Flexible multibody impact simulations based on the isogeometric analysis approach

AbstractUsually detailed impact simulations are based on isoparametric finite element models. For the inclusion in multibody dynamics simulation, e.g., in the framework of the floating frame of reference, a previous model reduction is necessary. A precise representation of the geometry is essential for modeling the dynamics of the impact. However, isoparametric finite elements involve the discretization of the geometry. This work tests isogeometric analysis (IGA) models as an alternative approach in the context of impact simulations in flexible multibody systems. Therefore, the adaption of the flexible multibody system procedure to include IGA models is detailed. The use of nonuniform rational basis splines (NURBS) allows the exact representation of the geometry. The degrees of freedom of the flexible body are afterwards reduced to save computation time in the multibody simulation. To capture precise deformations and stresses in the area of contact as well as elastodynamic effects, a large number of global shape functions is required. As test examples, the impact of an elastic sphere on a rigid surface and the impact of a long elastic rod are simulated and compared to reference solutions.

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Reduced Isogeometric Analysis Models for Impact Simulations

10.1115/detc2021-67417 ◽

2021 ◽

Author(s):

Tobias Rückwald ◽

Alexander Held ◽

Robert Seifried

Keyword(s):

Isogeometric Analysis ◽

Multibody Systems ◽

Degrees Of Freedom ◽

Computation Time ◽

Flexible Multibody Systems ◽

Shape Functions ◽

Elastic Rod ◽

Flexible Multibody ◽

Impact Simulations ◽

The Impact

Abstract Detailed impact simulations in flexible multibody systems are usually based on isoparametric finite element models. For modeling the dynamics of an impact, a precise representation of the geometry is essential. However, isoparametric finite elements involve the discretization of the geometry. This work tests the isogeometric analysis (IGA) as an alternative approach in flexible multibody systems. The IGA enables the exact representation of the geometry by using non-uniform rational basis splines (NURBS) as element shape functions. In the context of an efficient impact simulation a model reduction and a possible inclusion of the floating frame of reference formulation is beneficial. The degrees of freedom of the flexible bodies are reduced using component mode synthesis to save computation time in the multibody simulation. For the precise description of deformations and stresses in the contact area as well as elastodynamic effects, a large number of global shape functions is required. As testing examples, the impact of two elastic spheres and a multibody multicontact problem including wave propagation in a long elastic rod are simulated and compared to reference solutions.

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Methods for Restricting Maximum Exposure Rate in Computerized Adaptative Testing

Methodology ◽

10.1027/1614-2241.3.1.14 ◽

2007 ◽

Vol 3 (1) ◽

pp. 14-23 ◽

Cited By ~ 9

Author(s):

Juan Ramon Barrada ◽

Julio Olea ◽

Vicente Ponsoda

Keyword(s):

Measurement Accuracy ◽

Computerized Adaptive Testing ◽

Computation Time ◽

Adaptive Testing ◽

Exposure Rate ◽

Control Parameters ◽

The Impact ◽

Two Alternatives ◽

Selection Of ◽

Maximum Exposure

Abstract. The Sympson-Hetter (1985) method provides a means of controlling maximum exposure rate of items in Computerized Adaptive Testing. Through a series of simulations, control parameters are set that mark the probability of administration of an item on being selected. This method presents two main problems: it requires a long computation time for calculating the parameters and the maximum exposure rate is slightly above the fixed limit. Van der Linden (2003) presented two alternatives which appear to solve both of the problems. The impact of these methods in the measurement accuracy has not been tested yet. We show how these methods over-restrict the exposure of some highly discriminating items and, thus, the accuracy is decreased. It also shown that, when the desired maximum exposure rate is near the minimum possible value, these methods offer an empirical maximum exposure rate clearly above the goal. A new method, based on the initial estimation of the probability of administration and the probability of selection of the items with the restricted method ( Revuelta & Ponsoda, 1998 ), is presented in this paper. It can be used with the Sympson-Hetter method and with the two van der Linden's methods. This option, when used with Sympson-Hetter, speeds the convergence of the control parameters without decreasing the accuracy.

