Numeric Approach Research Articles

Assessing the cost-optimal mileage of medium-duty electric vehicles with a numeric simulation approach

Electric freight vehicles have the potential to mitigate local urban road freight transport emissions, but their numbers are still insignificant. Logistics companies often consider electric vehicles as too costly compared to vehicles powered by combustion engines. Research within the body of the current literature suggests that increasing the driven mileage can enhance the competitiveness of electric freight vehicles. In this paper we develop a numeric simulation approach to analyze the cost-optimal balance between a high utilization of medium-duty electric vehicles – which often have low operational costs – and the common requirement that their batteries will need expensive replacements. Our work relies on empirical findings of the real-world energy consumption from a large German field test with medium-duty electric vehicles. Our results suggest that increasing the range to the technical maximum by intermediate (quick) charging and multi-shift usage is not the most cost-efficient strategy in every case. A low daily mileage is more cost-efficient at high energy prices or consumptions, relative to diesel prices or consumptions, or if the battery is not safeguarded by a long warranty. In practical applications our model may help companies to choose the most suitable electric vehicle for the application purpose or the optimal trip length from a given set of options. For policymakers, our analysis provides insights on the relevant parameters that may either reduce the cost gap at lower daily mileages, or increase the utilization of medium-duty electric vehicles, in order to abate the negative impact of urban road freight transport on the environment.

Mobile Flywheel Energy Storage Systems: Determining Rolling Element Bearing Loads to Expand Possibilities

Efficient energy storage is the key to modern hybrid or zero emission vehicles and low carbon mobility in general. Compared to conventional storage technologies like batteries, flywheel energy storage systems (FESSs) offer various theoretical advantages, such as high cycle life, no capacity fade over time, temperature independence, easy determination of state of charge, and complete recyclability. However, the special operating conditions of FESSs-such as vacuum, high rotational speeds, and high gyroscopic reactions, etc.-make bearing design a complex and crucial endeavor. This article describes methods of determining loads for rolling element bearings in automotive FESSs. An overview of FESS technology is given, followed by the discussion of an analytic, numeric, and empiric approach, including a detailed comparison of the different methods. Furthermore, the concept of a test bench investigating flywheel behavior in a resilient mount is described, and its results regarding the design of an FESS-tovehicle mount are discussed in depth.

Parents’ Preferences Regarding Public Reporting of Outcomes in Congenital Heart Surgery

Calls for public reporting of outcomes in congenital heart surgery have led to several different reporting schemes, including a star rating system and benchmark procedure-specific mortality data tables. Important unanswered questions remain about the optimal format and content of public reporting of congenital heart surgery outcomes. In conjunction with three parent advocacy groups, we developed a questionnaire to gauge parents' attitudes regarding the format and content of an "optimal" public reporting scheme. Parents were solicited for participation through email lists of members of parent advocacy groups and from a cohort of parents whose children had undergone an STS benchmark procedure of the Society of Thoracic Surgeons at the Children's Hospital of Philadelphia after January 1,2007. The 1,297 responses received provided complete data for analysis. Nearly all the participants were mothers of children with congenital heart disease, and most were white. About half of the children were diagnosed prenatally, and 63% underwent initial repair of the defect in the neonatal period. Parents identified survival statistics, surgeon-specific experience, and complication rates as most important. Presented with three display formats for mortality rates, most parents (89%) identified a numeric procedure-based approach as the best format, and more than half identified the hospital star rating system as the worst format. Parents of children with congenital heart disease identify survival statistics, surgeon-specific experience, and complication rates as the most important outcome measures to report publicly. Additionally, parents preferred mortality data to be presented in aprocedure-specific format using a numeric procedure-based approach, as opposed to the star rating system.

