Theoretical Dynamic Model Research Articles

Digital Platforms for SMME Enablement

The challenges facing SMME’s are diverse ranging from skills challenges to value chain optimization, concept management and operations management. The entrepreneur navigates a typical SMME cycle from idea generation to sustainable business single-handed. Each phase of SMME development is a challenge but is not unique to the individual SMME. Financial management, marketing, logistics, people management and general strategy to execution against challenges are endured and overcome by SMME’s. SMME’s form the majority of businesses, in most economies and is a source of GDP growth. SMME failure rates are high across the globe with significant challenges to survive. Innovation centers, incubation models and various other interventions have impacted SMME survival but more should be done. The research presented in this paper revolves around a theoretical digital platform for SMME sustainability. The platform is evolutionary and based on large corporate processes and systems, subdued and modified for SMME support. Core SMME processes are digitalized and provide for a single strategy. The evolutionary platform builds over time and evolves to an intuitive digital SMME support system. An initial literature analysis leading onto a theoretical SMME framework and systems dynamics model is presented.

Frequency modelling and dynamic identification of cross-flow water turbines

The cross-flow turbines cover from the point of view hydraulic power the running domain of some well-known turbines such as Pelton, Francis or Kaplan. This type of turbine has a simple construction, long life and low execution cost, which makes it very suitable for on and off grid small to medium hydro power plants. It is quite difficult to establish an exact theoretical dynamic model for this type of turbines, due to the complex flow phenomenon (bi phase flow water and air). In order to obtain the exact dynamic behavior of the hydraulic machine, experimental dynamic identification will be done. In automation, the dynamic properties, represent the fundamental characteristic of the object which must be regulated. When the dynamic properties of the regulated object are obtained experimentally, we analyze the characteristics of the transient regime, which appears because of the application at the system inlet of some stochastic or deterministic signals (sine waves for our case). The hydraulic turbine is modeled as an informational quadrupole having the inlet parameters the movement of the wicket gate and the turbine head and outlet parameters the torque and the speed. In this paper it will be presented the frequency modelling of the cross-flow turbine and the validation of the mathematical model through experimental dynamic identification.

Catch, Restrict, and Release: The Real Story of Bank Bailouts

Bank bailouts are not the one-shot events commonly described in the literature. These bailouts are instead dynamic processes in which regulators catch financially distressed banks; restrict their activities over time; and release the banks from restrictions at sufficiently healthy capital ratios. The catch-restrict-release approach is a global phenomenon, which we document using hand-collected data on capital injection and debt guarantee bailouts in the European Union (EU) over 2008-2014. We present a dynamic theoretical model of socially-optimizing regulators engaging in catch-restrict-release capital injection and debt guarantee bailouts, and empirically test model predictions. Observed EU bailouts are qualitatively consistent with optimizing behavior.

Robust control of a space robot based on an optimized adaptive variable structure control method

Space robot has been playing an increasingly important role in on-orbit service missions. Dynamic coupling exists between the space robot arm and the floating base, and an inaccurate dynamic model will deteriorate the control accuracy of space robot motion. This paper proposed an optimized adaptive variable structure control method to realize coordinate motion control of space robot base and its arm. The controller can adapt its gain to match system uncertainties and external disturbances so that the error dynamics converge to the origin following a parabola-like path which is close to the natural behavior of a second-order system. Therefore, the controller will eliminate the chattering phenomenon and reduce the settling time. Further, taking the motion error as the objective function, the gain parameter is optimized by adopting the modified Gaussian barebones differential evolution method. Numerical simulations aimed at verifying the space robot dynamic model and the effectiveness of the controller are carried out based on Simscape Multibody. The results prove that the theoretical dynamic model of the space robot is accurate. In addition, the controller is demonstrated to present reduced settling time and higher control accuracy in comparison with the boundary layer sliding mode control method.

