Explicit Dynamic Model Research Articles

Effects of corrosion on the strength of self-drilling screw connections in cold-formed steel structures-experiments and finite element modeling

Cold-formed steel (CFS) self-drilling screw connections are popular in construction industry due to rapid fastening and ease of installation. However, the performance of the CFS connections is very critical when they are exposed to corrosive environments such as humid and acidic or chloride-rich environments. The corrosion damage of CFS structures when exposed to these environments can result in significant reduction of mechanical properties, which can affect the safety and durability of such structures. Very limited research is available in the literature to investigate the effect of corrosion on the behaviour of CFS connections. This issue is addressed herein through an experimental investigation. This paper presents a total of 36 new experiments on different types of CFS self-drilling screws (12 and 14 gauge) and steel sheet thickness (2.5 mm). Half of the tests were for corroded specimens and the remaining half were for non-corroded specimens. Further, one to two screws per arrangements connecting the steel sheets having yield strength of 450 MPa, were tested. Screws were immersed for 31 days and the CFS plates were immersed for 8 weeks in corrosion chamber before the tests were conducted. The experimental program was designed to investigate the effect of number of screws on shear strength of corroded specimens. Furthermore, a nonlinear explicit dynamic FE model was developed and validated against the experimental test results. The FE results were in reasonable agreement with the test results, both in terms of connection strength and failure modes.

Analysis of the dynamic characteristics of the cage of high-speed angular contact bearings under preloaded load

First, the law of motion of the bearing cage, inner ring, and ball are theoretically analyzed. Combining the nonlinear contact and deformation relationship between the various elements of the bearing, an explicit dynamic model of the high-speed angular contact bearing is established. Second, the stability and motion characteristics of the cage are analyzed from four aspects: the three-dimensional center of mass motion track of the cage with time, the deviation ratio of the center of mass vortex velocity, the angular velocity, and the linear velocity. The dynamic characteristics of the cage during the start-up phase of unsteady operation have been emphatically studied. The research results show that during the start-up phase, the greater the preload, the later the circle of the center of mass motion track of the cage expands outward, and the better the stability. The higher the rotation speed, the earlier the vortex trajectory circle of the center of mass of the cage expands outward, and the motion stability first strengthens and then weakens. Finally, the simulated value of the linear velocity of each bearing element changes with time are compared with the theoretical value, the correctness of the established explicit dynamic model was verified.

Passive Safety Solutions on Coach according ECE R29: Experimental and Numerical analyses

Accidents involving vehicles for public transportation can endanger both the driver and the passengers, due to the proximity of the impacting region, and the correspondent violation of the safety cell. The vehicle structural design and the high rate of energy or accelerations involved are important aspects during an accident. To improve the current design applied to public vehicles, structural optimization research, with the goal of improving safety, is needed.The objective of this study is the development of new technologies for new passive safety solutions, employed on coaches. Initially, a study on the improvement of the driver safety, during a frontal collision, will be developed. The final outcome of the present study is the development of new generation of coaches outfitted with technology capable of reducing the impact's unforeseen consequences.To study the structural behavior of a coach (M3 Class III vehicle) in the event of a head-on collision, the ECE R29 Regulation will be considered. The current safety standards only focus on the certification of large vehicles with separate driver's cabs, with no requirements addressing coaches. An experimental setup was built to conduct a frontal crash test. An impactor hanging by two steel bars impacted against the structure crushing it, with an energy of 55 kJ. A Digital Image Correlation (DIC) system, strain gauges, and accelerometers fitted on the structure were used for data acquisition. The experimental setup was also numerically simulated, using the Finite Element Method (FEM). A dynamic explicit model was considered to determine the dynamic structural response. The evolution of the strain, accelerations and displacements were obtained and compared with the experimental results. The internal energy was evaluated and compared to the reference value. With the different obtained results, it was possible to decide whether the current models satisfy the safety criteria of or whether a solution proposal is necessary to improve the outcomes.

