Force Moment Research Articles

Influence of restricted visual input on lower limb joint works of female children during sit-to-stand

BackgroundThe ankle-knee-hip joint systems have structures that can produce mechanical work through elastic, viscoelastic mechanisms or muscle activity. This study aimed to compute sit-to-stand (STS) joint works in lower limbs between blind and sighted children to find the relationship between visual memory and STS joint work variables. MethodsThis study included fifteen female children with congenitally blind (CB) and 30 healthy girls without visual impairments. The children with no visual impairments were randomly divided into two condition groups with 15 each, the eyes open (EO) and the eyes closed (EC). Inverse dynamics calculated joint works by integrating multiple the moment and angular velocity (F1) and force and velocity (F2). They were normalized to body mass and body height. ResultsGenerally, the sensitivity of F1 (on both sides in the sagittal and frontal planes) was more than F2 (on the non-dominant side in the mediolateral and vertical axes). In the ML axis, the EC group had insufficient maximal non-dominant hip work relative to the EO group (p = 0.002). In addition, the CB group suffered from low hip efficiency (p = 0.003) and high knee (p < 0.001) mechanical work. ConclusionsNumerous differences between CB and EC groups (on knee and hip works) showed that the time of visual input deprivation could change the type of human body's strategies to reach the consolidation process and keep adequate balance during STS. Therefore, rehabilitation programs should be aimed at addressing the impairments in the management of restricted visual input during STS performance.

Numerical Study of the Ultimate Bearing Capacity of Two Adjacent Rough Strip Footings on Granular Soil: Effects of Rotational and Horizontal Constraints of Footings

In this paper, the numerical study of the ultimate bearing capacity (UBC) of two closely spaced strip footings on granular soil is investigated using the finite element method (FEM) and upper bound limit analysis (UBLA). Although the UBC of two adjacent footings has previously been studied in other experimental and numerical research, in all the previously reported studies, the footings were not allowed to rotate and move horizontally freely. Due to the deformation of the soil medium, two closely spaced footings are subjected to horizontal movements and tilting, even under central vertical loads. When the two adjacent footings are not permitted to rotate and move in the horizontal directions, the unwanted bending moment and horizontal force act on the footings. Indeed, the UBC of two closely spaced rough footings is evaluated under incorrect constraints in earlier research. In the present research, the UBC of two adjacent rough footings is evaluated with and without these incorrect constraints. The key finding of this study is that constraining the horizontal and rotational movement of the foundation artificially increases the UBC, which does not reflect field conditions. When foundations are permitted to rotate and move horizontally, there is no increase in UBC; however, there is an increased risk of differential settlement and structural instability.

Evolution of Runner Forces during Simultaneous Pump-Trip Transient Process of Two Pump-Turbines

Abstract To ensure no cavitation and water column separation in pump-turbines, the suction heights of pump-turbines in high-head pumped-storage hydropower stations have to be decreased to about –100 m, which leads to high pressure in the draft-tube. During the pump-trip transient process of pump-turbines, the positive water hammer wave in draft-tube superposing the initial high pressure may cause an imbalance of rotating parts and even a lifting-up accident. To quantify the runner forces, two typical transient processes, with and without guide-vane closure after the simultaneous power-off of the two pump-turbines in one hydraulic system, were simulated by using the one-dimensional and three-dimensional coupled (1D-3D) computational fluid dynamics (CFD) method. The results show that the maximum upward axial force on the runner during the process without guide-vane closure (runaway) is significantly higher than that during the process with guide-vane closure. Two significant maximum upward axial forces were observed during the runaway process, and they were around the zero and the valley speed moments. The main causes are the pressure decrease in the runner’s high-pressure zone owing to high-speed bypass flows, and the spiral-case negative water-hammer wave and draft-tube positive water-hammer wave caused by discharge rise. However, the draft-tube positive water hammer wave superposing the high pressure did not cause the maximum axial force. The above two moments of highest axial forces during the runaway process and the proper guide-vane closure rule deserve special attention in the design and operation phases.

