Required Load Capacity Research Articles

Numerical Analysis of a Self-Acting Gas Bearing Lubricated with a Low-Boiling-Point Medium Using an Advanced Model Based on the Finite Difference Methods and Universal Computational Fluid Dynamics Software

Methods for determining the characteristics of self-acting (aerodynamic) gas bearings have been developed for many years, but many researchers and engineers still question how sophisticated a model of such bearings should be to obtain reliable results. This is the subject of this article, which presents a numerical analysis of aerodynamic gas bearings using two alternative methods: a specialized program based on the finite difference method, and a universal CFD program using the finite volume method. Gas bearings with a nominal diameter of 49 mm, designed for a 10 kW turbogenerator operating at a rotational speed of 40,000 rpm, are analyzed. The vapor of the low-boiling medium, designated HFE-7100, is used as the bearing lubricant. The calculations focus on determining the position of the bearing journal where the bearing achieved the required load capacity and checking the bearing characteristics beyond the nominal operating point. The most important results obtained by the two independent methods are compared, and recommendations are made for those interested in the numerical analysis of self-acting gas bearings.

Analytical Approach for Forecasting the Load Capacity of the EN AW-7075-T6 Aluminum Alloy Joints Created Using RFSSW Technology.

To ensure the high reliability of aircraft structures, the Refill Friction Stir Spot Welding (RFSSW) process must be characterized by a high load capacity of the welds and a small standard deviation of the load capacity spread. This allows us to obtain uniform functional properties in the connections, ensuring the high quality of the process. This work aims to select the most favorable technological parameters for the welding process of EN AW-7075-T6 Alclad aluminum alloy sheets, which are used for the production of aircraft structures. The best networks were calculated using the Statistica 13.3 program. The obtained results were compared with the results of previous investigations. It has been shown that a model using neural networks allows for the determination of connection parameters with much greater accuracy than the classical model. The maximum error in estimating the load capacity of the connection for the mathematical model was 6.13%, and the standard deviation was 14.51%. In the case of neural networks, the maximum error value did not exceed 1.55%, and the standard deviation was 3.74%. It was shown that, based on the neural model, it is possible to determine the process parameters that ensure the required quality capacity of the process, ensuring a probability of obtaining the required load capacity of the connections amounting to P = 0.999935 with a defect rate of 0.0065%. This possibility is not provided by the classical model due to its large error in estimating the process spread and the high sensitivity of the process input parameters to the output parameters.

Human Factors in the Development of the Hydraulic System of the Powered Roof Support

The growing demand for mineral resources, including hard coal, requires the continuous improvement and development of technologies to improve safety, productivity and performance. The implementation of automation and digitization in mines has been ongoing for several years. Machinery and equipment development and improvement is also ongoing. The authors discuss the development and improvement of powered roof support, which is a critical part of the longwall system. The powered roof support is responsible for the safety of equipment and people working in the longwall. It supports the face and immediate roof and moves the longwall system forward as the shearer removes the coal and the roof collapsing (goafing) behind the shields. The aim of this study was to examine the human factors involved in the development and improvement of the hydraulic support system of powered roof support. The research was carried out among employees in hard coal mines using mainly surveys. The research allowed the authors to examine and analyze the information provided by the miners concerning powered roof support in the era of Industry 4.0 (the Fourth Industrial Revolution). According to the research findings, miners expect improvement in the reliability of the powered roof support, and they want the key operating parameters, especially the required load capacity, to be monitored in real-time so adjustments and improvements can be made. The results of the research point out the needs and expectations of miners. Their opinions should determine the direction and any research gaps into powered roof support.

Waste Slag Management with help of Air Blaster in CFBC Boiler

Abstract: This research paper addresses the issue of excess ash content in CFBC boilers when lower quality fuel, such as the lower or upper layer of lignite, is supplied. The increase in ash content leads to the continuous draining of bed ash and often results in the restriction of bed material flow in the furnace inlet pipe to the slag cooler. While this may not have a significant impact on the required load in normal conditions, it can severely affect the unit's load capacity in the case of poor-quality coal. The paper proposes a solution for waste slag management using air blasters in 135 MW CFBC boiler, which can effectively prevent the choking of inlet pipes and ensure uninterrupted operation at the required load capacity. The implementation of this solution has the potential to significantly improve the operational efficiency and reliability of CFBC boilers, particularly when using lower quality fuels.

