Search results

The purpose of this paper is to discuss the asymptotic models of different parts with a pitting fault in rolling bearings.

For rolling bearings with a pitting fault, the displacement deviation between raceways and rolling elements is usually considered to vary instantaneously. However, the deviation should change gradually. Based on this shortcoming, the variation rule and calculation method of the displacement deviation are explored. Asymptotic models of different parts with a pitting fault are discussed, respectively. Besides, rolling bearing systems have prominent fractional characteristics unconsidered in the traditional models. Therefore, fractional calculus is introduced into the modeling of rolling bearings. New dynamic asymptotic models of different parts with a pitting fault are proposed based on fractional damping. The numerical simulation is performed based on the proposed model, and the dynamic characteristics are analyzed through the bifurcation diagrams, trajectory diagrams and frequency spectrograms.

Compared with the model based on integral calculus, the proposed model can better reflect the periodic characteristics and fault characteristics of rolling bearings. Finally, the proposed model is verified by the experiment. The dynamic characteristics of rolling bearings at different rotating speeds are analyzed. The experimental results are consistent with the simulation results. Therefore, the proposed model is effective.

(1) The above models are idealized, i.e. the local pitting fault is treated as a rectangle. When a component comes into contact with the fault, the displacement deviation between the component and the fault component immediately releases if the component enters the fault area and restores if the component leaves. However, the displacement deviation should change gradually. Only when the component touches the fault bottom, the displacement deviation reaches the maximum. (2) Due to the material's memory and fluid viscoelasticity, rolling bearing systems exhibit significant fractional characteristics. However, the above models are all proposed based on integral calculus. Integral calculus has some local characteristics and is not suitable for describing historical dependent processes. Fractional calculus can better describe the essential characteristics of the system.

The paper investigates the dynamic relationship between oil prices, the USA dollar exchange rate and the Saudi stock market index.

The authors perform a novel dynamic simulated the autoregressive distributed lag (ARDL) on weekly data from 2010 to 2021.

The authors' work reveals three main results: First, a cointegration relationship exists between oil prices and the Saudi stock market index. Second, the Saudi stock market is strongly affected by fluctuations in oil prices in both the short and long run. Third, the exchange rate of the USA dollar has a slight influence on the movements of the Saudi stock market. The simulations show that the Saudi stock market index has a long-run upward trend after an oil price shock, while the dollar index rises moderately after a similar shock. Moreover, the first months of the COVID-19 pandemic coincided with a significant decline in the Saudi stock market index, particularly the substantial drop in oil prices.

These findings encourage domestic and foreign investors to benefit from an upward trend in oil prices, especially after the opening of the Saudi market to foreign investment. On the other hand, it raises questions about the Saudi economy's dependence on oil as the sole vehicle for output growth. It highlights the urgent need for diversification and productivity growth in the non-oil sector and other renewable natural resources to increase Saudi competitiveness.

The novelty of the research lies in the following. First, the authors apply one of the latest developments in time-series modeling techniques. This dynamic ARDL simulation model provides a worthwhile alternative way to explore dynamic correlations in the short and long run and assess the choc effects. Secondly, the study would enable us to track the impact of the COVID-19 health crisis on the Saudi stock market.

The aim of this paper is to develop a model based on system dynamics (SD) approach, which integrates three subsystems for simulating construction and demolition (C&D) waste management in Shenzhen, Mainland China.

SD approach was first used to construct the model for C&D waste management in Shenzhen. The model was then converted for running on computer through the software package “iThink”, which was specifically designed for SD modeling. The data required for model simulation was derived through various ways, including literature review, examination of official reports and yearbooks, and questionnaires. After all the parameters in the model were determined, simulation was carried out.

The model proposed in this research can provide an experimental simulation platform to investigate the complexity and interdependencies of factors in managing C&D waste in Shenzhen, Mainland China. The simulation results show that the pressing situation of C&D waste management in Shenzhen would aggravate if no effective measures were taken to address it during the simulation period. Participants' active participation and cost consideration are the two major factors affecting C&D waste reduction. Furthermore, new landfills should be planned to properly handle the C&D waste accumulated in Shenzhen over the past few years.

Although some studies have been conducted under the topic of C&D waste management during the past few years in Shenzhen – how to effectively and efficiently handle the waste is still unsolved. Factors affecting the effectiveness of C&D waste management have separately been examined in the previous studies, without considering their interrelations. The SD‐based model is developed in this research to investigate the complex and interdependent relationships among these factors. The model can deepen participants' understandings about C&D waste management and help explore the major factors affecting the effectiveness of management activities. The measures, which are proposed based on the simulation results, can serve as a valuable reference for planning C&D waste management in Shenzhen.