A new desorption-induced permeability dynamic model and its application in primary coalbed methane recovery

AbstractIn the process of dewatering and recovery of coalbed methane, coal permeability exhibits a quite unique feature due to the interference of matrix shrinkage and stress effects. A new theoretical dynamic model was proposed for coal permeability based on the assumptions of matchstick geometry of the coal and uniaxial strain condition. Distinct from previous models such as P&M and S&D models, our model relates the gas-sorption-reduced strain to the change of surface energy of coal solids. One of the advantages of this model is that it does not require the sorption-reduced strain as an essential input, and therefore eliminates the related laborious and expensive laboratory measurement. The model was validated by fitting it to two sets of public data and shows an excellent match with the observed data. The results also indicate that our model has a better performance in predicting the permeability dynamics than P&M and S&D models. Additionally, a sensitivity analysis of the effect of input parameters on permeability dynamics was conducted by gray-relation theory, and the initial porosity and reservoir temperature are demonstrated to exert a most distinguished effect on the permeability dynamics. Finally, the proposed model was incorporated into a numerical simulator and successfully applied to conduct a history match of the gas and water production rate in a developed territory.

Economic Stress and Body Weight During the COVID-19 Pandemic

The COVID-19 pandemic has caused income loss for many households, disrupting food consumption patterns and contributing to weight loss for some, and weight gain for others. In this article, I build a dynamic theoretical model that explains those empirical facts. The novelty of this paper is to incorporate stress caused by a lower than ideal income (economic stress) in a model of optimal intertemporal food consumption decisions made by a rational eater. In this framework, economic stress causes disutility and individuals can cope by increasing high-calorie food consumption (stress eating). The limitation to this coping mechanism is that being overweight from excessive calorie intake also decreases utility. Thus, a decrease in income causes updates of the constraints faced by rational consumers of food, which are a budget constraint, a stress constraint and a weight gain constraint. As a consequence, the effect of a decrease in income on body weight reflects a competing income effect as well as two effects specific to economic stress, which are an intertemporal substitution effect and a stress eating effect. Those effects explain opposite weight patterns observed during the pandemic. JEL Classification: D11, D91, I12, I14

Mathematical Models of Plasmid Population Dynamics.

With plasmid-mediated antibiotic resistance thriving and threatening to become a serious public health problem, it is paramount to increase our understanding of the forces that enable the spread and maintenance of drug resistance genes encoded in mobile genetic elements. The relevance of plasmids as vehicles for the dissemination of antibiotic resistance genes, in addition to the extensive use of plasmid-derived vectors for biotechnological and industrial purposes, has promoted the in-depth study of the molecular mechanisms controlling multiple aspects of a plasmids’ life cycle. This body of experimental work has been paralleled by the development of a wealth of mathematical models aimed at understanding the interplay between transmission, replication, and segregation, as well as their consequences in the ecological and evolutionary dynamics of plasmid-bearing bacterial populations. In this review, we discuss theoretical models of plasmid dynamics that span from the molecular mechanisms of plasmid partition and copy-number control occurring at a cellular level, to their consequences in the population dynamics of complex microbial communities. We conclude by discussing future directions for this exciting research topic.

A Review of Dynamic-Tribological Simulation Methods for Sliding Bearings in Internal Combustion Engines

The problem of friction reduction and wear resistance of sliding bearings is one of the key factors in determining the overall performance of internal combustion engines. This paper investigated and summarized the theoretical and simulation models of multi-body dynamics of crankshaft system, tribology of sliding bearings, and the wear calculation methods of the shaft-bearing friction pairs. Existing studies show that the dynamics model, hybrid lubrication model, and the friction and wear models request to be upgraded by comprehensively considering the material, structure, manufacturing process, working conditions, and etc. Based on the research status and existing problems of the above analyses, this paper summarizes the simulation models applicable to the field of dynamics and tribology of sliding bearings and presents the prospects for optimization of wear calculation methods for sliding bearings.

