Simple Mechanical Model Research Articles

Experimental and nonlinear analytical of the flexural performance of timber-filled steel tubular composite beams

Steel-timber composite structures present excellent and stable engineering performance. This study presents a novel timber-filled steel tubular composite beam consisting of cold-formed thin-walled rectangular steel and timber.Eleven timber-filled steel tubular composite beams were prepared with various section parameters. A four-point bending test was conducted to evaluate the flexural behaviour of the beams. The failure mode, deflection deformation, and load-carrying capacity were analysed based on the test phenomena and data; the influences of the various parameters on the flexural behaviour were explored.Finally, a simplified mechanical model for flexural bearing capacity was established based on the assumption of plane section and the ideal elastic-plastic.The results show that compared to the timber-filled steel tubular composite beams with composite connection combined the shear screw and the epoxy resin viscose, the beam with a simple epoxy resin adhesive connection has high bearing capacity and deformation performance. The screws have little effect on the bearing capacity and bending stiffness of the composite beam, but can effectively improve the residual bearing capacity of the beam.

Numerical Study on the Impact of Locked-In Stress on Rock Failure Processes and Energy Evolutions.

Locked-in stress refers to internal stress present within rock formations that can influence the failure process of rocks under specific conditions. A simplified mechanical model is applied, drawing on elasticity and the hypothesis of locked-in stress, to explore the influence of locked-in stress on the mechanical properties of loaded rocks. An analytical solution is obtained for the stress distribution in a failure model of rocks that include locked-in stress. The findings demonstrate that the geometry and orientation of stress inclusions within the rock influence the initiation and propagation of cracks under the combined influence of locked-in stress and high-stress conditions. Moreover, the presence of locked-in stress substantially reduces the rock's capacity to withstand maximum stress, thereby increasing its susceptibility to reaching a state of failure. The increase in closure stress leads to a significant increase in the magnitude of the maximum stress drop and radial strain variation within the rock, resulting in reduced strength and a shortened life of the ageing failure of the rock. In addition, the influence of stress inclusions on energy dissipation is investigated, and a novel relationship is established between the roughness coefficient of the rock structure surface and the angle of the rock failure surface. This relationship serves to characterize the linear dynamic strength properties of rock materials containing locked-in stress. This investigation not only advances the comprehension of stress distribution patterns and the effects of locked-in stress on rock failure patterns but also facilitates a more precise portrayal of the nonlinear features of alterations in the rock stress-strain curve under the influence of confined stress. These findings provide a solid theoretical foundation for ensuring the safety of excavations in various deep engineering projects.

Design charts for hydraulic twister based aircraft arrester gear

In this article, arrestment of an aircraft by a hydraulic twister based system is modeled and reduced to simple design charts. We are primarily interested in performance parameters like maximum deceleration, run-out distance, and maximum tape force. We first present a simplified mechanical model for the system. Some analytical progress is possible with the governing nonlinear differential equation, yielding expressions for velocity and acceleration in terms of displacement. The system has only two nondimensional parameters. This allows us to present simple design charts for the performance parameters. The same approach is extended to secondary performance parameters namely maximum jerk and the time at which maximum deceleration occurs. We choose some practical parameter sets and demonstrate the use of our charts. These charts can be used for design calculations and quick performance prediction of an arresting gear design for different weight classes of aircraft and practical initial velocities.

Structural Design and Optimization of the Milling Force Measurement Tool System Embedded with Thin-Film Strain Sensors.