Optimization of the Load Capacity System of Powered Roof Support: A Review

Powered roof support is equipped with a hydraulic control system to ensure its required load capacity. The main problem arising from powered roof support during exploitation is providing the necessary load capacity. A decrease in load capacity is mainly associated with internal and external leakage in the cylinders, mainly in the hydraulic props. The hydraulic prop’s role is to ensure stability for the powered roof support. A special double block with an additional pressure boost was developed to counter the props’ leakage phenomenon. Pressure loss is replenished based on the solution proposed here. For this purpose, bench tests were commenced, in which a prop with an internal leakage was used. The research included the analysis of the operation of a boosted double block. The results allowed us to assess whether the developed solution can be the subject of further research conducted in real conditions.

The stone cantilevers rehabilitation of heritage buildings

Abstract The aim of this article is to analyse multiple solutions for the stone cantilevers rehabilitation commonly found in heritage buildings. The stone cantilevers are arranged in the inner courtyards of historical buildings and ensure horizontal circulation. Throughout the article will analyse two categories of situations encountered in the rehabilitation practice: for the first situation the cantilever rehabilitation can be done after the stone plate demolition, and for the second situation the cantilever rehabilitation must be done without having the option of demolishing the flat plates. The difficulty of the intervention is given by the fact that the fixed ending restrain of the cantilever was ensured during the execution technology, the cantilever fixed in the masonry being ensured during the building of the wall. The rehabilitation of the stone cantilevers is conditioned by the fact that the fixed ending restrain point cannot be rebuild on the initial principles. This fact requires the adoption of rehabilitation principles based on a different approach to ensure the fixed end point. The proposed solutions solve both issues ensuring the required load capacity of the cantilever and ensuring the required level of fixed end restrain

유도코일을 이용한 3상 전류 검출기용 센서모듈 설계

According to the increase of required load capacity for the low-voltage AC system, compact current detection modules are required to secure the safety of electric systems. In particular, low-voltage infrastructure is required due to the increase in electricity demand for intelligence, customer convenience, and safety in the railway sector. In this paper, design consideration of inductive coil sensor for 3-phase current detector is proposed to expand linearity and improve measurement precision. The design method considering the limited space and practical implementation constraints was studied. To verify the proposed method, a 150A-class prototype was designed. Several induction coil sensor output variations with different specifications were verified through experiments.

Worm Gear Drives with Improved Kinematic Accuracy.

This paper presents the fundamentals of the design and applications of new worm gear drive solutions, which enable the minimisation of backlash and are characterised by higher kinematic accuracy. Different types of worm surfaces are briefly outlined. Technological problems concerning the principles of achieving a high degree of precision in machining are also described. Special attention is paid to the shaping of conical helical surfaces. Increasing the manufacturing precision of drive components allows one to achieve both lower backlash values and lower levels of its dispersion. However, this does not ensure that backlash can be eliminated, with its value being kept low during longer periods of operation. This is important in positioning systems and during recurrent operations. Various design solutions for drives in which it is possible to reduce backlash are presented. Results of experiments of a worm gear drive with a worm axially adaptive only locally, in its central section, are presented. In this solution, it is possible to reduce backlash by introducing adjustment settings without disassembling the drive. An important scientific problem concerned defining the principles of achieving a compromise between the effectiveness of reducing backlash and the required load capacity of the drive. In this paper it has been shown that in worm gear drives with a locally axially adaptive worm, as well as with a worm wheel with a deformable rim, it is possible to achieve significant reduction of backlash. In high precision drives—for example, those with an average backlash value of <15 micrometers—this can enable more than a two-fold reduction of the average backlash value and more than a three-fold decrease of the standard deviation of local backlash values.

Electromagnetic Bearings With Power Electronic Control for High-Speed Rotating Machines: Review, Analysis, and Design Example

This article reviews electromagnetic bearings with power electronic control for high-speed machinery, which are termed active magnetic bearings (AMBs). AMB is a contactless-type bearing, which uses magnetic force to support the rotor. This is suitable for high-speed applications, harsh operating conditions, and also clean environments. However, the AMB has nonlinear characteristics and is inherently unstable. Due to recent advancements in fast-switching power devices, high-switching-frequency power converters, high-bandwidth current control, nonlinear control strategies, advanced digital controllers, and sensors, AMBs have become promising for high-speed aerospace, industrial, and energy applications. This article contains a brief tutorial on the AMB, covering its operating principle, system-level block diagram, magnetic-circuit-based analysis, dynamic load due to rotor mass unbalance, load capacity, force slew rate, and response to large force disturbance. Furthermore, a design example of an eight-pole AMB with four excitation coils is presented to achieve a load capacity of 180 N. A preliminary design, based on magnetic circuit analysis, is seen to fall short in terms of load capacity. Iterative changes to the AMB dimensions achieve the required load capacity, but the characteristics are still nonlinear. Finite-element analyses bring out the effects of magnetic saturation on load capacity, linearity between force and current, force slew rate, and relationships between maximum force generated and AMB dimensions. An improved design procedure is presented to achieve both desired load capacity and linear characteristics, while balancing the compactness requirement. The improved design also achieves the desired slew rate besides faster response and improved stability.