Steady-State Dynamics of Exclusion Process with Local Reversible Association of Particles

Many biological processes are supported by special molecules, called motor proteins or molecular motors, that transport cellular cargoes along linear protein filaments and can reversibly associate to their tracks. Stimulated by these observations, we developed a theoretical model for collective dynamics of biological molecular motors that accounts for local association/dissociation events. In our approach, the particles interacting only via exclusion move along a lattice in the preferred direction, while the reversible associations are allowed at the specific site far away from the boundaries. Considering the association/dissociation site as a local defect, the inhomogeneous system is approximated as two coupled homogeneous sub-lattices. This allows us to obtain a full description of stationary dynamics in the system. It is found that the number and nature of steady-state phases strongly depend on the values of association and dissociation transition rates. Microscopic arguments to explain these observations, as well as biological implications, are also discussed. Theoretical predictions agree well with extensive Monte Carlo computer simulations.

Polymerization kinetics of tubulin from mung seedlings modeled as a competition between nucleation and GTP-hydrolysis rates.

Microtubules (MTs) form physiologically important cytoskeletal structures that are assembled by tubulin polymerization in nucleation- and guanosine triphosphate (GTP)-dependent manner. GTP hydrolysis competes with the addition of monomers, to determine the GTP-cap size, and the onset of shrinkage, which alternates with growth. Multiple theoretical models of MT polymerization dynamics have been reconciled to the kinetics of animal brain tubulins, but more recently, rapid kinetics seen in Arabidopsis tubulin polymerization suggest the need to sample a wider diversity in tubulin polymerization kinetics and reconcile it to theory. Here, we isolated tubulin from seedlings of Vigna sp. (mung bean), compared polymerization kinetics to animal brain tubulin, and used a computational model to understand the differences. We find that activity-isolated mung tubulin polymerizes in a nucleation-dependent manner, based on turbidimetry, qualitatively similar to brain tubulin, but with a 10-fold smaller critical concentration. GTP-dependent polymerization kinetics also appear to be transient, indicative of high rates of GTP hydrolysis. Computational modeling of tubulin nucleation and vectorial GTP hydrolysis to examine the effects of high nucleation and GTP-hydrolysis rates predicts a dominance of the latter in determining MT lengths and numbers. Microscopy of mung tubulin filaments stabilized by GMPCPP or taxol results in few and short MTs, compared to the many long MTs arising from goat tubulin, qualitatively matching the model predictions. We find GTP-hydrolysis outcompetes nucleation rates in determining MT lengths and numbers.

Theoretical Model for Luminescence Broadening and Anomalous Carrier Dynamics in Chalcopyrite Quantum Dots

Theoretical Model for Luminescence Broadening and Anomalous Carrier Dynamics in Chalcopyrite Quantum Dots

Micro windmill piezoelectric energy harvester based on vortex-induced vibration in tunnel

A micro windmill piezoelectric energy harvester is proposed to explore the wind energy translation based on vortex-induced vibration(VIV). The novel power takeoff is composed of a wind turbine with three blades, an air blast blower, an ancillary wind tunnel, and a circular PVDF piezoelectric converter. The air blower improves the airflow speed in the wind tunnel. A bluff body is fixed in the flow field to induce vortex and excite the circular PVDF piezoelectric film vibration. Theory and experiments are conducted to investigate the energy translation. Based on the blade element momentum method(BEM), the theoretical model of the air blast blower is derived. The calculation results show that the axial fan blasts the air into the wind tunnel, and the airflow speeds range from 1.37 m/s to 18.78 m/s. Furthermore, the theoretical model of the VIV is developed to decorated the airflow aerodynamic characteristics around the bluff body. The vortex-induced high-frequency resonance consequently improves the piezoelectric energy harvesting efficiency and promotes the excitation force amplitudes. Correspondingly, the output electric power on the piezoelectric plate is numerically investigated based on the theoretical model and experiment. The optimal output power matches the load resistance and the wind velocity on the bluff body. The maximal output power arrived at 8.97 μW on the external load resistance of 650 KΩ with a wind velocity of 19 m/s. Furthermore, experimental results validate the theoretical dynamic model and show that a windmill piezoelectric energy harvester based on vortex-induced vibration (VIV-WPEH) can increase the output power over either range of the low natural airflow speed and the optimizing bluff body individually.

