A Model Predictive Control (MPC) LIDAR-based constant speed local obstacle avoidance algorithm has been implemented on rigid terrain and granular terrain in Chrono to examine the robustness of this control method. Provided LIDAR data as well as a target location, a vehicle can route itself around obstacles as it encounters them and arrive at an end goal via an optimal route. Using Chrono, a multibody physics API, this controller has been tested on a complex multibody physics HMMWV model representing the plant in this study. A penalty-based DEM approach is used to model contacts on both rigid ground and granular terrain. We draw conclusions regarding the MPC algorithm performance based on its ability to navigate the Chrono HMMWV on rigid and granular terrain.

We provide an overview of a multi-physics dynamics engine called Chrono. Its forte is the handling of complex and large dynamic systems containing millions of rigid bodies that interact through frictional contact. Chrono has been recently augmented to support the modeling of fluid-solid interaction (FSI) problems and linear and nonlinear finite element analysis (FEA). We discuss Chrono’s software layout/design and outline some of the modeling and numerical solution techniques at the cornerstone of this dynamics engine. We briefly report on some validation studies that gauge the predictive attribute of the software solution. Chrono is released as open source under a permissive BSD3 license and available for download on GitHub.

Two approaches are commonly used for handling frictional contact within the framework of the discrete element method (DEM). One relies on the complementarity method (CM) to enforce a nonpenetration condition and the Coulomb dry-friction model at the interface between two bodies in mutual contact. The second approach, called the penalty method (PM), invokes an elasticity argument to produce a frictional contact force that factors in the local deformation and relative motion of the bodies in contact. We give a brief presentation of a DEM-PM contact model that includes multi-time-step tangential contact displacement history. We show that its implementation in an open-source simulation capability called Chrono is capable of accurately reproducing results from physical tests typical of the field of geomechanics, i.e., direct shear tests on a monodisperse material. Keeping track of the tangential contact displacement history emerges as a key element of the model. We show that identical simulations using contact models that include either no tangential contact displacement history or only single-time-step tangential contact displacement history are unable to accurately model the direct shear test.

We perform a micromechanical analysis of general isotropic non-cohesive particulate materials idealized as three-dimensional random assemblies of uniform spheres with a simple linear elastic inter-particle contact force law and inter-particle Coulomb friction law. We obtain analytical relationships between the inter-particle friction coefficient \(\mu\) (or inter-particle friction angle \(\phi _\mu = \tan ^{-1} \mu\)) on the microscale and the material friction angle \(\phi\) on the macroscale. Our micromechanical analysis directly employs force and moment equilibrium (together with compatibility and the contact constitutive assumptions noted) rather than energy methods, and thus can account for the effects of particle rotation, and in particular the effects of mechanisms or zero-energy modes due to particle rotation. To explore the effects of particle rotation, we perform analyses with particle rotation either allowed or prohibited. To validate the analytical results obtained here, we compare the \(\phi\) versus \(\phi _\mu\) curves determined theoretically to those obtained by the discrete element method (DEM) for six randomly packed specimens of 3430–29, 660 uniform spherical elements with uniform inter-element Coulomb friction in Fleischmann et al. in Geotech Geol Eng 32(4):1081–1100, (2014). The \(\phi\) versus \(\phi _\mu\) curves derived here show remarkable agreement with those obtained via DEM simulations in Fleischmann et al. in Geotech Geol Eng 32(4):1081–1100, (2014), especially for the case in which particle rotation is not artificially restrained.