Polyoptimisation of the refill friction stir spot welding parameters applied in joining 7075-T6 Alclad aluminium alloy sheets used in aircraft components

In the aerospace industry, the refill friction stir spot welding (RFSSW) method is increasingly used to join thin sheets, especially those made of 2xxx and 7xxx series aluminium alloys. This paper presents the results of spot welding lap joints of 7075-T6 aluminium alloy sheets. The load capacity of joints was determined by tensile/shear tests using a universal testing machine. The effect of tool plunge depth, tool rotational speed and duration of welding on joint load capacity and failure mode was investigated. The polyoptimisation of the values of welding process parameters was carried out to ensure the highest load capacity of the joint at a minimum variance of the results obtained. The selection of the optimal parameters of the RFSSW process was carried out using an adequate mathematical model obtained on the basis of Weierstrass’ theorem. It was found that tool rotational speed had the greatest impact on the load capacity of the joints. It was possible to increase the load capacity of the joint by increasing the duration of welding but only to a limited extent. The selection of optimal welding parameters requires a compromise solution, i.e. the selection of a tool rotational speed that ensured adequate plasticisation of the material with a welding duration that ensured that an appropriate joint microstructure was obtained and assured the required load capacity of the joint. The methodology of mathematical modelling of polyoptimisation presented can be useful in optimising similar joining processes.

Precast Slab Structures Made of Carbon Reinforced Concrete

Carbon reinforced concrete allows a new way to think of and design structural load bearing elements. Two different lightweight load bearing structures were developed, produced and tested at the Technische Universität (TU) Dresden. The first main structure is a 4.5 m long semi-precast ceiling element, which consists of a 45 mm thick shell in longitudinal direction and two 40 mm thin webs below the shell at the longitudinal edges of the element. A reduction of the dead load up to 70%, compared to a usual rectangular cross section made of common steel reinforcement and the same concrete, could be achieved. The second precast element type is 5.0 m long and has a maximum height of 200 mm. Two versions of this element type – one unstressed and one externally post-tensioned with carbon strips – were produced. Both structures are reinforced with carbon textile and carbon rebars. The required load capacity and deflection stiffness for both precast slab structures with a conventional construction height could be verified and proved by experimental large-scale tests which will be focus of the paper.

Short-Cut Method to Assess a Gross Available Energy in a Medium-Load Screw Friction Press

The present study proposed a rapid method, based on a previous universal compression tests, to estimate the required load capacity to cold forge different specimen quantity in a screw press. Accordingly, experimental and theoretical approach are performed to check new adjustable drive motor of the modified forging machine to achieve a gross available energy to deform the specimens preventing damage of the forging machine. During the forging experiments, two screw friction presses (as-received and modified) are used to validate the theoretical approach. The modified press exhibits an increase of 51% of gross energy and 11% of maximum load capacity compare to the as-received press. This method is used to improve the effective of the forging process avoiding excessive loads that could promote machine failure. Therefore, a low-cost and easy to implement methodology is proposed to determine the energy and load capacity of a screw friction press to forge different specimen quantities with symmetry pattern configurations.

Vehicle Loads for Assessing the Required Load Capacity Considering the Traffic Environment

The effects of traffic loads on existing bridges are quite different from those of design live loads because of the various traffic environments. However, the bridge maintenance and safety assessment of in-service bridges maintain the design load capacity without considering the current traffic environment. The real traffic conditions on existing bridges may require a load capacity that is considerably different from the design. Therefore, the required load capacity of an existing highway bridge should be determined according to the extreme load effects that the bridge will experience from the actual traffic environment during its remaining service life for more rational maintenance of the infrastructure. A simulation process was developed to determine evaluation vehicle loads for bridge safety assessment based on the extreme load effects that may occur during the remaining service life. Realistic probabilistic traffic models were used to reflect the actual traffic environment. The presented model was used to analyze the extreme load effect on pre-stressed concrete (PSC) and steel box girder bridges, which are typical bridge types. The traffic environmental conditions included the traffic volume (2000–40,000), the proportion of heavy vehicles (15–45%), and the consecutive vehicle traveling patterns. The spans of the sample bridges were 30 m (PSC bridge) and 45 or 60 m (steel box girder bridge). In the results, the extreme load effects tended to increase with either the traffic volume or proportion of heavy vehicles. The evaluation vehicle loads for bridge safety assessment may be adjusted with the traffic conditions, such as the traffic volume, the proportion of heavy vehicles, and the consecutive vehicle traveling patterns.