A developed soil reaction model for large- diameter monopiles in sand based on hyperbolic curves

Given the preference as the foundation for offshore wind turbines, this paper focuses on large-diameter monopiles and presents a series of finite element analyses to investigate the response to lateral loads. The contribution of four soil reactions, including distributed lateral load (p-y), distributed moment (m-θ), and base shear force and base moment, to the lateral resistance encountered by monopiles is quantified. It can be found that apart from the distributed lateral load, the contribution of distributed moment exceeds 14 %, while the proportion of base shear force and base moment is less than 5 % and is considered negligible. This research investigates how the diameter and embedded length of monopiles impact the load-bearing characteristics. A 'p-y + m-θ' model based on the two-parameter soil reaction curve is proposed. This model is not only straightforward and easy to use for engineering design but also considers the effect of rotational deformation on the soil reaction curves. Additionally, a relationship between ultimate lateral soil resistance and relative density is established, leading to an analysis model suitable for sands of various relative densities. Finally, the model effectively predicts the load–displacement relationship for large-diameter monopiles under lateral loads, providing valuable support for monopile design in the offshore wind industry.

Contact force and pressure analysis of the three-row roller pitch bearing in a large-scale wind turbine

Pitch bearings are the key components of wind turbines (WTs). The reliability of pitch bearings affects the electric energy output efficiency of WTs. Due to its large loading ability, constant contact angle and high stiffness, the three-row roller slewing bearing (TRSB) is becoming a more attractive choice as a pitch bearing, especially in large-scale WTs. The contact force and pressure distributions significantly affect the fatigue life of a three-row roller pitch bearing (TRPB). Therefore, it is essential to propose a precise calculation method for the contact force and pressure. The present work establishes a quasi-static five degree-of-freedom (DOF) mathematical model for TRPBs, in which the bearing under general loading conditions is considered. The influences of combined external forces, overturning moments and inner ring misalignment angle on the contact force and pressure distributions of TRPBs are comprehensively investigated. According to the analysis results, the overturning moment and axial force can significantly affect the number of load-carrying rollers in each row. Furthermore, a slight variation of the inner ring angular misalignment has a significant effect on the contact force and pressure of TRPBs. Finally, it is more prone to pressure concentration in the non-crowned roller than that in the crowned roller, especially in the case of the inner ring with a misalignment angle. Since the high calculation efficiency and accuracy, the proposed method has remarkable potential applications in the fatigue life prediction and design of TRPBs.

Numerical and artificial neural network analysis of tunnel liner design parameters – a comparative study

ABSTRACT This paper proposes the development of an analytical-based Artificial Neural Network (ANN) model for predicting the concrete segmental lining parameters and comparing it with the finite element method, Rocscience tool. To achieve this aim, the dataset was prepared for twelve different loading conditions using the analytical equations by Muir Wood and Curtis. Using this dataset, an ANN model was developed for predicting the segmental lining parameters, viz. displacement, bending moment, axial and shear force. Furthermore, the Rocscience tool was used to analyse the aforementioned design parameters, and the results of these two methods were compared and summarised. It is found that the developed ANN model shows reasonable results of liner design parameters with the Rocscience program. The efficiency of both techniques was evaluated using the statistical measures viz. Mean Absolute Error, Root Mean Square Error, and Coefficient of Efficiency. It is observed that the ANN model is best fitted for the prediction of liner shear and axial force, while it could not find the optimised solution for liner displacement and bending moment. The finding of this study showed that the developed ANN model can be applied to predict the tunnel liner design parameters instead of the alternative complicated and time-consuming techniques.

Limit state equation and failure pressure prediction model of pipeline with complex loading

Assessing failure pressure is critical in determining pipeline integrity. Current research primarily concerns the buckling performance of pressurized pipelines subjected to a bending load or axial compression force, with some also looking at the failure pressure of corroded pipelines. However, there is currently a lack of limit state models for pressurized pipelines with bending moments and axial forces. In this study, based on the unified yield criterion, we propose a limit state equation for steel pipes under various loads. The most common operating loads on buried pipelines are bending moment, internal pressure, and axial force. The proposed limit state equation for intact pipelines is based on a three-dimensional pipeline stress model with complex load coupling. Using failure data, we investigate the applicability of various yield criteria in assessing the failure pressure of pipelines with complex loads. We show that the evaluation model can be effectively used as a theoretical solution for assessing the failure pressure in such circumstances and for selecting appropriate yield criteria based on load condition differences.

