bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic Modeling and Force Control of a Redundant Robot for Polishing Applications
Authors: Parzer Herbert , Gattringer Hubert , Neubauer Matthias 
Published: December 2014

AbstractFor many robotic applications with tasks such as cutting, assembly or polishing, it is necessary to get in contact with the surrounding. In this paper a redundant robot with seven degrees of freedom in a metal polishing task is considered. For simulation as well as for the controller design a dynamic model of the robot and a contact model are required. The equations of motion of the robot are calculated with the Projection Equation in subsystem representation and the contact model contains linear tool elasticities and work piece elasticities. In the case of a polishing task, a constant contact force during the process is required even if the robot moves along a trajectory. Thus some degrees of freedom of the robot tool center point have to be position controlled while the other ones have to be force controlled. The redundant robot offers the possibility to avoid singular positions or to maximize the available end‐effector forces within the inverse kinematics and is therefore best suited for polishing large objects. The actual process forces are measured with a six axis force‐torque‐sensor mounted at the tool center point. These forces are used in a parallel force/position control law to achieve the desired behavior. Results from measurements of a test arrangement are presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydraulic effects of fracture in brittle porous materials
Authors: Nguyen Minh N. , Timothy Jithender J. , Beckhuis Sven , Meschke Günther 
Published: December 2014

AbstractThis paper presents a multi‐level model for the description of hydraulic effects of fracture within the context of Enhanced Geothermal Systems. The standard Biot's poroelastic formulation is used to model the physical processes in a geomechanical reservoir in terms of the material deformation and the fluid pressure. Crack propagation is modeled using the phase field method. The influence of a propagating fracture on permeability is taken into account by using a micromechanical homogenization technique. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microsopic Simulation of Thermally‐Induced 2nd Order Eigenstresses in AlSi‐Alloys
Authors: Staub Sarah , Kabel Matthias , Andrä Heiko , Hofmann Michael , Schöbel Michael 
Published: December 2014

AbstractDue to the different coefficients of thermal expansion of aluminium and silicon, high residual stresses of second order occur in Al‐Si alloys depending on the cooling rate during the molding process. In products as for example crank cases made of Al‐Si alloys these residual stresses may cause microcracks. In the work at hand measurements of the eigenstresses in the single phases (i.e. residual stresses of second kind) performed via neutron diffractometry are compared to numerical simulations for a specific cooling rate. To this end a three‐phase model is presented, which considers the α aluminium, the eutectic aluminium, and the silicon particles. The presented model is able to predict the residual stresses in the single phases within an elastoplastic framework. The simulation of tensile loadings of these structures are compared to experiments. The numerical computations are carried on stochastic geometry models by using a fast solver [1] for the Lippmann‐Schwinger integral equation, which is based on the fast Fourier transformation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling of non‐conforming NURBS patches with the weak substitution method
Authors: Klinkel Sven , Dornisch Wolfgang , Vitucci Gennaro 
Published: December 2014

AbstractIsogeometric analysis unifies the data model for the description of the geometry for design and analysis. The analysis is altered towards compatibility with the geometry model used in the design work flow. The basis functions of the geometry descriptions are used to approximate all unknown quantities in the numerical simulation. The most common geometry model in design industry is NURBS surfaces. The properties of NURBS surfaces do not allow local refinement. Geometrical models in industrial applications generally consist of several NURBS patches, which usually neither have conforming knot vectors nor the same degree. Thus, the control points do not coincide and a connection by shared control points is not possible. Special methods to avoid mutual refinement are necessary. This works presents a new method for the coupling of non‐conforming patches. A relation between the deformations of control points having influence on shared edges is established. This relation allows expressing the deformations of a set of slave control points as a function of the deformations of the appropriate master control points. Thus, the slave control points, as well as the associated degrees of freedom can be removed from the global system of equation. The method can also be used for nonlinear computations without additional effort. The derivation of the proposed relation is shown. Numerical examples show the high accuracy of the presented method. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A dynamic friction model for the pre‐sliding behavior of a tangentially loaded single asperity contact
Authors: Krasmik Viktor , Schlattmann Josef 
Published: December 2014