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Mechanically-Tunable Quantum Interference in Ferrocene-Based Single-Molecule Junctions

10.26434/chemrxiv.12252059 ◽

2020 ◽

Author(s):

María Camarasa-Gómez ◽

Daniel Hernangómez-Pérez ◽

Michael S. Inkpen ◽

Giacomo Lovat ◽

E-Dean Fung ◽

...

Keyword(s):

Single Molecule ◽

Quantum Interference ◽

Degrees Of Freedom ◽

Building Blocks ◽

Ferrocene Derivative ◽

Single Molecule Junctions ◽

Molecule Junction ◽

Single Molecule Junction ◽

The Impact ◽

D Orbitals

Ferrocenes are ubiquitous organometallic building blocks that comprise a Fe atom sandwiched between two cyclopentadienyl (Cp) rings that rotate freely at room temperature. Of widespread interest in fundamental studies and real-world applications, they have also attracted<br>some interest as functional elements of molecular-scale devices. Here we investigate the impact of<br>the configurational degrees of freedom of a ferrocene derivative on its single-molecule junction<br>conductance. Measurements indicate that the conductance of the ferrocene derivative, which is<br>suppressed by two orders of magnitude as compared to a fully conjugated analog, can be modulated<br>by altering the junction configuration. Ab initio transport calculations show that the low conductance is a consequence of destructive quantum interference effects that arise from the hybridization of metal-based d-orbitals and the ligand-based π-system. By rotating the Cp rings, the hybridization, and thus the quantum interference, can be mechanically controlled, resulting in a conductance modulation that is seen experimentally.<br>

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Reversibly Sampling Conformations and Binding Modes Using Molecular Darting

10.26434/chemrxiv.12670676.v2 ◽

2020 ◽

Author(s):

Samuel C. Gill ◽

David Mobley

Keyword(s):

Monte Carlo ◽

Ligand Binding ◽

Binding Sites ◽

Degrees Of Freedom ◽

Dynamics Simulation ◽

Hiv Integrase ◽

Binding Modes ◽

System A ◽

Multiple Binding ◽

Internal Degrees Of Freedom

<div>Sampling multiple binding modes of a ligand in a single molecular dynamics simulation is difficult. A given ligand may have many internal degrees of freedom, along with many different ways it might orient itself a binding site or across several binding sites, all of which might be separated by large energy barriers. We have developed a novel Monte Carlo move called Molecular Darting (MolDarting) to reversibly sample between predefined binding modes of a ligand. Here, we couple this with nonequilibrium candidate Monte Carlo (NCMC) to improve acceptance of moves.</div><div>We apply this technique to a simple dipeptide system, a ligand binding to T4 Lysozyme L99A, and ligand binding to HIV integrase in order to test this new method. We observe significant increases in acceptance compared to uniformly sampling the internal, and rotational/translational degrees of freedom in these systems.</div>

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Impact Load Buffering Method Based on Stress Wave Attenuation Principle

International Journal of Applied Mechanics ◽

10.1142/s1758825119500194 ◽

2019 ◽

Vol 11 (02) ◽

pp. 1950019 ◽

Cited By ~ 2

Author(s):

Lin Gan ◽

He Zhang ◽

Cheng Zhou ◽

Lin Liu

Keyword(s):

Stress Wave ◽

Wave Attenuation ◽

Impact Load ◽

Dynamics Simulation ◽

Scanning System ◽

Isolation Method ◽

Element Analysis ◽

System A ◽

High Emission ◽

The Impact

Rotating scanning motor is the important component of synchronous scanning laser fuze. High emission overload environment in the conventional ammunition has a serious impact on the reliability of the motor. Based on the theory that the buffer pad can attenuate the impact stress wave, a new motor buffering Isolation Method is proposed. The dynamical model of the new buffering isolation structure is established by ANSYS infinite element analysis software to do the nonlinear impact dynamics simulation of rotating scanning motor. The effectiveness of Buffering Isolation using different materials is comparatively analyzed. Finally, the Macht hammer impact experiment is done, the results show that in the experience of the 70,000[Formula: see text]g impact acceleration, the new buffering Isolation method can reduce the impact load about 15 times, which can effectively alleviate the plastic deformation of rotational scanning motor and improve the reliability of synchronization scanning system. A new method and theoretical basis of anti-high overload research for Laser Fuze is presented.

