3D modelling and model management applied to ship design

The application of a Computervision CADCAM system in ship design and building is presented. The complexity of the design of ships meant that the Computervision software had to be adapted to the specific requirements of the ship design company, Vosper Thornycroft. The objectives, approach and method used by Vosper Thornycroft in developing the software is described, and problems experienced in applying the system are examined.     

输入饱和情况下农用拖拉机的直线导航控制

本文以农用拖拉机为研究对象, 提出了一种基于饱和方法的直线路径跟踪导航算法. 该算法可以为农用拖拉机导航中普遍存在的输入饱和控制问题提供一种有效的解决办法. 首先, 基于直线导航系统运动学模型, 将其线性化得到易于控制设计的线性系统模型. 其次, 设计非饱和控制器, 使得系统在该非饱和控制器作用下全局镇定. 最后, 结合饱和函数和非饱和控制器, 构造出饱和控制器, 并证明在该饱和控制器作用下系统全局渐近稳定. 该控制方案的优点在于: 控制器结构较为简单, 且饱和控制器中从外到内的饱和度并不需要按照递减顺序选取, 从而提高了闭环系统的收敛性能. 仿真结果验证了上述方法的有效性.     

拖拉机动力输出轴扭矩CAT系统设计与应用

为了测量拖拉机动力输出轴的输出扭矩 ,设计了一套计算机辅助测试系统。本文介绍了扭矩传感器的标定系统以及扭矩田间测量系统的硬件组成、工作原理、应用及与其配套的数据处理软件     

Whole-body vibration: Measurement of horizontal and vertical transmissibility of an agricultural tractor seat

The seats may significantly reduce the exposures levels transmitted to the driver, but the European Directive 2002/44/EC (2002) requires only tests on the damping seat capacity along the vertical direction, whereas nothing is required for the longitudinal and transversal directions.Field tests were carried out using a 93 kW tractor to verify the vibrational comfort values given by seat with pneumatic suspension. The tests were executed with the tractor running on different surfaces, at two different forward speed and tire pressures and with different tractor masses. Three repetition were carried out for each configuration. Accelerations were always measured on both the seat and the cabin platform and the calculations were done using the ISO 2631 standard suggestions. The vibration total values and the acceleration transmissibility along the 3 perpendicular axes were calculated and analysed.Despite different boundary conditions (surface, tire pressure, forward speed and tractor mass distribution), along the Z axis the transmissibility was constantly around 0.7, to confirm that the seat worked well to damp the vertical exposures. Different were the situations for the X and the Y axes. Excluding the asphalt, on the other crossed surfaces high transmissibility values were observed (never less than 1), especially along the X axis.Relevance to industry. This paper describes the vibration transmissibility of an agricultural tractor seat. Tests were carried out with the tractor running on different surfaces and with different configurations. The seat transmissibility along the three orthogonal directions was acquired.Results suggest that the tractor manufacturer should consider, during the machine design, also the rolling and pitching movements, because the seat accelerations along the X and Y axes are influenced by them. The seat manufacturer could reduce the rolling and pitching effects using specific suspension systems along the horizontal and lateral directions.     

Architecture without numbers — CAAD based on a 3D modelling system

The paper describes an advanced demonstration system which brings together a number of recent developments in CAAD (computer-aided architectural design). This demonstration system illustrates how an important new form of input device, a 3D modelling systemm can be linked with building performance software and ‘indicative’ computer output graphics. The 3D modelling system uses electronically interrogable building elements. The user assembles these elements on a baseboard, providing a tangible model of the design. The model is then interrogated by the CAD system, which recovers the geometry data describing the topology of the model. The user changes the design by reassembling the model elements. A particular aspect of this demonstration is that the user has the option to generate building design data and assimilated building performance data without the need to handle this data in numeric form. It is likely that many of the features present in this demonstration system will be evident in future ‘production’ CAAD systems.     

Experimental analysis of occupational whole-body vibration exposure of agricultural tractor with large square baler

This study investigates longitudinal whole-body vibration in agricultural tractors powering a large square baler. The aim is to test the hypothesis that four-wheel drive has an influence on the longitudinal dynamic response. A number of experimental measurements are carried out on a specific vehicle combination driving uphill and downhill. The whole-body vibration exposure is measured at the operator seat under different conditions.The statistic results show a significant difference on the whole-body vibration exposure depending on operating conditions. Driving uphill and downhill with four-wheel drive activated showed the highest difference with increased vibration level at downhill driving.The results indicate that four-wheel drive influences the longitudinal dynamics and hence the whole-body vibration exposure on tractors with large square balers.Relevance to industryThe findings of this work are highly relevant to the manufacturers of agricultural tractors and machinery as well advisers within occupational health. The paper demonstrates potential in reducing damaging vibrations by simple manual or automatic control of four-wheel drive.     

