Local Force Distribution Research Articles

Wind-Induced Aerodynamic Effects on Set-Back Tall Buildings Using LES

Set-back modification represents a dependable method to reducing the wind effects on high-rise buildings, but the flow mechanism and aerodynamic responses of set-back tall buildings have not been explored systematically. Using the square building as the benchmark model, six set-back building models with varying steps and sizes were chosen for numerical simulation in this study. The results of mean wind pressure and local wind force distribution, power spectral densities of base moment, flow field, and structural response of the proposed building models are compared and analysed using the Large Eddy Simulation (LES) technique. The results demonstrate that the aerodynamic performance of set-back tall buildings dramatically improved, with the actual optimization in the cross-wind direction being more significant. Generally, a single set-back measure can enhance the aerodynamic performance of high-rise buildings more effectively than a double set-back measure. The outcome of this study provides an aerodynamic design guide for set-back tall buildings.

Bending theory of composite pressure vessels: A closed-form analytical approach

Composite pressure vessels are strategic for the present and future of the aerospace, transportation, and energy industries. These shell structures are utilized to store and transport liquids and gases and are principally composed of a cylindrical shell and two elliptical heads. The current rules for the structural design of composite pressure vessels make use of the membrane theory that excludes the bending of the structure. Nevertheless, the cylindrical shell and the elliptical heads present different curvature radii. These changes generate a localized bending deformation that determines an increase in the stress state as an effect of a local bending moment and shear force distributions that arise in the geometric transition zone. The stresses related to the bending effects die out rapidly, moving away from the junction plane, but they are sensibly higher than the membrane stress and, therefore, cannot be neglected in the mechanical assessment. Here, a closed-form analytical solution for the bending theory of composite shells is proposed. It can assist in the design of composite pressure vessels and drive the design towards reliable configurations for structural integrity. Using the Donnell–Mustari–Vlasov theory for thin-walled composite shells, the governing fourth-order differential equation is deduced and solved to obtain the displacements and stresses acting in the junction. The analytical results are successfully compared with those of reference finite element models for validation; their accuracy is proved considering different thicknesses, lay-ups, and flattening factors of the vessel

Twisted-wind effect on the aerodynamic force acting on varying side-ratios tall buildings

The influence of side ratio on the aerodynamic performance of tall buildings is investigated by pressure measurement experiments in a mimicked twisted wind field (TWF) with the maximum twisted angle of 30° and its corresponding conventional wind field (CWF). The global wind loads and distribution of local wind forces on the buildings with different side ratios are analyzed in TWF and compared with those in CWF. Additionally, the effect of side ratio on the spatial correlations of aerodynamic forces in temporal and frequency domains and their spectral features are discussed in the two fields. The results show that the aerodynamic forces are largely affected by the side ratio of tall buildings in TWF. The correlation coefficients of local lateral wind force in the TWF are decreased by 0.1–0.4 compared with those in CWF. The trajectory envelopes of the base moment components in lateral and torsional directions are positively inclined, and the building with B/D = 2 takes the maximum correlation coefficient. The spectral peak of local torsional forces is diminished with the increasing side ratio in TWF and CWF, and the peak frequency in TWF deviates from that in CWF even though the building is under the equivalent wind direction at some specific elevations. This study aims to provide some useful insights into the twisted wind effect on tall buildings with varying side ratios.

Wearable and wireless performance evaluation system for sports science with an example in badminton

Two capacitive sensing units were designed, fabricated, and embedded into two corresponding fingerstalls through microelectronic and additive manufacturing with flexible materials and ergonomic considerations in this study. The sensing units were routed to an adaptor, which in turn was routed to a transmission port (comprising a signal converter and a Bluetooth module), realizing a wearable and wireless force sensing system for sports science applications as the objective. The collected capacitive signals were converted through a preliminarily established database, indicating local force distributions on finger segments. Practical examinations with badminton actions (forehand cross-net shots) were conducted by players to show the effectiveness of the proposed system as an application example. Statistical and quantified results reflected the visual observations on valid shots (67% and 39% for the professional and amateur players, respectively) and well-controlled racket-holding attitude (19.69% and 35.31% force application difference between the first two segments of the index finger of the professional and amateur player, respectively). These proved that the proposed system outperforms existing similar systems in the market and is able to not only classify players with different skill levels but also distinguish attitude stability and controllability, showing scientific evidence in sports science for the first time.

