar joints, subjected to compression, is calibrated. The experimental analysis of these small walls was conducted at the Laboratory for Experimental Analysis of Structures at the Federal University of Minas Gerais, and the experimental results are used to calibrate the numerical simulation. The numerical model was developed in the finite element program ABAQUS CAE. A detailed micromodeling strategy was adopted, that is, the models were developed considering the individual representation of bricks and mortars, in addition to the interface between the materials. Using the proposed finite element model, a numerical investigation was conducted to verify the validation of the model concerning experimental investigations. The present study allowed us to adequately replicate the concentration of damage in the bricks, corroborating what was observed in the experimental tests.

INVESTIGATION OF IMPACT PERFORMANCE OF CYLINDER CORRUGATED SANDWICH STRUCTURES WITH DIFFERENT GEOMETRIC CONFIGURATIONS

The aim of this study is to numerically investigate and compare the impact performance of CFRP composite cylinder sandwich structures with five different geometric configurations. The impact performances and damage types of composite cylinder structures for different core configurations were determined. The impact analyses were performed in LS DYNA finite element program using MAT-54 material model with Progressive damage analysis based on the combination of Hashin damage criterion, Cohesive zone model and Bilinear traction-separation law. Among the five different specimens in the study, the highest peak force (PF) value of 1.88 kN was obtained at impact point P2 of the Trapeozidal sandwich structure. The lowest value was obtained at P1 impact point in Triangular sandwich structure with 0.62 kN. The highest and lowest energy absorption efficiency occurred in the Triangular structure, 78% and 38% respectively. The PF value at P2 point is higher than P1. The effect of core support on PF is very important. Since point P1 is not supported by the core, it is determined that the deformation is larger than P2.

Study on the Damage Effect of Shaped Charge Jet Penetrating Multi-layer Spaced Inclined Target Plates

Abstract This study aims to investigate the formation characteristics and penetration performance of multi-layer spaced inclined target plates by shaped charge jets. Based on a multi-material fluid-structure interaction algorithm, a three-dimensional simulation model of a shaped charge jet penetrating multi-layer spaced inclined target plates was established. The process was numerically simulated using a nonlinear finite element program. Relevant validation experiments were conducted, and the causes of discrepancies between numerical simulations and experimental results were analyzed. The effect of the target plate placement angle on the damage effect of the shaped charge jet penetrating multi-layer spaced inclined target plates was discussed. The results show that the numerical simulations are in good agreement with the experimental results. The impact of the shaped charge jet on the spaced inclined target plates diminishes as the placement angle increases. The penetration time and velocity reduction values of the jet on various target plates at different angles were measured. It was found that the size of the openings in the target plates positively correlates with the placement angle, and the symmetry of the opening shapes degenerates with increasing placement angles.

A Data-Driven Seismic Fragility Model for Post-Earthquake Repairable Performance of Highway Curved Bridge Portfolios

The rapid assessment of seismic fragility for highway curved bridges is crucial for enhancing the seismic resilience of transportation infrastructure. However, commonly used performance limit states fail to fully capture post-earthquake rehabilitation requirements. To address this, this paper proposes a data-driven, system-level seismic fragility assessment method for post-earthquake repairable performance of highway curved bridge portfolios. A sample database of curved bridge portfolios is generated using uniform design (UD) and a parametric finite element program, which then drives machine learning (ML) algorithms to develop a seismic fragility prediction model for post-earthquake repairable performance. The model is used to analyze the influence of various structural attributes on the median values of fragility curves (mR) for curved bridges. Additionally, a simplified fragility estimation method is developed based on the analysis results, and its reliability is validated through typical case studies. The results show that the central discrepancy of the UD sampling method is 0.0649, providing reliable and comprehensive data support for the ML prediction model. The fragility prediction model based on an artificial neural network (ANN) exhibits favorable fidelity and robustness. Curved bridges with central angles (α) in the range of 00.5rad show significant variations in mR, with a coupling effect observed between α and column height (H). The median absolute percentage error (MAPE) of the simplified fragility parameter calculation formula is below 11%, offering a preliminary reference for assessing the post-earthquake repairable performance of curved bridges.

Experimental and Numerical Investigation of Steel Panel Links with Different Trapezoidal Corrugations

A novel type of steel panel link with a trapezoidal corrugated section is developed, which is called the corrugated steel panel (CSP) link, aiming to improve both the strength and energy dissipation capacity of the steel links. Quasi-static tests were carried out on two specimens with different corrugation inclination angles to investigate their seismic performance. Test results indicated that Specimen CSP-V (corrugation inclination angle of 90°) and Specimen CSP-H (corrugation inclination angle of 0°) exhibited distinct failure modes due to the differing out-of-plane constraints provided by their corrugations. Numerical analysis was conducted using the general finite element program, ABAQUS, to supplement the test results. Analytical findings suggested that CSPs with a 90° corrugation inclination angle could provide superior ductility, both yield and peak strengths demonstrated a strong linear correlation with the aspect ratio (H/L ratio). For CSPs with a 0° inclination angle, superior strength and stiffness were observed, the relationship between lateral strength and the H/L ratio was better described by a power-law correlation. Furthermore, to achieve comparable seismic performance, the H/L ratio of CSPs with a 0° inclination angle should be at least twice that of CSPs with a 90° inclination angle.

Numerical validation of an innovative 3D calculation method of high‐rise buildings under consideration of component and soil stiffness

AbstractAt the end of the PORR Bau GmbH research project, which ran from 2015 to 2022 and which provided data on strain and settlement sensors from a total of four high‐rise buildings, an innovative calculation method for three‐dimensional building models was finally developed. This is based on a stiffness combination vector that can be applied independently of the finite element program and the modeling quality of the responsible structural engineer. Furthermore, the bedding modulus for supporting the floor slab is varied within the limits specified by the soil expertise by dividing the floor slab into quadrants.