Study on the influence of structure shape of semi armour piercing warhead on vertical armour piercing efficiency

In order to evaluate the impact of different warhead shapes on the damage efficiency of semi armour piercing warhead effectively, four common semi armour piercing warhead models are established based on Solidworks, and the deck model is established with reference to the deck data of an aircraft carrier. And then the material setting and grid division are carried out based on Ansys so as to construct the explicit dynamic simulation model. The credibility of the model is verified based on the residual velocity theory after the model being established. Finally, based on the established model, the simulation research on the influence of warhead shape on vertical armour piercing ability is carried out. The results show that under the same velocity, the armour piercing ability of sharp oval and conical warheads are better and their residual velocity are higher.

A Dynamic Model and Parameter Identification of High Viscosity Magnetorheological Fluid-Based Energy Absorber with Radial Flow Mode.

The excellent suspension stability of the high-viscosity linear polysiloxane magnetorheological fluid (HVLP MRF) makes it a great controlled medium for magnetorheological energy absorbers (MREAs). In our previous work, the Herschel–Bulkley flow model (HB model) was used to describe the shear-thinning rheological behavior and establish the dynamic model of an HVLP MRF-based MREA with radial flow mode. However, as the established model was implicit, the MREA response time increased and the buffer effect was degraded. To improve the time response characteristics, an explicit dynamic model based on the HB model incorporating minor losses (called the E-HBM model) is proposed in this study. The model parameters were identified based on the HBM model. To verify the E-HBM model, five evaluation parameters for the energy absorption performance of the MREA, that is, peak force, mean force, crush force efficiency, specific energy absorption, and stroke efficiency, were introduced to compare the theoretical results with the experimental results obtained using a high-speed drop tower facility with a mass of 600 kg. Then, the relative error of the crush force efficiency, specific energy absorption, and stroke efficiency was quantitatively and comprehensively analyzed considering the E-HBM model and experimental results. The results indicate that the proposed E-HBM model agrees with the impact behavior of the radial flow mode MREA.

More pests but less pesticide applications: Ambivalent effect of landscape complexity on conservation biological control.

In agricultural landscapes, the amount and organization of crops and semi-natural habitats (SNH) have the potential to promote a bundle of ecosystem services due to their influence on ecological community at multiple spatio-temporal scales. SNH are relatively undisturbed and are often source of complementary resources and refuges, therefore supporting more diverse and abundant natural pest enemies. However, the nexus of SNH proportion and organization with pest suppression is not trivial. It is thus crucial to understand how the behavior of pest and natural enemy species, the underlying landscape structure, and their interaction, may influence conservation biological control (CBC). Here, we develop a generative stochastic landscape model to simulate realistic agricultural landscape compositions and configurations of fields and linear elements. Generated landscapes are used as spatial support over which we simulate a spatially explicit predator-prey dynamic model. We find that increased SNH presence boosts predator populations by sustaining high predator density that regulates and keeps pest density below the pesticide application threshold. However, predator presence over all the landscape helps to stabilize the pest population by keeping it under this threshold, which tends to increase pest density at the landscape scale. In addition, the joint effect of SNH presence and predator dispersal ability among hedge and field interface results in a stronger pest regulation, which also limits pest growth. Considering properties of both fields and linear elements, such as local structure and geometric features, provides deeper insights for pest regulation; for example, hedge presence at crop field boundaries clearly strengthens CBC. Our results highlight that the integration of species behaviors and traits with landscape structure at multiple scales is necessary to provide useful insights for CBC.