A milling force measurement tool system is designed with an elastic beam structure, which is divided into a two-end ring hoop compression sensor mode and a two-end square hoop compression sensor mode to improve the strain sensitivity. A simplified mechanical model of the elastic beam is established, and the relationship between the strain and force of the elastic beam under the action of three cutting force components is investigated, which can act a guide for subsequent milling force measurement tool system calibration tests. Thin-film strain sensors occupy a central position in the milling force measurement tool system, which consists of a substrate, transition layer, insulating layer and resistance grid layer. The resistance grid layer has a particularly significant effect on the thin-film strain sensor's performance. In order to further improve the sensitivity of thin-film strain sensors, the shapes of the substrate, the transition layer, the insulating layer and the resistance grid layer are optimized and studied. A new thin-film strain sensor is designed with a resistance grid beam constructed from an insulating layer and a resistive grid layer double-end-supported on the transition layer. The flow of the wet-etching process of thin-film strain sensors is studied and samples are obtained. The surface microforms of the sensor samples are observed by extended depth-of-field microscopy, confocal microscopy and atomic force microscopy. It can be seen that the boundary of the resistance grid layer pattern is tidy and has high dimensional accuracy, thus enabling the basic achievement of the expected effect of the design. The electrical performance of the samples is tested on an experimental platform that we built, and the results show that the resistive sensitivity coefficient of the samples is increased by about 20%, to 51.2%, compared with that of the flat thin-film strain sensor, which fulfils the design's requirements.

A model for predicting the stability of ceramic suspensions

The prediction of the stability of ceramic suspensions with multiple particles is limited depend on classical DLVO theory or Stokes equation. The mechanical effect of particles settling in suspension was studied, and a simplified mechanical equilibrium model of particles was proposed, shown as follows: u=Δρgd218η−τyd36η. The sedimentation of particles is mainly influenced by the density difference between particles and fluid Δρ, particle size d, suspension viscosity η, as well as shear yield stress τy. For a given suspension, Δρ, d and η are constants, and τy can be directly measured through rheological methods. When calculated settling velocity of particles approaches infinitely small values, the suspensions can be considered stable. The expression derived in this work had been verified by the experimental data. In addition, correlation between the results from improved settlement height method and the calculated settling velocity was established.To further investigate the impact of additives on suspensions stability, the Kelvin-Voigt rheological model was employed to characterize viscoelastic properties during oscillation, and a coefficient K (K=τy−G'γcτy) was proposed to quantitatively determine the contribution of the “dashpot” component in influencing the yield stress τy. The regulation strategy for additives in suspensions was established based on experiments: a K value exceeding 0.274 indicates excessive additives concentration and necessitates reduction, whereas a K value below 0.274 suggests an insufficient additives concentration and requires additional dosage. In summary, the above model is helpful to predict the stability of ceramic suspensions.

Research on launching, water exiting, and river crossing of an amphibious vehicle

The main focus of this paper is the amphibious vehicle's water-land trans-media capability, specifically its ability to efficiently carry out transportation tasks in rivers and nearshore areas. This capability relies on three key processes: launching, water exiting, and river crossing. To study these processes, hydrodynamic numerical simulations are conducted. The Reynolds-averaged Navier–Stokes) equation, simplified terra mechanics model, and body force method are adopted to analyze the trans-media and self-propulsion processes. Results indicate that the optimal launching speed is around 15 km/h, with a stable trim and heave, and a launching angle range of 15°–25° for insubmersibility and stability. Furthermore, high-speed water exiting enhances insubmersibility and imposes lower requirements on road adhesion conditions, outperforming low-speed water exiting. In terms of self-propelled river crossing, higher heading angles and faster river currents improve hydrodynamic lift, with the fastest crossing achieved at a 10° heading angle for a current speed of 2.5 m/s and a forward speed of 30 km/h.

Accurate prediction of protein folding mechanisms by simple structure-based statistical mechanical models

Recent breakthroughs in highly accurate protein structure prediction using deep neural networks have made considerable progress in solving the structure prediction component of the ‘protein folding problem’. However, predicting detailed mechanisms of how proteins fold into specific native structures remains challenging, especially for multidomain proteins constituting most of the proteomes. Here, we develop a simple structure-based statistical mechanical model that introduces nonlocal interactions driving the folding of multidomain proteins. Our model successfully predicts protein folding processes consistent with experiments, without the limitations of protein size and shape. Furthermore, slight modifications of the model allow prediction of disulfide-oxidative and disulfide-intact protein folding. These predictions depict details of the folding processes beyond reproducing experimental results and provide a rationale for the folding mechanisms. Thus, our physics-based models enable accurate prediction of protein folding mechanisms with low computational complexity, paving the way for solving the folding process component of the ‘protein folding problem’.