Control Effect Analysis and Engineering Application of Anchor Cable Beam-Truss Structure on Large-Deformation Roadway in Deep Coal Mine

In response to the shortcomings of the small support scope of single anchor cable and failure to fully utilize the joint anchoring for surrounding rock, this study summarizes the classification of basic support forms for coal mine roadway surrounding rock and clarifies the main composition and mechanism of anchor cable beam-truss structure. A mechanical model of roadway roof beam under the conditions of no support, single anchor cable support, and anchor cable beam-truss structure support at both ends of the roadway is constructed, and the force and maximum bending moment of roadway roof beam under different support types are compared and analyzed. The study clarifies the bending moment reduction rate of anchor cable beam-truss structure relative to unsupported and single anchor cable support and combines numerical simulation to analyze the response laws of anchor cable beam-truss to prestress distribution and stress shell in roadway surrounding rock. Based on the on-site engineering application of a typical large-deformation mining roadway in a deep coal mine, the important role of anchor cable beam-truss structure in ensuring the safety and stability of surrounding rock in deep high-stress and intense-mining large-deformation roadway is revealed, providing technical references for surrounding rock control of similar conditions in deep roadways.

Numerical Analysis of the Dynamic Response of Concrete Bridge Piers under the Impact of Rock Debris Flow

The impact and damage caused by debris flow on concrete bridges have become a typical disaster scenario. However, the impact disaster mechanism of debris flow on bridge structures remains unclear. This study focused on investigating the impact mechanism of debris avalanches on concrete bridge piers. By employing the discrete element numerical simulation method to examine the effect of debris on concrete bridge piers, the analysis explored the influence of three significant factors: the pier’s section shape, the impact distance, and the slope angle of the sliding chute. The discussions included the accumulation pattern of rock debris, the impact force on the pier, and the shear force and bending moment at the pier’s bottom, as well as the displacement and velocity response laws at the pier’s top. The results demonstrate that rectangularly shaped piers have a high efficiency in obstructing debris, leading to higher impact forces and internal forces on piers. Arched-shaped piers exhibit a short-duration, high-peak instantaneous impact from debris. Increasing the impact distance of the piers can significantly reduce the impact force of debris. The accumulation height of debris, pier impact force, and the pier’s bottom internal forces decrease and then increase with the increase in slope angles, with a 45° slope angle being the critical point for the transition of debris impact on piers. The results can provide references for the disaster prevention design of concrete bridge structures in hazardous mountainous areas.

Experimental Study on Shear Lag Effect of Long-Span Wide Prestressed Concrete Cable-Stayed Bridge Box Girder under Eccentric Load

Based on the engineering background of the wide-width single cable-stayed bridge, the shear lag effects of the cross-section of these bridge box girders under the action of the eccentric load were experimentally studied. The behavior of shear lag effects in the horizontal and longitudinal bridge directions under eccentric load in the operational stage of a single cable-stayed bridge was analyzed by a model testing method and a finite element (FE) analytical method. The results showed that the plane stress calculation under unidirectional live load was similar to the results from spatial FE analysis and structural calculations performed according to the effective flange width described in the design specification. At the position of the main beam near the cable force point of action, the positive stress at its upper wing edge was greatest. At a distance from the cable tension point, the maximum positive stress position trend showed that from the center of the top flange to the junction of the top flange and the middle web to the junction of the top flange and the middle web and the side web. Under eccentric load, the positive and negative shear lag effects on the end fulcrum existed at the same time, and the shear lag coefficient on the web plate was larger than the shear lag coefficient on the unforced side. Due to the influence of constraint at the middle fulcrum near the middle pivot point, positive and negative shear lag effects were significant, and the coefficient variation range was large, resulting in large tensile stress on the roof plate in this area. According to FE analytical results, stress and shear forces of a single box three-chamber box girder under eccentric load were theoretically analyzed, the bending load decomposed into the accumulation of bending moment and axial force, using the bar simulation method, and the overall shear lag effect coefficient λ was obtained and verified.

