By having the input quantities close to 1, the influence of round-off errors and truncation errors are reduced. The best set of units will depend on the problem typically, the most accurate results are obtained if the units are chosen such that the value s of the input quantities to the FE simulation are close to unity. There are numerous different sets of units that can be used when performing FE simulations.
In this case the fundamental units could be tonnes (1 tonne = 1000 kilograms), millimeters, and seconds. For example, Young’s modulus is frequently specified in terms of MegaPascals (MPa) (or, equivalently, N/mm2), where 1 Pascal = 1 N/m2. Sometimes the standard units are not convenient to work with. Definition of derived units is based on fundamental physical relations:įor example, A unit of force in the SI system is called a Newton (N):Īnother example is the unit of energy, called a Joule (J): Choosing a suitable consistent system of units The fundamental units in the SI system are length in meters (m), mass in kilograms (kg), time in seconds (s), temperature in degrees Kelvin (K), and electric current in Amperes (A).Ĭombinations of base and derived units may be used to express other derived units. The International System of Units (SI) is an example of a self-consistent set of units. Generally, any consistent system of units consists of some fundamental units such as Length (L), Mass (M) or Force (F), Time (T) as base units and the other units named derived units, which are formed by powers, products, or quotients of the base units and are potentially unlimited in number. Therefore, the units chosen must be self-consistent, which means that derived units of the chosen system can be expressed in terms of the fundamental units without conversion factors. Units in AbaqusĪbaqus has no units built into it except for rotation and angle measures. It is the user’s responsibility to ensure that the given numbers have consistent units.
Not only Abaqus, almost any finite element programs (Ansys, LS-Dyna…) do not consider the units of given quantities.
They get confused about the stress unit or when inputting parameters like Young Modulus, density… For every beginner users, it is really strange that why quantities in Abaqus have no units.
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