DE VELO PMENT SIMUL ATION
Numerical Simulation of Large Metallic Insulation Assemblies
In times of Industry 4.0 and Digital Twin the supply chain for high temperature insulation components faces significant challenges. The usual trust in a manual capability and experience in this industry is no longer enough today to keep pace with the digital world. Thermamax uses the numerical simulation to design metallic insulating claddings that best meet customer needs in off-highway applications and to realise the optimum product with as few prototype cycles as possible.
© Thermamax
60
AUTHORS
Dipl.-Ing. (FH) Dominic Düser, M. Sc. is CAE-Engineer in the Area of Construction and Development at Thermamax Hochtemperaturdämmungen GmbH in Mannheim (Germany).
Dipl.-Ing. (FH) Thomas Schramm is Director Engineering at Thermamax Hochtemperaturdämmungen GmbH in Mannheim (Germany).
Dipl.-Ing. (FH) Peter Cappellucci is Research and Development Manager at Thermamax Hochtemperaturdämmungen GmbH in Mannheim (Germany).
ATZ offhighway worldwide
04|2017
MOTIVATION
The technical advance, particularly in the current computing capacity and the continuing output increase in software capability, is allowing companies who hitherto relied on experience to achieve best project results, to validate these results through simulation, and, using interdisciplinary teams, to intensify and accelerate development activities. In the area of thermal and acoustic insulation technology there is focus on the particular thermal and vibration-dependent demands on components and assemblies, as well as application-related issues with connection technology. In order to present the potential use of simulation technology in insulation systems the first part of this paper explores the dynamic characteristics of sheet metal assemblies. Following that will be the procedure for the arithmetic validation of weld points and bolted connections. Finally, the application of flow simulation for illustrating surface temperature conditions on insulation enclosures will be investigated. OPTIMISING THE DYNAMIC CHARACTERISTICS OF FABRICATED ASSEMBLIES
In the dynamic field, mainly modal and harmonic analysis is significant, meaning simulation of system natural frequency and determination of system base point excitation. Vibrational excitation inevitably occurs due to piston movements in the insulated engine components, which can lead to long-term failure for instance in production related weak points in the structure. This condition will be exacerbated when the natural frequencies of the insulation coincide with the excitation frequencies of the engine to produce a resonance effect. Based on simulations carried out together with subsequent verification in the laboratory, a standardised layout for beaded sheet could be quickly developed, that significantly increases the natural frequency spectrum of large area sheets, ensuring that fewer of the relevant frequencies coincide with those in the operating range of the engine, resulting in better longterm component durability. As insula-
tion assemblies can comprise more than 1000 individual parts, (including components such as outer sheets, insulation material, inner sheets, and installation materials), the existing CAD model is simplified in operation so that a manageable data set for the simulation software is created. The number of equations to be solved, and the realistic result from the modelling, show only minor deviations from the results of the laboratory tests. The design shown in FIGURE 1 for a turbocharger cladding for a locomotive was developed on the computer in the concept phase in close cooperation with the design and simulation departments. A study was made firstly simulating seven different variants and the most promising design chosen from these. This design was then optimised in four virtual prototype cycles to achieve the lowest number of natural frequencies in the range up to 250 Hz, simultaneously noting possibilities for optimising the design and improving the long-term durability characteristics. The final design was then manufactured as a prototype and validated in the in-house test laboratory with a vibration test, FIGURE 2. A further area of application for simulations of large, self-supporting systems, is structural simulation, mainly involving the effects of external factors such as potholes, or on water, by wave action either quasi-static or in transient simulation. Here it’s mainly fixation points and brackets that are of interest, where significant tension occurs in often small cross-sectional areas. Also, areas of high load within the assembly can be identified and neutralised using targeted design measures. Simulations can allow the bracket design, choice of material and number of fixing points to be checked and, with potential for improvement recognised, a redesign initiated by the design engineer. In the development process, this can often mean that design iterations can be avoided, the number of prototypes minimised, and the best possible products with minimum development times achieved. ARITHMETIC VALIDATION OF WELD POINTS AND BOLTED CONNECTIONS
In the design of production-optimised insulation claddings weld points and
61
DE VELO PMENT SIMUL ATION
FIGURE 1 Modal simulation result of a turbocharger cladding (deformation/tension) (© Thermamax)