Export pricing and exchange rate expectations under uncertainty

This paper contributes to the literature on firms’ export pricing by assessing whether and to what extent firms take into account the expected future evolution of the exchange rates while setting their prices. Using French micro-level trade data, our empirical analysis reveals that by adjusting their export prices, firms partly absorb information about future exchange rate variations. The extent to which individual exporters absorb future exchange rate fluctuations is found to depend on their market power, in accordance with theoretical dynamic demand-side models encompassing mechanisms creating an inter-temporal relationship between current market shares and future profits. The analysis also shows that the strength of such expectation-related mechanism is considerably reduced with greater future exchange rate uncertainty, in line with an interpretation of pricing-to-market as an investment decision under uncertainty. In a comparative perspective our results are shown to drive asymmetric responses across destinations of aggregate bilateral export flows to expected exchange rate movements.

Friction-induced vibration of a slider-on-rotating-disc system considering uniform and non-uniform friction characteristics with bi-stability

The friction-induced vibration of a novel slider-on-rotating-disc system is studied by a combination of numerical analysis on the theoretical model and experimental investigation on the test rig. In this system, the rotation of an L-shaped component couples with the friction-induced stick–slip vibration in the tangential direction and produces a state-dependent normal force. The numerical results of the dynamic responses by employing the Coulomb friction model and the friction model with Stribeck effect are both in good agreement with the experimental results, therefore the credibility of the numerical analysis on the theoretical dynamic model is validated. The bi-stability phenomenon, i.e., there is coexistence of a stable pure sliding response and a stable stick–slip limit cycle in a certain parameter range, is not only revealed in the numerical analysis but also observed experimentally. Moreover, a novel approach to constitute a non-uniform friction interface on the disc surface is explored for its efficacy in suppressing the friction-induced stick–slip vibration of the system also by both numerical analysis and experimental testing, namely, the disc surface is divided into sectors assigned with different friction properties. Both the numerical and experimental results show that the non-uniform friction interface of the disc with appropriate friction properties of these sectors can be an effective approach to diminish the range of the operating parameters where the stick–slip vibration occurs and thereby reduce the possibility of occurrence of stick–slip vibration in the system.

Temporal order of mutations influences cancer initiation dynamics

Cancer is a set of genetic diseases that are driven by mutations. It was recently discovered that the temporal order of genetic mutations affects the cancer evolution and even the nature of the decease itself. The mechanistic origin of these observations, however, remain not well understood. Here we present a theoretical model for cancer initiation dynamics that allows us to quantify the impact of the temporal order of mutations. In our approach, the cancer initiation process is viewed as a set of stochastic transitions between discrete states defined by the different numbers of mutated cells. Using a first-passage analysis, probabilities and times before the cancer initiation are explicitly evaluated for two alternative sequences of two mutations. It is found that the probability of cancer initiation is determined only by the first mutation, while the dynamics depends on both mutations. In addition, it is shown that the acquisition of a mutation with higher fitness before mutation with lower fitness increases the probability of the tumor formation but delays the cancer initiation. Theoretical results are explained using effective free-energy landscapes.

The Long‐Term Response of Alternate Bars to the Hydrological Regime

AbstractMigrating bars are large‐scale, alternate bedforms that often develop in channelized river reaches, as a consequence of an intrinsic instability of the erodible channel bed. Their behavior under steady flow conditions has been widely investigated by means of theoretical, experimental, and numerical models, which revealed that bar formation occurs when the width‐to‐depth ratio of the channel exceeds a critical threshold value. Conversely, no much information is available about the long‐term, average characteristics of alternate bars in the case of a complex flow regime, which makes the width‐to‐depth ratio highly variable in time. Starting from the state‐of‐the‐art theoretical models of bar dynamics, we propose a novel methodology to determine the long‐term bar response to the hydrological river regime and the associated “bar‐forming” discharge that, if applied steadily, would produce the same morphological response. We derive a generalized criterion to define whether bars are expected to form and to estimate the long‐term bar topography, depending on flow probability density function and channel characteristics (width, slope and sediment size). Our procedure differs from the classical methods to define formative discharge, inasmuch as it accounts for the specific and reversible response of bar topography to the different flow stages that compose the hydrological regime. Application to four different gravel bed reaches in the Alpine region shows the capability of the procedure to interpret remarkably different riverbed morphologies and to provide a reasonable prediction of the observed bar height, thus suggesting its potential to analyze long‐term morphological trajectories following hydrological alterations and river restoration projects.