STANDARD SECTION DESIGN OF FRP DSCT TOWER SUPPORTING 3MW WIND TURBINE

A modular FRP DSCT (Fiber Reinforced Polymer Double-Skinned Composite Tubular) wind power tower was suggested and its standard section supporting 3MW wind turbine was designed. An FRP DSCT tower is composed of two concentric FRP tubes and concrete filled between the inner and outer tubes. A DSCT structure has hollowed section which reduces its self-weight. Due to inner and outer tubes, concrete is confined to increase strength and ductility. The performance of the new-type wind power tower was assessed via structural analysis. Design and analysis were carried with AutoDSCT and CoWiTA programs with consideration of confining effect of concrete and large displacement by wind turbine weight itself. The bottom diameter of the tower was set as 4.5 m as a standard. The towers which have 100%, 95%, 90% and 85% of bottom diameter were considered for design. Top diameter of the tower was set as 3.6m. For the consideration of constructing and installing the tower, each tower was divided into modules. The module sections were designed on the basis of the idea that module sections should satisfy the required bending moment and axial load. As a result, bottom diameter of 4.5m with hollow ratios below 0.85 satisfied the required load capacity and the bottom diameter of 95%, 90% and 85% with the hollow ratios below 0.82, 0.76 and 0.7 satisfied the required capacity.

Abrasion process between a fibre mooring line and a corroded steel element during the transit and commissioning of a marine renewable energy device

a bstract The interaction between fibre rope and steel parts on vessels (fairlead and roller) is technically well understood but not commonly published in codes or practised by mariners. What appears to be a smooth steel surface to the naked eye can still be abrasive medium to synthetic mooring components. There are very few reports of external rope abrasion tests in the literature. The surface finish at the contact between the rope and the steel guide can cause damage and consequently prematurely degrade the exposed yarns of the rope and thus reduces the overall load bearing capacity of the rope. The standard ISO 18692 [1] recommends that prolonged cycling of a rope around rollers should be avoided, however it is specified that occasional bending and running over rollers are allowable. There are two guides to specify surface roughness. MEG 3 [2] states that steel fairleads should be polished to Ra 10, but in practise this may be difficult to achieve or obtain with carbon steel. The US Navy guide also states that the surface of steel should have better than 125 μi or 3.2 Ra [3] . The study presented here discusses the bending of a synthetic rope around a roller during transportation. It relates the motion behaviour of the vessel to rope wear and provides a detailed numerical simulation correlated with post analysis of the rope after the failure. The investigations show that the roughness of the steel roller caused the abrasion of the rope which was exacerbated through the vessel dynamics, resulting in the rope having an estimated residual strength of 14% MBL before rupture. The experimental tests have established a linear relation between strength loss and surface roughness and it was observed that the abrasion mainly occurs in the early stages of load cycling. The presented work recommends the use of lubricated nylon instead of carbon steel rollers to limit abrasive rope wear. The paper also devises a methodology to carefully assess and quantify potential rope abrasion to ensure that the residual rope strength withstands the required load capacity.

Optimal design of non-contact thrust bearing using permanent magnet rings

This paper describes an optimal design process of a permanent-magnet thrust bearing. The bearing consists of two sets of permanent magnet rings. One set is located inside the other. An axial displacement between the two sets creates an axial force, thereby achieving a thrust bearing function. In order to obtain an optimal design of the bearing where the required load capacity of bearing is achieved with the least magnet volume, we derived analytical design equations based on the equivalent current sheet (ECS) method. We considered two types of magnet arrays: axial arrays and Halbach arrays. Optimization is carried out for these two types. The results show that the Halbach array can achieve the load capacity requirement with smaller magnet volume than the axial array. We also found that there exists an optimal axial separation of rings for the axial array. The efficacy of the ECS method is verified against the results from three-dimensional finite element analyses and experiments. It is found that the Halbach array is more sensitive to the underlying assumptions of ECS method than the axial array.