Rapid damage assessment of regional beam bridges after earthquake based on simplified models and different seismic inputs

As the hub of the traffic network, the rapid damage assessment of bridges after earthquake is of great significance for post-disaster rescue. Traditional vulnerability-based method can only provide the probability of different damage states of structures under different earthquake intensity indicators, which confuses the selection of post-disaster rescue routes. Therefore, this paper proposes a post earthquake damage assessment technique for regional bridges based on nonlinear dynamic time-history response analysis. First, a simplified mechanical model for a single pier was established for a large number of beam bridges in the region, achieving standardized and batch rapid finite element model establishment. Secondly, using Kriging interpolation method and continuous wavelet transform technology, the surface seismic response of geological drilling points is calculated to obtain the seismic motion history of any bridge site in the region. Finally, using parallel computing technology, nonlinear dynamic time-history response analysis was conducted on the simplified beam bridge model, and the bridge damage status was quantitatively evaluated based on the calculation results. Eighty-five bridges in a specific area are considered as an example to verify the proposed method. The results show that the proposed method has high calculation efficiency and can consider the site characteristics and structural design parameters. Also, the calculation results can better reflect the actual earthquake damage distribution, providing strong technical support for post-disaster rescue.

Using Footpad Sculpturing to Enhance the Maneuverability and Speed of a Robotic Marangoni Surfer.

From insects to arachnids to bacteria, the surfaces of lakes and ponds are teaming with life. Many modes of locomotion are employed by these organisms to navigate along the air-water interface, including the use of lipid-laden excretions that can locally change the surface tension of the water and induce a Marangoni flow. In this paper, we improved the speed and maneuverability of a miniature remote-controlled robot that mimics insect locomotion using an onboard tank of isopropyl alcohol and a series of servomotors to control both the rate and location of alcohol release to both propel and steer the robot across the water. Here, we studied the effect of a series of design changes to the foam rubber footpads, which float the robot and are integral in efficiently converting the alcohol-induced surface tension gradients into propulsive forces and effective maneuvering. Two designs were studied: a two-footpad design and a single-footpad design. In the case of two footpads, the gap between the two footpads was varied to investigate its impact on straight-line speed, propulsion efficiency, and maneuverability. An optimal design was found with a small but finite gap between the two pads of 7.5 mm. In the second design, a single footpad without a central gap was studied. This footpad had a rectangular cut-out in the rear to capture the alcohol. Footpads with wider and shallower cut-outs were found to optimize efficiency. This observation was reinforced by the predictions of a simple theoretical mechanical model. Overall, the optimized single-footpad robot outperformed the two-footpad robot, producing a 30% improvement in speed and a 400% improvement in maneuverability.

A Simplified Mechanical Model and Analysis for the Settlement Deformation of Buried Pipelines Caused by Open-Cut Excavation

This study aims to reveal the deformation characteristics of buried pipelines and the effects of various parameters on settlement displacement using the analytical analysis method. A simplified mechanical model for the settlement displacement of buried pipelines is proposed with the theory of the Winkler model, and the sensitivity impacts of various parameters are performed by comparing them with those given by other cases. The rationality of the proposed approach is verified by a comparison with previous cases, and it also turned out that the present method performed better than the other two methods in the literature in its overall tendency of settlement displacement and error precision. The parameter analysis results of this study indicate that the maximum settlement displacement of the buried pipelines only increases linearly with the increase in ground displacement. Other parameters such as the subgrade modulus and calculated length increase to a certain threshold; the maximum settlement displacement will remain stable. However, the diameter and elastic modulus of the pipelines only have a small effect on the maximum settlement displacement of the pipelines, so they are not a sensitive factor and these effects can be ignored. In addition, an engineering example of pipeline deformation in a deep foundation pit from open-cut excavation is researched to verify the practicality of this present method.