A phase-field model for the brittle fracture of Euler–Bernoulli beams coupling stretching and bending

Damage gradient models seek to simulate fracture mechanics by modulating the material stiffness. Within this framework, a singular scalar field representing damage is commonly utilized to globally decrease elastic energy. However, when considering structural models like beams and plates, this approach often fails to adequately capture important aspects due to the interaction between stretching and bending contributions. In this work, we propose a model for planar Euler–Bernoulli beams that incorporates the following features: firstly, we utilize two phase-field damage parameters to describe material damaging, specifically addressing the ‘erosion’ occurring above and below the original, undamaged beam; secondly, we assume a simple linear dependence of the axial stress field on the thickness coordinate, along with linear dependence on the axial force and bending moment. By appropriately identifying the constitutive response, our model effectively considers the coupling between stretching and bending induced during through-the-thickness damage, demonstrating good agreement with 2D observations.

The influence of the layout of shear walls on internal forces and horizontal displacements in an 18-story building

High-rise buildings are highly sensitive to horizontal loads. Therefore, any changes made to the arrangement, size, or shape of the shear walls will have significant effects on the strength and performance of the building. In this article, the author conducted an investigation on specific cases: walls located at the corner of the building, walls present in both directions, and reinforced concrete frames. The results of the analysis suggest that changing the placement of walls located at the four corners of the structure will significantly influence the bending moment, shear force, and axial force observed at the base of the columns. At the same time, it also affects the top displacement based on the direction of the main bearing of the structure. The survey results include diagrams showing the bending moment, the shear force, and the axial force in the main frame of the building. These values are then compared with each other at BoC in the main frame. It is evident that the bending moment and shear force values for Case 1 and Case 3 are significantly lower compared to Case 2. This suggests that Case 1 and Case 3 are the most favorable options for calculating and designing the structure of this high-rise building.

Shear performance of tapered box girders with corrugated steel webs in extradosed cable-stayed bridges under cable forces

The integration of box girders with corrugated steel webs (CSWs) and an extradosed cable-stayed design gives rise to an innovative and distinctive bridge design, recognized as the extradosed cable-stayed bridge with CSWs. The synergistic integration of the technical benefits facilitates expanding the maximum span and enhancing the adaptability of this structural configuration. Subjected to cable forces, the main bridge superstructure featuring a box girder with CSWs experiences vertical shear, substantial axial force, and bending moments. Shear buckling on the CSWs emerges as a prominent issue influencing design considerations. In response to heightened internal forces near support, the main girder is typically configured with variable height. The Resal effect in the tapered girder leads to additional shear stresses from axial forces and bending moments, consequently modifying the effective shear stress on the CSWs. Therefore, traditional basic calculation assumptions that solely account for the vertical component of cable forces in shear stress calculations are frequently inaccurate. This study presents a modified theoretical method for calculating shear stress in tapered box girders with CSWs subjected to cable forces by considering the Resal effect. The proposed modified method incorporates not only the vertical shear but also considers bending moments and axial forces. The finite element simulation and experimental results showcase its remarkable accuracy, concurrently validating the presence of the Resal effect in tapered box girders with CSWs under cable forces. Additionally, this study quantitatively analyzes the shear force redistribution phenomenon induced by vertical shear, axial force, and bending moments considering the Resal effect. This reveals the shear performance of tapered box girders with CSWs under cable forces. The study is expected to provide a strategy and theoretical guideline for rapidly and efficiently obtaining the shear stresses of tapered box girders with CSWs in extradosed cable-stayed bridges under cable forces.

The experimental and numerical investigation of fracture behaviour in PMMA notched specimens under biaxial loading conditions – Tension with torsion

This paper presents the results of experimental fracture test of flat PMMA specimens under biaxial loading condition tension with torsion (proportional). The specimens were made in two thicknesses: 5 and 15 mm and were weakened with V-type edge notches with different root radii: 0.5; 2 and 10 mm. Thanks to the ARAMIS 3D 4 M non-contact vision system, measurement of the elongation and twist angle were recorded. During experimental part all of the deformation processes were observed using PHANTOM cameras. Obtained records made it possible to precisely indicate the moment of crack initiation (tensile force and torsional moment values). Using the microscopic observations the location of crack initiations were determined. Results obtained for biaxial loading were compared with those obtained for uniaxial tension and torsion. Based on experimental data the numerical calculation with FEM were carried out. The principal stress and plastic strain distribution under critical load, were obtained. The points of occurrence of stress maxima and plastic strain were indicated, which were taken as potential crack initiation sites. On the basis of the stress and plastic strain values measured at the critical points, a stress–strain fracture criterion was formulated, which was then positively verified. Additionally, new form of stress–strain fracture criterion was proposed. The bilinear form of the fracture criterion can be successfully used to predict fracture in PMMA flat specimens, regardless of the notch root radius, type of load or element thickness.