Analysis of installation aerodynamics and comparison of optimised configuration of an ultra-high bypass ratio turbofan nacelle

The installation aerodynamics of ultra-high bypass ratio turbofan engine nacelles involves a strong interaction with the wing and a complex dependency of the forces from the geometric assembly. In the paper, we present a detailed numerical analysis of the flow field and the propulsive metrics for a baseline and an optimised nacelle model mounted under the NASA Common Research Model wings at cruise condition. The wing/nacelle offset represents the main parameter affecting the resulting performance for a given nacelle shape. An extended range of positions is first examined at constant lift, showing the existence of a local maximum for the net resulting force and a larger sensitivity to the horizontal displacement. The installation effect results much stronger on the inboard side with a relevant coupling caused by potential interaction, flow channelling under the wing, and jet/wing interference. The reference baseline nacelle is compared with a sample optimised for the maximum installed net resulting force, analysing local force distributions bringing the overall improvement. Finally, a newly developed automatic procedure to achieve a zero net resultant in numerical simulations is applied. By using an equivalent shaft power, the optimised nacelle is found to provide a 1.79% saving, estimated to amount to a 0.98% fuel burn reduction in the cruise operating point considered.

Combining Image Restoration and Traction Force Microscopy to Study Extracellular Matrix-Dependent Keratin Filament Network Plasticity.

Keratin intermediate filaments are dynamic cytoskeletal components that are responsible for tuning the mechanical properties of epithelial tissues. Although it is known that keratin filaments (KFs) are able to sense and respond to changes in the physicochemical properties of the local niche, a direct correlation of the dynamic three-dimensional network structure at the single filament level with the microenvironment has not been possible. Using conventional approaches, we find that keratin flow rates are dependent on extracellular matrix (ECM) composition but are unable to resolve KF network organization at the single filament level in relation to force patterns. We therefore developed a novel method that combines a machine learning-based image restoration technique and traction force microscopy to decipher the fine details of KF network properties in living cells grown on defined ECM patterns. Our approach utilizes Content-Aware Image Restoration (CARE) to enhance the temporal resolution of confocal fluorescence microscopy by at least five fold while preserving the spatial resolution required for accurate extraction of KF network structure at the single KF/KF bundle level. The restored images are used to segment the KF network, allowing numerical analyses of its local properties. We show that these tools can be used to study the impact of ECM composition and local mechanical perturbations on KF network properties and corresponding traction force patterns in size-controlled keratinocyte assemblies. We were thus able to detect increased curvature but not length of KFs on laminin-322 versus fibronectin. Photoablation of single cells in microprinted circular quadruplets revealed surprisingly little but still significant changes in KF segment length and curvature that were paralleled by an overall reduction in traction forces without affecting global network orientation in the modified cell groups irrespective of the ECM coating. Single cell analyses furthermore revealed differential responses to the photoablation that were less pronounced on laminin-332 than on fibronectin. The obtained results illustrate the feasibility of combining multiple techniques for multimodal monitoring and thereby provide, for the first time, a direct comparison between the changes in KF network organization at the single filament level and local force distribution in defined paradigms.

Elastoplastic frictional collisions with Collisional-SPH

Elastoplastic frictional collisions are encountered in a wide range of applications. For modelling these, inclusion of both the elastoplastic material response and history-dependent collisional forces is essential. The Collisional-SPH method, originally developed for elastic collisions, incorporates frictional collision forces into SPH and accounts for their history-dependence. In this paper, CSPH is extended to model elastoplastic collisions by incorporating an elastoplastic material model. A thorough validation of this elastoplastic CSPH method is presented. CSPH is then used to analyse the influence of deformation on history-dependent collision forces. It is found that the elastoplastic deformation and the resulting shape change of the substrate alter the contact-zone mechanics by influencing the local tangential force distribution. These effects become more pronounced with increasing deformation.

Bridging pico-to-nanonewtons with a ratiometric force probe for monitoring nanoscale polymer physics before damage

Understanding the transmission of nanoscale forces in the pico-to-nanonewton range is important in polymer physics. While physical approaches have limitations in analyzing the local force distribution in condensed environments, chemical analysis using force probes is promising. However, there are stringent requirements for probing the local forces generated before structural damage. The magnitude of those forces corresponds to the range below covalent bond scission (from 200 pN to several nN) and above thermal fluctuation (several pN). Here, we report a conformationally flexible dual-fluorescence force probe with a theoretically estimated threshold of approximately 100 pN. This probe enables ratiometric analysis of the distribution of local forces in a stretched polymer chain network. Without changing the intrinsic properties of the polymer, the force distribution was reversibly monitored in real time. Chemical control of the probe location demonstrated that the local stress concentration is twice as biased at crosslinkers than at main chains, particularly in a strain-hardening region. Due to the high sensitivity, the percentage of the stressed force probes was estimated to be more than 1000 times higher than the activation rate of a conventional mechanophore.

