Effects of Clearance Size on the Dynamic Response of Planar Multi-body Systems with Differently Located Frictionless Revolute Clearance Joints

This paper numerically investigates the effects of clearance size of differently located revolute clearance joints without friction on the overall dynamic characteristics of a multi-body system. A typical planar slider-crank mechanism is used as a demonstration case in which the effects of clearance size of a revolute clearance joint between the crank and connecting rod (c-cr), and between the connecting rod and slider (s-cr) are separately investigated with comprehensive observations numerically presented. It is observed that, different joints in a multi-body system have different sensitivities to the clearance size. Therefore the dynamic behavior of one clearance revolute joint cannot be used as a general case for a mechanical system. Also the location of the clearance revolute joint and the clearance size play a crucial role in predicting accurately the dynamic responses of the system. Keywords: Chaotic behavior, Contact-impact force, Dynamic response, Multi-body mechanical system, Periodic behavior, Poincare Map, Quasi-periodic behavior, revolute clearance joint

Thermal performance analysis of near infra-red reflection and green roof cooling techniques on buildings made of mild steel

This paper investigates the thermal performance of green roofs, cool roofs, and their combined effects in tropical climates. Although each technology has been studied independently for its potential to reduce cooling energy consumption in buildings, their combined effects have not been thoroughly examined in tropical climates. The study employed experimental and numerical methods, demonstrating that combining green and cool roofs can lead to even greater cooling energy savings. The research involved fabricating four identical cubicles made of mild steel sheets and placing them in an open space for testing under two operational conditions: closed window and open window/door. The combined green and cool roof technology achieved a temperature difference reduction of 4.14 °C compared to the original roof under the closed window and door state, with green and cool roofs achieving 0.72 °C and 0.79 °C, respectively. Combining green and cool roofs led to even more significant cooling energy savings, with 53.57 kWh energy savings compared to 20.1 kWh and 3.68 kWh for combined, green, and cool cubicles, respectively. The study found that combining green and cool roofs led to even more significant cooling energy savings, with 53.57 kWh energy savings compared to 20.1 kWh and 3.68 kWh for combined, green, and cool cubicles, respectively. The research suggests that combining these technologies can lead to greater cooling energy savings and highlights the potential benefits of green and cool roofs for tropical climates

A comprehensive survey of the analytical, numerical and experimental methodologies for dynamics of multibody mechanical systems with clearance or imperfect joints

"Available online 19 December 2017"A comprehensive survey of the literature of the most relevant analytical, numerical, and experimental approaches for the kinematic and dynamic analyses of multibody mechanical systems with clearance joints is presented in this review. Both dry and lubricated clearance joints are addressed here, and an effort is made to include a large number of research works in this particular field, which have been published since the 1960′s. First, the most frequently utilized methods for modeling planar and spatial multibody mechanical systems with clearance joints are analyzed, and compared. Other important phenomena commonly associated with clearance joint models, such as wear, non-smooth behavior, optimization and control, chaos, and uncertainty and links’ flexibility, are then discussed. The main assumptions procedures and conclusions for the different methodologies are also examined and compared. Finally, future developments and new applications of clearance joint modeling and analysis are highlighted.This research was supported in part by the China 111 Project (B16003) and the National Natural Science Foundation of China under Grants 11290151, 11472042 and 11221202. The work was also supported by the Portuguese Foundation for Science and Technology with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941.info:eu-repo/semantics/publishedVersio

Study of the effect of contact force model on the dynamic response of mechanical systems with dry clearance joints : computational and experimental approaches

The main objective of this work is to present a computational and experimental study on the contact forces developed in revolute clearance joints. For this purpose, a well-known slider-crank mechanism with a revolute clearance joint between the connecting rod and slider is utilized. The intra-joint contact forces that generated at this clearance joints are computed by considered several different elastic and dissipative approaches, namely those based on the Hertz contact theory and the ESDU tribology-based for cylindrical contacts, along with a hysteresis-type dissipative damping. The normal contact force is augmented with the dry Coulomb’s friction force. In addition, an experimental apparatus is use to obtained some experimental data in order to verify and validate the computational models. From the outcomes reported in this paper, it is concluded that the selection of the appropriate contact force model with proper dissipative damping plays a significant role in the dynamic response of mechanical systems involving contact events at low or moderate impact velocities.Fundação para a Ciência e a Tecnologia (FCT

Coupling dynamics of a geared multibody system supported by Elastohydrodynamic lubricated cylindrical joints

