Ole Ø. Mouritsen

Comparison of Post Weld Treatment of High Strength Steel Welded Joints in Medium Cycle Fatigue

This paper presents a comparison of three post-weld treatments for fatigue life improvement of welded joints. The objective is to determine the most suitable post-weld treatment for implementation in mass production of certain crane components manufactured from very high-strength steel. The processes investigated are: burr grinding, TIG dressing and ultrasonic impact treatment. The focus of this investigation is on the so-called medium cycle area, i.e. 10 000–500 000 cycles and very high stress ranges. In this area of fatigue design, the use of very high-strength steel becomes necessary, since the stress range can exceed the yield-strength of ordinary structural steel, especially when considering positive stress ratios (R > 0). Fatigue experiments and qualitative evaluation of the different post-weld treatments leads to the selection of TIG dressing. The process of implementing TIG dressing in mass production and some inherent initial problems are discussed. The treatment of a few critical welds leads to a significant increase in fatigue performance of the entire structure and the possibility for better utilization of very high-strength steel.

An experimental displacement and over 50 years of tag-recoveries show that monarch butterflies are not true navigators

Monarch butterflies (Danaus plexippus) breeding in eastern North America are famous for their annual fall migration to their overwintering grounds in Mexico. However, the mechanisms they use to successfully reach these sites remain poorly understood. Here, we test whether monarchs are true navigators who can determine their location relative to their final destination using both a “compass” and a “map”. Using flight simulators, we recorded the orientation of wild-caught monarchs in southwestern Ontario and found that individuals generally flew in a southwest direction toward the wintering grounds. When displaced 2,500 km to the west, the same individuals continued to fly in a general southwest direction, suggesting that monarchs use a simple vector-navigation strategy (i.e., use a specific compass bearing without compensating for displacement). Using over 5 decades of field data, we also show that the directional concentration and the angular SD of recoveries from tagged monarchs largely conformed to two mathematical models describing the directional distribution of migrants expected under a vector-navigation strategy. A third analysis of tagged recoveries shows that the increasing directionality of migration from north to south is largely because of the presence of geographic barriers that guide individuals toward overwintering sites. Our work suggests that monarchs breeding in eastern North America likely combine simple orientation mechanisms with geographic features that funnel them toward Mexican overwintering sites, a remarkable achievement considering that these butterflies weigh less than a gram and travel thousands of kilometers to a site they have never seen.

A new quasi-static multi-degree of freedom tapered roller bearing model to accurately consider non-Hertzian contact pressures in time-domain simulations

The accuracy of the fatigue life calculations in rolling bearing simulations is highly dependent on the precision of the roller-raceway contact simulations and the ability to accurately include structural deflections of the supporting structure. Several different methods exist to simulate the pressure distributions, and in time-domain bearing simulations, where many contacts need evaluation, the simple and time efficient methods are more popular. These methods underestimate the fatigue life reduction due to roller end effects, overload and misalignments. Furthermore, existing time-domain rolling bearing models assume that the bearing rings remain circular, which can be a poor approximation, especially for large and flexible supported bearings. This paper presents a new multi-degree of freedom frictionless quasi-static time-domain tapered roller bearing model that uses high precision elastic half-space theory to simulate the contact pressures and allows for an arbitrary stiffness of the outer ring supporting structure. The potentially higher computational demand using the advanced contact calculations is addressed by pre-processing series of contacts at different centreline approaches and roller tilt angles, which are used for interpolating contact results during time-domain simulations. The stiffness of the outer ring supporting structure is included by condensing a FE-model using an assumed modes method also known as modal flexibility. It is demonstrated that this new model allows for simulation of bearing misalignments and structural deflections, and that the effect of these conditions is directly evaluated in a detailed fatigue life analysis.

Reply to Oberhauser et al.: The experimental evidence clearly shows that monarch butterflies are almost certainly not true navigators

Oberhauser et al. (1) raise several concerns related to our recent PNAS paper (2), all of which we address here. To test for true navigation, one can use translocation experiments (3) and modeling (4). Truly navigating animals know where they are relative to their goal and thus can correct their orientation if they drift “off-course.” A proper test of true navigation requires distant displacements, because the correction angles would be too small to be reliably detected using short displacements (2, 3, 5). Furthermore, per definition, one must move animals away from their migratory path (ref. 3 and others) to test for true navigation. Therefore, our displacement location was highly appropriate for testing true navigation. Reciprocal translocations are not necessary (ref. 3 and many others), and because monarchs do not occur regularly in Calgary, this was not possible.

