Your way to get in is to roll kick and dive kick in and not get stuffed, and FAing limbs such that it works, and using GT sparsely if ever.
Now that I’m done with my douche post, I’ll try to help. As a previous dhalsim player I feel I know this matchup more than most from both sides.
First and foremost, you need to be patient and understand that your goal is to get close to dhalsim and hopefully get close to him when he’s cornered. It is important that you realize that once you get in you should be dishing out ~20-30% damage or more, which is why you can’t be afraid to take damage while getting in. You have a lot of life to work with. Trades are almost always in your favour.
FA dashing limbs is very strong to close space, as is roll kick to a lesser extent. However your main method of closing space should be knowing how you can mixup your jump-ins such that it is impossible for sim to anti-air you with any one button on reaction. Sure j.fp from mid screen or so gets smoked by s.rh and b+rh if timed late, but both lose or whiff if you angle a dive kick such that it’ll stuff s.rh or land beside b+rh. Also, if he’s doing s.rh to beat out your jumps he needs to time it such that he’s pressing it fairly shortly after he sees you leave your feet, meaning that you can net some damage by doing short dive kicks that land before his move comes out, allowing you to get in with either rollkick or FA dash.
The main goal is to mix it up and learn the ranges from which he can AA. One important thing is to know the ranges where his #1 go to option will be b+rh, as it is extremely hard for sim to guess or even react to the j.fp/late dive kick/max height dive kick mixup. He has other options from this range, such as possibly slide into b+mp or jump back mp or even ex flames, but all of those options will put him at an unfavourable position afterwards.
So to summarize and add a little bit more.
- If you choose to get in by air, you can do so by mixing up your jumpins
- To really concentrate on reacting to dive kick timing with the right anti-air sim’s ground game begins to slack, so you can try walk blocking or FA dashing a lot more
- You WILL take damage getting in on sim, there is no avoiding it. Take it like the big man rufus is and bring the fight to him.
- Once you’re in, stay on him. This means don’t cross him up in the corner, don’t let him TP away unpunished and never miss an opportunity to do big damage or knock him down.
- If it matters, tell yourself the matchup is in your favour and tell yourself that even if you’re down by 50% you’re STILL winning, because all you need to do is hit him once to even it out. This kind of mindset tends to help me when I feel I’m losing in a matchup vs. a zoning character. One hit is all you need just like in marvel…
PS - I use U1 vs. sim but most on here will probably tell you to use U2. I feel its Sim’s worst matchup either way, but U2 should put it even more in your favour if you’re patient enough to just turtle it out, build U2, and then approach by ground with FA-dashes without the threat of him ever throwing an fb at you. Up to you on how you want to play it. I like playing it just like vanilla and using the large life and damage advantage to my favour. He can’t AA everything you do 
[media=youtube]I70IBZjEIpo[/media]
This is the matchup in vanilla. This sim is playing extremely solid for this matchup, but as you can see, kindevu wins that match and only really got pressure going on sim 3 times. One round he only needed to get in once, the other he guessed wrong with an EX Messiah to beat out a limb and let sim out, had to make up for it later by doing ex messiah into ultra in a similar situation.
Important to see that he ate a PILE of anti-airs and zoning pokes, but you just can’t let that phase you vs. sim. Eventually the trades start to add up or your mixups eventually allow him to make a mistake and you’re in, or just as good he has zoned you out perfectly but has gotten himself cornered, at which point he’s as good as dead just the same.