Stability of arches with internal hinge

The in-plane stability of internally hinged, end-fixed shallow arches is in the spotlight. The non-linear model accounts for the coupled effect of the bending moment and axial force on the membrane strain. The model itself can handle homogeneous or non-homogeneous material distributions along the thickness of the uniform arch. Analytical findings reveal how the typical geometrical data, like arch length, radius of gyration, and arch angle, affect the lowest buckling loads. The typical non-linear behaviour of arches is also assessed including the equilibrium path and the internal force system.

A Comparative Study on Load Assessment Methods for Offshore Wind Turbines Using a Simplified Method and OpenFAST Simulations

Simplified methods are often used for load estimations during the initial design of the foundations of offshore wind turbines (OWTs). However, the reliability of simplified methods for designing different OWTs needs to be studied. This paper provides a comparative study to evaluate the reliability of simplified approaches. The foundation loads are calculated for OWTs at the mudline level using a simplified approach and OpenFAST simulations and compared. Three OWTs, NREL 5 MW, DTU 10 MW, and IEA 15 MW, are used as reference models. An Extreme Turbulence Model wind load at a rated wind speed, combined with a 50-year Extreme Wave Height (EWH) and Extreme Operating Gust (EOG) wind load and a 1-year maximum wave height are used as the load combinations in this study. In addition, the extreme loads are calculated using both approaches for various metocean data from five different wind farms. Further, the pile penetration lengths calculated using the mudline loads via two methods are compared. The results show that the simplified method provides conservative results for the estimated loads compared to the OpenFAST results, where the extent of conservativism is studied. For example, the bending moment and shear force at the mudline using the simplified approach are 23% to 69% and 32% to 53% higher compared to the OpenFAST results, respectively. In addition, the results show that the simplified approach can be effectively used during the initial phases of monopile foundation design by using factors such as 1.5 and 2 for the shear force and bending moment, respectively.

Improved pseudostatic analysis of pile response to seismic ground movement: Multiple characteristic ground displacement profiles

Piles may be subjected to significant kinematic loading from ground movement under earthquakes. Pseudostatic analysis, which is based on the Winker beam model, traditionally adopts a single ground displacement profile, known as the characteristic ground displacement profile, for assessments of pile response under this loading condition. This study conducts dynamic analyses with different soil, pile-head-fixity, and seismic conditions and generates displacement, moment, and shear force response envelopes to evaluate the appropriateness of the characteristic displacement profiles of four common methods. These methods give inconsistent predictions because the maximum responses at different depths in the pile response envelopes occur at different points in time. To address this issue, we propose using multiple characteristic ground displacement profiles, which are determined by the maximum ground relative deformation or rotation. These multiple profiles, when used in pseudostatic analyses, give consistent predictions with dynamic pile response envelopes in most scenarios, thus overcoming the limitations of conventional single-profile methods.

