Evaluating demand driven MRP: a case based simulated study

This study evaluates the assumption underpinning Material Requirements Planning (MRP), buffer management and DDMRP before analysing the case company and evaluating the potential benefits, utilizing simulated data from the existing ERP system. The purpose of this research is to evaluate DDMRP in the context of improving the performance of a printing ink manufacturing company. The main issues the company is facing using a traditional MRP system include poor due-date performance, stock levels not corresponding to the actual market needs and overall system instability leading to inefficiencies. The findings indicate the potential of DDMRP to improve system stability and product availability

Compositional inhomogeneities as a source of indirect combustion noise

The generation of indirect combustion noise by compositional inhomogeneities is examined theoretically. For this, the compact nozzle theory of~\cite{MARBLE_CANDEL_JSV1977} is extended to a multi-component gas mixture, and the chemical potential function is introduced as an additional acoustic source mechanism. Transfer functions for subcritical and supercritical nozzle flows are derived and the contribution of compositional noise is compared to entropy noise and direct noise by considering an idealized nozzle downstream of the combustor exit. It is shown that compositional noise is dependent on the local mixture composition and can exceed entropy noise for fuel-lean conditions and supercritical nozzle flows. This suggests that the compositional indirect noise requires potential consideration with the implementation of low-emission combustors.Financial support through NASA with award number NNX15AV04A and the Ford–Stanford Alliance project no. C2015-0590 is gratefully acknowledged.This is the author accepted manuscript. The final version is available from Cambridge University Press via http://dx.doi.org/10.1017/jfm.2016.39

Interpreting and applying demand driven MRP: a case study

Purpose – The purpose of this research is to evaluate Demand Driven Material Requirements Planning (DDMRP) in the context of improving the performance of a printing ink manufacturing company. The main issues the company is facing include poor due-date performance, stock levels not corresponding to the actual market needs and overall system instability leading to inefficiencies. The research evaluates the assumption underpinning Material Requirements Planning (MRP) and the Theory of Constraints (TOC) before considering their integration to meet the requirements of this company, with particular reference to a recent development entitled DDMRP. Design/methodology/approach – Case research was used to establish the underlying issues through semi-structured interviews, observation, Enterprise Resource Planning (ERP) data and questionnaires. This analysis was then compared with the assumption underpinning generic TOC solutions before conducting a simulated evaluation to compare past ERP decision making with DDMRP. Findings – DDMRP is shown to embody the concepts of buffer aggregation and buffer management within the context of dependent demand planning, effectively integrating MRP and TOC. The underlying production planning and control issues of the company were found to be consistent with the literature associated with the limitations of MRP and a good fit for the core issues traditionally addressed through TOC applications such as Drum Buffer Rope (DBR). The integration of this aggregated buffer management approach with MRP dependent demand within DDMRP provided further enhancements applicable to the company. This evaluation involved simulation, which shows the merits of DDMRP in the area of standardization of production-relevant decision-making and stock adjustment towards improving availability shown by roughly 45% reduction of high and low inventory alerts and a 95% reduction of stock outs over the period in focus. However, it is acknowledged that the improved simulated performance was not fully attributable to the adoption of DDMRP concepts. Research limitations/implications – The document uses a selection of relevant pieces of the literature from the areas of MRP/ERP, continuous improvement and DDMRP that have the potential to be supportive for assessing DDMRP as a performance improving methodology. However, since the amount of literature available on DDMRP is very limited, a comparison of the results with others’ findings is not possible. Furthermore, the primary data used originates from one specific company only. The resulting case study approach is therefore limited to a single case, which might limit the generalizability of the findings to an extent. However, since many companies are suffering from MRP shortcomings and TOC ideas like buffer management or dynamic buffers have been proven to deliver promising results in many applications, at least an assumption of a certain degree of generalizability could be justified. Further research needs to verify if the findings are replicable in comparable scenarios. Originality/value – DDMRP is a new commercial development that has not previously been the subject of a research study. The value of this research is in evaluating the key features of this planning and control system using real company data. By doing this, it is one of the first published projects in this area

Unconventional carrier-mediated ferromagnetism above room temperature in ion-implanted (Ga, Mn)P:C

Ion implantation of Mn ions into hole-doped GaP has been used to induce ferromagnetic behavior above room temperature for optimized Mn concentrations near 3 at.%. The magnetism is suppressed when the Mn dose is increased or decreased away from the 3 at.% value, or when n-type GaP substrates are used. At low temperatures the saturated moment is on the order of one Bohr magneton, and the spin wave stiffness inferred from the Bloch-law T^3/2 dependence of the magnetization provides an estimate Tc = 385K of the Curie temperature that exceeds the experimental value, Tc = 270K. The presence of ferromagnetic clusters and hysteresis to temperatures of at least 330K is attributed to disorder and proximity to a metal-insulating transition.Comment: 4 pages, 4 figures (RevTex4

Lyapunov exponent as a metric for assessing the dynamic content and predictability of large-eddy simulations