AbstractWe introduce a dynamic friction model for the pre‐sliding behavior of a single asperity subjected to a constant normal and a varying tangential load based on Cattaneo‐Mindlin's theory. The geometry of an arbitrary, axisymmetric asperity is included in the formulation of the governing differential equation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Introducing parametric uncertainty into a nonlinear friction model
Authors: Seibel Arthur , Schlattmann Josef 
Published: December 2014

AbstractWe introduce parametric uncertainty into a nonlinear model for static and kinetic friction of solids. The uncertain parameters are modeled by possibility distributions and an analytical approach is used to propagate the uncertainties through the computations. As a result, we obtain a symbolic expression for the whole spectrum of possible calculation results. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Functional Fatigue in polycrystalline Shape Memory Alloys
Authors: Waimann Johanna , Junker Philipp , Hackl Klaus 
Published: December 2014

AbstractShape memory alloys show the well known effect of pseudo‐elasticity associated with the formation of two stress plateaus in the stress/strain diagram for tension tests. Due to cyclic loading, the stress plateaus decrease with every load cycle, particularly the upper one. This important effect of functional fatigue results from plastic deformations that are produced during solid‐solid phase transformations between the austenitic and martensitic state. Outgoing from a polycrystalline approach for shape memory alloys we develop a micromechanical material model that is based on the Principle of the Minimum of the Dissipation Potential and predicts the evolution of plastic strains. Therefore, only a small number of material parameters is necessary and additionally, only a few assumptions are sufficient to model the effect of functional fatigue. We present yield functions as well as evolution equations for the volume fractions of austenite and martensite, and the plastic strains. Furthermore, we show an exemplary calculation for Nickel Titanium and compare it with experimental measurements to demonstrate the ability of our model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An experimental study towards micro‐mechanical modeling of fiber‐reinforced aerogels
Authors: Rege Ameya , Dargazany Roozbeh , Itskov Mikhail , Deo Akash 
Published: December 2014

AbstractFiber‐reinforced aerogels are a class of reinforced aerogels characterized by very low thermal conductivity, hydrophobicity and most importantly load bearing capability. In this work, an experimental study describing the damage in these fiber‐reinforced aerogels through various uniaxial compression tests is presented. While understanding the damage evolution at the micro‐scale, we come across three probable sources contributing towards the damage evolution. They are: (a) matrix cracks, (b) debonding of particles due to fiber sliding, and (c) breakage of fibers. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐dimensional elastic phase‐field simulation of fcc to bcc martensitic phase transformations in polycrystals
Authors: Kochmann Julian , Rezaeimianroodi Jaber , Reese Stefanie , Svendsen Bob 
Published: December 2014

AbstractNumerical results of two‐dimensional elastic phase‐field simulations of martensitic phase transformations (fcc‐bcc) in polycystals are presented. The stresses and strains in the diffuse interface domain are described by following Khachaturyan's approach of microelasticity. A fixed‐point iteration algorithm in Fourier space is used to solve the mechanical equilibrium condition for the microscopic, inhomogeneous strain field and apply mechanical loadings to the system. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determining the limits of geometrical tortuosity from seepage flow calculations in porous media.
Authors: Uribe David , Osorno Maria , Sivanesapillai Rakulan , Steeb Holger , Ruiz Oscar 
Published: December 2014