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The Impact of the Electric Field on Surface Condensation of Water Vapor: Insight from Molecular Dynamics Simulation

Nanomaterials ◽

10.3390/nano9010064 ◽

2019 ◽

Vol 9 (1) ◽

pp. 64 ◽

Cited By ~ 7

Author(s):

Qin Wang ◽

Hui Xie ◽

Zhiming Hu ◽

Chao Liu

Keyword(s):

Molecular Dynamics ◽

Water Vapor ◽

Electric Field ◽

Intermolecular Forces ◽

Dynamics Simulation ◽

Water Molecules ◽

Attraction Force ◽

Condensation Rate ◽

Shape Transformation ◽

The Impact

In this study, molecular dynamics simulations were carried out to study the coupling effect of electric field strength and surface wettability on the condensation process of water vapor. Our results show that an electric field can rotate water molecules upward and restrict condensation. Formed clusters are stretched to become columns above the threshold strength of the field, causing the condensation rate to drop quickly. The enhancement of surface attraction force boosts the rearrangement of water molecules adjacent to the surface and exaggerates the threshold value for shape transformation. In addition, the contact area between clusters and the surface increases with increasing amounts of surface attraction force, which raises the condensation efficiency. Thus, the condensation rate of water vapor on a surface under an electric field is determined by competition between intermolecular forces from the electric field and the surface.

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The halo model as a versatile tool to predict intrinsic alignments

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3802 ◽

2020 ◽

Author(s):

Maria Cristina Fortuna ◽

Henk Hoekstra ◽

Benjamin Joachimi ◽

Harry Johnston ◽

Nora Elisa Chisari ◽

...

Keyword(s):

Degrees Of Freedom ◽

Power Spectra ◽

Stage Iv ◽

Stage Iii ◽

Radial Dependence ◽

Additional Parameter ◽

Small Scales ◽

Cosmic Shear ◽

Galaxy Populations ◽

The Impact

Abstract Intrinsic alignments (IAs) of galaxies are an important contaminant for cosmic shear studies, but the modelling is complicated by the dependence of the signal on the source galaxy sample. In this paper, we use the halo model formalism to capture this diversity and examine its implications for Stage-III and Stage-IV cosmic shear surveys. We account for the different IA signatures at large and small scales, as well for the different contributions from central/satellite and red/blue galaxies, and we use realistic mocks to account for the characteristics of the galaxy populations as a function of redshift. We inform our model using the most recent observational findings: we include a luminosity dependence at both large and small scales and a radial dependence of the signal within the halo. We predict the impact of the total IA signal on the lensing angular power spectra, including the current uncertainties from the IA best-fits to illustrate the range of possible impact on the lensing signal: the lack of constraints for fainter galaxies is the main source of uncertainty for our predictions of the IA signal. We investigate how well effective models with limited degrees of freedom can account for the complexity of the IA signal. Although these lead to negligible biases for Stage-III surveys, we find that, for Stage-IV surveys, it is essential to at least include an additional parameter to capture the redshift dependence.

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A Superfluid Perspective on Neutron Star Dynamics

Universe ◽

10.3390/universe7010017 ◽

2021 ◽

Vol 7 (1) ◽

pp. 17

Author(s):

Nils Andersson

Keyword(s):

Neutron Star ◽

Degrees Of Freedom ◽

Temperature Scale ◽

Fluid System ◽

Fluid Core ◽

State Of Matter ◽

Entrainment Effect ◽

Neutron Component ◽

The Impact

As mature neutron stars are cold (on the relevant temperature scale), one has to carefully consider the state of matter in their interior. The outer kilometre or so is expected to freeze to form an elastic crust of increasingly neutron-rich nuclei, coexisting with a superfluid neutron component, while the star’s fluid core contains a mixed superfluid/superconductor. The dynamics of the star depend heavily on the parameters associated with the different phases. The presence of superfluidity brings new degrees of freedom—in essence we are dealing with a complex multi-fluid system—and additional features: bulk rotation is supported by a dense array of quantised vortices, which introduce dissipation via mutual friction, and the motion of the superfluid is affected by the so-called entrainment effect. This brief survey provides an introduction to—along with a commentary on our current understanding of—these dynamical aspects, paying particular attention to the role of entrainment, and outlines the impact of superfluidity on neutron-star seismology.