Effect of energy equation in one control-volume bulk-flow model for the prediction of labyrinth seal dynamic coefficients

Abstract The influence of sealing components on the rotordynamic stability of turbomachinery has become a key topic because the oil and gas market is increasingly demanding high rotational speeds and high efficiency. This leads the turbomachinery manufacturers to design higher flexibility ratios and to reduce the clearance of the seals. Accurate prediction of the effective damping of seals is critical to avoid instability problems; in recent years, “negative-swirl” swirl brakes have been used to reverse the circumferential direction of the inlet flow, which changes the sign of the cross-coupled stiffness coefficients and generates stabilizing forces. Experimental tests for a teeth-on-stator labyrinth seal were performed by manufacturers with positive and negative pre-swirl values to investigate the pre-swirl effect on the cross-coupled stiffness coefficient. Those results are used as a benchmark in this paper. To analyse the rotor-fluid interaction in the seals, the bulk-flow numeric approach is more time efficient than computational fluid dynamics (CFD). Although the accuracy of the coefficients prediction in bulk-flow models is satisfactory for liquid phase application, the accuracy of the results strongly depends on the operating conditions in the case of the gas phase. In this paper, the authors propose an improvement in the state-of-the-art bulk-flow model by introducing the effect of the energy equation in the zeroth-order solution to better characterize real gas properties due to the enthalpy variation along the seal cavities. The consideration of the energy equation allows for a better estimation of the coefficients in the case of a negative pre-swirl ratio, therefore, it extend the prediction fidelity over a wide range of operating conditions. The numeric results are also compared to the state-of-the-art bulk-flow model, which highlights the improvement in the model.

Application of Computer Algebra System and the Mean-Value Theory for Evaluating Electrostatic Potential and Its Associated Field for Nontrivial Configurations

Evaluation of electrostatic potential at an arbitrary point within a two dimensional region free of electric charge containing geometrically dispersed nontrivial configurations electrified to constant potentials applying the standard classic approach, i.e. Laplace equation is challenging. The challenge stems from the fact that the solution of the Laplace equation needs to be adjusted to the boundary conditions imposed with the configurations. Numeric solution of the latter is challenging as it lacks generalities. There exist an alternative numeric method which is based on the application of The Mean-Value Theory. The latter is a pure numeric approach; although the output of its iterated refined version is successful, it is cumbersome. In this investigation utilizing the powerful features of Computer Algebra Systems, specifically Mathematica by a way of example we show an innovative approach. Our approach is based on a combination of numeric aspect of The Mean-Value Theory on one hand and Mathematica features on the other hand. This semi numeric-symbolic approach not only provides the desired output, but it also generates information beyond the scope of the standard classic method. By way of example we present the intricacies of our approach, showing (1) how the potential is evaluated and (2) how corollary essential information not addressed in classic cases such as electric field is calculated as well. Our method is applied to a two-dimensional case; its three dimensional version may easily be applied to cases of interest.

A regularizing Kohn–Vogelius formulation for the model-free adsorption isotherm estimation problem in chromatography

Competitive adsorption isotherms must be estimated in order to simulate and optimize modern continuous modes of chromatography in situations where experimental trial-and-error approaches are too complex and expensive. The inverse method is a numeric approach for the fast estimation of adsorption isotherms directly from overloaded elution profiles. However, this identification process is usually ill-posed. Moreover, traditional model-based inverse methods are restricted by the need to choose an appropriate adsorption isotherm model prior to estimate, which might be very hard for complicated adsorption behavior. In this study, we develop a Kohn–Vogelius formulation for the model-free adsorption isotherm estimation problem. The solvability and convergence for the proposed inverse method are studied. In particular, using a problem-adapted adjoint, we obtain a convergence rate under substantially weaker and more realistic conditions than are required by the general theory. Based on the adjoint technique, a numerical algorithm for solving the proposed optimization problem is developed. Numerical tests for both synthetic and real-world problems are given to show the efficiency of the proposed regularization method.

Quantification of Human Cortical Bone Bound and Free Water in Vivo with Ultrashort Echo Time MR Imaging: A Model-based Approach.