영구자석형 스러스트 베어링의 최적 설계

In this paper, we describe a process for optimally designing a ring-type permanent magnet thrust bearing. The bearing consists of two sets of permanent magnet rings. One set is located inside the other set. An axial offset between the two sets creates axial force, which results in a thrust bearing function. In order to realize an optimal design of the bearing where the required load capacity of the bearing is achieved with the least magnet volume, we derived analytical design equations by adopting the equivalent current sheet (ECS) method. We considered the following two types of magnet arrays: axial arrays and Halbach arrays. These two types of arrays are optimized using the analytical design equations. The results of the optimization are verified using three dimensional (3D) finite element analyses (FEA). The results show that the Halbach array can achieve the required load capacity with less amount of permanent magnet than the axial array does. The efficacy of the ECS method is also verified by using 3D FEA. It is found that the accuracy of ECS method is more sensitive to the underlying assumptions for the Halbach array than for the axial array.

산업용 단선 궤도 차량의 주행 동특성에 관한 연구

An OHT(Over Head Transportation) vehicle is an example of the industrial monorail vehicle, and it is used in the automobile, semiconductor, LCD manufacturing industries. OHT vehicle is moved by main wheels and guide rollers. The major function of the main wheel is to support and drive the OHT vehicle. The roles of the guide roller is the inhibition of derailment and steering of the OHT vehicle. Since the required vehicle velocity becomes faster and the required load capacity is increased, the durability characteristics of the wheel and roller, which was made of urethane. need to be increased. So it is necessary to estimate the fatigue life cycle of the wheel and roller. In this study, OHT dynamic model was developed by using the multi body dynamic analysis program ADAMS. Wheel and roller are modeled by the 3-D surface contact module. Especially. motor cycle tire mechanics is used in the wheel contact model. The OHT dynamic model can analyze the dynamic characteristic of the OHT vehicle with various driving conditions. And the result was verified by a vehicle traveling test. As a result of this study, the developed model is expected to predict wheel dynamic load time history and makes a contribution to design of a new monorail vehicle.

Instrumented load tests in mudstone: pile capacity and settlement prediction

The present work stems from the design of a viaduct in South Wales, U.K., where full-scale pile testing was carried out to assess whether the proposed design methods would meet the required load capacity and settlement criteria for the working piles. Five fully instrumented large diameter bored cast in situ piles, up to 30 m deep, were installed in weathered mudstone and tested under vertical loading. A sixth pile, which had no shaft instrumentation, was formed with a voided toe. In conjunction with vast soil data from 218 site investigation boreholes, the extensive data produced from the load tests were analyzed to quantify the key parameters considered to influence load transfer and settlement behaviour. Each pile was first calibrated using four methods to establish the as-built stiffness, taking into account the nonlinearity of concrete and the effect of partial steel encasement. It is demonstrated that the current national norms for bored pile design in cohesive soil – soft rock are overconservative for South Wales ground conditions. To ameliorate this, alternative methods are proposed, which lead to improved reliability and accuracy in shaft and base capacity assessment. In addition, a numerical model is developed that can be used to predict the complete load-settlement variation up to the ultimate state. The model is sufficiently expounded to allow its immediate application in pile design by geotechnical engineers.Key words: piled foundations, load tests, bearing capacity and settlement, Mercia mudstone.

Application of the finite-element method to a design of optimized tool geometry for the O.S.U. formability test

A new, plane-strain, sheet-formability test (the O.S.U. Formability Test, OSUFT) has been recently proposed, and it has shown many improvements over the limiting dome height (LDH) test. However, the prototype tool geometry was initially determined arbitrarily for the experiment so that an enhancement of the tool geometry was made with dual purpose: to design the tool geometry to generate consistent planestrain state up to failure under various lubrication states and different testing materials and, at the same time, to make the testing equipment cost as low as possible so that the test may be readily available for small- and medium-scale stamping companies. The latter demands a compact tool geometry to minimize the required press capacity, while the former requires wider blanks that increase the punch load. Considering these conflicting conditions, computer simulation technique using three-dimensional finite-element method was introduced, rather than performing numerous die tryouts, to design the optimal tool geometry from simulative trial and error. By reducing the size of the entire tool and controlling the width-to-length ratio of the blank, an enhanced tool geometry was found that generates stable plane-strain state up to failure and still features low required load capacity for materials with r-values up to 2.0, friction coefficient ranges of 0.15 to approximately 0.35, and thicknesses up to 1.5 mm. The bending-dominant failure due to smaller radii of the tool was avoided. Comparison of LDH simulation showed that the enhanced configuration of the test will produce more proportional strain path and larger plane-strain area near the predicted failure region. It was also predicted that the testing results will be less sensitive to the lubrication state on the tool surface and the material anisotropy of the sheet, which will contribute to a better repeatability of the test. Experiments revealed that the optimized tool showed significantly less scatter in measurement compared with that of the LDH and the original O.S.U. formability tests.