We provide a brief overview of the Discrete Element Method (DEM) for modeling large frictional contact problems in granular flow dynamics and quasi-static geomechanics applications. In terms of contact, DEM can be divided into two approaches: the Constraint Method (CM) or rigid-body approach, and the Penalty Method (PM) or soft-body approach. We give a detailed presentation of a DEM-PM contact model that includes multi-time-step tangential contact displacement history. We compare results from direct shear simulations performed with Chrono using this contact model to results from identical simulations using contact models that include either no tangential contact displacement history or only single-time-step tangential contact displacement history. We show that neither of the latter two models are able to accurately model the direct shear test. In particular, the ratio of shear stress to normal stress during direct shear simulations is under-predicted by a factor of about ten when the true tangential contact displacement history model is not used. The new multi-step tangential contact displacement history model we have implemented in Chrono was validated using direct shear simulations of small randomly packed specimens of 1, 800 and 5, 000 identical spheres. The shear-displacement curves obtained from Chrono were compared against physical direct shear experiments performed on identical glass spheres as well as against results obtained from LIGGGHTS, an open-source DEM code that specializes in granular simulations. These comparisons show that the tangential contact displacement history model currently implemented in Chrono is (1) comparable to the model implemented in LIGGGHTS, and (2) capable of accurately reproducing results from physical tests typical of the field of geomechanics. In the appendices, we provide the details of the DEM-PM contact models currently implemented in Chrono, as well as some alternative contact models found in the literature.

We perform numerical simulations using the discrete element method (DEM) to determine yield surfaces for large samples of randomly packed uniform spheres with constant normal and tangential contact stiffnesses (linear spring model) and uniform inter-particle friction coefficient μ , for a large range of values of the inter-particle friction coefficient μ . The beauty of DEM is that the micromechanical properties of the spheres, especially the inter-particle friction coefficient μ , are known exactly. Further, simulations can be performed with particle rotation either prohibited or unrestrained, which provides an effective means for evaluating analytical models that employ these assumptions. We compare the resulting yield surfaces to the Mohr–Coulomb, Matsuoka–Nakai, Lade–Duncan, and Drucker–Prager yield surfaces, and determine the relationship between the resulting material friction angle ϕ on the macroscale and the inter-particle friction coefficient μ (or the inter-particle friction angle ϕ μ ) on the microscale. We find the Lade–Duncan yield surface provides the best agreement, by far, with the simulations in all cases. We also monitor inter-particle friction work and particle rotation within each specimen during the DEM simulations, both globally and on a particle-by-particle basis, and we compare the results obtained from DEM simulations in which the spheres were allowed full three-dimensional translational and rotational freedom of motion and DEM simulations in which particle rotation was prohibited.

Results obtained from numerical simulations of direct (or ring) shear tests on ASTM standard graded (Ottawa) sand using the discrete-element method with periodic boundary conditions in both two and three dimensions are reported. The data obtained from these simulations are quantitatively compared to experimental data for ASTM standard graded sand. The results show that the three-dimensional (3D) effects of nonplanar interparticle contact forces and particle motion are significant in the 3D discrete-element method simulations, even during nominally two-dimensional (2D) shear flow. Moreover, the 3D discrete-element method simulations accurately predict the peak and residual friction angles of ASTM standard graded sand. On the other hand, the 2D discrete-element method simulations fail to accurately predict the peak and residual friction angles. It is argued that the failure of the 2D discrete-element method simulations and the success of the 3D discrete-element method simulations in providing quantitatively accurate predictions of peak and residual friction angles are attributable largely to the respective absence or presence of 3D effects, including nonplanar interparticle contact forces and nonplanar particle motion, in these discrete-element method simulations. (C) 2013 American Society of Civil Engineers.

In Part I, Fleischmann et al. (2013), we performed theoretical analyses of three cubic packings of uniform spheres (simple, body-centered, and face-centered) assuming no particle rotation, employed these results to derive the effective elastic moduli for a statistically isotropic particulate material, and assessed these results by performing numerical discrete element method (DEM) simulations with particle rotations prohibited. In this second part, we explore the effect that particle rotation has on the overall elastic moduli of a statistically isotropic particulate material. We do this both theoretically, by re-analyzing the elementary cells of the three cubic packings with particle rotation allowed, which leads to the introduction of an internal parameter to measure zero-energy rotations at the local level, and numerically via DEM simulations in which particle rotation is unrestrained. We find that the effects of particle rotation cannot be neglected. For unrestrained particle rotation, we find that the self-consistent homogenization assumption applied to the locally body-centered cubic packing incorporating particle rotation effects most accurately predicts the measured values of the overall elastic moduli obtained from the DEM simulations, in particular Poisson's ratio. Our new self-consistent results and theoretical modeling of particle rotation effects together lead to significantly better theoretical predictions of Poisson's ratio than all prior published results. Moreover, our results are based on a direct micromechanics analysis of specific geometrical packings of uniform spheres, in contrast to prior theoretical analyses based on hypotheses involving overall inter-particle contact distributions. Thus, our results permit a direct assessment of the reasons for the theory–experiment discrepancies noted in the literature with regard to previous theoretical derivations of the macroscopic elastic moduli for particulate materials, and our new theoretical results greatly narrow such discrepancies.