Purpose To quantify free and bound water components of cortical bone with a model-based numeric approach with use of ultrashort echo time (UTE) magnetic resonance (MR) imaging in vivo in order to introduce a new predictor for age-related deterioration of cortical bone structure. Materials and Methods Human studies were compliant with HIPAA and approved by the institutional review board. Dual-repetition time three-dimensional hybrid-radial UTE imaging was performed, followed by the application of postprocessing algorithms, to quantify free and bound water parameters (concentration [ρ] and longitudinal relaxation time [T1]) of human cortical bone in vivo. The postprocessing algorithms included the decomposition of bulk equations into free- and bound-associated equations and solving resulted inverse problem by using evolutionary strategy methods. To test the validity of the introduced biomarker, it was measured in 40 healthy women by using the proposed method, and associations among parameters were evaluated with the Pearson correlation coefficient. Results The mean free water concentration, bound water concentration, free water T1, and bound water T1 in the recruited population were 5.9%, 19.6%, 306.79 msec, and 162.47 msec, respectively. All reported values were in good agreement with those in the literature. Cortical bone free water T1 (R2 = 0.72) and cortical bone free water concentration (R2 = 0.62) showed strong positive correlations with age. Conclusion The cortical bone free water concentration and free water T1 derived with UTE imaging are good predictors of age-related deterioration of cortical bone structure and are potentially superior to previously introduced measures such as bone water concentration and suppression ratio. © RSNA, 2017.

Discrete Elements Model of an Abrasive Water-jet through the Focal Canon to the Work-piece

Abrasive water-jet manufacturing process can shape a lot of materials ranging from metals to glasses. It has a lot of advantages, as its low cutting forces, but remains quite difficult to control. Indeed, the process is leaded by the abrasive particle trajectories which depends on the water static pressure and many other parameters. The impact pressure on the work-piece is commonly modeled by a two Gaussian fit sum which are representative of the particles velocity distribution and the granulometry respectively. Today no studies based on discrete elements take into account the mixing chamber and the focal canon which are the two main steps of the abrasive water-jet tool constitution. In this preliminary work we propose to model the flow through the focal canon until the target impact by an original numeric granular approach. The Non-Smooth Contact Dynamics is an efficient method on a large range of simulation domains. In our case, we consider the water phase and the abrasive phase as two collections of distinct polydisperse elements. The masses are corrected and the contact interaction laws are adjusted to account for an equivalent fluid which similar mechanical properties. These two phases are mixed in a chamber and focalised through the canon, knowing water static pressure and abrasive mass rate. After the canon end the abrasive water-jet evolves in air and thus decelerates by friction. The tool-fluid adapts its geometric configuration from this kinetic energy decrease and impacts a target plane located at a known distance from the canon. Such a model is built on some classic process parameters as the water static pressure, the abrasive mass rate or the work-piece vs. canon distance, but it also naturally takes into account finer mechanical parameters as the abrasive granulometry or friction dissipation. Simulations gives interesting results of impact pressure distribution on the target work-piece with dynamic data of all the collection particles. More generally, this work final aim is to link elemental particle damage studies with a macroscopic wear prediction law.

Investigation of Conduction and Switching Power Losses in Modified Stacked Multicell Converters

Considering the advantage of the modified stacked multicell converter over flying capacitor and stacked multicell converters, and noting that investigation of the conduction and switching power losses can be advantageous in the design of multilevel converters, an analytical approach to calculate and analyze conduction and switching power losses in modified stacked multicell converter is presented in this paper. First, rms and average currents flowing through the insulated-gate bipolar transistors (IGBTs) and antiparallel diodes are analytically calculated by considering the duty cycle of each IGBT and diode in terms of converter modulation index, load current, and power factor. For validation, numerical results of the derived closed-form equations for computation of the rms and average currents are compared with simulation results and experimental measurements. Numeric computations of the closed-form equations match the simulation results and experimental measurements very well, which verifies the analytic equations. Next, derived equations for rms and average currents computation are utilized to calculate the conduction power losses. Finally, switching power loss analysis is performed by numeric approach and curve fitting method.