Explicit dynamic modeling of epoxy resin against the water drop impact

Purpose of this paper to investigate erosion wear of wind turbine blades. The effect of raindrops that falls into in wind turbine blades. The erosion wear plays a major role in the life cycle or endurance limit of wind turbine parts when we talk about wind turbine blades. Wind turbine blades getting more affected by raindrop erosion performance of epoxy resin materials. A mechanical design was created and used to conduct erosion test various environment conditions the experiment was carried out using water as raindrop and epoxy resin as the blade of the wind turbine the experiment was conducted with the help of ANSYS software and validate it to the analytical expression. The experiment going on, on the basis of time parameter range 30–120 min and also impacted by angle which is used to strike on the direction downward is about to maximum 90, velocity is the main parameter for investigate erosion wear which is varies in each step of experiment in this paper we trying to represent the future scope of epoxy resin which can be used in aircraft wing and wind turbine blade these research paper also clear that we can use ANSYS Software for investigate erosion wear of any materials The value obtain in Table 3 and Table 4 has the similar on both analytical and simulated rain drop impact on the epoxy resin material which can be used in real blade. It is found that the stress in Fig. 4. Which is shows the minimum and maximum drop impact with velocity variation. The tip speed and Wendy speed incident is large. for the force of significant has transmit on the edge and the material create stress access 164.39Mpa on the epoxy resin compressive strength range from 41.2280 to 247.728Mpa the tensile strength of epoxy resin from 9.12 to 117.5Mpa the fact that rainfall on a regular basis add to potential effect which can be noted down in the real blade.

Regional-scale data assimilation with the Spatially Explicit Individual-based Dynamic Global Vegetation Model (SEIB-DGVM) over Siberia

This study examined the regional performance of a data assimilation (DA) system that couples the particle filter and the Spatially Explicit Individual-based Dynamic Global Vegetation Model (SEIB-DGVM). This DA system optimizes model parameters of defoliation and photosynthetic rate, which are sensitive to phenology in the SEIB-DGVM, by assimilating satellite-observed leaf area index (LAI). The experiments without DA overestimated LAIs over Siberia relative to the satellite-observed LAI, whereas the DA system successfully reduced the error. DA provided improved analyses for the LAI and other model variables consistently, with better match with satellite observed LAI and with previous studies for spatial distributions of the estimated overstory LAI, gross primary production (GPP), and aboveground biomass. However, three main issues still exist: (1) the estimated start date of defoliation for overstory was about 40 days earlier than the in situ observation, (2) the estimated LAI for understory was about half of the in situ observation, and (3) the estimated overstory LAI and the total GPP were overestimated compared to the previous studies. Further DA and modeling studies are needed to address these issues.

Dynamic Model of TRMS Based on Homogeneous Transformation and Euler-Lagrange Equation

The aerodynamic experimental set TRMS (Twin Rotor MIMO System) is a strong nonlinear system, which has been taken by many scientists as an object to test modern control algorithms. The paper built a complete and explicit dynamic model for the TRMS based on dissociating TRMS into 3 subsystems, using homogeneous transformations in orthogonal coordinate systems to calculate the mass point’s position and velocity in component sub-systems; Euler - Lagrange equation was applied to model the dynamics for the object. Keywords— TRMS, dynamics, homogeneous transformation, mechanical system dissociation, Euler - Lagrange.

Explicit dynamic modeling with joint friction and coupling analysis of a 5-DOF hybrid polishing robot

Aiming at a 5-DOF hybrid optical mirror polishing robot, the explicit dynamic model considering the joint friction is established and the inertia coupling distribution is studied. Firstly, the kinematics of the manipulator is solved based on closed-loop vector method, and the dynamic model is established with Newton-Euler method based on the force analysis of manipulator components. Secondly, the kinematic parameters of the reference point of the moving platform are selected as the intermediate variables, and the explicit dynamic model of the parallel manipulator is obtained by parameters substitution considering the friction effects of spherical joints, universal joints and ball screws. Finally, on the basis of the dynamic model, the inertia coupling strength evaluation index for active branched-chains is proposed, and the distribution law of the coupling strength in a certain trajectory and workspace is studied. The results show that the inertia coupling strength indices between active branched-chains vary with the manipulator position and are symmetrically distributed in the workspace. This paper provides a theoretical basis for the joint controller design and structural parameter optimization of the polishing robot.