We define notions of homomorphism, submodel, and sandwich of Kripke models, and we define two syntactic operators analogous to universal and existential closure. Then we prove an intuitionistic analogue of the generalized (dual of the) Lyndon-Log-Tarski Theorem, which characterizes the sentences preserved under inverse images of homomorphisms of Kripke models, an intuitionistic analogue of the generalized Log-Tarski Theorem, which characterizes the sentences preserved under submodels of Kripke models, and an intuitionistic analogue of the generalized Keisler Sandwich Theorem, which characterizes the sentences preserved under sandwiches of Kripke models. We also define several intuitionistic formula hierarchies analogous to the classical formula hierarchies 11) and 3,, (= E), and we show how our generalized syntactic preservation theorems specialize to these hierarchies. Each of these theorems implies the corresponding classical theorem in the case where the Kripke models force classical logic.

From classical, Fraïissé-homogeneous, ( ≤ ω )-categorical theories over finite relational languages, we construct intuitionistic theories that are complete, prove negations of classical tautologies, and admit quantifier elimination. We also determine the intuitionistic universal fragments of these theories.

We define two notions for intuitionistic predicate logic: that of a submodel of a Kripke model, and that of a universal sentence. We then prove a corresponding preservation theorem. If a Kripke model is viewed as a functor from a small category to the category of all classical models with (homo)morphisms between them, then we define a submodel of a Kripke model to be a restriction of the original Kripke model to a subcategory of its domain, where every node in the subcategory is mapped to a classical submodel of the corresponding classical model in the range of the original Kripke model. We call a sentence universal if it is built inductively from atoms (including inverted perpendicular and perpendicular to) using boolean AND, boolean OR, for all, and -> with the restriction that antecedents of -> must be atomic. We prove that an intuitionistic theory is axiomatized by universal sentences if and only if it is preserved under Kripke submodels. We also prove the following analogue of a classical model-consistency theorem: The universal fragment of a theory Gamma is contained in the universal fragment of a theory Delta if and only if every rooted Kripke model of Delta is strongly equivalent to a submodel of a rooted Kripke model of Gamma. Our notions of Kripke submodel and universal sentence are natural in the sense that in the presence of the rule of excluded middle, they collapse to the classical notions of submodel and universal sentence. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim

Hard turning processes promise affordable fabrication of machined components with high dimensional accuracy requirements. In an effort to achieve the desired economics a vast array of process variables must be considered including tool material, geometry, edge preparation, wear, speed and feed selection, while maintaining part quality. One method to reduce the number of necessary experiments is through accurate and reliable modeling. A three-dimensional finite element model is presented which includes fully adaptive unstructured mesh generation, tight thermo-mechanically coupling, deformable tool-chip-workpiece contact, interfacial heat transfer across the tool-chip boundary, momentum effects at high speeds and constitutive models appropriate for high strain rate, finite deformation analyses. The model is applied to nose turning of hardened steel workpieces, HRc 60. Metal cutting tests are performed, cutting forces collected, and validation comparison is made.

