Numerical Evaluation of Dynamic Response by Using Modified Newmark’s Method

It is well known that the Newmark’s method is considered one of the most popular methods for structural dynamic analysis. In this study, starting from the basic Newmark’s method, a new accurate method is investigated and developed. The basic idea of the proposed method is to use Richardson’s extrapolation to improve the basic Newmark’s method. To observe the accuracy of the proposed method, several numerical tests are performed for a single degree-of-freedom (SDM) dynamic system and the results are compared with results from Newmark’s method and the exact solution. The results show that the proposed method improves the solution accuracy of the structural dynamic problems compared to the Newmark’s method. Moreover, the results of the free oscillating case show that the modified Newmark’s method has more computational efficiency compared to the Newmark’s method.Scopu

A mathematical model for supermarket location problem with stochastic station demands

This paper aims to investigate the effect of station demands variations on supermarket location problem (SLP). This problem arises in the real-world assembly line part feeding (PF) context where supermarkets are used as the intermediate storage areas for stations. To this purpose a stochastic SLP model is developed to optimize the total cost of PF in terms of shipment, inventory and installation costs. The computational results over a real case as well as different test instances verify that the station demands variation has an effect on the SLP solutions.CC BY-NC-ND 4.0</p

Central Air Conditioning: Systems and Applications

It became evident nowadays that modernization influences domestic and commercial HVAC industry, and thus high technological and energy-efficient central air conditioning systems are demanded. Therefore, the selection of proper type of central air conditioning system is a crucial target in the construction industry as improper selection can maximize initial and/or running costs of the system and decreases the human comfort and indoor air quality levels. In fact, a pre-assessment of the construction type and budget available is required for selecting the proper type of central air conditioning system. Therefore, there is a continuous need for an updated material in the literature that reviews the central air conditioning systems and applications, which is the motivation of the present chapter. The present chapter reviews the central air conditioning systems and applications. Specifically, all-air systems, all-water systems, and air-water systems are discussed. In addition, all provided systems are further explored through several developed schematic diagrams enabling the identification of their various components and the understanding of their working principles. It is may be of interest to note that this chapter is suitable for undergraduate level students in the fields of HVAC and R, mechanical, and construction engineering

Experimental Evaluation of a Hybrid FRP-Concrete Bridge Superstructure System under Negative Moment Flexural Loads

Fiber Reinforced Polymer (FRP) bridge systems are gaining wide acceptance among bridge engineers. At the same time, FRP bridge systems are relatively expensive when compared to traditional reinforced concrete bridge systems. In this study, the concept of the hybrid FRP-concrete structural systems is applied to a bridge superstructure. The hybrid FRP-concrete superstructure system is intended to have durable, structurally sound and cost effective hybrid system that will take full advantage of the inherent properties of both FRP materials and concrete. The primary objective of this study is to examine the structural behavior of an FRP-concrete hybrid bridge superstructure system subjected to negative moment flexural loads through experimental procedures. The experimental results showed that the design of the hybrid FRP-concrete bridge superstructure under a negative flexural moment is found to be stiffness- driven instead of strength-driven

Neural network and multiple linear regression to predict school children dimensions for ergonomic school furniture design

The current study investigates the possibility of obtaining the anthropometric dimensions, critical to school furniture design, without measuring all of them. The study first selects some anthropometric dimensions that are easy to measure. Two methods are then used to check if these easy-to-measure dimensions can predict the dimensions critical to the furniture design. These methods are multiple linear regression and neural networks. Each dimension that is deemed necessary to ergonomically design school furniture is expressed as a function of some other measured anthropometric dimensions. Results show that out of the five dimensions needed for chair design, four can be related to other dimensions that can be measured while children are standing. Therefore, the method suggested here would definitely save time and effort and avoid the difficulty of dealing with students while measuring these dimensions. In