Representation learning for neural population activity with Neural Data Transformers

Neural population activity is theorized to reflect an underlying dynamical structure. This structure can be accurately captured using state space models with explicit dynamics, such as those based on recurrent neural networks (RNNs). However, using recurrence to explicitly model dynamics necessitates sequential processing of data, slowing real-time applications such as brain-computer interfaces. Here we introduce the Neural Data Transformer (NDT), a non-recurrent alternative. We test the NDT’s ability to capture autonomous dynamical systems by applying it to synthetic datasets with known dynamics and data from monkey motor cortex during a reaching task well-modeled by RNNs. The NDT models these datasets as well as state-of-the-art recurrent models. Further, its non-recurrence enables 3.9ms inference, well within the loop time of real-time applications and more than 6 times faster than recurrent baselines on the monkey reaching dataset. These results suggest that an explicit dynamics model is not necessary to model autonomous neural population dynamics. Code: https://github.com/snel-repo/neural-data-transformers

Neural monocular 3D human motion capture with physical awareness

We present a new trainable system for physically plausible markerless 3D human motion capture, which achieves state-of-the-art results in a broad range of challenging scenarios. Unlike most neural methods for human motion capture, our approach, which we dub physionical, is aware of physical and environmental constraints. It combines in a fully differentiable way several key innovations, i.e., 1. a proportional-derivative controller, with gains predicted by a neural network, that reduces delays even in the presence of fast motions, 2. an explicit rigid body dynamics model and 3. a novel optimisation layer that prevents physically implausible foot-floor penetration as a hard constraint. The inputs to our system are 2D joint keypoints, which are canonicalised in a novel way so as to reduce the dependency on intrinsic camera parameters -- both at train and test time. This enables more accurate global translation estimation without generalisability loss. Our model can be finetuned only with 2D annotations when the 3D annotations are not available. It produces smooth and physically principled 3D motions in an interactive frame rate in a wide variety of challenging scenes, including newly recorded ones. Its advantages are especially noticeable on in-the-wild sequences that significantly differ from common 3D pose estimation benchmarks such as Human 3.6M and MPI-INF-3DHP. Qualitative results are available at this http URL

Neural monocular 3D human motion capture with physical awareness

We present a new trainable system for physically plausible markerless 3D human motion capture, which achieves state-of-the-art results in a broad range of challenging scenarios. Unlike most neural methods for human motion capture, our approach, which we dub "physionical", is aware of physical and environmental constraints. It combines in a fully-differentiable way several key innovations, i.e. , 1) a proportional-derivative controller, with gains predicted by a neural network, that reduces delays even in the presence of fast motions, 2) an explicit rigid body dynamics model and 3) a novel optimisation layer that prevents physically implausible foot-floor penetration as a hard constraint. The inputs to our system are 2D joint keypoints, which are canonicalised in a novel way so as to reduce the dependency on intrinsic camera parameters---both at train and test time. This enables more accurate global translation estimation without generalisability loss. Our model can be finetuned only with 2D annotations when the 3D annotations are not available. It produces smooth and physically-principled 3D motions in an interactive frame rate in a wide variety of challenging scenes, including newly recorded ones. Its advantages are especially noticeable on in-the-wild sequences that significantly differ from common 3D pose estimation benchmarks such as Human 3.6M and MPI-INF-3DHP. Qualitative results are provided in the supplementary video.