Identification of joints for a load-adapted shape in a body in white using steady state vehicle simulations

Joints are cost-intensive and have a great influence on the properties of a joined assembly. There is a wide variety of research on optimizing the joint distribution in an assembly. These optimizations are performed with joint models, which are rotational symmetrical and thus have transversely isotropic properties. The potential of joints with direction-dependent stiffness is not exploited in those studies. Joints with different shear stiffness can be oriented concerning the local planar force distribution. In this way, individual joints can be designed regarding the local force distribution and the overall properties of the assembly.This paper presents a method to identify these joints based on numerical simulations. For this purpose, a multibody full vehicle model is created, and various steady state driving simulations are carried out. Within these simulations, both the forces at the suspension struts and the connections between subframe and body are determined. Subsequently, these forces are defined as input of an implicit finite element model of the vehicle body, where the joint forces are calculated. Finally, the joint forces of various driving maneuvers and static load cases are superposed and evaluated.With the presented methodology the joints which are suitable for a load adapted shape are successfully determined. The results show great potential for the use of joints with fully anisotropic properties in a vehicle body, which is currently not realized. Joints with three different stiffness could enhance the stiffness properties of a vehicle body.

Developing a Lung Model in the Age of COVID-19: A Digital Image Correlation and Inverse Finite Element Analysis Framework.

Pulmonary diseases, driven by pollution, industrial farming, vaping, and the infamous COVID-19 pandemic, lead morbidity and mortality rates worldwide. Computational biomechanical models can enhance predictive capabilities to understand fundamental lung physiology; however, such investigations are hindered by the lung’s complex and hierarchical structure, and the lack of mechanical experiments linking the load-bearing organ-level response to local behaviors. In this study we address these impedances by introducing a novel reduced-order surface model of the lung, combining the response of the intricate bronchial network, parenchymal tissue, and visceral pleura. The inverse finite element analysis (IFEA) framework is developed using 3-D digital image correlation (DIC) from experimentally measured non-contact strains and displacements from an ex-vivo porcine lung specimen for the first time. A custom-designed inflation device is employed to uniquely correlate the multiscale classical pressure-volume bulk breathing measures to local-level deformation topologies and principal expansion directions. Optimal material parameters are found by minimizing the error between experimental and simulation-based lung surface displacement values, using both classes of gradient-based and gradient-free optimization algorithms and by developing an adjoint formulation for efficiency. The heterogeneous and anisotropic characteristics of pulmonary breathing are represented using various hyperelastic continuum formulations to divulge compound material parameters and evaluate the best performing model. While accounting for tissue anisotropy with fibers assumed along medial-lateral direction did not benefit model calibration, allowing for regional material heterogeneity enabled accurate reconstruction of lung deformations when compared to the homogeneous model. The proof-of-concept framework established here can be readily applied to investigate the impact of assorted organ-level ventilation strategies on local pulmonary force and strain distributions, and to further explore how diseased states may alter the load-bearing material behavior of the lung. In the age of a respiratory pandemic, advancing our understanding of lung biomechanics is more pressing than ever before.

The Effect of Patellar Surface Morphology On Subchondral Bone Alignment When Matching Patellar Osteochondral Allografts (206)

The Effect of Patellar Surface Morphology On Subchondral Bone Alignment When Matching Patellar Osteochondral Allografts (206)

Conductance-strain behavior in silver-nanowire composites: network properties of a tunable strain sensor

Highly flexible and conductive nano-composite materials are promising candidates for stretchable and flexible electronics. We report on the strain–resistance relation of a silver-nanowire photopolymer composite during repetitive stretching. Resistance measurements reveal a gradual change of the hysteretic resistance curves towards a linear and non-hysteretic behavior. Furthermore, a decrease in resistance and an increase in electrical sensitivity to strain over the first five stretching cycles can be observed. Sensitivity gauge factors between 10 and 500 at 23% strain were found depending on the nanowire concentration and stretching cycle. We model the electrical behavior of the investigated silver nanowire composites upon repetitive stretching considering the strain induced changes in the local force distribution within the polymer matrix and the tunnel resistance between the nanowires by using a Monte Carlo method.