The Effect of ChatGPT on Education in the UAE

This study examines the impact of ChatGPT on undergraduate students’ learning. The study utilizes a survey to gather authentic data from a sample of 316 bachelor students from 15 universities across the UAE. The survey comprises 22 dimensions categorized into four constructs related to ChatGPT usage, benefits, drawbacks, and the types of questions ChatGPT can address. A statistical analysis was conducted to explore three primary hypotheses. The analysis involved using Excel and R software to perform one-sample t-tests, two-sample t-tests, ANOVA, and correlation. The findings indicate that students’ use of ChatGPT for various assignments is still infrequent, despite their familiarity with it. This suggests that educators have not yet integrated ChatGPT into assignments and view it more as a threat than an opportunity. Students acknowledge both the advantages and disadvantages of ChatGPT. However, students in medical fields expressed more criticism towards ChatGPT compared to students in engineering, computer science, and business disciplines. Additionally, male and female students hold similar perceptions, except for two dimensions. The results also suggest that educators should pose questions that necessitate personal arguments, experiences, and critical thinking to deter academic dishonesty

Developing an integrated sustainable sanitation system for urban areas: Gaza strip case study

A vertical flow (reed bed) constructed wetland was used for treating bio-solid and gray water. The results present a positive performance in treating the bio-solids and well-stabilized accumulated organic material in the bed formed fertile soil. Moreover, using vertical flow reed bed of liquid waste treatment showed removal of around 70% of organic matter indicator Biological Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD). The Fecal Coliform (FC) removal was around 2 logs (99.9%) with a retention time of less than two days. The effluent can be used in agriculture or groundwater recharge. A semi-dry toilet followed by anaerobic/aerobic units is in planning to be coupled with an existing system. The system mainly depended on separating of the human excreta from the urine and gray water. The two separated fractions will be treated in vertical flow reed bed to produce organic fertilizer and reclaimed water for reuse. Such systems could be a suitable solution for wastewater problems in Gaza strip and similar regions. The designed and planned system integrated environmental and technical sound approaches with socio-economical aspects. In addition, the designed system implemented the idea of a natural and closed circle of water and nutrients “from food to food”

Cantilever Beam Metastructure for Passive Broadband Vibration Suppression

This paper presents a beam structure of a new metamaterial-inspired dynamic vibration attenuation system. The proposed experimental research presents a designed cantilevered zigzag structure that can have natural frequency orders of magnitude lower than a simple cantilever of the same scale. The proposed vibration attenuation system relies on the masses placed on the zigzag structure thus changing the dynamic response of the system. The zigzag plates are integrated into the host structure namely a cantilever beam with openings, forming what is referred to here as a metastructure. Experimental frequency response function results are shown comparing the response of the structure to depending on the natural frequency of the zigzag structures. Results show that the distributed inserts in the system can split the peak response of the structure into two separate peaks rendering the peak frequency a low transmission frequency. These preliminary results provide a view of the potential of research work on active-controlled structures and nonlinear insert-structure interaction for vibration attenuation

Rheology and Durability of Alkali-Activated Materials Made of Rice Husk Ash-Derived Sodium Silicates