Use of the Conduit Flow Process for the simulation of passive mitigation measures against the piezometric damming effect at the new underground High Speed railway station of Florence

The new High Speed railway station of the city of Florence will be located below ground level inside a huge excavation, 25 m b.g.s deep, 450 m long and 50 m wide; the pit, already built, is surrounded by concrete cut-off walls causing a piezometric damming effect against the main aquifer of the Arno River. As permanent mitigation measure against the piezometric mounding, the design of the station considers a series of drain pipes drilled horizontally on up and down gradient sides of the pit and connected by blind wall tubes. A numerical finite differences model has been implemented with the Modflow code, in order to quantify the expected damming effect and to properly design the drain-based mitigation measures (i.e. frequency and length of the drains). One of the major challenges of the numeric approach was the coupling between the groundwater flow in the porous medium and the water flow towards and through the drains and the blind wall tubes connecting the sides of the excavation. Thus, the drains were simulated using a recently published Modflow Process originally developed for karst conduits (Conduit Flow Process – CFP), which allows combining the groundwater flow in the porous medium with laminar or turbulent flow into pipes. In order to guarantee an acceptable head differential between both sides of the excavation, the results showed that the system should permit a discharge flow rate of about 0.026 m3/s, considering a hydraulic gradient equal to 0.5% (i.e. hydraulic gradient from the averaged piezometric distribution before pit excavation). Conductance turned out to be the most influent parameter towards the effectiveness of the drainage system.

Dissipative effect in long baseline neutrino experiments

The propagation of neutrinos in long baselines experiments may be influenced by dissipation effects. Using Lindblad Master Equation we evolve neutrinos taking into account these dissipative effects. The MSW and the dissipative effects may change the probabilities behavior. In this work, we show and explain how the behavior of the probabilities can change due to the decoherence and relaxation effects acting individually with the MSW effect. A new exotic peak appears in this case and we show the difference between the decoherence and relaxation effects in the appearance of this peak. We also adapt the usual approximate expression for survival and appearance probabilities with all possible decoherence effects. We suppose the baseline of DUNE and show how each decoherence parameters change the probabilities analyzing the possible modification using numeric and analytic approach.

On the mixing in confined impinging jet mixers – Time scale analysis and scale-up using CFD coarse-graining methods

Confined impinging jet mixers (CIJMs) are widely used in laboratory applications due to the generation of high turbulent energy dissipation (>103W/kg) and, thus, intensive mixing. In addition to the possibility of achieving highly reproducible mixing conditions, these mixers enable a sensitive control of fast reactions, an efficient initial homogenization of educts and, consequently, a rapid buildup of supersaturation as the driving force for precipitation. The characteristic mixing times as the competing time scale to the reaction time is of fundamental interest. Proper descriptions of parallel or consecutive processes, the correct interpretation of results, such as the particle size distribution, or the setup of an adequate process design depend strongly on this time constant. Since the mixing influence refers to a span of time in the range of milliseconds, experimental access with an appropriate accuracy is very challenging or even impossible.Therefore, this contribution tackles this sensitive topic using experimentally validated computational fluid dynamics (CFD) calculations. Thereby, mixing times are extracted from CFD using the spatially and temporally reduced numeric measurement approach (STAR NM), lately presented by the authors. These mixing times, sampled over a wide range of flow rates and inherently a wide range of energy dissipation rates (10−1–107W/kg) in a CIJM, are interpreted in the framework of classic mixing theory. Comparison to mixing times calculated with the engulfment model of mixing and some modifications such as the Global Mixing Approach are made. Based on the STAR NM data that are taken for reference, a modified mixing approach is developed that takes meso and micro time scales into account. An outlook of certain scale-up rules for CIJMs is made.