A comprehensive computational methodology to study the coupling dynamics of a geared multibody system supported by ElastoHydroDynamic (EHD) lubricated cylindrical joints is proposed throughout this work. The geared multibody system is described by using the Absolute-Coordinate-Based (ACB) method that combines the Natural Coordinate Formulation (NCF) describing rigid bodies and the Absolute Nodal Coordinate Formulation (ANCF) characterizing the flexible bodies. Based on the finite-short bearing approach, the EHD lubrication condition for the cylindrical joints supporting the geared system is considered here. The lubrication forces developed at the cylindrical joints are obtained by solving the Reynolds’ equation via the finite difference method. For the evaluation of the normal contact forces of gear pair along the Line Of Action (LOA), the time-varying mesh stiffness, mesh damping and Static Transmission Error (STE) are utilized. The time-varying mesh stiffness is calculated by using the Chaari’s methodology. The forces of sliding friction along the Off-Line-Of-Action (OLOA) are computed by using the Coulomb friction models with a time-varying coefficient of friction under the EHD lubrication condition of gear teeth. Finally, two numerical examples of application are presented to demonstrate and validate the proposed methodology.National Natural Science Foundations of China under Grant 11290151, 11221202 and 11002022, Beijing Higher Education Young Elite Teacher Project under Grant YETP1201

A comparative study of the viscoelastic constitutive models for frictionless contact interfaces in solids

The nature of the constitutive contact force law utilized to describe contact-impact events in solid contact interfaces plays a key role in predicting the response of multibody mechanical systems and in the simulation of engineering applications. The goal of this work is to present a comparative study on the most relevant existing viscoelastic contact force models. In the sequel of this process, their fundamental characteristics are examined and their performances evaluated. Models developed based on the Hertz contact theory and augmented with a damping term to accommodate the dissipation of energy during the impact process, which typically is a function of the coefficient of restitution between the contacting solids, are considered in this study. In particular, the identified contact force models are compared in the present study for simple solid impact problems with the sole purpose of comparing the performance of the various models and examining the corresponding system behavior. The outcomes indicate that the prediction of the dynamic behavior of contacting solids strongly depends on the selection of the contact force model.Fundação para a Ciência e a Tecnologia (FCT

Inclusion Modeling of Bucket Elevator Conveyor Chain Links

Inclusions, pores, and cracks which are defects in materials are important in determining the structural integrity and durability of components. Modeling accurately, these defects are hence of interest to both theorist and the practitioner. CAD models were designed using Autodesk Inventor software, and simulation was performed using ANSYS academic software. Material saving in design of conveyor chain links has gained popularity, and this has led to the introduction of necks in its geometry. However, the effect of necking on various parameters was not considered. Also, inclusions which are defects in material are known to have adverse effect on the conveyor chain link. It is, therefore, imperative to predict numerically, the effects that inclusions and necking have on conveyor chain links This paper focusses on modeling nonmetallic inclusions and also tests various models of different neck radii using the finite element method so as to predict its effect

A Targeted Mobile Phone Intervention Use in Antenatal Care is Associated with Improved Antenatal and Postnatal Clinic Attendance amongst Pregnant Women in A Pastoralist Community in Narok County, Kenya: A randomized controlled trial

Background: Antenatal care is a key high impact strategy to improve maternal and child health globally. This study examined the effects of a targeted mobile-phone intervention on ANC and Postnatal Clinic (PNC) attendance in a pastoralist community. Materials and Methods: An RCT was conducted in Narok County on pregnant mothers recruited early in pregnancy, enrolled and followed up to 42 days postpartum starting in June 2018. The intervention was bi-component; an SMS and a phone call reminder were administered in the intervention arm while the non-intervention group received routine care. Results: The 131 study participants in the intervention arm had a mean of 4.10 visits (SD 0.76, 95% CI 3.97-4.23). The 128 study participants in the non-intervention arm had a mean of 2.84 visits (SD 0.95, 95% CI 2.68-3.01). The difference in means was 1.256 (95% CI 1.044-1.256), which was statistically significant at a 95% confidence level (p-value <0.0001). For the 60 study participants in the intervention arm, 41.67% (n=25) attended the PNC while 58.33% (n=35) did not attend. The 76 study participants in the non-intervention arm, 21.05% (n=16) attended the PNC while 78.95% (n=60) did not attend. The null hypothesis of there being no difference in the likelihood of a mother attending PNC by study group was rejected (X 2 =6.7658, p=0.009). Conclusion: A targeted mobile-phone intervention improved ANC and PNC attendance in a pastoralist community in Narok, Kenya