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Long-term effectiveness of elderly health care voucher scheme strategies: a system dynamics simulation analysis

BMC Public Health ◽

10.1186/s12889-021-11280-z ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Ka Chun Chong ◽

Hong Fung ◽

Carrie Ho Kwan Yam ◽

Patsy Yuen Kwan Chau ◽

Tsz Yu Chow ◽

...

Keyword(s):

Primary Care ◽

Chronic Disease ◽

Public Sector ◽

System Dynamics ◽

The Elderly ◽

Healthcare Services ◽

Dynamics Simulation ◽

Public And Private ◽

The Public ◽

The Impact

Abstract Background The elderly healthcare voucher (EHCV) scheme is expected to lead to an increase in the number of elderly people selecting private primary healthcare services and reduce reliance on the public sector in Hong Kong. However, studies thus far have reported that this scheme has not received satisfactory responses. In this study, we examined changes in the ratio of visits between public and private doctors in primary care (to measure reliance on the public sector) for different strategic scenarios in the EHCV scheme. Methods Based on comments from an expert panel, a system dynamics model was formulated to simulate the impact of various enhanced strategies in the scheme: increasing voucher amounts, lowering the age eligibility, and designating vouchers for chronic conditions follow-up. Data and statistics for the model calibration were collected from various sources. Results The simulation results show that the current EHCV scheme is unable to reduce the utilization of public healthcare services, as well as the ratio of visits between public and private primary care among the local aging population. When comparing three different tested scenarios, even if the increase in the annual voucher amount could be maintained at the current pace or the age eligibility can be lowered to include those aged 60 years, the impact on shifts from public-to-private utilization were insignificant. The public-to-private ratio could only be marginally reduced from 0.74 to 0.64 in the first several years. Nevertheless, introducing a chronic disease-oriented voucher could result in a significant drop of 0.50 in the public-to-private ratio during the early implementation phase. However, the effect could not be maintained for an extended period. Conclusions Our findings will assist officials in improving the design of the EHCV scheme, within the wider context of promoting primary care among the elderly. We suggest that an additional chronic disease-oriented voucher can serve as an alternative strategy. The scheme must be redesigned to address more specific objectives or provide a separate voucher that promotes under-utilized healthcare services (e.g., preventive care), instead of services designed for unspecified reasons, which may lead to concerns regarding exploitation.

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Integrated IEW-TOPSIS and Fire Dynamics Simulation for Agent-Based Evacuation Modeling in Industrial Safety

Safety ◽

10.3390/safety7020047 ◽

2021 ◽

Vol 7 (2) ◽

pp. 47

Author(s):

Wattana Chanthakhot ◽

Kasin Ransikarbum

Keyword(s):

Emergency Evacuation ◽

Industrial Sector ◽

Industrial Safety ◽

Dynamics Simulation ◽

Entropy Weight ◽

Fire Dynamics ◽

Evacuation Simulation ◽

Evacuation Modeling ◽

Agent Based ◽

The Impact

Emergency events in the industrial sector have been increasingly reported during the past decade. However, studies that focus on emergency evacuation to improve industrial safety are still scarce. Existing evacuation-related studies also lack a perspective of fire assembly point’s analysis. In this research, location of assembly points is analyzed using the multi-criteria decision analysis (MCDA) technique based on the integrated information entropy weight (IEW) and techniques for order preference by similarity to ideal solution (TOPSIS) to support the fire evacuation plan. Next, we propose a novel simulation model that integrates fire dynamics simulation coupled with agent-based evacuation simulation to evaluate the impact of smoke and visibility from fire on evacuee behavior. Factors related to agent and building characteristics are examined for fire perception of evacuees, evacuees with physical disabilities, escape door width, fire location, and occupancy density. Then, the proposed model is applied to a case study of a home appliance factory in Chachoengsao, Thailand. Finally, results for the total evacuation time and the number of remaining occupants are statistically examined to suggest proper evacuation planning.

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