Due to the structural layout, mining process, and working environment, curved chains such as horizontal and vertical bends inevitably exist in the armoured face conveyor (AFC). With the increasing power, conveying capacity, and distance of the AFC, the dynamic influence of these curved chains should be highly emphasized. This paper establishes a dynamic model of the AFC by multi-body system theory and finite segment method, in which the curved chains can be fully considered.

The scraper chains are firstly grouped into the straight, horizontal bend, vertical convex and concave bend sections. Each bend section running in a circle is simplified as an ideal arc. Through solving its differential equilibrium equation and using Newton's second law, its running resistance is derived. Then the grouped chains are discretized into finite control elements according to the Kelvin model, and the governing equation of each control element is established. The dynamic model of the AFC is obtained by assembling these equations, and the corresponding simulation model is developed by using MATLAB/Simulink.

Case studies with real scenarios are provided, and simulations are carried out. The results show that the running resistance contributed by the curved chains is larger than the traditional empirical value.

The work in this paper helps the dynamic performance design of AFC, with a deep understanding of the curved chains.

Simulation is a well-known technique for using computers to imitate or simulate the operations of various kinds of real-world facilities or processes. The facility or process of interest is usually called a system, and to study it scientifically, we often have to make a set of assumptions about how it works. These assumptions, which usually take the form of mathematical or logical relationships, constitute a model that is used to gain some understanding of how the corresponding system behaves, and the quality of these understandings essentially depends on the credibility of given assumptions or models, known as VV&A (verification, validation and accreditation). The main purpose of this paper is to present an in-depth theoretical review and analysis for the application of VV&A in large-scale simulations.

After summarizing the VV&A of related research studies, the standards, frameworks, techniques, methods and tools have been discussed according to the characteristics of large-scale simulations (such as crowd network simulations).

The contributions of this paper will be useful for both academics and practitioners for formulating VV&A in large-scale simulations (such as crowd network simulations).

This paper will help researchers to provide support of a recommendation for formulating VV&A in large-scale simulations (such as crowd network simulations).

This paper focuses on the application of a robotic technique for modeling a three-wheeled mobile robot (WMR), considering it as a multibody polyarticulated system. Then the dynamic behavior of the developed model is verified using a physical model obtained by Simscape Multibody.

Firstly, a geometric model is developed using the modified Denavit–Hartenberg method. Then the dynamic model is derived using the algorithm of Newton–Euler. The developed model is performed for a three-wheeled differentially driven robot, which incorporates the slippage of wheels by including the Kiencke tire model to take into account the interaction of wheels with the ground. For the physical model, the mobile robot is designed using Solidworks. Then it is exported to Matlab using Simscape Multibody. The control of the WMR for both models is realized using Matlab/Simulink and aims to ensure efficient tracking of the desired trajectory.

Simulation results show a good similarity between the two models and verify both longitudinal and lateral behaviors of the WMR. This demonstrates the effectiveness of the developed model using the robotic approach and proves that it is sufficiently precise for the design of control schemes.

The motivation to adopt this robotic approach compared to conventional methods is the fact that it makes it possible to obtain models with a reduced number of operations. Furthermore, it allows the facility of implementation by numerical or symbolical programming. This work serves as a reference link for extending this methodology to other types of mobile robots.

The purpose of this paper is to propose a new model for studying the patron’s satisfaction level over time for library systems. For this purpose, it is necessary to identify the key factors that are influential in nature. Thereafter, this paper explains and shows the procedure used for developing the causal loop diagram, the flow diagram, mathematical modelling and the simulation of the problem. A sample problem is used to show the applicability of the proposed model. Because the proposed methodology allows management to look into the patrons’ satisfaction level over time, it makes a significant contribution to the literature of the library and information management, as well as dynamic simulation modelling.

This paper is written based on the studies and observations from scientific journals and reports. For model development purposes, the author has used the concept of systems thinking and systems dynamics to model the complex systems and simulate that using Vensim computer simulation software.

As the trend of patron’s satisfaction shows, it is possible to improve the satisfaction level over time to a level above 60 per cent from 48 per cent over the simulation running periods. Meanwhile, the level of donation is up from 10 to 40 per cent in the same period as the satisfaction level has been studied. Because this is the first paper that looks into such important variables over time using systems dynamics, it makes significant contribution to the field of library and information management.