PURPOSE:To evaluate the role of adjuvant interferon alfa after complete resection of locally extensive renal cell carcinoma.PATIENTS AND METHODS:A total of 283 eligible patients with pT3-4a and/or node-positive disease were randomly assigned after radical nephrectomy and lymphadenectomy to observation or to interferon alfa-NL (Wellferon, Burroughs-Wellcome, Research Park, NC) given daily for 5 days every 3 weeks for up to 12 cycles. Patients were stratified on the basis of pathologic stage. Patients remained on treatment until documented recurrence, excessive toxicity, or patient/physician preference deemed removal appropriate.RESULTS:At median follow-up of 10.4 years, median survival was 7.4 years in the observation arm and 5.1 year in the treatment arm (log-rank P =.09). Median recurrence-free survival was 3.0 years in the observation arm and 2.2 years in the interferon arm (P =.33). Performance status (P =.003), nodal status (N2 v N0, P <.0001), and tumor stage (P =.0002) were significant prognostic factors in multivariate analysis. A proportional hazards model examining the effects of treatment arm and time to recurrence on survival after recurrence among patients who recurred found that random assignment to interferon treatment (P =.009) and shorter time to recurrence (P <.0001) were independent predictors of shorter survival after recurrence. Although no lethal toxicities were observed, severe (grade 4) toxicities including neutropenia, myalgia, fatigue, depression, and other neurologic toxicities occurred in 11.4% of those randomly assigned to interferon treatment.CONCLUSION:Adjuvant treatment with interferon did not contribute to survival or relapse-free survival in this group of patients.

Gonadal possession of the vascular supply and anatomical separation from the surrounding fascia generally spare the testes from Fournier's gangrene. To our knowledge the presence of air on plain film of the kidneys, meters and bladder in the setting of necrotizing fasciitis has not been previously described. We report on a patient with Fournier's gangrene and plain film evidence of testicular involvement.

OBJECTIVE:To explore the utility of intraoperative cavernosal nerve stimulation in facilitating atraumatic nerve dissection during radical prostatectomy, and thus help predict postoperative erectile function.PATIENTS AND METHODS:Fourteen patients (aged 51-72 years) underwent nerve-sparing radical retropubic prostatectomy (NSRRP); 10 were potent before surgery (group 1), and four had erectile dysfunction (group 2). A multi-acquisition system (MacLab/8e) with a Macintosh computer was used for real-time display and recording of intracavernosal pressure (ICP) during surgery. Nerves were stimulated with a bipolar probe (monophasic rectangular pulses, 10 mA, 20 Hz, 0.22 s) before and after removal of the gland. The follow-up consisted of interviews with patients and their partners' 12-18 months after treatment.RESULTS:The mean (sem) basal ICP of 8. 0 (2.0) cmH2O remained unchanged during nerve dissection. The mean increase in ICP during electrical stimulation was >50 cmH2O in seven potent patients (group 1) and was sustained as long as the nerve was stimulated. Postoperatively, these seven patients reported erections sufficient for sexual intercourse. However, the three remaining patients in group 1 had pressure rises of <30 cmH2O, of whom two reported partial erections and one reported total impotence postoperatively. The recovery time for erectile function was 6-12 months after surgery. Two patients from group 2 had transient increases in ICP to <40 cmH2O; one had an increase to 20 cmH2O and one had no response at all. All four patients remained totally impotent postoperatively. There were no complications.CONCLUSIONS:Intraoperative electrical stimulation of the cavernosal nerves with ICP monitoring before and after NSRRP is a safe and reliable method for documenting nerve continuity and its functional status. Patients who have normal preoperative erectile function and show an adequate rise in ICP upon electrical nerve stimulation during NSRRP will almost certainly be potent after surgery. This tool may be used to facilitate atraumatic nerve dissection during NSRRP.

Objectives. To better define the techniques of nerve-sparing prostate dissection that would result in preservation of erectile function, we characterize the effects of physical pressure on the prostate and cavernous nerve, electrical stimulation of the cavernous nerve, and pharmacologic manipulations on intracavernous pressure (ICP) in normal and diabetic rats.Methods. Fischer-34 rats, both normal and diabetic, underwent dissections that isolated the cavernous bodies and cavernous nerves. Cavernous body pressures were characterized during surgical manipulation, during electrical stimulation of the cavernous nerves, and following papaverine hydrochloride injection.Results. In normal rats, baseline cavernous pressures ranged from 5 to 15 cm H2O (mean 12.29). In diabetic rats, the baseline pressure was significantly lower (3 to 7.5 cm H2O). Lateral nerve displacement caused ICP to rise to approximately 35 cm H2O in normal rats, but only to 20 cm H2O in diabetic rats. Electrostimulation resulted in cavernous pressure increases of 10-fold from baseline in normal rats and sevenfold from baseline in diabetic rats. ICPs were not disturbed appreciably with nerve-sparing dissection techniques. Neurotomy resulted in declines in baseline cavernous pressures in all rats. Electrostimulation of the distal end of a severed nerve resulted in pressure rises to 50% of those observed in rats with intact cavernous nerves. Intracavernous papaverine injection before or after nerve stimulation masked subsequent (expected) pressure changes.Conclusions. A change in cavernous pressure is a sensitive indicator of cavernous nerve manipulation. Both cavernous pressure measurements and electrostimulation of cavernous nerves may aid surgeons during radical prostatectomy. (C) 1998, Elsevier Science inc. Ail rights reserved.