The development of alternative binders as a replacement for Portland cement can be one of the means to meet both the growing demand and sustainability of cement in the construction industry. Alkali-activated materials (AAMs) are increasingly attracting attention as a promising sustainable alternative to Portland cement-based materials. However, the manufacturing process of alkaline activators is energy-intensive that leads to an increase in the overall embodied energy and greenhouse gas emissions of AAM systems. Waste-derived activators have been promoted as an effective way not only to reduce the greenhouse gas emissions but also to reprocess wastes into valuable activators that can substitute the conventional alkali-silicate activators. To advance the understanding of the performance of AAMs and the synthesis of waste-derived activators, the present research focuses on three aspects: (a) fundamental differences in rheological properties between AAM and cement systems, (b) systematic synthesis and characterisation of rice husk ash (RHA) derived sodium silicates (SSs), and (c) the effect of RHA derived SSs on the rheology, structural build-up and durability of AAMs compared to commercially available SS. An alternative SS solution was synthesised by mixing RHA with NaOH solution. The influence of different parameters, including the processing duration (1 to 5 h of stirring) and temperature (60 to 100 °C), on the dissolution efficiency of silica from RHA was examined. The results showed that the extraction of silica from RHA was effective using the hydrothermal process (heating and stirring). The proper selection of the raw RHA and the extraction conditions allow for maximising the yield of silica, where most of the amorphous silica in RHA was dissolved within 1 h at 80 °C. The silicate species in the activator is a determinant component that affects the overall performance of AAMs. First, a test program was designed to understand the distinctive rheological and temporal viscoelastic behaviour of AAMs compared to cement pastes. After that, the effect of RHA-derived SSs on the structural build-up of AAM pastes was investigated. The results revealed that the high viscous activator increased the plastic viscosity of AAM pastes by 4 – 8 times higher than that of cement paste and drastically decreased the yield stress due to viscous effects and weak inter-particle interactions. Temporal changes in viscoelasticity showed that the negligible colloidal interactions between particles in AAM paste made the system non-percolated until the initial setting. This behaviour was very different from the well-percolated network that forms in cement paste a few minutes after mixing. In AAMs activated with RHA SSs, filtered and unfiltered solutions were used from the optimised process (1 h at 80 °C) to study the evolution of the viscoelasticity, ultrasonic pulse waves, infrared spectra, and flowability. The overall structural build-up of AAM paste activated using RHA SS was very comparable to the one activated using commercially available SS. This suggests the formation of identical reaction products and the minor effect of the nature of the silicate species in the activator. In terms of flowability, the residues in the unfiltered RHA SS increased the yield stress and reduced the flowability of the paste. Finally, the ability of AAMs made of RHA SSs to resist aggressive media was evaluated using various tests, including water absorption, sorptivity, acid attack, sulphate attack, rapid chloride-ions penetration, chloride migration and chloride diffusion. The durability performance was comparable between the AAMs activated by the filtered RHA and commercial SSs. On the other hand, the unfiltered RHA SS showed some adverse effects on some durability properties. For instance, the residues in the unfiltered RHA SS resulted in a slight increase in the expansion caused by sulphate attacks. However, these residues had insignificant impacts on the compressive strength when using identical SiO2/Na2O and Na2O/binder ratios in the mix design. It is believed that the results of this research will provide an advanced understanding of the early-age evolution of the AAM paste from the fresh condition to the initial setting. In addition, better insights were described on the effect of various processing parameters on the availability and structure of silicate species during the preparation of RHA SSs. Moreover, this research proved that the use of unfiltered RHA SS containing undissolved particles is still practically viable, but special attention should be paid to flowability and some durability properties