Sea Surface Salinity Estimation and Spatial-Temporal Heterogeneity Analysis in the Gulf of Mexico

As an important parameter to characterize physical and biogeochemical processes, sea surface salinity (SSS) has received extensive attention. Cubist is a data mining model, which can be well-suited to estimate and analyze SSS in the Gulf of Mexico (GOM) because it can reflect the SSS internal heterogeneity in the GOM—overall circular distribution, and the seasonality related to temperature and river discharge changes. Using remote sensing reflectance (Rrs) at 412, 443, 488 (490), 555, and 667 (670) nm and sea surface temperature (SST), a cubist model was developed to estimate SSS with high accuracy with the overall performance demonstrates a root mean square error (RMSE) of 0.27 psu and correlation coefficient of 0.97 of R2. The model divides the GOM area according to model rules into four sub-regions, which include estuary, nearshore, and open sea, reflecting the gradient distribution of SSS. The division of sub-regions and seasonal changes can be explained by the distribution of water bodies, river discharges, and local wind forces since it is obvious that the estuary region reaches the largest low-value area and spreads eastward with the monsoon in the spring when the river flow increases to the highest value. While the east to west wind in the non-summer monsoon period guides the plume westward, and the lowest river discharge in winter corresponds to the smallest low value area. After comparison with other statistical models, the cubist model showed satisfactory results in independent verification of cruise data, proving the estimation capability under different geographical conditions (such as estuaries and open seas) and seasons. Therefore, considering high accuracy and heterogeneity mining, the cubist-based model is an ideal method for coastal SSS estimation and spatial-temporal heterogeneity analysis, and can provide ideas for model construction for coastal areas with similar geographic environments.

Numerical investigation on the shear behavior of prestressed concrete beams with small rectangular openings

AbstractThe numerical investigation focused on the shear behavior of prestressed concrete (PC) beams with small rectangular openings, using the software ABAQUS. Three variables, including the prestressing force, the height of the opening and its length, were considered. The numerical results exhibited a good agreement with the previous experimental outcomes, and the parametric analysis was conducted to study the local internal force distribution of two chords during the loading process. The results indicate that for RC beams with openings, the shear proportion variation of the top chord is stable as the opening size changes, while it decreases almost linearly with the increase of prestressing force for PC beams with openings. The position of contraflexure point is found to be proportional to the root of the reinforcement ratio of the chord, and it moves towards the support with the increase of the prestressing force. Furthermore, the empirical equations to determine the shear proportions and the position of contraflexure point between chords are established.

Matrix-Addressed Flexible Capacitive Pressure Sensor With Suppressed Crosstalk for Artificial Electronic Skin

Matrix-addressed flexible pressure sensors, being able to accurately measure both local contact force and spatial distribution, are pursued for many electronic skin applications. One key issue to be addressed is that the local force being applied onto the target areas may be passed to the neighboring pixels through deformation of the touched top electrode layer. It causes significant signal crosstalk and also loss of measurement accuracy. A new top electrode layer structure is proposed with the development of processes for matrix-addressed pressure sensor systems. It is composed of a patterned layer of high Young’s modulus and a low-modulus encapsulation layer. The former is able to sustain a relatively high processing temperature for forming reliable and high-density electrical connections. The latter is to protect the patterned layer while having low Young’s modulus to minimize the spreading of local deformation at the pressed pixel to the surrounding ones. A $10 \times 10$ matrix-addressed flexible capacitive pressure sensor system is constructed to verify this design, showing effective suppression of the pixel-to-pixel signal crosstalk and improvement of measurement accuracy. The flexible pressure sensor system is integrated onto a prosthetic hand, showing capabilities of differentiating details of massage balls.

Multidisciplinary Analysis and Multiobjective Design Optimization of a Switched Reluctance Motor for Improving Sound Quality

In this study, the design optimization method for improving sound quality (SQ) of a switched reluctance motor (SRM) is proposed. The multidisciplinary finite element analysis (FEA) of an SRM is performed to evaluate both average torque and the SQ metrics to design the rotor configuration of the SRM. Specifically, the magneto-static FEA of the SRM is used to evaluate the average torque which is the most important performance of motors, and the local force distribution applied to the stator. Also, the transient structural FEA of the stator excited by the local force distribution, and the transient acoustic FEA are conducted to get the sound pressure radiated by the vibration of the stator. Then, the SQ metrics of loudness, sharpness, fluctuation strength and roughness can be obtained from the radiated sound pressure. We define the correlation function between the SQ metrics and the jury test results of the different types of SRMs. The weighted sum of the torque and the correlation function is set as an objective function. After that, design optimization method of the SRM using a design of experiments is discussed. This study does not consider the nonlinear material properties and is based on 2D analysis; however, with all these limitations, note that this is the first study to propose an overall procedure to increase the SQ of an SRM.