Analytical determination of conduction power loss and investigation of switching power loss for modified flying capacitor multicell converters

Considering advantages of modified flying capacitor multicell (MFCM) converter over conventional flying capacitor multicell converter, and noting that conduction loss investigation can be very advantageous in design phase of multilevel converters, this study presents an analytical approach to calculate and investigate conduction losses in MFCM converters. First, rms and average currents of insulated gate bipolar transistors (IGBTs) and anti-parallel diodes are analytically calculated by considering the associated duty cycle of each IGBT/diode in terms of the converter modulation index, load current, and load power factor. Numerical results of derived closed-form equations to calculate rms and average currents of IGBTs/diodes are compared with simulation results and experimental measurements. All simulation, analytic, and experimental results agree well with each other which validate derived closed-form equations. Afterwards, derived equations for rms and average current computations are utilised to calculate the conduction power losses in a 12.4 MVA, 3.3 kV, nine-level (line-to-line) MFCM converter. A 2.5 kV, 1.5 kA IGBT module from ABB is considered as a power switch in the performed case study for MFCM converter. In addition, switching power loss investigation is performed using numeric approach and curve-fitting method for aforementioned MFCM converter. Comparative analysis and evaluation of conduction and switching losses are presented.

Simulation-based deburring tool and process development

This paper presents a simulation-based development of a new deburring tool and a CAM-assisted method to deburr intersections of cross-drilled holes. By analyzing and applying derived mathematic equations to construct a three-dimensional view of these contours, a cutting edge specifically aligned to the intersection is developed. The intervention conditions and the synchronization of the tool and numeric control approach require 3-axis machining. This ensures a uniform chamfer along the circumference of the intersection despite the fluctuating cutting conditions. CAM-assisted deburring reveals the exact position of the burr, allowing the deburring tool to adapt to cross-drilled holes of different diameters.

Interval computation and constraint propagation for the optimal design of a compression spring for a linear vehicle suspension system

In this paper an optimization design method based on existing intervals and constraint satisfaction problem “CSP” computer tools is proposed. The method was used in the preliminary design to size a compression spring implemented in a linear vehicle suspension system. Compared to conventional design methods, our design method avoids the passing through two stages of sizing (static and dynamic). Using the numeric CSP approach, static and dynamic requirements can be coupled in the same step of sizing. It also avoids the falling on the loop “design–simulate–back to the initial step in case of failure”, as the design parameter values of the compression spring generated by the numeric CSP satisfy all imposed requirements, and the simulation results of the system behavior are always successful and respect all posted constraints. This is due to the fact, that in the CSP, all analytical relation types static and/or dynamic defining the product and its behavior are implemented and integrated from the beginning. So the production of a qualifying system can be achieved from the first time without any need for resizing the system. The general idea of the proposed design method consists of expressing the design variables by intervals; integrate all imposed constraints of different types before the simulation step and solve the problem using the CSP. The generated intervals represent the domains of possible values for the design variables of the product. The obtained result which can be a solution or set of solutions, affirms that the suggested method is valid and potentially useful to size dynamic systems easily and effectively.

An error reduction algorithm for numeric calculation of the spatial impulse response

The most frequently used method for calculation of the pulsed pressure field of ultrasonic transducers is the spatial impulse response (SIR) method. This paper presents a numeric approach that reduce the numeric error by weighting the contribution of each source element into the SIR time array, by considering the exact time of arrival of each contribution. The resolution of the time array Δt must be finite. This results in an error in travel time of ±Δt/2. However, knowledge of the exact travel time can be used to share the contribution from each source element between the two closest time elements so that the average time corresponds to the exact travel time and thereby reduce the numeric error. This study compares the standard and the proposed numeric algorithm with the analytic solution for a planar circular disc because it has a simple analytic solution. The paper presents calculations of the SIR for selected points in space and calculations of the RMS-error between the numeric algorithms and the analytic solution. The proposed numeric algorithm decreases the numeric noise or error with a factor of five compared to the standard numeric algorithm.