Efficient Material Flow in Mixed Model Assembly Lines

Effizienten Materialfluss im Mischmodell Montagelinien Diese Arbeit untersucht ein Materialflusssystem für Fließlinien zur Fertigung von variantenreichen Produkten. Sogenannte Routenzüge kommen häufig zur Bereitstellung von Teilen an den Arbeitsstationen einer Variantenfließlinien zum Einsatz. Die Teile werden in kleinen Behältern (Kleinladungsträgern) im Zentrallager oder in verteilten Zwischenlagern, sogenannten Supermärkten, auf den Routenzug geladen. Bei jeder Tour des Routenzugs werden mehrere Arbeitsstationen mit Kleinladungsträgern versorgt. Der zeitliche Abstand zwischen zwei Belieferungen definiert die Zugumlaufzeit. Ein derartiges Materialbereitstellungssystem, bezeichnet als In-Plant Milk Run, reduziert Bestands- und Transportkosten, weil es eine regelmäßige Just-in-Time Anlieferung der Materialien realisiert. Außerdem bringt es aufgrund der Nutzung kleiner Behälter ergonomische Vorteile mit sich. Weiterhin sinkt das Unfallrisiko. Deshalb findet das In-plant Milk Run System als Alternative zu Gabelstaplern in vielen Branchen, insbesondere in der Automobilindustrie, zunehmend Verwendung. Die Untersuchung dieser Systeme und die optimale Auswahl ihrer Parameter sind wichtige Anliegen, um die Transport- und Bestandskosten zu reduzieren. Diese Arbeit unterscheidet bei der Gestaltung von In-plant Milk Run Systemen fünf verschiedene Problemstellungen (Systeme). Für jedes System wird ein bestimmtes Planungsvorgehen zur Minimierung der kritischen Kosten vorgeschlagen. Zwischen den Systemen gibt es sowohl Ähnlichkeiten als auch Unterschiede. Die Methodik verwendet genetische Algorithmen, ganzzahlige und dynamische Programmierung, Simulation und analytische Untersuchung. Die fünf Systeme werden anhand von Kriterien klassifiziert. Als solche werden das Ausmaß von Störungen, die Verfügbarkeit der Routenzüge, die Genauigkeit der Materialbedarfsschätzungen, die Länge der Montagelinien, der mittlerer Teilebedarf und die Verfügbarkeit von technischer Infrastruktur, wie RFID- oder Barcode-Systemen, herangezogen. Unterschieden werden damit das bedarfsorientierte Zentrallager, der dezentrale bedarfsorientierte Supermarkt, das traditionelle Kanban-System, das elektronische Kanban-System und ein hybrides System, bestehend aus bedarfsorientiertem und e-Kanban-System. Dabei kann das Kanban-System sowohl im Zentrallager, als auch im System dezentraler Supermärkte zum Einsatz kommen. In bedarfsorientierten Systemen wird der Materialbedarf der Arbeitsstationen für eine gewisse Anzahl an Schichten aus der Produktionssequenz und den entsprechenden Stücklisten abgeleitet und ist damit exakt bekannt. In allen Systemen werden einige Restriktionen berücksichtigt. Hierunter fallen die Routenzugkapazität, die Dauer einer Tour und die Kapazität der Lagerflächen direkt an der Montagelinie. In jedem System sind drei Entscheidungsprobleme, das Routing, Scheduling und Loading Problem, zu lösen. Das Routing Problem beinhaltet die Zuordnung von Zügen zu Gruppen von Arbeitsstationen. Im Scheduling Problem werden die Zugumlaufzeit und der Zeitpunkt der ersten Belieferung für jeden Routenzug festgelegt. Die Lösung des Loading Problems erfordert die Determinierung von Art und Menge der in jedem Zyklus und an jede Arbeitsstation ausgelieferten Behälter. Im Falle des Vorhandenseins von Zyklen, in denen der Materialbedarf an einzelnen Arbeitsstationen die Routenzugkapazität übersteigt, werden einige Behälter vorzeitig angeliefert. Dieser Fall wird als „Early Loading“ bezeichnet und tritt in Kanban-Systemen nicht auf. Im System dezentraler bedarfsorientierter Supermärkte ist zusätzlich die Anzahl und der Standort der Supermärkte zu bestimmen („Supermarket Location Problem“). Im traditionellen Kanban-System erfolgt die Festlegung der Kanbanzahl basierend auf dem Zielkonflikt zwischen mittlerem Linienbestand und Fehlbestandswahrscheinlichkeit. Im e-Kanban-System wird der Umfang des zirkulierenden Bestands analog bestimmt. Außerdem wird ein neues Konzept, der sogenannte „Adjusted Electronic Kanban“, zur Behandlung von Kapazitätsengpässen des Routenzugs vorgestellt. Die Ergebnisse sind abhängig vom betrachteten System. Die Leistungsfähigkeit des genetischen Algorithmus zur Lösung des Supermarket Location Problems wurde anhand der Ergebnisqualität, CPU Zeit und der Variabilität dieser beiden Größen untersucht. Es wurden akzeptable CPU Zeiten und eine hohe Ergebnisqualität erreicht. Die Leistungsfähigkeit der drei Kanban-Systeme wurde unter Verwendung von Simulation getestet. Hierbei wurde die Vorteilhaftigkeit des Adjusted Electronic Kanban insbesondere im Fall begrenzter Routenzugkapazität bewiesen. Der inverse Zusammenhang zwischen mittlerem Linienbestand und Fehlbestandswahrscheinlichkeit konnte aufgezeigt werden. Im Falle der bedarfsorientierten Systeme wurde der Effekt von dynamischer Disposition, Early Loading und Minimierung der Anzahl zusätzlicher Anhänger deutlich gemacht. Bei Verwendung des hybriden Systems aus e-Kanban und bedarfsorientiertem System, liefert die dynamische Disposition