bolts are particularly important connection elements. In the sheet metal working industry weld points are the preferred joining technology for quickly and safely joining components. The best possible compromise between cost and component durability must always be found. The particular requirement most frequently presented is the temperature difference between the inner and outer areas of the cladding, which can quickly exceed 500 °C. The dominant load here
is due to thermally-induced tension in the area of the spot welds. Thermamax has been able to develop a calibration model through tensile and material tests, which allows prediction of the optimal spot weld configurations, FIGURE 3. In order to be able to firstly install and later remove spot welded components for maintenance purposes, bolted connections are made for the insulation assembly which even under short-term loadings of more than ten times gravitational
accelerations, cannot fail. To guarantee this requirement, an initial structural analysis with the maximum expected acceleration values is carried out in the high loaded areas. The results of the simulation are used to ensure the connections by a bolt calculation according to VDI 2230. Only when all areas show an acceptable margin of safety against failure is approval granted. In the course of design verification on an internal research project for a
FIGURE 2 Installation of insulation assembly on the shaker test stand (© Thermamax)
62
FIGURE 3 Simulation of welding points (left: stresses on spot weld connection; right: temperature distribution) (© Thermamax)
complete insulation cladding, FIGURE 4, more than 600 individual components were simulated under field conditions, with more than 300 bolted connections of different sizes in the cladding itself to achieve satisfactory safety levels. Due to this examination, the number of necessary screw specifications could be reduced, leading to cost savings in the overall operation, (purchasing, stock, logistics, assembly), and to an increase in the quality of the installation.
FLOW OPTIMISATION OF CONJUGATE HEAT TRANSFER APPLICATIONS
In thermal applications control of the temperatures existing in the combustion process play a decisive role, particularly with regard to compliance with statutory standards and regulations. Due to ever increasing legal requirements for strict compliance with emission levels it is essential to be able to retain the heat from the
combustion process within the system, for instance using catalytic converters for the processes in exhaust aftertreatment. Uses for computational fluid dynamics (CFD), are increasingly common in order to be able to predict on thermal high load components, whether surface temperatures for example on insulated components, are below the ignition temperature of potentially leaked fuel or other fluids, ensuring that self-ignition cannot occur. A special application in fluid technology is conjugate heat transfer simulation which is employed when simple thermal simulation, for example due to forced ventilation, reaches its limits. This application of simulation was used in the framework of a project for agricultural machinery, FIGURE 5, to establish a confident prediction of possible hotspots which would be above the ignition temperature of fuel oil (> 220 °C), and organic dusts, (cereal approximately > 250 °C) [1], and to be able to produce an optimised design even before the first prototype. A model was produced that internally mirrored the contours of the hot engine components that bring the heat energy into the system. The first flow chamber is filled with air with the complete insulation cladding, consisting of inner sheet, insulating material and outer sheet. A further air-filled flow chamber
FIGURE 4 Assembly for bolted joint calculations (© Thermamax)
ATZ offhighway worldwide
04|2017
63
DE VELO PMENT SIMUL ATION
FIGURE 5 Temperature distribution on insulation assembly of an agriculture machine (© Thermamax)
provided the necessary surface cooling. As a starting point, empirical values were used for the surface temperature of the engine components and the air in the two chambers, and the insulating components were detailed with the relevant heat transfer values for stainless steel and insulating material. As a result, the surface temperature could be recorded at each point on the cladding and potential hotspots eliminated by
64
design changes or by increasing the thickness of the insulating material. SUMMARY
In the supply industry for metallic insulations in the off-highway market, new possibilities exist through the introduction of simulation technology for the safeguarding of development, and testing processes, which contribute significantly
to the understanding of systems and product optimisation. In the past few years, since the introduction of numerical simulation, great progress has been made, a methodology built up and simulation in the product development process successfully integrated into all areas. REFERENCE [1] N. N.: Zündtemperatur. Online: https://de. wikipedia.org/wiki/Z%C3%BCndtemperatur, access: 05.07.2017
Digital, interactive, mobile: the new IST eMagazine New and free of charge in addition to the printed version – exclusively for subscribers
dded for
s
A
e u l a vs er
u b s cri b
Your eMagazine is now available at: http://emag.springerprofessional.de/ist Access from stationary and mobile devices
Keyword search for instant results in seconds
Easy and direct without an app due to HTML5 technology
Convenient downloading and saving of articles
Linked source references and interactive recommendations
To the article with a single click from the interactive list of contents
ATZ offhighway worldwide
04|2017
65