AbstractRecent investigations have found a distinct correlation of effective properties of porous media to sigmoidal functions, where one axis is the Reynolds number Re and the other is the effective property dependent of Re, Θi = Si(Re). One of these properties is tortuosity. At very low Re (seepage flow), there is a characteristic value of tortuosity, and it is the upper horizontal asymptote of the sigmoidal function. With higher values of Re (transient flow) the tortuosity value decreases, until a lower asymptote is reached (turbulent flow).Estimations of this parameter have been limited to the low Reynolds regime in the study of porous media. The current state of the art presents different numerical measurements of tortuosity, such as skeletization, centroid binding, and arc length of streamlines. These are solutions for the low Re regime. So far, for high Re, only the arc length of stream lines has been used to calculate tortuosity. The present approach involves the simulation of fluid flow in large domains and high Re, which requires numerous resources, and often presents convergence problems. In response to this, we propose a geometrical method to estimate the limit of tortuosity of porous media at Re → ∞, from the streamlines calculated at low Re limit. We test our method by calculating the tortuosity limits in a fibrous porous media, and comparing the estimated values with numerical benchmark results. Ongoing work includes the geometric estimation of different intrinsic properties of porous media. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Consolidation of a poroelastic sphere: Numerical investigations of Cryer's problem
Authors: Pollmann Nele , Steeb Holger 
Published: December 2014

AbstractIn geomechanics the consolidation of a fluid‐saturated soil is of great interest and many theories have been proposed in the recent years. A special case is the consolidation problem in a porous, fluid‐saturated sphere under drainage and hydrostatic pressure. For this configuration Cryer [2] discussed the special effect of pore pressure response. We increase the complexity of the classical approach, taking into account a modified sphere with an undrained layer. This modification is an expansion of the original problem towards more realistic situations of a poroelastic rock which contains a heterogeneity (modified Cryer problem). It results in nearly effective drainage for the heterogeneity and significant differences in momentary stress state. The interaction between the skeleton and the pore fluid of the porous sphere is implemented numerically with Biot's theory of linear consolidation in an us‐p‐formulation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of Surfactant Concentration in a Coupled Bulk Surface Problem
Authors: Hahn Andreas , Held Kristin , Tobiska Lutz 
Published: December 2014

AbstractSurface active agents (surfactants) are on high interest for physical and chemical industries. Their presence lowers the surface tension of fluids. This is used to achieve special flow properties. These mechanisms are not only influenced by the overall amount of surfactant. They highly depend on the local surfactant distribution. The surfactant concentration is modeled by two convection diffusion equations, one in the bulk and the other on its surface. Adsorption‐ and desorption processes are included and lead to a (non linear) coupling of both equations. We present a numerical scheme for solving the coupled problem. Additionally, first analytical results will be given. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A model describing pressure buildup in rough surfaces with partially filled gaps
Authors: Mueller Michael , Bubser Florian , Ostermeyer Georg‐Peter 
Published: December 2014

AbstractBecause of an ecological and economical need to reduce the application of lubricants, the tribological regime of starved lubrication in the field of mechanical engineering has gained importance during the last decades. In order to describe the respective processes properly, models should consider that the gap between the bodies is not fully but only partially filled with a fluid. Recently, the authors introduced a model which explicitly describes the fluid flow and its interaction with the buildup of pressures under these conditions [1]. This paper points out that the correlation between the filling ratio and a time‐ and space‐averaged pressure value is highly nonlinear. This is due to the fact that the system's load bearing character changes from being a local effect to a global effect, in particular near the fully filled regime. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An analysis of the different parameters influence on the microbearing load carrying capacity
Authors: Stevanovi´ c Nevena D. , Mili´ cev Snežana S. 
Published: December 2014

AbstractAn analytical solution for the two‐dimensional non‐isothermal compressible gas flow in a slider microbearing is presented in this paper. The solutions enable analysis of the relevant parameters influences on the load carrying capacity of the micro‐bearing. Hence, the influences of the flow conditions expressed by Mach, Reynolds and Knudsen numbers, the ratio of the inlet to outlet heights, bearing number, as well as temperature field are investigated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of Injection Molding using OpenFOAM
Authors: Ospald Felix 
Published: December 2014