Nonlinear sliding mode control of an unmanned agricultural tractor in the presence of sliding and control saturation

The paper considers the problem of automatic path tracking by autonomous farming vehicles subject to wheel slips, which are characteristic for agricultural applications. Two guidance laws are proposed to solve this problem, and both explicitly take into account the constraints on the steering angle and ensure tracking an arbitrarily curved path. The first law is implemented by the pure sliding-mode controller, whereas the second one combines the sliding mode approach with a smooth nonlinear control law and requests control chattering at the reduced amplitude as compared with the first law. Mathematically rigorous proofs of global convergence and robust stability of the proposed guidance laws are presented. In doing so, the slipping effects are treated as bounded uncertainties. Simulation results and real world experiments confirm the applicability and performance of the proposed guidance approach.     

Real-time vibration monitoring and analysis of agricultural tractor drivers using an IoT-based system

Agricultural tractor drivers experience a high amplitude of vibration, especially during soil tillage operations. In the past, most research studied vibration exposure with more focus on the vertical (z) axis than on the fore-and-aft (x) and lateral (y) axes. This study examines how rotary soil tillage affects the vibration acceleration and frequency, and the power spectral densities (PSDs) at the seat pan and head along three translational axes in a real-field multiaxis vibration context. Moreover, this study aimed to identify the characteristics of the seat-to-head transmissibility (STHT) response to identifying the most salient resonant frequencies along the x-, y-, and z-axes. Nine (9) male tractor drivers operated the tractor with a mounted rotary tiller throughout the soil tillage process. In the event of a COVID-19 pandemic, and to respect social distancing, this study developed an Internet of Things (IoT) module with the potential to integrate with existing data loggers for online data transmission and to make the experimentation process more effective by removing potential sources of experimenter errors. The raw acceleration data retrieved at the seat pan and the head were utilized to obtain daily exposure (A(8)), PSDs, and STHT along the x-, y-, and z-axes. The vibration energy was found to be dominant along the z-axis than the x- and y-axes. A(8) response among tractor drivers exceeds the exposure action value explicitly stated by Directive 2002/44/EU. PSDs along the x-, y-, and z-axes depicted the low-frequency vibration induced by rotary soil tillage operation. The STHT response exhibited a higher degree of transmissibility along the y- and z-axes when compared with that along the x-axis. The frequency range of 4–7 Hz may plausibly be associated with cognitive impairment in tractor drivers during rotary soil tillage.     

Rounding facility for solid modelling of mechanical parts

A rounding facility is described that can perform some of the most common edge and corner smoothings encountered in the design of mechanical parts. The roundings are based on the rolling ball principle and the underlying geometric modeller uses boundary representation. The surfaces used are natural quadrics and tori.     

由二维正投影重建三维实体算法的评述

近二十年来，由二维正投影视图重建三维实体已成为计算机视觉和ＣＡＤ／ＣＡＭ两个不同领域共同关心的一个研究课题。本文综述了１９７３－１９９１期间发表的１４种算法。文中评述了诸算法的特点，并给出了一个汇总表。     

基于改进的弹簧-质点模型的三维服装模拟

针对三维服装造型与效果仿真中存在的模型复杂、模拟效率低、忽略服装的结构特征等问题,提出了改进的弹簧-质点模型.利用该模型统一建立了2D→3D映射和服装真实感模拟方程,给出方程中质点所受内力和外力的组成与表达式以及动态系统的推导和求解过程,并且描述了模拟的具体实现算法.改进的弹簧-质点模型克服了原有模型对服装织物的材料性能表达单一的缺点,考虑了拉伸、剪切、弯曲等力学性能以及省/褶等结构因素对服装外观的影响,实现了较复杂的服装外型.通过从效率与效果两个方面与其他模拟系统进行比较,发现该技术的模拟效率较高而且模拟结果较为真实.该模拟技术已经在服装企业推广应用,用户反映良好.     

An Algorithm for Constructing 3D Struts

A simple robust"strut algorithm"is presented which, when given a graph embedded in 3D space, thickens its edges into solid struts. Various applications, crystallographic and sculptural, are shown in which smooth high-genus forms are the output. A toolbox of algorithmic techniques allow for a variety of novel, visually engaging forms that express a mathematical aesthetic. In sculptural examples, hyperbolic tessellations in the Poincaréplane are transformed in several ways to three-dimensional networks of ...     

Normal orientation methods for 3D offset curves, sweep surfaces and skinning

Computing an offset curve to a 3D curve involves the basic problem of normal orientation in space. The same thing is encountered when interpolating surfaces with 3D sweep or skinning methods. Different methods for normal orientation are discussed an this article. A new method is presented for normal orientation on general parametric curves.     

Limitations in fields of vision for simulated young farm tractor operators

Farm tractors account for the majority of deaths and injuries among youths working on North American farms. A vehicle operator's field of vision is an important operational aspect for safe driving. However, very little is known about visual limitations of young tractor operators compared to adult operators. The main purpose of this study was to quantify limitations in fields of vision of children with different anthropometry. The study was based on assessment of 42 farm tractors in popular use in the USA. The results showed that youth operators typically had diminished fields of vision compared to the average adult operator. The degree of visual limitation is greatest for objects at close distances and when objects are straight in front of the operator/tractor. This has serious implications in terms of risks for runovers, rollovers and collisions. Study findings may help illuminate the development of policies and guidelines in tractor-related jobs for children.