Analytic versus CFD approach for kinetic modeling of gas phase photocatalysis

In this work two methods for determining the Langmuir–Hinshelwood kinetic parameters for a slit-shaped flat bed photocatalytic reactor are compared: an analytic mass transfer based model adapted from literature and a computational fluid dynamics (CFD) approach that was used in conjunction with a simplex optimization routine. Despite the differences between both approaches, similar values for the kinetic parameters and similar trends in terms of their UV intensity dependence were found. Using an effectiveness-NTU (number of transfer units) approach, the analytic mass transfer based method could quantify the relative contributions of the rate limiting steps through a reaction effectiveness parameter. The numeric CFD approach on the other hand could yield the two kinetic parameters that determine the photocatalytic reaction rate simultaneously. Furthermore, it proved to be more accurate as it accounts for the spatial variation of flow rate, reaction rate and concentrations at the surface of the photocatalyst. We elaborate this dual kinetic analysis with regard to the photocatalytic degradation of acetaldehyde in air over a silicon wafer coated with a layer of TiO2 P25 (Evonik) and study the usefulness and limitations of both strategies.

Narrative transparency

In this paper, we look at how alternative marketing organisations communicate transparency in a climate of generalised risk and scepticism. We contrast the traditional numeric approach to transparency, which involves auditing and third-party certifications; with an alternative approach that we call narrative transparency. Central to narrative transparency is an emphasis on stake-holder dialogue and an invitation to stake-holders to play the role of auditor. This article illustrates how alternative marketing organisations engage in rhetorical tactics central to a narrative approach, to communicate transparency to their stakeholders. These rhetorical tactics include persona, allegory, consumer sovereignty and enlightenment. Community supported agriculture programmes from across the United States are the context for this study. Findings enrich discussions about best practices for transparency and communications. The central contribution is identification of a narrative approach to transparency, the rhetorical techniques such an approach employs, and an explanation of why an alternative approach to transparency reporting emerges.

Hybrid testing of masonry structures subjected to seismic loading / Hybride Versuche an Mauerwerkskonstruktionen unter Erdbebenbeanspruchung

AbstractThe combination of experiments and numeric description in a test makes it possible to realistically investigate almost any type of system subjected to dynamic loading without requiring the extremely expensive device of a shaking table. With the numeric approach it is possible to examine the behaviour of even very large and complex structures, thus reducing the experimental investigations to the essential part of the system – for example, bracing masonry walls. This test method has proved to be very helpful, particularly for the investigation of seismic loading, and it allows the synchronous examination of several force and displacement variables (horizontal, vertical, rotational). A new laboratory is presented for the investigation of full‐scale building structures up to three storeys high.

Intracranial aneurysmal pulsatility as a new individual criterion for rupture risk evaluation: biomechanical and numeric approach (IRRAs Project).

The present study follows an experimental work based on the characterization of the biomechanical behavior of the aneurysmal wall and a numerical study where a significant difference in term of volume variation between ruptured and unruptured aneurysm was observed in a specific case. Our study was designed to highlight by means of numeric simulations the correlation between aneurysm sac pulsatility and the risk of rupture through the mechanical properties of the wall. In accordance with previous work suggesting a correlation between the risk of rupture and the material properties of cerebral aneurysms, 12 fluid-structure interaction computations were performed on 12 "patient-specific" cases, corresponding to typical shapes and locations of cerebral aneurysms. The variations of the aneurysmal volume during the cardiac cycle (ΔV) are compared by using wall material characteristics of either degraded or nondegraded tissues. Aneurysms were located on 6 different arteries: middle cerebral artery (4), anterior cerebral artery (3), internal carotid artery (1), vertebral artery (1), ophthalmic artery (1), and basilar artery (1). Aneurysms presented different shapes (uniform or multilobulated) and diastolic volumes (from 18 to 392 mm3). The pulsatility (ΔV/V) was significantly larger for a soft aneurysmal material (average of 26%) than for a stiff material (average of 4%). The difference between ΔV, for each condition, was statistically significant: P=.005. The difference in aneurysmal pulsatility as highlighted in this work might be a relevant patient-specific predictor of aneurysm risk of rupture.