The phrase "are sometimes designed" is correct and usable in written English.
It can be used when discussing the purpose or intention behind the creation of something, indicating that it is not always the case but occurs occasionally.
Example: "These products are sometimes designed to enhance user experience while maintaining functionality."
Alternatives: "are occasionally created" or "are sometimes intended".
To minimize diffraction effects, optical microscopes are sometimes designed to use ultraviolet light rather than longer-wavelength visible light.
Animal and inanimate characters are sometimes designed on the bases of stereotypical female and male role models and sometimes these characters are seen as asexual or homosexual.
Countertops are sometimes designed to span significant distances — over dishwashers, breakfast bars and desks, for example.
The idea that RCTs are themselves infallible is every bit as silly as the questions they are sometimes designed to answer.
The checklists and scales currently used for assessing study validity of animal studies [ 10- 14] vary greatly, are sometimes designed for a specific field (i.e., toxicology) and often assess reporting quality and internal and external validity simultaneously.
Not even race courses - which are sometimes designed with erratic flow to throw off a racer's rhythm - should make this trail building faux pas.
First, tax expenditures distort market behavior — which they're sometimes designed to do, and sometimes not.
Elephants and rhinoceroses, which are among the largest mammals, are often accommodated within the same building, which is sometimes designed also to house hippopotamuses and tapirs.
They were highly reliable, and, because they frequently served vital needs in an organization, they were sometimes designed with redundant components that let them survive partial failures.
High-quality copper objects dating from the 17th and 18th centuries were sometimes designed and worked in the same way as the silver of the period.
Although the software is sometimes designed to work on both Java and Android phones, it usually has to work on lower cost mobiles.