Utjecaj ekscentrične porivne sile na odabir statvenog kliznog ležaja

Stern tube slide bearing of the shaft line of the ship's propulsion system causes losses during operation. Friction and material wear of the tribosystem occur. One of the reasons is the different navigating regimes of the ship, which have an influence on the formation of the velocity field on the ship's propeller. The variable velocity field defines the magnitude and the position of the thrust force. The methodology presented in this paper is based on the fact of the existence of the eccentricity of the thrust force, i.e. loads due to the action of the moment of the eccentric thrust force. Due to the changing position of the thrust force, the curvature of the elastic line of the sleeve inside the stern tube bearing, which is mostly spatial, changes. Spatial elastic line of the sleeve has an influence on the working area of the slide bearing. Therefore, the importance of a sufficient thickness of the lubricant layer for lubrication in relation to these changes was highlighted. In this paper, this is the initial criterion for the selection of materials and lubricants of the stern tube bearing. An equally important criterion would be to define the possible harmful impact of lubricant leakage with particles of bearing bush material on the ecosystem. In order to facilitate the whole process, the simplified analytical model is presented, which can be used in the initial stage of stern tube bearing selection. Such a model allows a simpler analysis of the influence of the elastic line on the condition of the stern tube bearing due to the loading by the weight of the ship's propeller and by the moment of the eccentric thrust force. The procedure for the initial selection of the stern tube bearing created by this methodological approach could have its practical application. For this reason, the paper analyzed different navigating regimes and their influence on the working area of the stern tube slide bearing. The obtained results can be useful in the selection of materials and lubricants for the stern tube bearing tribosystem.

ФОРМАЛИЗМ РЕШЕНИЯ ПЕРВОЙ ЗАДАЧИ ДИНАМИКИ ШАГАЮЩИХ И КОЛЕСНО-ШАГАЮЩИХ МАШИН

The aim is to solve the first problem of the dynamics of machines moving their bodies with the help of legs, i.e., to calculate the control actions of the leg actuators that provide the given dynamics of the absolute motion of the body and satisfy the constraints, when fulfilled, there is no sliding of the supporting legs relative to the supporting surface. The research methods are related to system analysis, mechanics of body systems and robotics. We consider walking and wheel-walking machines with legs suspended from the body, in which the last kinematic pair is translational, there is no controlled foot, and the foot and the supporting surface interact at a single point. The resultsof the study contain analytical formulas for calculating dynamic reactions at the points of contact between the legs and the supporting surface, as well as driving forces and moments of forces in the drives of the supporting and carrying legs, providing a given motion of the body relative to the supporting surface, as well as its corresponding relative motion of the bodies of the supporting legs. A formalism for solving such problems is described, based on inverse vector recurrence formulas for calculating forces and moments of forces of dynamic reactions in kinematic pairs of tree-like systems of bodies with closure of the last body of the branch on the supporting surface. This formalism is extended to wheeled, wheel-walking and walking machines, which is demonstrated by appropriate examples. Analytical conditions for realizing a step without slipping of the support legs relative to the support surface are written down. Two simple wheel-walking machines, consisting of a linear electric drive and a driven (passive) wheelset, are proposed for the experimental determination of sliding and rolling friction coefficient values. In analytical forms of deduced calculation formulas (equations and inequalities) the structural, geometric, inertial and kinematic parameters of the investigated machines are explicitly expressed. The proposed formalism is demonstrated on the solutions of four problems from simple to complex through the reuse of formulas. Conclusion. The obtained mathematical models can be used in the processes of calculation and design of similar machines and their layouts.

Development and verification of shield thrust vector self-adaptive control technology in soft soil strata

To solve the difficulty in automatically obtaining an effective total thrust vector relative to the shield posture adjustment requirements during self-driving in soft soil strata, a shield thrust vector self-adaptive control technology for shield machines was proposed. Subsequently, a large-scale model platform was established to simulate the straight-line advancement of the testing shield machine under dynamic loads, and the feasibility of steady shield driving was verified. The test results showed that: the actual total thrust force exhibited the same variation characteristics according to load force, while a relatively fixed difference of 1000 kN between the two caused by the system friction was observed. A quick recovery after an abrupt jump of the shield speed was discovered once there was a sudden, significant change in the load. The actual resultant moment of total thrust force effectively responded to the load force, and the shield postures were maintained well. Further, the driving speed and the horizontal stroke difference were controlled in the ranges of ±3 mm/min and ±5 mm of each set values, respectively. Subsequently, this technology was applied to the Wusongkou Yangtze River Tunnel project in Shanghai, and the on-site test results verified its feasibility in actual soft soil strata. The shield speed remained stable as the actual thrust forces shared the same changing low of the target values, and a fixed difference between the two was maintained to ensure the movement of the shield machine. The variation curves of the actual steering angles in both the horizontal and vertical directions coincided with those of the target steering angles because the resultant horizontal and vertical moments of the thrust force effectively responded to each steering requirement, which was executed with high quality.