The hydrodynamic forces on a circular cylinder in proximity to a wall with intermittent contact in steady current

We present a three-dimensional Large Eddy Simulations (LES) study on the hydrodynamics of a circular cylinder close to a wall. Intermittent gaps between the cylinder and wall, forming spanning and non-spanning sections along the span are considered. This geometry setting represents an idealized model of pipelines laid on an uneven seabed. As compared to that of the corresponding spanwise-uniform cylinders, the drag coefficient on spanning sections is generally smaller, while the drag on non-spanning sections is slightly larger. Large amplitudes of the sectional forces are observed, partially due to the variations of the gap flow under the spanned sections. Flow deflection from the non-spanning section to the spanning section induces changes in local force and pressure distributions. Despite these changes, the mean force on the cylinder with intermittent contact as a whole is shown to be reasonably estimated by pro rata of forces from spanwise-uniform cylinders over the parameter space considered in this study.

Theoretical investigations of the load distribution of small sized crown gear sets different material pairings

An analytical approach for the calculation of the load distribution on the flank of crown gears, based on the theory according Placzek, is proposed. The teeth of the face gear and the pinion are divided into equidistant slices perpendicular to the normal plane, where the local forces, resulting from the acting torque, are calculated under consideration of the local deformation behavior of the gear system. By considering the geometrical conditions like radii of curvature, etc., the local Hertian stresses can be determined. Based on these considerations, the impact of the stiffness, the helix angle and the offset on the local force or load distribution is illustrated. Finally the lubricant film thickness is calculated by using the EHD-theory.

Evaluation of mechanical deformation and distributive magnetic loads with different mechanical constraints in two parallel conducting bars

Mechanical deformation, bending deformation, and distributive magnetic loads were evaluated numerically and experimentally for conducting materials excited with high current. Until now, many research works have extensively studied the area of magnetic force and mechanical deformation by using coupled approaches such as multiphysics solvers. In coupled analysis for magnetoelastic problems, some articles and commercial software have presented the resultant mechanical deformation and stress on the body. To evaluate the mechanical deformation, the Lorentz force density method (LZ) and the Maxwell stress tensor method (MX) have been widely used for conducting materials. However, it is difficult to find any experimental verification regarding mechanical deformation or bending deformation due to magnetic force density. Therefore, we compared our numerical results to those from experiments with two parallel conducting bars to verify our numerical setup for bending deformation. Before showing this, the basic and interesting coupled simulation was conducted to test the mechanical deformations by the LZ (body force density) and the MX (surface force density) methods. This resulted in MX gave the same total force as LZ, but the local force distribution in MX introduced an incorrect mechanical deformation in the simulation of a solid conductor.

Influence of spinal disc translational stiffness on the lumbar spinal loads, ligament forces and trunk muscle forces during upper body inclination

Inverse dynamic musculoskeletal human body models are commonly used to predict the spinal loads and trunk muscle forces. These models include rigid body segments, mechanical joints, active and passive structural components such as muscles, tendons and ligaments. Several studies used simple definition of lumbar spinal discs idealized as spherical joints with infinite translational stiffness. The aim of the current sensitivity study was to investigate the influence of disc translational stiffness (shear and compressive stiffness) on the joint kinematics and forces in intervertebral discs (L1−L5), trunk muscles and ligaments for an intermediately flexed position (55°).Based on in vitro data, a range of disc shear stiffness (100−200N/mm) and compressive stiffness (1900−2700N/mm) was considered in the model using the technique of force dependent kinematics (FDK). Range of variation in spinal loads, trunk muscle forces and ligaments forces were calculated (with & without load in hands) and compared with the results of reference model (RM) having infinite translational stiffness. The discs’ centers of rotation (CoR) were computed for L3−L4 and L4−L5 motion segments.Between RM and FDK models, maximum differences in compressive forces were 7% (L1−L2 & L2−L3), 8% (L3−L4) and 6% (L4−L5) whereas in shear forces 35% (L1−L2), 47% (L2−L3), 45% (L3−L4) and more than 100% in L4−L5. Maximum differences in the sum of global and local muscle forces were approximately 10%, whereas in ligament forces were 27% (supraspinous), 40% (interspinous), 56% (intertransverse), 58% (lig. flavum) and 100% (lig. posterior). The CoRs were predicted posteriorly, below (L3−L4) and in the disc (L4−L5).FDK model predicted lower spinal loads, ligament forces and varied distribution of global and local muscle forces. Consideration of translational stiffnesses influenced the model results and showed increased differences with lower stiffness values.