Power Transmission Using Circular Elements Bounded by Given Central Angle in Rolling Contact

In the present study, the concept of utilizing two circular cam-track disks, of the same central angle, in combination with one circular roller is presented. The roller is restrained to move within a vertical groove, and at the same time it rotates with rolling-contact on both cam tracks. When the upper cam is fully travelled by the roller, the same occurs with the lower one, despite their different lengths. Therefore, during the rolling contact, the two cams always sweep the same central angle. The aforementioned configuration of the two circular arcs may be considered as a unit cell, which can be repeated an even number of times, and when folded forms a closed circular groove between two cam-track disks. For better understanding, a manufactured prototype and 3D CAD-models have been developed. The operation of this setup as a gearless automotive differential is demonstrated by performing two bench experiments, which are then explained by a simplified mechanical model. The latter focuses on the implementation of the principle of the inclined plane, in which an upper limit of the inclination angle is imposed in accordance with the coefficient of friction at the friction disks. Previous patents on gearless differentials are discussed and other possible applications in mechanical engineering are outlined.

Research and outlook of steel beam‐to‐column joints retrofitted by welding haunches

AbstractA critical issue in structural retrofitting is to enhance the moment resistance of steel beam‐to‐column joints. The authors have investigated the cyclic behaviour and design of existing welded unreinforced flange‐bolted web (WUF‐B) joints, in which welding haunches were utilised to retrofit weak panel zones. In this study, three full‐scale joint specimens were retrofitted by haunches and stiffeners after applying axial column compression load. Then, cyclic tests, numerical simulations, and finite element parametric analyses were conducted. Results indicated that the retrofitted joints exhibited increased moment resistance and satisfactory seismic performance, meeting the ductility requirement of Special Moment Frames in the AISC 341 provision. The force‐transferring mechanism was substantially changed after adding haunches, and thus, a simplified mechanical model has been established to predict the force distribution. Furthermore, parameters influencing the joint behaviour (i.e., haunch geometries and axial column load before retrofitting) were involved in parametric analyses. Based on the above experimental and numerical results, the design method has been proposed, including the recommended configurations, calculations of the moment resistance and initial rotational stiffness, and detailed seismic checking procedures. This study reports a feasible solution to retrofit weak panel zones with column compression remaining and provides an outlook on retrofitting beam‐to‐column joints in future investigations.

A study of the phenomenon of “crackle” associated with the noise of high-performance aircraft at afterburner

Ffowcs Williams et al were the first to discover crackle in the noise of the Concorde when the Olympus 593 engine which propelled Concorde was operating at afterburner power. Ffowcs Williams et al described crackle as a transient phenomenon. The primary objective of the present investigation is to show that the noise of F-18E aircraft has crackle. The fundamental elements in the noise of a crackling jet described by Ffowcs Williams et al are sawtooth-like pulses, bursts and trains of bursts. All these characteristic features of pressure pulses are identified in the noise of F-18E aircraft. By including a minimum pulse amplitude requirement based on the level found in the noise of the Concorde by Ffowcs Williams et al, a set of sufficiency conditions for the presence of crackle is established. It is found that crackle exists in the noise of an F-18E aircraft over a fairly large angular sector in the downstream direction. In the literature, the existence of sawtooth-like sound pulses in a noise field is often taken as an indicator of the presence of crackle. The importance of pressure pulse waveform on its impact on human hearing is briefly investigated by using a simple mechanical model of the ear.