Time domain simulation of large-scale material handling chains using an unconstrained formulation

This article presents a dynamic time domain simulation model of loop-sortation systems. Loop-sortation systems for sortation of medium-size items are designed as a closed chain of carts guided in a closed loop track with a view to meet customers’ requirements of capacity and space available. Loop-sortation systems are complex mechatronic systems which require the use of simulation models in order to analyse, predict, and improve the dynamic performance in a cost efficient way. The model utilizes theory for unconstrained rigid multibody dynamics where contact between carts and between cart and track are modelled through the use of force elements. To determine contact between the track and the chain of carts, a rapid and robust contact search formulation has been developed and implemented in the model. Comparisons of main forces of the chain model are made with experimental measurements on three different test layouts. Verification results show that the normalized root mean square deviations are generally less than 10 per cent.

A ride comfort tyre model for off-highway vehicles

Tyre modelling is a major challenge when using time domain multibody simulation models to evaluate ride comfort on off-highway commercial vehicles. Further, parameters for these big tyres are difficult to obtain and thus, commercial car tyre models are difficult to apply. In this research work, a simple vertical tyre model for off-highway ride comfort evaluation is suggested. A displaced volume approach has been developed and combined with the slip theory to yield a tyre model that can be characterised by only three parameters. Full scale measurements on a dump truck have been carried out. Force responses from measurements are compared to the simulation results. Acceleration responses and the level of whole-body vibrations have also been compared.

Numerical and experimental study of hydrostatic displacement machine

Abstract This paper presents a simulation tool to determine the structural deflections and corresponding leakage flow in a hydrostatic displacement motor. The simulation tool is applied to a new motor principle that is categorized as an extreme low speed high torque motor with dimensions that calls for attention to the volumetric efficiency. To counteract structural deflections the motor is equipped with compensation pressure volumes that may be used to limit the leakage flow across the end faces of the circular rotor. This leakage flow is investigated by solving Reynolds equation for the pressure distribution across both end faces. The fluid pressure is combined with structural calculations in a fluid structural interaction simulation which evaluates the influence of structural deflections on the gaps and the leakage flow. The numerical work is validated by prototype tests. Both deflections and leakage flows are measured and compared with those from the simulations with good correlation. The deflections, and hence leakage flow, are reduced by the use of compensation pressure volumes, which is validated both numerically and experimentally.

A Method for Linked Discrete Design Variables Applied to Lifting Tables

A method for design optimization of lifting tables using mapping parameters to handle the discrete design variables has been examined for robustness. The mapping parameters are an approach to link discrete design variables. In this context the discrete design variables are listed in tables describing the components of a typical lifting table and the mapping parameters simply describes the number in the data base that is to be used in the design. These numbers are determined by means of multi criteria optimization in which the mapping parameters are allowed, initially, to vary continuously before being pushed gradually towards integer values. A non-gradient optimization method, the Complex method, is used and it is this method in combination with the mapping technique that is subjected to a robustness evaluation. In general, the results of this paper clearly indicates that the mapping method requires that some consideration is put into the arrangement of the component candidate lists.

Proceedings of the ASME 2009 International Design Engineering Technical Conferences & Computer and Information in Engineering Conference: CD-ROM

Manufacturers of construction machinery are challenged to accommodate legal requirements on the vibration exposure associated with their products. Hence, the ability to evaluate ride comfort by virtual prototyping is needed. One of the derived necessities is a modeling approach that can handle big off-road tires on irregular terrain and even the passing of sharp corner obstacles. In this paper a simple tire model combining the well known slip theory and a displaced volume approach is presented. A non-gradient optimization routine is applied for parameter identification by minimizing the difference between simulated data and experimental data obtained from a full vehicle model passing a set of well defined obstacles. The two most important deviations have been identified as frequency and force amplitude response because comfort is computed as a frequency weighted acceleration of the operator. Based on the obtained agreement between simulated and measured results the tire model is considered as well suited for comfort evaluation and, subsequently, reliable model based design.Copyright

A Model for Implementing Practical Design in the Education of Mechanical Engineers

In this paper the PBL model used at Aalborg University in the mechanical engineering is shortly presented. A specific semester with a both theoretical and practical content that allow the students to is presented in detail. It is then used as a reference project for a subsequent discussion on three potential concerns with respect to the continued succes of problem and project based learning in mechanical and mechatronics engineering namely: individual assessment, bologna (student exchange) model and research based teaching.Copyright