Modeling multi‐scale occupancy for monitoring rare and highly mobile species

AbstractOccupancy‐based methods are commonly used to model the distribution, habitat use, and relative abundance of species. In particular, occupancy‐based methods are often recommended for monitoring species, allowing researchers to track population trends using detection–non‐detection data alone. Occupancy models, however, have proven difficult to apply to rare, highly mobile species. Species’ movements outside of sampling areas may lead to violation of the geographic closure assumption of occupancy models and overestimated occupancy probability. Low detection probability may further inflate occupancy probability estimates. We developed a novel continuous‐time, multi‐scale occupancy model to simultaneously account for closure assumption violations and low detection probability. We used a simulation study to test our model relative to a discrete‐time multi‐scale model, and we conducted a power analysis to assess the ability of an instantaneous occupancy parameter to detect trends in abundance, relative to standard occupancy alone. The continuous‐time model was competitive with the discrete‐time model and was generally computationally faster than and outperformed the discrete‐time model when detection probability was low. The instantaneous occupancy parameter outperformed occupancy in terms of power to detect trends when we used an implicit (i.e., estimating occupancy independently in each primary occasion) dynamic occupancy model, but performed no better when we used an explicit (i.e., estimating colonization and extinction) dynamic occupancy model. We applied both discrete‐time and continuous‐time multi‐scale occupancy models to a case study of data collected on wolverines (Gulo gulo) in Washington, USA. We found improved precision in estimates with the continuous‐time model and that asymptotic occupancy of wolverines was high, but short‐term use of any given area was low. Our multi‐scale, continuous‐time occupancy model can be used to detect trends in abundance of rare, highly mobile species, regardless of how occupancy dynamics are modeled. Furthermore, our model can allow for more efficient data collection and analysis than traditional discrete‐time or spatially multi‐scale approaches, as our model uses all available detections and requires only one detector per sampling unit by substituting time for space.

DEM/FEM simulation of the shot peening process on sharp notches

The residual stress field produced by shot peening on Al-7075-T651 prismatic samples carrying V-edge notches is evaluated through combined Discrete Element Modeling (DEM) and Finite Element Modeling (FEM) simulations. Special care is paid to faithfully model the interaction between peening nozzle, shots and notched target through DEM analyses and to understand the coverage level at the notch root. The simulated stream of shots with randomly distributed size, location and velocity is imported into an explicit dynamic FE model of a neighborhood of the notch tip. The resulting residual stress (RS) field is compared to the RS field computed using thermal fields in a FEM simulation, calibrated with experimental data collected through Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction techniques. The obtained results are in good agreement with experimentally reconstructed RS and suggests the hypothesis that the notch tip RS field is dictated only by impacts occurring in the very vicinity of the notch apex.

Comparative analysis of different approaches for computing axial, torsional and bending stiffnesses of cables and wire ropes

In the field of cables and wire ropes modeling, many different approaches have been developed over the years to simulate the mechanical response of such structural components. The present work aims to compare, for a wide range of helix angles, the axial, torsional, axial/torsional coupling, and bending stiffness of a single-layered wire rope, computed through classical analytical models and finite element numerical models. Three different approaches were applied to the numerical models: in the first one, the wires were modeled with beam elements, solid elements were used in the second model, while the third employed solid elements under explicit dynamic conditions. While the numerical beam model yielded results close to the analytical models, decreasing its accuracy for low helix angles, the explicit dynamic model could reproduce with reasonable accuracy the results for the solid element under static behavior.

Dynamic analysis of a novel spatial multiple-loop mobile lunar landing mechanism: An efficient approach based on explicit dynamics

The Movable lunar landing leg is a novel multi - closed parallel mechanism with sub-closed loop. Moreover, there are multiple passive and active joint variables in the mobile lunar landing legged mechanism (MLLLM), Due to the complex dynamic relationship between the passive joint variables and the active joint variables, it is difficult to derive the dynamic modeling of parallel mechanisms by the non-redundant parallel mechanism using the traditional Lagrangian formulation method. In order to solve this problem, the utilization of the virtual work principle makes the application of the Lagrangian formulation for parallel mechanisms possible and efficient. The MLLLM is divided into several serial open-loop sub-chains. Explicit dynamic equations of each sub-chain can be derived by using the Lagrangian formalism straightforwardly with respect to their own local generalized coordinates. Secondly, when transforming between different generalized coordinates, the dynamic equation is transformed into different coordinate subsystems by using the principle of virtual work, and the Jacobian matrix and Hessen matrix are introduced as constraints to ensure the explicit form of the dynamic equation, by combining the differential dynamics equations of each subsystem with the virtual work principle, the explicit dynamics model of the MLLLM under the active generalized coordinates is obtained. Finally, the position error of the end-effector caused by the active and passive joints of the parallel mechanism was evaluated. Compared with the previous methods, the inverse dynamic analysis formula presented in this paper is more concise, the calculation efficiency is higher, and the position error evaluation method is more accurate than the traditional method.