Envy effects on conflict dynamics in supervised work groups

At the end of the last century, chaos theory principles have helped organizational theorists to analyze several aspects of organizations and to account for their dynamic evolution. However, most of contributions remained relegated as qualitative discussions of organizational phenomena. In this paper, starting from effort allocations of subordinates in supervised work groups which were observed in a human participants interaction, we found evidence of nonlinear relation between the colleagues’ effort. In order to explain the large variability of behavior we observed, we consider those activated by unfavorable social comparison and propose a dynamical model. A theoretical dynamic model based on the empirical results appears to be powerful for modeling repeated interactions in a work group. Research and intervention design should focus on individual intolerance and beliefs about the reciprocal capacities between subordinates, which, according to our study, appear to play a key role in the inefficiency of equilibria observed in supervised work groups.

AC flashover dynamic theoretical and experimental model under fan‐shaped and longitudinal pollution on silicone rubber insulator

AC flashover dynamic theoretical and experimental model under fan‐shaped and longitudinal pollution on silicone rubber insulator

Dynamic Modeling and Frequency Characteristic Analysis of a Novel 3-PSS Flexible Parallel Micro-Manipulator.

Dynamic modeling and frequency characteristic analysis of a novel 3-PSS (three-prismatic-spherical-spherical) flexible parallel micro-manipulator with three translational DOF in space were investigated in this paper. Firstly, the kinematics analysis was developed based on the pseudo-rigid body model. The Jacobian matrix and the relationship between the micro angular deformation of the flexible spherical hinge and the end pose of mobile platform were respectively obtained by employing vector closed-loop method and coordinate transformation method. Then, taking into account the elastic strain energy of the flexible spherical hinge, dynamic model of this mechanism was established via Lagrange equations, and the expression of natural frequency was further derived. Combined with a set of given parameters, natural frequencies of the system were calculated by using MATLAB software. For the comparison purpose, a simulated modal analysis of the mechanism with the same parameters was also performed by employing finite element ANSYS software. Results from numerical calculation and finite element simulation indicated that maximum error of their natural frequencies was 2.71%, which verified the correctness of the theoretical dynamic model. Finally, variations of natural frequencies with changes of the basic parameters were analyzed. Analysis results show that natural frequencies increase with the increase of the bending stiffness kbm of flexible spherical hinge and the difference in radius Er between static platform and mobile platform, while decrease with the increase of the length l of the link rod and the masses of the main components of mechanism. Besides, it can be further drawn from these obtained results that the natural frequencies increase with the increase of the angle θl between the link rod and the z axis of reference coordinate system. Considering that the increase of the stiffness kbm and the angle θl will reduce the scope of working space, it is recommended in designing the structure to choose a set of larger stiffness kbm and angle θl as much as possible under the premise of satisfying the working space.

A new three dimensional dissipative Boussinesq equation for Rossby waves and its multiple soliton solutions

A new three dimensional nonlinear dynamic theoretical model is derived from fluid mechanics system. In this paper, From the quasi-geostrophic barotropic potential vorticity equation, we obtain a three dimensional dissipative Boussinesq equation by the reduced perturbation method, i.e.utt+e1uxx+e2(u2)xx+e3utxy+e4uxxxx+e5uxxyy=0. It is emphasized that the new equation is different from the existing Boussinesq equations, which describe the three dimensional nonlinear Rossby waves in the atmosphere. Moreover, we explore the dispersion relation of the linear wave through the new equation. Using the travelling wave method and simplest equation method, the general solution and soliton solutions of the equation are obtained successfully respectively. Finally, the formation mechanism of Rossby waves is discussed by multiple soliton solutions.