In almost all library models for patron’s satisfaction calculation, the proposed models are static and can find this value for a point of time rather than over a long period of time. In this paper, a system with an initial value of patron’s satisfaction level was used, and by taking all key factors into consideration, the author has developed a system that calculates patron’s satisfaction trend over time. Also, the proposed dynamic model is able to determine the level of donations that patrons can make to the library over time.

Aiming at the unbalancing problem of the neutral equilibrium characteristic for balance hoist in the loading process, the purpose of this paper is to establish a dynamic equation for multi-body using the Lagrange method. It is not difficult to find that the deformation of the boom system has a great influence on the stability of the whole system, through the simulation analysis of the multi-rigid-body system model.

Aiming at the unbalancing problem of the neutral equilibrium characteristic for balance hoist in the loading process, the dynamic equation for multi-body is established by Lagrange method. It is not difficult to find that the deformation of the boom system has a great influence on the stability of the whole system, through the simulation analysis of the multi-rigid-body system model.

Result shows that different weights have a great influence on the force deformation and vibration of the boom system of balance hoist. With the increase in lifting weight, the force and deformation of the boom system increase; lead to balance hoist unique with characteristics of indifferent equilibrium, proportional amplification, labor-saving operation will be lost, easy to cause the imbalance of balance hoist. Therefore, the appropriate increase in the basic length of the compression bar, reduction in the basic length of the tension rod and the increase stiffness of the boom system can improve the stability of balance hoist, which provides a reference for the optimization and manufacture of the balance hoist structure.

The simulation model was established by analyzing the working principle and the load condition of the balance hoist, and the simulation and dynamic characteristics of three typical working conditions are analyzed by using ADAMS; result shows that different weights have a great influence on the force deformation and vibration of the boom system of balance hoist. With the increase in lifting weight, the force and deformation of a boom system increase, lead to balance hoist unique with characteristics of indifferent equilibrium, proportional amplification, labor-saving operation will be lost, easy to cause the imbalance of balance hoist.

The aim of this paper is to propose a simulation study of the “steel supply chain” to demonstrate the effect of inventory management and demand variety on the bullwhip effect mitigation.

The relevant literature is reviewed, and then the simulation model proposed.

This study identifies reasons for sharing information under varying levels of demand and some variants, and demonstrates the benefits of mitigating the bullwhip effect by applying a design of experiment. It is shown that the information sharing is able to mitigate the bullwhip effect in the steel supply chain by extending the order interval and minimising the order batch size.

This study explores the factors associated with the bullwhip effect. This research is focused on built‐to‐order simulation, so the results are only oriented on the basis of orders; hence a simultaneous order‐ and forecast‐based steel supply chain should be carried out in the future.

This framework is expected to provide a convenient way to measure the optimum inventory level against a limited level of demand uncertainty, and thus enterprises can promote the supply chain coordination.

An innovative simulation model of the “steel supply chain” is proposed, which includes information sharing in the simulation model. Furthermore, dynamic scheduling is shown by applying a continuous ordering and order prioritization rule to replace traditional scheduling methods.

The objective of this paper is to propose a holistic dynamic model for understanding the behavior of a complex and internet‐based kind of knowledge market by considering both social and economic interactions.

A system dynamics (SD) model is formulated in this study to investigate the dynamic characteristics of complex interactions in a fee‐based online question & answer (Q&A) knowledge market. The proposed model considers the dynamic, non‐linear, asymmetric, and reciprocal relationships between its components, and allows the study of the evolution of the market under assumed conditions.

Some illustrative results show that: this market is very sensitive to the prices that the customers choose; low‐priced questions are as important as high‐priced ones; gradually increasing experts' proportion of a question's price reduces customer satisfaction and experts' reputation; and training programs for experts result in higher customer satisfaction and researchers' reputation. Furthermore, three types of customers are identified and discussed.

This model can be used to change, manage, and control this market and also helps to design new similar markets. In addition, the proposed model helps to observe the behavior of a market under one or more policies before applying to the real world.

Since GA was shut down in 2006, the implications of this research serve as a strategic tool (strategic evaluation software) for understanding and examining the effects of policies for many existing similar Q&A business models. Furthermore, the SD approach can provide new insights into the field of online Q&A knowledge markets and overcome traditional econometric treatment of data for understanding the dynamic behavior of these markets.

Understanding the complex social and economic behavior of Q&A markets is one of the most important concerns for academics and practitioners in the areas of online markets' management. The paper shows how SD can provide attractive insights into the field of online fee‐based knowledge markets based on a qualitative and quantitative modeling. However, the background literature lacks a holistic view of these kinds of markets.