Sheep scab transmission: a spatially explicit dynamic metapopulation model

Psoroptic mange (sheep scab), caused by the parasitic mite, Psoroptes ovis, is an important disease of sheep worldwide. It causes chronic animal welfare issues and economic losses. Eradication of scab has proved impossible in many sheep-rearing areas and recent reports of resistance to macrocyclic lactones, a key class of parasiticide, highlight the importance of improving approaches to scab management. To allow this, the current study aimed to develop a stochastic spatial metapopulation model for sheep scab transmission which can be adapted for use in any geographical region, exhibited here using data for Great Britain. The model uses agricultural survey and sheep movement data to geo-reference farms and capture realistic movement patterns. Reported data on sheep scab outbreaks from 1973 to 1991 were used for model fitting with Sequential Monte Carlo Approximate Bayesian Computation methods. The outbreak incidence predicted by the model was from the same statistical distribution as the reported outbreak data ({chi }^{2} = 115.3, p = 1) and the spatial location of sheep scab outbreaks predicted was positively correlated with the observed outbreak data by county (tau = 0.55, p < 0.001), confirming that the model developed is able to accurately capture the number of farms infected in a year, the seasonality of scab incidence and the spatial patterns seen in the data. This model gives insight into the transmission dynamics of sheep scab and will allow the exploration of more effective control strategies.

Assessment of submarine pipeline damages subjected to falling object impact considering the effect of seabed

Untrenched submarine pipelines lying on the seabed are vulnerable and can be damaged by the impact of falling objects. This may cause significant economic costs for repair and even environmental contamination in case of rupture and oil leakage. This paper presents assessment of submarine pipeline damage subjected to falling object impact considering the effect of seabed through nonlinear explicit dynamic finite element modelling. The numerical model was first verified against existing experimental results and established studies. A total of 209 cases of parametric study was then conducted to assess pipeline damage by accounting for various factors, including object mass, velocity and seabed conditions. The results show that the pipeline damage can be directly related to the impact kinetic energy of the falling object for pipelines sitting on rigid bed. In other words, falling objects with the same impact energy (while mass and velocity may vary) cause the same damage to a pipeline. For a pipeline on a soil seabed, however, this study shows that pipeline damage is no longer simplistically determined by the impact kinetic energy of the falling objects. Falling objects with different mass and velocity may cause different pipeline damages, even though the impact energy is the same. It is interesting to find out that objects with a smaller mass (i.e. higher velocity) tend to cause greater damage than objects with a greater mass (i.e. lower velocity), when the total impact kinetic energy of the falling objects is the same. These observations are explored in this paper, which is explained with the variation of the energy absorption due to the existence of soil seabed.

Numerical analysis for estimating ballistic performance of armour material

Ballistic performance of naval ship structured material is analysed by formulating numerical simulation technique using 3-D explicit dynamic nonlinear finite element model in ANSYS®19. The methodology includes the effects of plastic deformation and facture of material describing flow stress, strain and strain rate hardening parameter under terminal high velocity ballistic impact. Initially, numerical simulation was carried on Weldox700E armour plate using Johnson-Cook strength and failure criteria with NATO ball bullet as impacting projectile for validation purpose. Further, the validated model is used to simulate the impact behaviour of Al5083 structural material subjected to high velocity impact of 7.62 × 39 mm mild steel core bullet having different thickness. The former simulation result was compared with available literature while the latter is evaluated using the experimental test findings. Residual velocity of projectile, failure mode and deformation pattern of target plate, projectile displacement and energy summary were used to determine characteristics of ballistic event. The methodology used in this paper demonstrates significant efficiency and adequacy of the implemented Johnson Cook model to determine a non-linear physical penetration mechanism and its experimental measurable parameters.