Metrics used to assess the quality of large-eddy simulations commonly rely on a statistical assessment of the solution. While thesemetrics are valuable, a dynamicmeasure is desirable to further characterize the ability of a numerical simulation for capturing dynamic processes inherent in turbulent flows. To address this issue, a dynamic metric based on the Lyapunov exponent is proposed which assesses the growth rate of the solution separation. This metric is applied to two turbulent flow configurations: forced homogeneous isotropic turbulence and a turbulent jet diffusion flame. First, it is shown that, despite the direct numerical simulation (DNS) and large-eddy simulation (LES) being high-dimensional dynamical systems with O(10^7) degrees of freedom, the separation growth rate qualitatively behaves like a lower-dimensional dynamical system, inwhich the dimension of the Lyapunov system is substantially smaller than the discretized dynamical system. Second, a grid refinement analysis of each configuration demonstrates that as the LES filter width approaches the smallest scales of the system the Lyapunov exponent asymptotically approaches a plateau. Third, a small perturbation is superimposed onto the initial conditions of each configuration, and the Lyapunov exponent is used to estimate the time required for divergence, thereby providing a direct assessment of the predictability time of simulations. By comparing inert and reacting flows, it is shown that combustion increases the predictability of the turbulent simulation as a result of the dilatation and increased viscosity by heat release. The predictability time is found to scale with the integral time scale in both the reacting and inert jet flows. Fourth, an analysis of the local Lyapunov exponent is performed to demonstrate that this metric can also determine flow-dependent properties, such as regions that are sensitive to small perturbations or conditions of large turbulence within the flow field. Finally, it is demonstrated that the global Lyapunov exponent can be utilized as a metric to determine if the computational domain is large enough to adequately encompass the dynamic nature of the flow

Multiple-scale thermo-acoustic stability analysis of a coaxial jet combustor

In this paper, asymptotic multiple-scale methods are used to formulate a mathematically consistent set of thermo-acoustic equations in the low-Mach number limit for linear stability analysis. The resulting sets of nonlinear equations for hydrodynamics and acoustics are two-way coupled. The coupling strength depends on which multiple scales are used. The double-time-double-space (2T-2S), double-time-single-space (2T-1S) and single-time-double-space (1T-2S) limits are revisited, derived and linearized. It is shown that only the 1T-2S limit produces a two-way coupled linearized system. Therefore this limit is adopted and implemented in a finite-element solver. The methodology is applied to a coaxial jet combustor. By using an adjoint method and introducing the intrinsic sensitivity, (i) the interaction between the acoustic and hydrodynamic subsystems is calculated and (ii) the role of the global acceleration term, which is the coupling term from the acoustics to the hydrodynamics, is analyzed. For the confined coaxial jet diffusion flame studied here, (i) the growth rate of the thermo-acoustic oscillations is found to be more sensitive to small changes in the hydrodynamic field around the flame and (ii) increasing the global acceleration term is found to be stabilizing in agreement with the Rayleigh Criterion.This is the accepted manuscript. The final version is available at http://www.sciencedirect.com/science/article/pii/S1540748916300670

Modeling Heatshield Erosion Due to Dust Particle Impacts for a Martian Entry Vehicle

Because planetary missions to Mars take years from initial design to arrival at Mars, and because of the unpredictability of major global dust storms, the de-sign of the thermal protection system (TPS) of a Mars entry vehicle requires an estimation for the potential damage caused by dust particle impacts on the heat-shield. This paper will review previous analytical and experimental approaches to modeling dust particle ero-sion and will compare the legacy models against more modern computational techniques and new dust ero-sion models that will be based on upcoming experi-ments in the German Aerospace Center (DLR) GBK facility. The various models will be compared by incorporating them into the Icarus material response code applied to a representative vehicle entering the Martian atmosphere

Evaluation of an Early Intervention Model for Child and Adolescent Victims of Interpersonal Violence

Only the minority of youth exposed to traumatic events receive mental health care, as trauma-informed clinical services are lacking or are poorly accessible. In order to bridge this gap, the Outpatient Trauma Clinic (OTC) was founded, an easily accessible early, short-time intervention, with onward referral to follow-up treatment. This report presents the OTC’s interventional approach and first outcome data. Using a retrospective naturalistic design, we analyzed trauma- and intervention-related data of the sample (n = 377, 55.4% female, mean age 10.95, SD = 4.69). Following drop-out analyses, predictors for treatment outcome were identified by logistic regression. The majority (81.9%) was suffering from posttraumatic stress disorder (PTSD) or adjustment disorders. Around one forth dropped out of treatment; these cases showed higher avoidance symptoms at presentation. In 91%, psychological symptoms improved. Experience of multiple traumatic events was the strongest predictor for poor treatment outcome (B = −0.823, SE = 0.313, OR = 0.439, 95% CI 0.238–0.811). Around two thirds were connected to follow-up treatment. The OTC realized a high retention rate, initial improvement of symptoms and referral to subsequent longer-term psychotherapeutic treatment in the majority. Further dissemination of comparable early intervention models is needed, in order to improve mental health care for this vulnerable group

Reduced-Order Modeling of Turbulent Reacting Flows with Application to Ramjets and Scramjets

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90621/1/AIAA-50272-117.pd

Simulation of a Shear Coaxial GO2/GH2 Rocket Injector with DES and LES Using Flamelet Models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97098/1/AIAA2012-3744.pd