A programmable modular lattice metamaterial with multiple deformations

This paper describes a class of lattice metamaterials with tunable mechanical properties controlled by the material modulus and structural parameters of the cellular units. The deformation shapes can also be changed by external control. We have developed 3D printed quadrilateral cellular TPU units with specially shaped edge walls. A simplified mechanical model of the different cell deformation processes is established and verified by numerical simulations and experiments. On this basis, by tessellating and matching these transformations together, we create assembly grids with adjustable stiffness and deformation shapes controlled by thermal and displacement constraints.

A novel approach for the mechanical response of cement concrete pavement structure considering the interlaminar interface shear slip effect

The traditional theoretical analysis method has many problems such as cumbersome calculation and low efficiency, and there is a relative lack of research on the simplified mechanical model in the field of road engineering. To further improve and enrich the existing theoretical analysis of pavement structures, and to realize the rapid analysis of the mechanical behavior of cement concrete pavement structure (CCPS), based on the state-space method, a new approach is proposed to analyze the mechanical response of the CCPS, taking the interlaminar interface shear slip effect into account. The CCPS is considered as a two-layered Euler beam. A state equation is established to investigate the static responses of the CCPS with explicit consideration of the interlaminar interface shear slip effect under the action of an arbitrary vertical load and is solved by matrix theory. Subsequently, the present solution is validated by the literature published and the numerical simulation. In addition, the effects of the interlayer shear stiffness, thickness of the base course, stiffness of Winkler foundation springs, and bending stiffness on the deformations of the CCPS, and the influence of external loads on the interlayer distributing shear forces are revealed. It is indicated that the interlaminar interface shear slip effect exhibits a significant influence on the deflection and bending deformation of the CCPS. Moreover, the proposed solution can not only be employed conveniently for the consideration of any interlaminar contact conditions and vertical load distributions but also be reduced to obtain the responses of a single-layer mechanical model.

Nonlinear interactions between vibration modes with vastly different eigenfrequencies

Nonlinear interactions between modes with eigenfrequencies that differ by orders of magnitude are ubiquitous in various fields of physics, ranging from cavity optomechanics to aeroelastic systems. Simplifying their description to a minimal model and grasping the essential physics is typically a system-specific challenge. We show that the complex dynamics of these interactions can be distilled into a single generic form, namely, the Stuart-Landau oscillator. With our model, we study the injection locking and frequency pulling of a low-frequency mode interacting with a blue-detuned high-frequency mode, which generate frequency combs. Such combs are tunable around both the high and low carrier frequencies. By discussing the analogy with a simple mechanical system model, we offer a minimalistic conceptual view of these complex interactions originating the frequency combs, together with showcasing their frequency tunability.

Experimental Study and Bearing Capacity Analysis of Retrofitted Built-Up Steel Angle Members under Axial Compression

Against the update of load design standards and requirement of long-term service, many latticed towers using steel angles subjected to gradual performance degradation must be retrofitted for bearing further social functions, e.g., electric power transmission and fifth-generation mobile communication. Therefore, this paper proposed a non-destructive reinforcement method for steel angles by avoiding unnecessary new construction or complex reinforcement procedure. The non-destructive reinforcement of a steel angle is composed of a steel angle, reinforcement plate, and fixture. Standardized fixtures are used to connect the reinforcement plate and steel angle to achieve steel angle reinforcement. In retrofitting tests, built-up steel angle members were loaded under axial compression, in which the failure mode and reinforcement effect of key parameters (e.g., clamp type, slenderness ratio, and clamp distance) were analyzed and compared, where a significant reinforcement effect was obtained with the capacity increment within 39~174%; the clamp types and clamp distance had a slight effect on bearing capacity; and the proposed reinforcement method was more effective for slender members. Based on the mechanical mechanism analysis and failure mode, the accuracy of the design method for calculating the bearing capacity of those built-up steel angle members was suggested and verified, in which a simplified mechanical model for the flexural-buckling mode was developed. The design method based on AISC360-16 agreed well with the test result and could be effectively used for calculating the flexural–torsional bearing capacity of those built-up steel angles. This study can provide a valuable reference for the design and application of non-destructive reinforcement of angle steel towers.