Statement of Relevance:This study provides an ergonomic approach for evaluation of children's visual limitations in tractor operations. This approach could be used in other related cases, where children are allowed to operate vehicles.     

Design of distributed hybrid electric tractor based on axiomatic design and Extenics

Led by the goals of energy saving and low emissions, tractors need more efficient operations under complex farmland working environments. The powertrain architecture of the tractor has a significant influence on the performance. Therefore, the research on the innovative design of the tractor powertrain architecture can improve the efficiency, energy saving, and environmental protection effects. Based on the creative design method of Axiomatic Design (AD) and Extenics, this paper conducts an innovative design analysis of the powertrain architecture of distributed hybrid electric tractor (DHET). Firstly, AD is used to perform the hierarchical analysis of the tractor powertrain architecture design. Then according to the design content, the design matrix (DM) is established, and the matrix is transformed to extract the 3 × 3 coupling contradiction matrix. Finally, the application of Extenics solves the contradictions in the innovative design of the tractor powertrain architecture. Simulation and prototype experiments have proved that DHET has the advantages of energy saving and emission reduction. This paper analyzes the innovative design of DHET's powertrain architecture, which can provide a theoretical basis and method support for the product's innovative design.     

大马力拖拉机驱动桥有限元分析及试验研究

驱动桥作为拖拉机的传动和承载部件,受力较大且使用频繁,通过对桥壳 模型的有限元分析,可以验证设计的安全性并可以通过分析结果来改进设计。首先采用Pro/E 对拖拉机驱动桥壳、转向节、半轴进行三维建模并导入Hypermesh 中进行有限元分析的前 处理工作,然后将导出的文件输入ANSYS 中进行有限元分析。最后通过桥壳的刚度试验和 疲劳试验验证了此驱动桥的安全性,并给出了改进意见。     

Quantitative analysis and evaluation of manipulation comfort of tractor gear shifting based on combined methods

Currently, studies of the manipulation comfort of agriculturalmachinery are mainly based on qualitative analysis and subjective evaluation. This study is mainly focused on the quantitative analysis and evaluation of the manipulation comfort of tractor gear‐shifting. By taking various factors into account, a combined evaluation model and the corresponding indicator system were proposed based on the method of maximizing deviations. The data of pedal force and stroke length of the clutch were collected from eight different types of agricultural tractors, which were used as the basic data for subsequent analyses. Then, five evaluation methods, including principal component analysis (PCA), comprehensive evaluation based on the entropy, ideal solution (TOPSIS), improved TOPSIS and grey correlation analysis, were adopted to evaluate the manipulation comfort of tractor gear‐shifting. A consistency check on the evaluation results of the five methods was conducted by using the concordance coefficient method of KENDALL. Furthermore, the combined weight vector of the compatible method set was calculated by maximizing the deviations. Through comparison, we found that the evaluation results of the combined methods were consistent with the subjective evaluation results. The method of combined evaluation can compensate for the insufficiency of single methods and overcome the inconsistency of the evaluation, and thus can produce more objective and accurate results. Our results can provide references for the quantitative research of manipulation comfort of agricultural machinery equipment.     

3D modelling of flexural isostatic deformation

Modelling of the isostatic loading of the earth's crust in three dimensions is a difficult problem due to the length scales involved, the lack of scalability of the underlying equations and the slow convergence of the solution under conventional techniques. In this paper, a new method to solve the three-dimensional (3D) flexure equation has been developed. The long-standing challenge in numerically modelling flexural isostasy at large scale and high rigidity is addressed. The program is capable of modelling both local and regional isostatic compensation. Compared with other schemes, the isostatic model presented here is more robust and computationally efficient.     

CAE/CAD/CAM curricula implementation - experience at the National University of Singapore

A step-by-step approach to implement CAE/CAD/CAM curricula for undergraduate engineering courses at the National University of Singapore is presented. As the student workload is already quite heavy, each course is examined in detail and the CAE/CAD/CAM contents are carefully blended with the existing course structure. Some students are also assigned CAE/CAD/CAM specific projects to allow them to develop expertise in developing new software packages and building interfaces to existing packages. Experience indicates that CAE/CAD/CAM programmes at the undergraduate level should be implemented in various phases. It is also necessary to consider the state of the local industries in the adoption of the CAE/CAD/CAM technology so that the effort by the university is well synchronized with industry.     

Analysis of tolerances and process inaccuracies in discrete part manufacturing

This paper discusses basic problems of tolerancing mechanical parts. The problem of part design analysis (determination of consistency, determinacy and stability) is reduced to the analysis of systems of linear inequalities. It is shown that the calculation of resulting tolerances between components of parts can be easily solved by linear programming. A method is provided for the construction of a system of inequalities which the working dimensions and inaccuracies of machining operations must satisfy if a given tolerance specification is to be met.