AbstractWe show how to use and extend OpenFOAM's incompressible two‐phase flow solvers for the simulation of injection molding with short fiber reinforced thermoplastics in a laminar flow regime. Second order fiber orientation tensors are computed using the Folgar‐Tucker equation (FTE) with quadratic closure. The FTE is coupled to the viscosity‐term of the Navier‐Stokes equations for the non‐Newtonian flow in a segregated manner. Phase dependent boundary conditions are implemented to simulate wall heat transfer, stickiness of the melt to the wall and to prevent air‐traps close to the wall. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivity of the slip rate coefficient in fluid flow – poroelastic coupling conditions
Authors: Beck Silja C. , Uphoff Sonja , Langer Sabine C. , Krafczyk Manfred 
Published: December 2014

AbstractTo model flow‐induced structural vibrations, an interface to couple fluid flow and poroelastic material in a finite element formulation has been developed. One parameter of this interface condition is the slip rate coefficient, resulting from the so‐called Beavers‐Joseph‐Saffman condition. This condition states that the jump in tangential velocity at a fluid flow – porous interface is proportional to the shear stress. Up to now no a priori determination of this parameter exists, and the known parameter range has been deducted from measurements, i. e., in our case from the results of the pore‐resolving simulations. When modeling realistic problems assuming incompressible fluids, vectorial flow velocity and scalar pressure interact with the poroelastic material. As the slip rate coefficient only influences the tangential contributions, its overall influence is not clear. In this work, the sensitivity of the slip rate coefficient regarding the interface's coupling conditions is evaluated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Navier‐Stokes equations with particle methods
Authors: Asanalieva Nazgul , Heutling Carolin , Varnhorn Werner 
Published: December 2014

AbstractWe consider the initial boundary value problem for the nonstationary Navier‐Stokes equations in a bounded three‐dimensional domain Ω with a sufficiently smooth boundary ∂Ω. These equations describe the motion of a viscous incompressible fluid contained in Ω for 0 < t < T. They represent a system of nonlinear partial differential equations concerning four unknown functions, i.e. the velocity vector v = (v1(t, x), v2(t, x), v3(t, x)) and the kinematic pressure function p = p(t, x) of the fluid at time t ∈ (0, T) in x ∈ Ω. The purpose of this paper is to construct a Leray‐Hopf type weak solution to the nonstationary Navier‐Stokes system, which exists globally in time. Our construction is based on a suitable approximation using particle methods for stationary fluid flow. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
About an analytical approach to a quasicontinuum method via Γ‐convergence
Authors: Schäffner Mathias , Schlömerkemper Anja 
Published: December 2014

AbstractWe report on an analytical study of a quasicontinuum method in the context of fracture mechanics in a one‐dimensional setting. To this end, we compare the asymptotic behaviour of a discrete model with nearest and next‐to‐nearest neighbour interactions of Lennard‐Jones type and its quasicontinuum approximation via Γ‐convergence. In case of fracture it turns out that one has to coarse grain in the continuum region and at the atomistic/continuum interface in order to capture the same behavior as the atomistic model, while this is not needed if the boundary conditions are such that the system behaves elastically. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Comparison of positivity preserving techniques without time step restriction for the DG scheme applied to shallow water flows
Authors: Ortleb Sigrun 
Published: December 2014

AbstractPositivity preservation in the context of shallow water flows is important as soon as wet regions become dry or a dry region is flooded. However, positivity preserving explicit time stepping of DG semi‐discretizations can not be applied in a straigthforward manner to the case of implicit time integration as the enforcement of non‐negativity generally demands rather restrictive time step constraints. In this context, we compare two different modifications to the strategy of positivity preservation based on a production‐destruction splitting of the DG scheme for the cell means of water height. One strategy uses the so‐called Patankar trick while the other one is based on an iterative redistribution of the water level. Both modifications guarantee non‐negativity of the water height for any time step size while still preserving conservativity. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact of Intravenous Acetaminophen on Reducing Opioid Use After Hysterectomy
Authors: Herring Brittany O. , Ader Sheila , Maldonado Angel , Hawkins Carla , Kearson Margaretta , Camejo Madeline 
Published: December 2014