in Bezug auf die Verarbeitung von Störungenerheblich bessere Resultate als die Einzelsysteme, insbesondere bei hohem Materialbedarf an den Arbeitsstationen.This study investigates the material handling system used in mixed model assembly lines which are important to produce diversified product models to satisfy the increasing customer demand. Tugger trains are used to feed by parts the workstations in the assembly lines. These parts are loaded on trains in small containers (bins) from the warehouse or intermediate stores scattered in the factory. These stores are called supermarkets, which are closer to workstations than the main warehouse. In each train tour, several workstations are replenished by bins every a certain time period called train cycle time. This replenishment system is called in-plant milk run which is used to reduce inventory and transportation costs because of its dependence on repetitive just-in-time parts delivery. Besides reducing costs, ergonomic advantages are obtained due to the use of small-sized bins. Safety hazards are also reduced. As an alternative to forklift system, in-plant milk run was used by several industries especially the automotive industry. It is important to investigate this system and to design its parameters to reduce the total material handling and inventory cost. The study divides the general problem to five different problems (systems) based on the situation on the ground. For each system, a certain planning approach is designed to optimize the parameters of the system to minimize its critical costs. There are some similarities and differences between the systems. The methodology is based on genetic algorithm, integer programming, dynamic programming, simulation, and analytical investigation. The five different systems are classified based on factors such as level of assembly line disturbances, availability of tugger trains, accuracy of expectation of workstations demand for parts, the length of assembly lines and their average demand for parts, and the availability of technical infrastructure such as radio frequency identification (RFID) or bar code technologies. These systems are main warehouse demand-oriented, decentralized supermarket demand-oriented, traditional kanban, electronic kanban, and a hybrid system of e-kanban and demand-oriented systems. The two kanban systems can be applied in both main warehouse and decentralized supermarkets systems. In demand-oriented systems, the exact workstations demand for parts is assumed to be known for the next few shifts based on the predetermined sequencing of product models and needed parts for each product model. Generally some constraints are considered in all the five systems. These constraints are tugger train capacity, tour time, and the capacity of area beside stations. There are three general problems that must be investigated in the systems. These problems are routing, scheduling, and loading problems. Routing problem is the assignment of trains to different stations. In scheduling problem, the train cycle time and the beginning of the movement of the each train are determined. In loading problem, the type and quantities of bins delivered in each train cycle to each workstation are determined. In the case that there are some peak demand periods in which the total stations demand for parts is more than the tugger trains capacity, some bins are delivered before they are needed. This case is called ‘early loading’. Early loading does not exist in both the traditional and electronic kanban systems. In decentralized supermarket demand-oriented system, the location and number of supermarkets are determined. In traditional kanban system, the number of kanban is determined based on the tradeoff between the average line-side inventory and workstation starvation. In e-kanban, the size of circulating inventory in the system is determined for the same purpose. A new approach namely, adjusted electronic kanban, is presented to accommodate train capacity problems. The results depend on the systems investigated. The performance of genetic algorithm used in supermarket location problem was tested based on the quality of the results, CPU time, and variability in both of them. Reasonable CPU time and high quality of results were obtained. The performances of e-kanban, adjusted electronic kanban, and traditional kanban were tested using simulation, where the superiority of adjusted electronic kanban was proven especially in the case of limited tugger trains capacity. The inverse relationship between the average line-side inventory and workstation starvation was presented. In the case of demand-oriented system, the effects of using dynamic scheduling, early loading, and the objective of minimizing the number of extra trailers were obvious to reduce the problems of tugger train limited capacity. In the case of using the hybrid system of e-kanban and demand-oriented systems, the dynamic planning approach outperforms the traditional systems to accommodate the line disturbances especially in the case of large workstations demand