For the treatment of existing transitional-cell carcinoma or for prophylaxis of recurrent disease, intravesical therapy should be chosen according to stage. Papillary disease (stages Ta, TI) may be treated effectively either with an alkylating agent or with bacillus Calmette-Guérin (BCG). BCG is the agent of choice for the treatment of Hat carcinoma in situ (Tis), with the recommended treatment course comprising 12 weekly and 12 monthly instillations. Intravesical interferon and many of the other biologic response modifiers mentioned herein may be effective for patients with Ta disease who have failed BCG therapy.

Objectives. This investigation attempted to determine whether the degree of fibronectin expression in the bladders of patients with invasive transitional cell carcinoma correlated with their clinical response to intravesical bacille Calmette-Guerin (BCC) therapy,Methods. Following transurethral resection of all invasive disease, 13 patients with Stages T2-T4 bladder cancer were administered intravesical BCG (for 6 weeks followed by monthly instillations), Fibronectin expression in the patients' resected tumors and normal mucosa was determined by immunohistochemical staining techniques. Minimum disease-free follow-up was 60 months.Results. Only 1 of 13 patients had neither local nor systemic disease recurrence; 10 of 13 patients developed systemic disease and 7 patients died from metastases. Fibronectin expression was nor correlated with the clinical response to BCG.Conclusions. Intravesical BCC therapy for the treatment of muscle invasive transitional cell carcinoma of the bladder is ineffective. Fibronectin expression in the bladder of patients with invasive disease is variable and does not correlate significantly With the clinical response to BCG therapy.

No AccessJournal of UrologyClinical Urology: Original Article1 Jul 1995Editorial: A Perspective on Renal Cell Carcinoma Jonathan Fleischmann Jonathan FleischmannJonathan Fleischmann More articles by this author View All Author Informationhttps://doi.org/10.1016/S0022-5347(01)67220-3AboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail "Editorial: A Perspective on Renal Cell Carcinoma." The Journal of Urology, 154(1), pp. 41–42 References 1 : Transthoracic nephrectomy. J. Urol.1948; 60: 855. Link, Google Scholar 2 : Radical nephrectomy for renal cell carcinoma. J. Urol.1963; 89: 37. Link, Google Scholar 3 : Indications for conservative surgery in certain renal tumors: a study based on the growth pattern of the clear cell carcinoma. J. Urol.1950; 64: 200. Link, Google Scholar 4 : The apparent disappearance of pulmonary metastases in a case of hypernephroma following nephrectomy. J. Urol.1928; 20: 185. Link, Google Scholar 5 : Is nephrectomy justified in patients with metastatic renal cell carcinoma?. J. Urol.1975; 114: 27. Abstract, Google Scholar 6 : The role of adjunctive nephrectomy in patients with metastatic renal cell carcinoma. J. Urol.1977; 117: 272. Link, Google Scholar 7 : Prognostic factors in metastatic renal carcinoma. J. Urol.1986; 136: 376. Link, Google Scholar Department of Urology, Albert Einstein College of Medicine, Bronx, New York.© 1995 by American Urological Association, Inc.FiguresReferencesRelatedDetails Volume 154Issue 1July 1995Page: 41-42 Advertisement Copyright & Permissions© 1995 by American Urological Association, Inc.MetricsAuthor Information Jonathan Fleischmann More articles by this author Expand All Advertisement PDF downloadLoading ...