Study ObjectiveTo examine the impact of intravenous acetaminophen on the total quantity of opioids (in morphine equivalents) administered within the first 48 hours postoperatively and perioperatively, while still affording patients adequate analgesia, in women who underwent total abdominal hysterectomies.DesignRetrospective chart review.SettingTertiary care community hospital.PatientsOne hundred women underwent total abdominal hysterectomies performed by a single surgeon: 50 patients received opioids only (fentanyl, morphine, hydromorphone, meperidine, or oxycodone), without the addition of any acetaminophen, between January 1 and March 28, 2011, and 50 patients received intravenous acetaminophen 1000 mg every 6 hours in addition to opioids (multimodal group) between May 1 and July 16, 2012 (time period coincided with the addition of intravenous acetaminophen to the hospital formulary). Patients in both groups were also given nonopioids (celecoxib, dexmedetomidine, aspirin, or tizanidine) perioperatively.Measurements and Main ResultsPatients in both groups had a mean age of 55 years (mean ± SD 55 ± 13 yrs in the multimodal group, 55 ± 15 yrs in the opioids‐only group), surgery time of ~2 hours (116 ± 51 min in the multimodal group, 118 ± 40 min in the opioids‐only group), and an anesthesia time of ~3.5 hours (209 ± 79 min in the multimodal group, 207 ± 79 min in the opioids‐only group). During postoperative days 1–2, intravenous acetaminophen reduced opioid use by 31% (mean ± SD 47 ± 24 mg in the multimodal group vs 68 ± 37 mg in the opioids‐only group, p=0.003) and by 26% during the total perioperative period, defined as preoperative, intraoperative, recovery room, and postoperative days 1–2 (73 ± 24 mg in the multimodal group vs 99 ± 39 mg in the opioids‐only group, p=0.001).ConclusionThe multimodal approach to perioperative analgesic management, which includes concurrent administration of intravenous acetaminophen and opioids, is effective in reducing the total average amount of opioids administered on postoperative days 1–2 and perioperatively. Limitations of this study include its short duration, retrospective design, and single‐site setting. These results may not be generalized to patients undergoing other types of obstetric‐gynecologic surgeries.
Optimizing Multimodal Analgesia with Intravenous Acetaminophen and Opioids in Postoperative Bariatric Patients
Authors: Song Kangwon , Melroy Michael J. , Whipple Oliver C. 
Published: December 2014

Study ObjectiveTo evaluate the effect of therapeutic doses of intravenous acetaminophen (IV APAP) on postoperative opioid use following bariatric surgery.DesignRetrospective review of medical records.SettingA 654‐bed academic hospital.PatientsRecords for 104 patients who underwent laparoscopic sleeve gastrectomy (LSG; 44 patients) or laparoscopic Roux‐en‐Y gastric bypass (LRYGB; 60 patients) were reviewed. Patients received IV APAP 1 g every 6 hours postoperatively (22 LSG patients and 30 LRYGB patients) or no IV APAP (22 LSG patients and 30 LRYGB patients).Measurements and Main ResultsBaseline demographic features were similar for both groups. Patients receiving IV APAP required fewer intravenous morphine equivalents than patients treated with opioids alone. Reductions in morphine equivalents with IV APAP were 21 mg (LSG), 33 mg (LRYGB), and 28 mg (all patients) (p<0.001 for all comparisons). IV APAP was associated with a shorter hospital length of stay (LOS) for the LRYGB (mean difference 1.47 days; p=0.039) and combined groups (mean difference 0.95 days; p=0.025). Patients who received IV APAP had earlier return of bowel sounds and flatus. IV APAP did not reduce mean pain scores in any group.ConclusionPatients undergoing bariatric surgery who received IV APAP during the 24‐hour postoperative period consumed fewer intravenous morphine equivalents and had similar pain scores as patients who were treated with opioids alone. Use of IV APAP reduced the hospital LOS and resulted in earlier return of bowel sounds and passage of flatus.