A hysteretic water retention model incorporating the soil deformability and its application to rainfall-induced landslides

Traditional water retention models often overlook the dynamic interplay between soil structure and moisture content, leading to inaccurate predictions of unsaturated soil behaviors. In this research, based on laboratory data, van Genuchten’s soil water characteristic (van Genuchten, 1980) is modified to establish two bounding surfaces that define the permissible range of soil states in terms of the void ratio (e), suction (s), and degree of saturation (Sl). Considering a bounding surface technique, the model effectively captures hysteresis in the soil water retention behavior, encompassing main curves and scanning paths. This approach presumesthat within the permissible range of soil states, which is included between two main surfaces, the derivative of the degree of saturation by void ratio and suction relieson the soil state’s proximity to the main bounding surface. This hypothesis guarantees that the wetting–drying or compressing-swelling scanning curves transit smoothly toward their corresponding main surfaces. The derived equations for Sl are integrated into closed forms, allowing all scanning curves to be distinguished by varying values of the integration constant. Model necessitates the determination of two parameters (b and β) related to the slope and intercept of the linear line interpolating experiments in the ln(s)-ln(eSl/s) plane, which can be defined based on at least a single wetting–drying test. The model predictions are validated against various data sets, including sands and clayey soils, published in the literature. This validation demonstrates the model’s ability to reflect the behavior observed in experimental tests accurately. This new technique offers a significant advantage in the simplicity of parameter determination. Finally, this hysteretic water retention procedure is implemented into a finite element program (Code_Bright), and its performance is evaluated by simulating the behavior of a representative slope subjected to rainfall conditions.

Numerical simulation of pendant droplet behavior on plain and patterned surfaces using Surface Evolver: Applications to condensation heat transfer

In this work, pendant water droplet behavior on a plain surface was simulated using the Surface Evolver (SE) finite element program to study the three-dimensional shape of the droplet on the surface. The critical droplet volume (CDV) before detachment from the surface was measured and compared against experimental data for different plain surfaces. These computational predictions were shown to agree well with experimental data. Next, patterned surfaces were studied which consisted of a central wetting region 2 mm to 5 mm wide sandwiched between two outer non-wetting superhydrophobic stripes. These superhydrophobic stripes served as “bumpers” to confine the droplet to the wetting region during its simulated growth. For these simulations, the primary inputs to the program were the droplet volume V, stripe width w, and surface static contact angle θ which was varied from 30° to 150°. Water droplet contact angle measurements on the plain surfaces used for initial benchmarking were also reported which included polished aluminum, mill finish aluminum, glass, plastic (acrylic), stainless steel, and copper. The idea of this study was to see if the superhydrophobic borders could be used to effectively “pinch off” a droplet in the wetting region, thereby reducing the critical droplet volume needed for detachment and drainage. The motivation for this work was condensation heat transfer which is common to many HVAC&R applications. In these systems, increasing the droplet shedding frequency is often associated with increased heat transfer and improved system efficiency.Therefore, the baseline surface adopted in this study was aluminum with and without the use of superhydrophobic stripes. For these simulations, properties of water at 20 °C were used, and the droplet volume was gradually increased until the critical condition was reached and detachment was detected. Typically, more than 1000 iterations were performed before the droplet geometry converged and was ready for measurement. Grid refinement was also performed to make sure that the results were grid independent. According to Surface Evolver, the lowest predicted critical droplet volume on the plain surfaces was <5 μL for θ1 = 150°, whereas the highest CDV was >295 μL for θ1 = 30°. For θ1 = 90° which is typical of aluminum, the CDV on the plain surface was 74 μL for the fine mesh and 83 μL for the rough mesh. When a 3-mm wide θ1 = 90° wetting region was used, however, bordered by two superhydrophobic stripes with θ2 = 150°, this CDV was reduced to 71 μL for the rough mesh, and when a 2-mm wide wetting region was used, the CDV was reduced even further to 55 μL. This shows both the promise of the idea and the possibility of using a striped / patterned tube to reduce the critical droplet volume needed for droplet shedding in a condensation environment.

Analyzing the Impact of Multiple Foundation Stiffness Correlation on the Natural Frequency of Offshore wind turbines

The analysis of wind turbine behavior should avoid unplanned resonance, as it can increase fatigue damage. It is essential to rigorously evaluate the natural frequency of wind turbines in the initial design stage. This estimation can be done through two steps, the first one is the computing of the fixed base natural frequency of the wind turbine. The second is the estimation of the foundation stiffness effect. This paper examines the error margin of four correlations of foundation stiffness namely Randolph, Davies and Budhu, DNV, and Higgins in the estimation of the natural frequency of wind turbines. The fixed base natural frequency was estimated in this paper using a special-purpose finite element computer program called TurbiSoft through beam and volume elements. A reference 5.0 MW offshore wind turbine and 9 other turbines from different wind farms have been analyzed. For the fixed base natural frequency, obtained results demonstrate the reliability of the finite element program TurbiSoft through an error margin between 1-4% for the reference 5.0 MW offshore wind turbine. For the natural frequency of the whole system, the estimated error marking was between 9-20% which is an important value.This significant error is attributed to the low accuracy of these four correlation formulas for predicting the foundation flexibility contribution. The results from the four correlation formulas used are quite similar, with a difference in the error margin of less than 1%. However, the largest error margins are observed with the Higgins formula, which has been originally developed for short monopiles, even though the analyzed monopiles can be considered short, with monopile slenderness ratios less than 8.