Lateral impact test and inertial force of concrete-filled steel tube column

The mechanical behavior of concrete-filled steel tube (CFST) subjected to lateral impact was studied by drop hammer test and finite element method (FEM). Lateral deformation occurred when the midspan of CFST was impacted by a drop weight. Two plastic hinges were formed in the mid-span and near the fixed support, respectively. The numerical and experimental results were compared to ensure that the numerical model was reasonable for investigating the stress development, damage, and inertial force of the CFST column. The effects of the impact velocity, impact mass, cross-sectional steel ratio, and boundary conditions on the inertial force of the CFST column were analyzed. During the impact process, the maximum stress was at the steel tube part of the impact location and the fixed support, while the other parts were still in the elastic or elastoplastic stages. The region under restraint at the fixed end of the CFST column exhibited the first signs of concrete core damage under tension, followed by the region near the location of the impact at midspan. At the peak impact force (Fp), the impact velocity had a considerable influence on the distribution of inertial force of CFST, while the impact mass and cross-sectional steel ratio had no discernible impact on the inertial force at the Fp, and boundary conditions had little impact on the distribution of inertial force. Based on a research of the inertial force at the Fp, a simple mechanical model of the inertial force was built.

Distinct nucleation and propagation of prismatic dislocation loop arrays in Ni and medium-entropy CrCoNi alloy: Insights from molecular dynamics simulations

This paper utilizes molecular dynamics simulations to investigate the mechanisms of nucleation and propagation of prismatic dislocation loop (PDL) arrays in single-crystal medium-entropy CrCoNi alloys and pure Ni, with a particular focus on understanding the different size-dependent plasticity. To explore this phenomenon, we varied the size of PDLs. Our findings suggest that the anticipated size effects (i.e., smaller is stronger) are observed in both the elastic and plastic stages of Ni samples, but they are less pronounced in CrCoNi samples. Furthermore, it is observed that PDLs in CrCoNi alloys are often trapped in stable pileups, which results in a surprisingly significant strengthening effect. In contrast, PDLs in similar Ni configurations glide easily and exit from the free bottom. The observed differences between the behavior of CrCoNi and Ni can be attributed to the dislocation-length-dependent lattice friction in CrCoNi, as well as a significant stress gradient resulting from localized loading during nanoindentation. A simple dislocation mechanics model is used to rationalize the abnormal size effect in CrCoNi. These findings provide an insightful understanding of the strengthening mechanisms due to complex dislocations in multi-principal element alloys.

Analysis of Dynamic Characteristics of Attached High Rise Risers

The exhaust chimney of third-generation nuclear power units is a typical attached high-rise riser structure. In this paper, the simplified mechanical model and dynamic model of China’s third-generation nuclear power Hualong-1 VNA system, including multiple nonlinear factors, are established for the first time. The DTM (differential transformation method) was first applied to solve the natural vibration characteristics of a multi-point constrained variable cross-section riser structure, and the effects of variable cross-section, variable mass, variable axial force, and different elastic constraint parameters on the natural vibration characteristics of the system were studied. The dynamic behavior of the VNA system under the combined action of internal flow velocity, vortex excitation, and foundation excitation was studied. The results show that the outer diameter function of the VNA system pipeline should be designed as a quadratic function or a near quadratic multi-segment constant value function. The “limiting” effect of constraining large stiffness can force low-order vibration modes with high constraint stiffness to jump to high-order vibration modes with low constraint stiffness. The elastic constraint arrangement scheme with near center symmetry can make the system vibration mode present a half stable and half-curved form. A new optimization design scheme has been proposed regarding the layout and stiffness parameters of the VNA system guide bracket. This can enable the VNA system pipeline to avoid severe oscillations near the response extreme values caused by multiple frequency excitations of seismic loads under design and accident conditions and ensure the service life of the equipment.