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While sophisticated numerical techniques that are based on finite element or finite volume methods are useful for gaining insight into these phenomena at the length scale of the melt pool ( 100–500 μm ) , they are ill-suited for predicting engineering trends over full part crosB-sections ( > 10 × 10 cm ) or many layers over long process times ( > many days ) due to the necessity of fully resolving the heat source characteristics .
 numerical techniques, finite element, finite volume methods, length scale, melt pool, engineering, crosB-sections, process times, heat source
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 numerical techniques, finite element, finite volume methods, length scale, melt pool, engineering, crosB-sections, process times, heat source